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Polymers, Volume 10, Issue 3 (March 2018)

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Cover Story (view full-size image) A key step in the manufacture of bioresorbable vascular scaffolds (BVSs) for treatment of coronary [...] Read more.
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Open AccessArticle A Novel Application of Phosphorene as a Flame Retardant
Polymers 2018, 10(3), 227; doi:10.3390/polym10030227
Received: 19 January 2018 / Revised: 22 February 2018 / Accepted: 23 February 2018 / Published: 26 February 2018
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Abstract
Black phosphorene-waterborne polyurethane (BPWPU) composite polymer with 0.2 wt % of black phosphorene was synthesized. Scanning electron microscopy (SEM) was used to observe the morphology of phosphorene in polyurethane matrix, which indicated that the phosphorene distributes uniformly in the PU matrix. The flammability
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Black phosphorene-waterborne polyurethane (BPWPU) composite polymer with 0.2 wt % of black phosphorene was synthesized. Scanning electron microscopy (SEM) was used to observe the morphology of phosphorene in polyurethane matrix, which indicated that the phosphorene distributes uniformly in the PU matrix. The flammability measurements were carried out to investigate the flame-resistant performances of phosphorene, which indicated that phosphorene could effectively restrict the degradation of the PU membrane. Compared by the pure WPU, the limiting oxygen index (LOI) of BPWPU increased by 2.6%, the heat flow determined by thermal analysis significantly decreased by 34.7% moreover, the peak heat release rate (PHRR) decreased by 10.3%. Full article
(This article belongs to the Special Issue Polymer Hybrid Materials)
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Open AccessArticle Two New Three-Dimensional Pillared-Layer Co(II) and Cu(II) Frameworks Involving a [M2(EO-N3)2] Motif from a Semi-Flexible N-Donor Ligand, 5,5′-Bipyrimidin: Syntheses, Structures and Magnetic Properties
Polymers 2018, 10(3), 229; doi:10.3390/polym10030229
Received: 30 January 2018 / Revised: 15 February 2018 / Accepted: 23 February 2018 / Published: 26 February 2018
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Abstract
Two new three-dimensional (3D) Co(II)- and Cu(II)-azido frameworks, [Co2(N3)4(bpym)2]n (1) and [Cu2(N3)4(bpym)]n (2), were successfully synthesized by introducing a semi-flexible N-donor ligand,
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Two new three-dimensional (3D) Co(II)- and Cu(II)-azido frameworks, [Co2(N3)4(bpym)2]n (1) and [Cu2(N3)4(bpym)]n (2), were successfully synthesized by introducing a semi-flexible N-donor ligand, 5,5′-bipyrimidin (bpym), with different bridging modes and orientations. Compounds 1 and 2 were structurally characterized by X-ray crystallography, IR spectroscopy, thermogravimetry and elemental analysis. Compounds 1 and 2 are 3D pillared-layer frameworks with double end-on (EO) azido bridged dinuclear motifs, [M2(EO-N3)2]. In Compound 1, the bpym ligands show trans μ2-bridging mode and the role as pillars to connect the Co(II)-azido layers, composed of [Co2(EO-N3)2] motifs and single end-to-end (EE) azido bridges, to a 3D network with BN topology. In contrast, in 2, the bpym ligand adopts a twisted μ4-bridging mode, which not only connects the adjacent [Cu2(EO-N3)2] units to a layer, but also functions as a pillar for the layers of the 3D structure. The structural diversities between the two types of architectures can be attributed to the coordination geometry preference of the metal ions (octahedral for Co2+ and square pyramidal for Cu2+). Magnetic investigations revealed that Compound 1 exhibits ferromagnetic-like magnetic ordering due to spin canting with a critical temperature, TC = 33.0 K, and furthers the field-induced magnetic transitions of metamagnetism at temperatures below TC. Compound 2 shows an antiferromagnetic ordering with TN = 3.05 K and a field-induced magnetic transition of spin-flop at temperatures below the TN. Full article
(This article belongs to the Special Issue Coordination Polymer)
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Open AccessArticle Performance of Plain Woven Jute Fabric-Reinforced Polyester Matrix Composite in Multilayered Ballistic System
Polymers 2018, 10(3), 230; doi:10.3390/polym10030230
Received: 19 January 2018 / Revised: 12 February 2018 / Accepted: 13 February 2018 / Published: 26 February 2018
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Abstract
The ballistic performance of plain woven jute fabric-reinforced polyester matrix composites was investigated as the second layer in a multilayered armor system (MAS). Volume fractions of jute fabric, up to 30 vol %, were mixed with orthophthalic polyester to fabricate laminate composites. Ballistic
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The ballistic performance of plain woven jute fabric-reinforced polyester matrix composites was investigated as the second layer in a multilayered armor system (MAS). Volume fractions of jute fabric, up to 30 vol %, were mixed with orthophthalic polyester to fabricate laminate composites. Ballistic tests were conducted using high velocity 7.62 mm ammunition. The depth of penetration caused by the bullet in a block of clay witness, simulating a human body, was used to evaluate the MAS ballistic performance according to the international standard. The fractured materials after tests were analyzed by scanning electron microscopy (SEM). The results indicated that jute fabric composites present a performance similar to that of the much stronger Kevlar™, which is an aramid fabric laminate, as MAS second layer with the same thickness. The mechanism of this similar ballistic behavior as well as the comparative advantages of the jute fabric composites over the Kevlar™ are discussed. Full article
(This article belongs to the Special Issue Textile and Textile-Based Materials)
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Open AccessArticle Electrospun Poly(ε-caprolactone) Nanofibrous Mesh for Imiquimod Delivery in Melanoma Therapy
Polymers 2018, 10(3), 231; doi:10.3390/polym10030231
Received: 5 January 2018 / Revised: 22 February 2018 / Accepted: 23 February 2018 / Published: 26 February 2018
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Abstract
Drug delivery systems (DDS) are commonly employed to administer drug-loaded composites to their therapeutic targets both in vitro and in vivo. Thus, we herein report the study of imiquimod-poly(ε-caprolactone) (IMQ-PCL) nanofibrous meshes for application in melanoma therapy. The preparation route employed was based
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Drug delivery systems (DDS) are commonly employed to administer drug-loaded composites to their therapeutic targets both in vitro and in vivo. Thus, we herein report the study of imiquimod-poly(ε-caprolactone) (IMQ-PCL) nanofibrous meshes for application in melanoma therapy. The preparation route employed was based on the electrospinning technique, with the melanoma cells being cultured on electrospun nanofibrous meshes to study their biocompatibility. All parameters employed, including the flow rate and polymer solution concentration, were examined to gain an improved understanding of the factors influencing the diameter and morphology of the electrospun fibre. The optimised parameters were employed to produce 12 IMQ-PCL nanofibrous meshes with diameters ranging from 100 to 900 nm to the melanoma cell viability. The relationship between the fibrous diameter and the imiquimod release profile was also determined using UV-Vis spectroscopy. In addition, similar results were obtained for the simulated imiquimod release profile obtained by COMSOL Multiphysics®. The IMQ-PCL nanofibrous meshes were found to decrease cell viability by ≥50%, with the number of cells dropping by ~10% over 48 h. As the cell viability was affected by the release of imiquimod, we believe that IMQ-PCL nanofibrous meshes are a promising drug delivery system for application in melanoma therapy. Full article
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Open AccessArticle Biocompatible Chitosan Oligosaccharide Modified Gold Nanorods as Highly Effective Photothermal Agents for Ablation of Breast Cancer Cells
Polymers 2018, 10(3), 232; doi:10.3390/polym10030232
Received: 5 February 2018 / Revised: 20 February 2018 / Accepted: 24 February 2018 / Published: 26 February 2018
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Abstract
Photothermal therapy (PTT) using biocompatible nanomaterials have recently attracted much attention as a novel candidate technique for cancer therapy. In this work we report the performance of newly synthesized multidentate chitosan oligosaccharide modified gold nanorods (AuNRs-LA-COS) as novel agents for PTT of cancer
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Photothermal therapy (PTT) using biocompatible nanomaterials have recently attracted much attention as a novel candidate technique for cancer therapy. In this work we report the performance of newly synthesized multidentate chitosan oligosaccharide modified gold nanorods (AuNRs-LA-COS) as novel agents for PTT of cancer cells due to their excellent biocompatibility, photothermal stability, and high absorption in the near-infrared (NIR) region. The AuNRs-LA-COS exhibit a strong NIR absorption peak at 838 nm with a mean length of 26 ± 3.1 nm and diameter of 6.8 ± 1.7 nm, respectively. The temperature of AuNRs-LA-COS rapidly reached 52.6 °C for 5 min of NIR laser irradiation at 2 W/cm2. The AuNRs-LA-COS had very low cytotoxicity and exhibited high efficiency for the ablation of breast cancer cells in vitro. The tumor-bearing mice were completely ablated without tumor recurrence after photothermal treatment with AuNRs-LA-COS (25 µg/mL) under laser irradiation. In summary, this study demonstrated that AuNRs-LA-COS with laser irradiation as novel agents pave an alternative way for breast cancer therapy and hold great promise for clinical trials in the near future. Full article
(This article belongs to the Special Issue Polymers for Therapy and Diagnostics)
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Open AccessArticle Parametric Study of Effects of Atmospheric Pressure Plasma Treatment on the Wettability of Cotton Fabric
Polymers 2018, 10(3), 233; doi:10.3390/polym10030233
Received: 17 January 2018 / Revised: 23 February 2018 / Accepted: 25 February 2018 / Published: 26 February 2018
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Abstract
In textiles processing, wettability of fabric plays a very important role in enhancing processes such as dyeing and printing. Although well-prepared cotton fabric has very good wettability, further enhancement of its wettability can effectively improve the subsequent dyeing and printing processes. Plasma treatment,
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In textiles processing, wettability of fabric plays a very important role in enhancing processes such as dyeing and printing. Although well-prepared cotton fabric has very good wettability, further enhancement of its wettability can effectively improve the subsequent dyeing and printing processes. Plasma treatment, especially atmospheric pressure plasma treatment (APPT), a continuous process, is now drawing attention of the industry. In this study, we investigated the effect of APPT under four operational parameters: (1) discharge power; (2) flow rate of oxygen; (3) jet travelling speed; and (4) jet-to-substrate distance on wettability (in terms of wickability and wetting area) of cotton fabric. Experimental results revealed that the four parameters interact with each other in affecting the wettability of the cotton fabric. The results are discussed comprehensively. Full article
(This article belongs to the Special Issue Textile and Textile-Based Materials)
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Open AccessArticle Optimization of Temperature Sensing with Polymer-Embedded Luminescent Ru(II) Complexes
Polymers 2018, 10(3), 234; doi:10.3390/polym10030234
Received: 29 January 2018 / Revised: 21 February 2018 / Accepted: 22 February 2018 / Published: 26 February 2018
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Abstract
Temperature is a key parameter in many fields and luminescence-based temperature sensing is a solution for those applications in which traditional (mechanical, electrical, or IR-based) thermometers struggle. Amongst the indicator dyes for luminescence thermometry, Ru(II) polyazaheteroaromatic complexes are an appealing option to profit
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Temperature is a key parameter in many fields and luminescence-based temperature sensing is a solution for those applications in which traditional (mechanical, electrical, or IR-based) thermometers struggle. Amongst the indicator dyes for luminescence thermometry, Ru(II) polyazaheteroaromatic complexes are an appealing option to profit from the widespread commercial technologies for oxygen optosensing based on them. Six ruthenium dyes have been studied, engineering their structure for both photostability and highest temperature sensitivity of their luminescence. The most apt Ru(II) complex turned out to be bis(1,10-phenanthroline)(4-chloro-1,10-phenanthroline)ruthenium(II), due to the combination of two strong-field chelating ligands (phen) and a substituent with electron withdrawing effect on a conjugated position of the third ligand (4-Clphen). In order to produce functional sensors, the dye has been best embedded into poly(ethyl cyanoacrylate), due to its low permeability to O2, high temperature sensitivity of the indicator dye incorporated into this polymer, ease of fabrication, and excellent optical quality. Thermosensitive elements have been fabricated thereof as optical fiber tips for macroscopic applications (water courses monitoring) and thin spots for microscopic uses (temperature measurements in cell culture-on-a-chip). With such dye/polymer combination, temperature sensing based on luminescence lifetime measurements allows 0.05 °C resolution with linear response in the range of interest (0–40 °C). Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications)
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Open AccessArticle Preparation of Amidoxime-Functionalized β-Cyclodextrin-Graft-(Maleic Anhydride-co-Acrylonitrule) Copolymer and Evaluation of the Adsorption and Regeneration Properties of Uranium
Polymers 2018, 10(3), 236; doi:10.3390/polym10030236
Received: 30 January 2018 / Revised: 20 February 2018 / Accepted: 22 February 2018 / Published: 27 February 2018
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Abstract
The β-cyclodextrin-graft-(maleic anhydride-co-acrylonitrule) copolymer (β-CD-g-(MAH-co-AN)) synthesized through radical polymerization reactions of β-cyclodextrin (β-CD) with maleic anhydride (MAH) and acrylonitrule (AN) in the special monomer proportion, chemically modify with amidoxime groups to obtained the new adsorbent, which was terms as
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The β-cyclodextrin-graft-(maleic anhydride-co-acrylonitrule) copolymer (β-CD-g-(MAH-co-AN)) synthesized through radical polymerization reactions of β-cyclodextrin (β-CD) with maleic anhydride (MAH) and acrylonitrule (AN) in the special monomer proportion, chemically modify with amidoxime groups to obtained the new adsorbent, which was terms as amidoxime-functionalized β-cyclodextrin-graft-(maleic anhydride-co-acrylonitrule) copolymer (β-CD-g-(MAH-co-AO)). Based on the characteristic results of Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM), X-ray Diffraction (XRD), and thermalgravity analysis (TGA) techniques, the grafted nitrile groups were successfully converted to amidoxime groups by reaction with hydroxylamine. In this report, the influence of different factors such as pH value and ionic strength, solid-liquid ratio, contact time, initial U(VI) concentration, and temperature on adsorption was investigated by a batch adsorption experiment. The adsorption process fitting results show that the adsorption followed the Langmuir isotherm model and the maximum adsorption capacity was 0.747 g/g at pH 4.0. In addition, the regeneration performance was investigated by varying the concentration of eluent, temperature, and contact time. Under the desorption condition of 0.10 M HNO3, the adsorbents can be reused 12 times in the case that the adsorption capacity was not significantly reduced. The functionalized copolymer exhibits high selectivity under circumstance of other co-existing ions is present in the solution. Full article
(This article belongs to the Special Issue Polymer-Based Nano-Sorbent Materials)
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Open AccessArticle Biosynthetic Pathway and Genes of Chitin/Chitosan-Like Bioflocculant in the Genus Citrobacter
Polymers 2018, 10(3), 237; doi:10.3390/polym10030237
Received: 23 January 2018 / Revised: 19 February 2018 / Accepted: 22 February 2018 / Published: 27 February 2018
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Abstract
Chitin/chitosan, one of the most abundant polysaccharides in nature, is industrially produced as a powder or flake form from the exoskeletons of crustaceans such as crabs and shrimps. Intriguingly, many bacterial strains in the genus Citrobacter secrete a soluble chitin/chitosan-like polysaccharide into the
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Chitin/chitosan, one of the most abundant polysaccharides in nature, is industrially produced as a powder or flake form from the exoskeletons of crustaceans such as crabs and shrimps. Intriguingly, many bacterial strains in the genus Citrobacter secrete a soluble chitin/chitosan-like polysaccharide into the culture medium during growth in acetate. Because this polysaccharide shows strong flocculation activity for suspended solids in water, it can be used as a bioflocculant (BF). The BF synthetic pathway of C. freundii IFO 13545 is expected from known bacterial metabolic pathways to be as follows: acetate is metabolized in the TCA cycle and the glyoxylate shunt via acetyl-CoA. Next, fructose 6-phosphate is generated from the intermediates of the TCA cycle through gluconeogenesis and enters into the hexosamine synthetic pathway to form UDP-N-acetylglucosamine, which is used as a direct precursor to extend the BF polysaccharide chain. We conducted the draft genome sequencing of IFO 13545 and identified all of the candidate genes corresponding to the enzymes in this pathway in the 5420-kb genome sequence. Disruption of the genes encoding acetyl-CoA synthetase and isocitrate lyase by homologous recombination resulted in little or no growth on acetate, indicating that the cell growth depends on acetate assimilation via the glyoxylate shunt. Disruption of the gene encoding glucosamine 6-phosphate synthase, a key enzyme for the hexosamine synthetic pathway, caused a significant decrease in flocculation activity, demonstrating that this pathway is primarily used for the BF biosynthesis. A gene cluster necessary for the polymerization and secretion of BF, named bfpABCD, was also identified for the first time. In addition, quantitative RT-PCR analysis of several key genes in the expected pathway was conducted to know their expression in acetate assimilation and BF biosynthesis. Based on the data obtained in this study, an overview of the BF synthetic pathway is discussed. Full article
(This article belongs to the Special Issue Advances in Chitin/Chitosan Characterization and Applications)
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Open AccessArticle Butyl Rubber Nanocomposites with Monolayer MoS2 Additives: Structural Characteristics, Enhanced Mechanical, and Gas Barrier Properties
Polymers 2018, 10(3), 238; doi:10.3390/polym10030238
Received: 31 January 2018 / Revised: 22 February 2018 / Accepted: 24 February 2018 / Published: 27 February 2018
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Abstract
Emerging two-dimensional (2D) materialsm, such as molybdenum disulfide (MoS2), offer opportunities to tailor the mechanical and gas barrier properties of polymeric materials. In this study, MoS2 was exfoliated to monolayers by modification with ethanethiol and nonanethiol. The thicknesses of resulting
[...] Read more.
Emerging two-dimensional (2D) materialsm, such as molybdenum disulfide (MoS2), offer opportunities to tailor the mechanical and gas barrier properties of polymeric materials. In this study, MoS2 was exfoliated to monolayers by modification with ethanethiol and nonanethiol. The thicknesses of resulting MoS2 monolayers were 0.7 nm for MoS2-ethanethiol and 1.1 nm for MoS2-nonanethiol. MoS2 monolayers were added to chlorobutyl rubber to prepare MoS2-butyl rubber nanocomposites at concentrations of 0.5, 1, 3, and 5 phr. The tensile stress showed a maximum enhancement of about 30.7% for MoS2-ethanethiol-butyl rubber and 34.8% for MoS2-nonanethiol-butyl rubber when compared to pure chlorobutyl rubber. In addition, the gas barrier properties were increased by 53.5% in MoS2-ethanethiol-butyl rubber and 49.6% in MoS2-nonanethiol-butyl rubber. MoS2 nanosheets thus enhanced the mechanical and gas barrier properties of chlorobutyl rubber. The nanocomposites that are presented here may be used to manufacture pharmaceutical stoppers with high mechanical and gas barrier properties. Full article
(This article belongs to the Special Issue Nanoparticle-Reinforced Polymers)
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Open AccessArticle Ring-Opening Polymerization of 1,3-Benzoxazines via Borane Catalyst
Polymers 2018, 10(3), 239; doi:10.3390/polym10030239
Received: 13 February 2018 / Revised: 22 February 2018 / Accepted: 24 February 2018 / Published: 27 February 2018
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Abstract
Tris(pentafluorophenyl)borane was used as Lewis acid catalyst to lower the ring opening polymerization temperature (ROP) of 1,3-benzoxazines. Dynamic scanning calorimeter studies revealed that on-set ROP temperatures were decreased as much as 98 °C for model benzoxazine compounds. Catalytic polymerization was traced by both
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Tris(pentafluorophenyl)borane was used as Lewis acid catalyst to lower the ring opening polymerization temperature (ROP) of 1,3-benzoxazines. Dynamic scanning calorimeter studies revealed that on-set ROP temperatures were decreased as much as 98 °C for model benzoxazine compounds. Catalytic polymerization was traced by both FTIR and 1H NMR, and revealed that tris(pentafluorophenyl)borane acted rapidly and fast curing achieved. Moreover, thermal properties of resulting polybenzoxazines were investigated by thermogravimetric analysis (TGA) and found out that the catalyst has high impact on char yield and even 3 mol % catalyst augmented char yields up to 13%. Full article
(This article belongs to the Special Issue Thermosets)
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Open AccessArticle Hydrogen-Deuterium Exchange Profiles of Polyubiquitin Fibrils
Polymers 2018, 10(3), 240; doi:10.3390/polym10030240
Received: 31 January 2018 / Revised: 23 February 2018 / Accepted: 24 February 2018 / Published: 27 February 2018
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Abstract
Ubiquitin and its polymeric forms are conjugated to intracellular proteins to regulate diverse intracellular processes. Intriguingly, polyubiquitin has also been identified as a component of pathological protein aggregates associated with Alzheimer’s disease and other neurodegenerative disorders. We recently found that polyubiquitin can form
[...] Read more.
Ubiquitin and its polymeric forms are conjugated to intracellular proteins to regulate diverse intracellular processes. Intriguingly, polyubiquitin has also been identified as a component of pathological protein aggregates associated with Alzheimer’s disease and other neurodegenerative disorders. We recently found that polyubiquitin can form amyloid-like fibrils, and that these fibrillar aggregates can be degraded by macroautophagy. Although the structural properties appear to function in recognition of the fibrils, no structural information on polyubiquitin fibrils has been reported so far. Here, we identify the core of M1-linked diubiquitin fibrils from hydrogen-deuterium exchange experiments using solution nuclear magnetic resonance (NMR) spectroscopy. Intriguingly, intrinsically flexible regions became highly solvent-protected in the fibril structure. These results indicate that polyubiquitin fibrils are formed by inter-molecular interactions between relatively flexible structural components, including the loops and edges of secondary structure elements. Full article
(This article belongs to the Special Issue NMR in Polymer Science)
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Open AccessArticle Tailoring Macromolecular Structure of Cationic Polymers towards Efficient Contact Active Antimicrobial Surfaces
Polymers 2018, 10(3), 241; doi:10.3390/polym10030241
Received: 25 January 2018 / Revised: 19 February 2018 / Accepted: 23 February 2018 / Published: 27 February 2018
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Abstract
The aim of this work is the preparation of contact active antimicrobial films by blending copolymers with quaternary ammonium salts and polyacrylonitrile as matrix material. A series of copolymers based on acrylonitrile and methacrylic monomers with quaternizable groups were designed with the purpose
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The aim of this work is the preparation of contact active antimicrobial films by blending copolymers with quaternary ammonium salts and polyacrylonitrile as matrix material. A series of copolymers based on acrylonitrile and methacrylic monomers with quaternizable groups were designed with the purpose of investigating the influence of their chemical and structural characteristics on the antimicrobial activity of these surfaces. The biocide activity of these systems was studied against different microorganisms, such as the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Pseudomona aeruginosa and the yeast Candida parapsilosis. The results confirmed that parameters such as flexibility and polarity of the antimicrobial polymers immobilized on the surfaces strongly affect the efficiency against microorganisms. In contrast to the behavior of copolymers in water solution, when they are tethered to the surface, the active cationic groups are less accessible and then, the mobility of the side chain is critical for a good contact with the microorganism. Blend films composed of copolymers with high positive charge density and chain mobility present up to a more than 99.999% killing efficiency against the studied microorganisms. Full article
(This article belongs to the Special Issue Antimicrobial Polymers)
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Open AccessArticle Exopolysaccharide Gellan Gum and Derived Oligo-Gellan Enhance Growth and Antimicrobial Activity in Eucomis Plants
Polymers 2018, 10(3), 242; doi:10.3390/polym10030242
Received: 11 January 2018 / Revised: 13 February 2018 / Accepted: 26 February 2018 / Published: 27 February 2018
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Abstract
One of the visible trends in the cultivation of plants, particularly of medicinal ones, is the increasing interest of researchers in polysaccharides and their derivatives that show biostimulatory properties and are also safe to use. In the current study, we evaluated the effects
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One of the visible trends in the cultivation of plants, particularly of medicinal ones, is the increasing interest of researchers in polysaccharides and their derivatives that show biostimulatory properties and are also safe to use. In the current study, we evaluated the effects of gellan gum and its depolymerized form oligo-gellan, on growth and antimicrobial activity of two ornamental species Eucomis bicolor and Eucomis comosa used in natural medicine. The biopolymers were applied in the form of bulb coating prepared by using polyelectrolyte complexes. In both species investigated, gellan gum and oligo-gellan enhanced the fresh weight of leaves and bulbs, the performance of the photosynthetic apparatus, and the leaf content of basic macronutrients. In comparison with the control, the plants treated with oligo-gellan accumulated more biomass, were first to flower, and had the highest leaf content of potassium. The extracts from the bulbs treated with gellan gum and oligo-gellan showed higher effectiveness in reducing the count of Bacillus atrophaeus, Escherichia coli, and Staphylococcus aureus than those from the bulbs not treated with the polysaccharides. The research described here largely expands our current knowledge on the effects of gellan gum derivatives and has a huge practical potential in agriculture production. Full article
(This article belongs to the Special Issue Polysaccharides)
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Open AccessArticle The Mixing Counterion Effect on DNA Compaction and Charge Neutralization at Low Ionic Strength
Polymers 2018, 10(3), 244; doi:10.3390/polym10030244
Received: 24 December 2017 / Revised: 24 February 2018 / Accepted: 26 February 2018 / Published: 28 February 2018
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Abstract
DNA compaction and charge neutralization in a mixing counterion solution involves competitive and cooperative electrostatic binding, and sometimes counterion complexation. At normal ionic strength, it has been found that the charge neutralization of DNA by the multivalent counterion is suppressed when being added
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DNA compaction and charge neutralization in a mixing counterion solution involves competitive and cooperative electrostatic binding, and sometimes counterion complexation. At normal ionic strength, it has been found that the charge neutralization of DNA by the multivalent counterion is suppressed when being added extra mono- and di-valent counterions. Here, we explore the effect mixing counterion on DNA compaction and charge neutralization under the condition of low ionic strength. Being quite different from normal ionic strength, the electrophoretic mobility of DNA in multivalent counterion solution (octalysine, spermine) increases the presence of mono- and di-valent cations, such as sodium and magnesium ions. It means that the charge neutralization of DNA by the multivalent counterion is promoted rather than suppressed when introducing extra mono- and di-valent counterions into solution. This conclusion is also supported by the measurement of condensing and unraveling forces of DNA condensates under the same condition by single molecular magnetic tweezers. This mixing effect can be attributed to the cooperative electrostatic binding of counterions to DNA when the concentration of counterions in solution is below a critical concentration. Full article
(This article belongs to the Special Issue Ionic Polymers)
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Open AccessArticle Influence of Selectively Localised Nanoclay Particles on Non-Isothermal Crystallisation and Degradation Behaviour of PP/LDPE Blend Composites
Polymers 2018, 10(3), 245; doi:10.3390/polym10030245
Received: 9 February 2018 / Revised: 24 February 2018 / Accepted: 25 February 2018 / Published: 28 February 2018
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Abstract
In immiscible polymer blend nanocomposites, nanoparticles can be localised either in polymer matrices or at the interface, invoking the simple question of how the spatial distribution of the nanoparticles and the resulting morphological changes affect the non-isothermal crystallisation and degradation kinetics. In this
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In immiscible polymer blend nanocomposites, nanoparticles can be localised either in polymer matrices or at the interface, invoking the simple question of how the spatial distribution of the nanoparticles and the resulting morphological changes affect the non-isothermal crystallisation and degradation kinetics. In this study, the non-isothermal crystallisation of polypropylene in polypropylene (PP)-rich compatibilised and non-compatibilised PP/low-density polyethylene (LDPE)/clay composites and their degradation are investigated. The non-isothermal crystallisation analyses show that the localisation of the clay particles in the blend composites has two opposing effects. First, the poorly dispersed clay particles at the PP/LDPE interface in the non-compatibilised blend composite has no significant effect on the crystallisation temperature of PP but allows the free movement of PP chains, resulting in a higher crystallinity of PP than that of PP in the neat blend. Second, the well-dispersed clay particles in the compatibilised blend composites disrupt the free movement of PP chains, resulting in a lower crystallisation temperature and crystallinity than that of PP in the neat blend. The influences of different selective localisations of clay particles on the activation energies of degradation are studied. The presence of maleated compatibilisers, clay, and the distribution of clay in the blend composite play important roles in determining the activation energies of degradation. Full article
(This article belongs to the Special Issue Polymer-Clay (Nano)Composites)
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Open AccessArticle Fique Fabric: A Promising Reinforcement for Polymer Composites
Polymers 2018, 10(3), 246; doi:10.3390/polym10030246
Received: 6 February 2018 / Revised: 23 February 2018 / Accepted: 24 February 2018 / Published: 28 February 2018
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Abstract
A relatively unknown natural fiber extracted from the leaves of the fique plant, native of the South American Andes, has recently shown potential as reinforcement of polymer composites for engineering applications. Preliminary investigations indicated a promising substitute for synthetic fibers, competing with other
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A relatively unknown natural fiber extracted from the leaves of the fique plant, native of the South American Andes, has recently shown potential as reinforcement of polymer composites for engineering applications. Preliminary investigations indicated a promising substitute for synthetic fibers, competing with other well-known natural fibers. The fabric made from fique fibers have not yet been investigated as possible composite reinforcement. Therefore, in the present work a more thorough characterization of fique fabric as a reinforcement of composites with a polyester matrix was performed. Thermal mechanical properties of fique fabric composites were determined by dynamic mechanical analysis (DMA). The ballistic performance of plain woven fique fabric-reinforced polyester matrix composites was investigated as a second layer in a multilayered armor system (MAS). The results revealed a sensible improvement in thermal dynamic mechanical behavior. Both viscoelastic stiffness and glass transition temperature were increased with the amount of incorporated fique fabric. In terms of ballistic results, the fique fabric composites present a performance similar to that of the much stronger KevlarTM as an MAS second layer with the same thickness. A cost analysis indicated that armor vests with fique fabric composites as an MAS second layer would be 13 times less expensive than a similar creation made with Kevlar™. Full article
(This article belongs to the Special Issue Textile and Textile-Based Materials)
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Open AccessArticle Acetalised Galactarate Polyesters: Interplay between Chemical Structure and Polymerisation Kinetics
Polymers 2018, 10(3), 248; doi:10.3390/polym10030248
Received: 15 February 2018 / Revised: 23 February 2018 / Accepted: 25 February 2018 / Published: 28 February 2018
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Abstract
In spite of the progress that has made so far in the recent years regarding the synthesis of bio-based polymers and in particular polyesters, only few references address the optimisation of these new reactions with respect to conversion and reaction time. Related to
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In spite of the progress that has made so far in the recent years regarding the synthesis of bio-based polymers and in particular polyesters, only few references address the optimisation of these new reactions with respect to conversion and reaction time. Related to this aspect, we here describe the transesterification reaction of two different acetalised galactarate esters with a model aliphatic diol, 1,6-hexanediol. The kinetics of these two apparently similar reactions is compared, with a focus on the conversion while varying the concentration of a di-butyltin oxide catalyst (DBTO), respectively, the used N2 flow-rate. During the first stage of polymerisation, the molecular weight of the end-products is more than doubled when using a 250 mL/min flow as opposed to an almost static N2 pressure. Additionally, the resulted pre-polymers are subjected to further polycondensation and the comparison between the obtained polyesters is extended to their thermal, mechanical and dielectrical characterisation. The influence of the acetal groups on the stability of the polyesters in acidic conditions concludes the study. Full article
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Open AccessArticle Gas Dissolution Foaming as a Novel Approach for the Production of Lightweight Biocomposites of PHB/Natural Fibre Fabrics
Polymers 2018, 10(3), 249; doi:10.3390/polym10030249
Received: 12 January 2018 / Revised: 26 February 2018 / Accepted: 27 February 2018 / Published: 28 February 2018
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Abstract
The aim of this study is to propose and explore a novel approach for the production of cellular lightweight natural fibre, nonwoven, fabric-reinforced biocomposites by means of gas dissolution foaming from composite precursors of polyhydroxybutyrate-based matrix and flax fabric reinforcement. The main challenge
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The aim of this study is to propose and explore a novel approach for the production of cellular lightweight natural fibre, nonwoven, fabric-reinforced biocomposites by means of gas dissolution foaming from composite precursors of polyhydroxybutyrate-based matrix and flax fabric reinforcement. The main challenge is the development of a regular cellular structure in the polymeric matrix to reach a weight reduction while keeping a good fibre-matrix stress transfer and adhesion. The viability of the process is evaluated through the analysis of the cellular structure and morphology of the composites. The effect of matrix modification, nonwoven treatment, expansion temperature, and expansion pressure on the density and cellular structure of the cellular composites is evaluated. It was found that the nonwoven fabric plays a key role in the formation of a uniform cellular morphology, although limiting the maximum expansion ratio of the composites. Cellular composites with a significant reduction of weight (relative densities in the range 0.4–0.5) were successfully obtained. Full article
(This article belongs to the Special Issue Polymers from Renewable Resources)
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Open AccessArticle Surface Characterisation of Atmospheric Pressure Plasma Treated Cotton Fabric—Effect of Operation Parameters
Polymers 2018, 10(3), 250; doi:10.3390/polym10030250
Received: 7 February 2018 / Revised: 26 February 2018 / Accepted: 27 February 2018 / Published: 28 February 2018
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Abstract
The surface of cotton fibre was modified by atmospheric pressure plasma treatment (APPT), using gas as the carrier. Effects of variations in four operational parameters, discharge power, oxygen flow rate, jet-to-substrate distance and speed of the jet movement were examined. Morphology of surface
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The surface of cotton fibre was modified by atmospheric pressure plasma treatment (APPT), using gas as the carrier. Effects of variations in four operational parameters, discharge power, oxygen flow rate, jet-to-substrate distance and speed of the jet movement were examined. Morphology of surface of cotton fabrics was examined by generating Scanning Electron Microscopy (SEM) images. Elementary composition of the surface of the fabric was examined by X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy-Attenuated. Total Internal Reflectance (FTIR-ATR) was used for examining functionality of the surface. In this study, we revealed that the operational parameters would physical and chemically after the surface characteristics of the cotton fibre. Physically, cracks and grooves were noted in the cotton fibre surface after APPT. Chemically, the oxygen content in the cotton fibre surface was increased after APPT. When the O/C ratio is taken into consideration, the surface oxidation was a steady effect in applying APPT for treating cotton fibre in this study. Full article
(This article belongs to the Special Issue Textile and Textile-Based Materials)
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Open AccessArticle Molecular and Supramolecular Changes in Polybutylene Succinate (PBS) and Polybutylene Succinate Adipate (PBSA) Copolymer during Degradation in Various Environmental Conditions
Polymers 2018, 10(3), 251; doi:10.3390/polym10030251
Received: 26 January 2018 / Revised: 19 February 2018 / Accepted: 27 February 2018 / Published: 1 March 2018
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Abstract
In this paper, the influence of the various degradation conditions, on the molecular and supramolecular structure of polybutylene succinate (PBS) and polybutylene succinate adipate (PBSA) copolymer during degradation is described. The experiment was carried out by the use of injection molded samples and
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In this paper, the influence of the various degradation conditions, on the molecular and supramolecular structure of polybutylene succinate (PBS) and polybutylene succinate adipate (PBSA) copolymer during degradation is described. The experiment was carried out by the use of injection molded samples and normalized conditions of biodegradation in soil, composting and artificial weathering. Materials were studied by size-exclusion chromatography (SEC) coupled with multiangle laser light scattering (MALLS) detection and wide-angle X-ray diffraction (WAXD). Additionally, the physical and mechanical properties of the samples were determined. The performed experiments clearly show difference impacts of the selected degradation conditions on the macroscopic, supramolecular and molecular parameters of the studied aliphatic polyesters. The structural changes in PBS and PBSA explain the observed changes in the physical and mechanical properties of the obtained injection molded samples. Full article
(This article belongs to the Special Issue Biodegradable and Biobased Polyesters)
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Open AccessArticle Starch-Chitosan Polyplexes: A Versatile Carrier System for Anti-Infectives and Gene Delivery
Polymers 2018, 10(3), 252; doi:10.3390/polym10030252
Received: 8 December 2017 / Revised: 25 February 2018 / Accepted: 27 February 2018 / Published: 1 March 2018
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Abstract
Despite the enormous potential of nanomedicine, the search for materials from renewable resources that balance bio-medical requirements and engineering aspects is still challenging. This study proposes an easy method to make nanoparticles composed of oxidized starch and chitosan, both isolated from natural biopolymers.
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Despite the enormous potential of nanomedicine, the search for materials from renewable resources that balance bio-medical requirements and engineering aspects is still challenging. This study proposes an easy method to make nanoparticles composed of oxidized starch and chitosan, both isolated from natural biopolymers. The careful adjustment of C/N ratio, polymer concentration and molecular weight allowed for tuning of particle characteristics. The system’s carrier capability was assessed both for anti-infectives and for nucleic acid. Higher starch content polyplexes were found to be suitable for high encapsulation efficiency of cationic anti-infectives and preserving their bactericidal function. A cationic carrier was obtained by coating the anionic polyplex with chitosan. Coating allowed for a minimal amount of cationic polymer to be employed and facilitated plasmid DNA loading both within the particle core and on the surface. Transfection studies showed encouraging result, approximately 5% of A549 cells with reporter gene expression. In summary, starch-chitosan complexes are suitable carriers with promising perspectives for pharmaceutical use. Full article
(This article belongs to the Special Issue Polymers from Renewable Resources)
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Open AccessArticle Behavior and Three-Dimensional Finite Element Modeling of Circular Concrete Columns Partially Wrapped with FRP Strips
Polymers 2018, 10(3), 253; doi:10.3390/polym10030253
Received: 21 January 2018 / Revised: 15 February 2018 / Accepted: 27 February 2018 / Published: 1 March 2018
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Abstract
Fiber-reinforced polymer (FRP) jacketing/wrapping has become an attractive strengthening technique for concrete columns. Wrapping an existing concrete column with continuous FRP jackets with the fiber in the jacket being oriented in the hoop direction is referred to as FRP full wrapping strengthening technique.
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Fiber-reinforced polymer (FRP) jacketing/wrapping has become an attractive strengthening technique for concrete columns. Wrapping an existing concrete column with continuous FRP jackets with the fiber in the jacket being oriented in the hoop direction is referred to as FRP full wrapping strengthening technique. In practice, however, strengthening concrete columns with vertically discontinuous FRP strips is also favored and this technique is referred to as FRP partial wrapping strengthening technique. Existing research has demonstrated that FRP partial wrapping strengthening technique is a promising and economical alternative to the FRP full wrapping strengthening technique. Although extensive experimental investigations have hitherto been conducted on partially FRP-confined concrete columns, the confinement mechanics of confined concrete in partially FRP-confined circular columns remains unclear. In this paper, an experimental program consisting of fifteen column specimens was conducted and the test results were presented. A reliable three-dimensional (3D) finite element (FE) approach for modeling of partially FRP-confined circular columns was established. In the proposed FE approach, an accurate plastic-damage model for concrete under multiaxial compression is employed. The accuracy of the proposed FE approach was verified by comparisons between the numerical results and the test results. Numerical results from the verified FE approach were then presented to gain an improved understanding of the behavior of confined concrete in partially FRP-confined concrete columns. Full article
(This article belongs to the Special Issue Polymers for Modern and Advanced Engineering Applications)
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Open AccessArticle Assessing Mucoadhesion in Polymer Gels: The Effect of Method Type and Instrument Variables
Polymers 2018, 10(3), 254; doi:10.3390/polym10030254
Received: 8 January 2018 / Revised: 8 February 2018 / Accepted: 27 February 2018 / Published: 1 March 2018
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Abstract
The process of mucoadhesion has been widely studied using a wide variety of methods, which are influenced by instrumental variables and experiment design, making the comparison between the results of different studies difficult. The aim of this work was to standardize the conditions
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The process of mucoadhesion has been widely studied using a wide variety of methods, which are influenced by instrumental variables and experiment design, making the comparison between the results of different studies difficult. The aim of this work was to standardize the conditions of the detachment test and the rheological methods of mucoadhesion assessment for semisolids, and introduce a texture profile analysis (TPA) method. A factorial design was developed to suggest standard conditions for performing the detachment force method. To evaluate the method, binary polymeric systems were prepared containing poloxamer 407 and Carbopol 971P®, Carbopol 974P®, or Noveon® Polycarbophil. The mucoadhesion of systems was evaluated, and the reproducibility of these measurements investigated. This detachment force method was demonstrated to be reproduceable, and gave different adhesion when mucin disk or ex vivo oral mucosa was used. The factorial design demonstrated that all evaluated parameters had an effect on measurements of mucoadhesive force, but the same was not observed for the work of adhesion. It was suggested that the work of adhesion is a more appropriate metric for evaluating mucoadhesion. Oscillatory rheology was more capable of investigating adhesive interactions than flow rheology. TPA method was demonstrated to be reproducible and can evaluate the adhesiveness interaction parameter. This investigation demonstrates the need for standardized methods to evaluate mucoadhesion and makes suggestions for a standard study design. Full article
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Open AccessArticle Extractable Free Polymer Chains Enhance Actuation Performance of Crystallizable Poly(ε-caprolactone) Networks and Enable Self-Healing
Polymers 2018, 10(3), 255; doi:10.3390/polym10030255
Received: 21 December 2017 / Revised: 23 February 2018 / Accepted: 27 February 2018 / Published: 1 March 2018
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Abstract
Crosslinking of thermoplastics is a versatile method to create crystallizable polymer networks, which are of high interest for shape-memory actuators. Here, crosslinked poly(ε-caprolactone) thermosets (cPCLs) were prepared from linear starting material, whereby the amount of extractable polymer was varied. Fractions of 5–60 wt
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Crosslinking of thermoplastics is a versatile method to create crystallizable polymer networks, which are of high interest for shape-memory actuators. Here, crosslinked poly(ε-caprolactone) thermosets (cPCLs) were prepared from linear starting material, whereby the amount of extractable polymer was varied. Fractions of 5–60 wt % of non-crosslinked polymer chains, which freely interpenetrate the crosslinked network, were achieved leading to differences in the resulting phase of the bulk material. This can be described as “sponge-like” with open or closed compartments depending on the amount of interpenetrating polymer. The crosslinking density and the average network chain length remained in a similar range for all network structures, while the theoretical accessible volume for reptation of the free polymer content is affected. This feature could influence or introduce new functions into the material created by thermomechanical treatment. The effect of interpenetrating PCL in cPCLs on the reversible actuation was analyzed by cyclic, uniaxial tensile tests. Here, high reversible strains of up to ∆ε = 24% showed the enhanced actuation performance of networks with a non-crosslinked PCL content of 30 wt % resulting from the crystal formation in the phase of the non-crosslinked PCL and co-crystallization with network structures. Additional functionalities are reprogrammability and self-healing capabilities for networks with high contents of extractable polymer enabling reusability and providing durable actuator materials. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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Open AccessArticle Thermal and Mechanical Characterization of EMA-TEGDMA Mixtures for Cosmetic Applications
Polymers 2018, 10(3), 256; doi:10.3390/polym10030256
Received: 17 January 2018 / Revised: 9 February 2018 / Accepted: 26 February 2018 / Published: 1 March 2018
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Abstract
Mixtures of methacrylic polymers are the most common materials for making composites to be used as resins for dental and cosmetic applications. Some of these mixtures are composed by poly(ethyl methacrylate) (PEMA) and poly(methyl methacrylate) (PMMA), which constitute a solid component to be
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Mixtures of methacrylic polymers are the most common materials for making composites to be used as resins for dental and cosmetic applications. Some of these mixtures are composed by poly(ethyl methacrylate) (PEMA) and poly(methyl methacrylate) (PMMA), which constitute a solid component to be mixed with a liquid component made out of methacrylate monomers. The reaction between the thermal initiator benzoyl peroxyde (BPO) present in the solid component and the activator of the polymerization process, N,N-dimethyl-p-toluidine (DMT) present in the liquid component, gives rise to thermoset materials. In the present study, different liquid formulations composed by a mixture of two methacrylic monomers, ethyl methacrylate (EMA) and triethylene glycol dimethacrylate (TEGDMA) for cosmetic applications, were prepared and characterized, using a commercial powder (POW) composed by PEMA and PMMA. With the aim of improving workability during final application of the material, it was necessary to slow down the polymerization rate of liquid formulations. Their thermal behavior was investigated by differential scanning calorimetric (DSC) in order to check the polymerization rate. Thermal stability of final materials was determined by thermogravimetric analysis (TGA). Dynamic mechanical thermal analysis (DMTA), microindentation hardness and impact tests were performed on final materials, to assess their performance with respect to standard formulation. The combination of thermal and mechanical properties allows choosing which formulations could be suitable for use in cosmetics. Full article
(This article belongs to the Special Issue Thermosets)
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Open AccessArticle Biomaterials Based on Electrospun Chitosan. Relation between Processing Conditions and Mechanical Properties
Polymers 2018, 10(3), 257; doi:10.3390/polym10030257
Received: 25 January 2018 / Revised: 16 February 2018 / Accepted: 26 February 2018 / Published: 1 March 2018
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Abstract
In this paper, it is shown that pure chitosan nanofibers and films were prepared with success in 0.5 M acetic acid as solvent using poly (ethylene oxide) (PEO) at different yields, allowing electrospinning of the blends. After processing, a neutralization step of chitosan
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In this paper, it is shown that pure chitosan nanofibers and films were prepared with success in 0.5 M acetic acid as solvent using poly (ethylene oxide) (PEO) at different yields, allowing electrospinning of the blends. After processing, a neutralization step of chitosan followed by water washing is performed, preserving the initial morphology of chitosan materials. The influence of the yield in PEO in the blend on the degree of swelling and hydrophilicity of films and nanofibers is demonstrated. Then, the mechanical behavior of blended nanofibers and films used as reference are determined for small stress applied in the linear domain by DMA and by uniaxial traction up to rupture. The dried and wet states are covered for the first time. It is shown that the mechanical properties are increased when electrospinning is performed in the presence of PEO up to a 70/30 chitosan/PEO weight ratio even after PEO extraction. This result can be explained by a better dispersion of the chitosan in the presence of PEO. Full article
(This article belongs to the Special Issue Advances in Chitin/Chitosan Characterization and Applications)
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Open AccessArticle Effects of Charge Density on Photophysics and Aggregation Behavior of Anionic Fluorene-Arylene Conjugated Polyelectrolytes
Polymers 2018, 10(3), 258; doi:10.3390/polym10030258
Received: 21 January 2018 / Revised: 23 February 2018 / Accepted: 26 February 2018 / Published: 2 March 2018
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Abstract
Three anionic fluorene-based alternating conjugated polyelectrolytes (CPEs) have been synthesized that have 9,9-bis(4-phenoxy-butylsulfonate) fluorene-2,7-diyl and 1,4-phenylene (PBS-PFP), 4,4′-biphenylene (PBS-PFP2), or 4,4″-p-terphenylene (PBS-PFP3) groups, and the effect of the length of the oligophenylene spacer on their aggregation and photophysics has been studied.
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Three anionic fluorene-based alternating conjugated polyelectrolytes (CPEs) have been synthesized that have 9,9-bis(4-phenoxy-butylsulfonate) fluorene-2,7-diyl and 1,4-phenylene (PBS-PFP), 4,4′-biphenylene (PBS-PFP2), or 4,4″-p-terphenylene (PBS-PFP3) groups, and the effect of the length of the oligophenylene spacer on their aggregation and photophysics has been studied. All form metastable dispersions in water, but can be solubilized using methanol, acetonitrile, or dioxane as cosolvents. This leads to increases in their emission intensities and blue shifts in fluorescence maxima due to break-up of aggregates. In addition, the emission maximum shifts to the blue and the loss of vibronic structure are observed when the number of phenylene rings is increased. Debsity Functional Theory (DFT) calculations suggest that this is due to increasing conformational flexibility as the number of phenylene rings increases. This is supported by increasing amplitude in the fast component in the fluorescence decay. The nonionic surfactant n-dodecylpentaoxyethylene glycol ether (C12E5) also breaks up aggregates, as seen by changes in fluorescence intensity and maximum. However, the loss in vibrational structure is less pronounced in this case, possibly due to a more rigid environment in the mixed surfactant-CPE aggregates. Further information on the aggregates formed with C12E5 was obtained by electrical conductivity measurements, which showed an initial increase in specific conductivity upon addition of surfactants, while at higher surfactant/CPE molar ratios a plateau was observed. The specific conductance in the plateau region decreased in the order PBS-PFP3 < PBS-PFP2 < PBS-PFP, in agreement with the change in charge density on the CPE. The reverse process of aggregate formation has been studied by injecting small volumes of solutions of CPEs dissolved at the molecular level in a good solvent system (50% methanol-water) into the poor solvent, water. Aggregation was monitored by changes in both fluorescence and light scattering. The rate of aggregation increases with hydrophobicity and concentration of sodium chloride but is only weakly dependent on temperature. Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications)
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Open AccessArticle Influence of Chitosan Ascorbate Chirality on the Gelation Kinetics and Properties of Silicon-Chitosan-Containing Glycerohydrogels
Polymers 2018, 10(3), 259; doi:10.3390/polym10030259
Received: 20 December 2017 / Revised: 15 February 2018 / Accepted: 28 February 2018 / Published: 2 March 2018
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Abstract
The influence of the chirality of chitosan ascorbate on the gelation kinetics and the properties of hybrid silicon-chitosan-containing glycerohydrogels were studied with a deep estimation of the stereospecificity of chitosan polysalts with l- and d-ascorbic acid diastereomers and their biological effects.
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The influence of the chirality of chitosan ascorbate on the gelation kinetics and the properties of hybrid silicon-chitosan-containing glycerohydrogels were studied with a deep estimation of the stereospecificity of chitosan polysalts with l- and d-ascorbic acid diastereomers and their biological effects. It has been established that l- and d-diastereomerically enriched chitosan ascorbates are characterized by a positive Cotton effect and differ in the wavelength of the maximum of the dichroic band (250 and 240 nm), as well as in the values of its specific ellipticity (21.8 × 105 and 39.2 × 105 deg·mL·dm−1·g−1), the sign of specific optical rotation (+ and −), the type of dispersion curves (anomalous and smooth), as well as the condensed phase morphology (anisodiametric particles with optical anisotropy and confocal domains of spherical shape, respectively). In the biomimetic sol-gel synthesis of silicon-chitosan-containing glycerohydrogels using silicon tetraglycerolate as a precursor, it was found that chitosan d-ascorbate retarded gelation. Thin congruent plates obtained from the corresponding glycerohydrogels based on chitosan d-ascorbate have higher mechanical strength and elasticity under uniaxial stretching and lower values of Young’s modulus. It has been shown that the systems based on chitosan d-ascorbate show the greatest antibacterial activity against Staphylococcus aureus 209P and Escherichia coli 113-13 and significantly promote the viability of normal human dermal fibroblasts. The results of our assessment of the biological properties of chitosan polysalts are unexpected, since ascorbic acid exhibits biological activity as its l-isomer only. Full article
(This article belongs to the Special Issue Hydrogels in Tissue Engineering and Regenerative Medicine)
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Open AccessArticle Humidity Induces Changes in the Dimensions of Hydrogel-Coated Wool Yarns
Polymers 2018, 10(3), 260; doi:10.3390/polym10030260
Received: 3 January 2018 / Revised: 16 February 2018 / Accepted: 28 February 2018 / Published: 2 March 2018
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Abstract
Polymeric hydrogel based on acrylic acid (AA) and N,N-dimethylacrylamide (DMAA) was prepared by photopolymerization reaction, using nano-alumina as the inorganic crosslinker. Hydrogel-coated wool yarns determine their dimensional changes under humidity conditions. Surface morphology of the hydrogel-coated wool yarns was carried
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Polymeric hydrogel based on acrylic acid (AA) and N,N-dimethylacrylamide (DMAA) was prepared by photopolymerization reaction, using nano-alumina as the inorganic crosslinker. Hydrogel-coated wool yarns determine their dimensional changes under humidity conditions. Surface morphology of the hydrogel-coated wool yarns was carried out using SEM microscopy. The hydrogel was further characterized by Fourier transformer infrared spectrum (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermogravimetry (DTG). This contribution showed that UV-initiated polymerization coating wool yarns can change the functional properties of wool fibers. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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Open AccessArticle Modelling of Rod-Like Fillers’ Rotation and Translation near Two Growing Cells in Conductive Polymer Composite Foam Processing
Polymers 2018, 10(3), 261; doi:10.3390/polym10030261
Received: 11 January 2018 / Revised: 14 February 2018 / Accepted: 27 February 2018 / Published: 2 March 2018
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Abstract
We developed a simple analytical model to describe the instantaneous location and angle of rod-like conductive fillers as a function of cell growth during the foaming of conductive polymer composites (CPCs). First, we modelled the motion of the fillers that resulted from the
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We developed a simple analytical model to describe the instantaneous location and angle of rod-like conductive fillers as a function of cell growth during the foaming of conductive polymer composites (CPCs). First, we modelled the motion of the fillers that resulted from the growth of one cell. Then, by taking into account the fillers located at the line that connected the centres of the two growing cells, we found the final filler’s angle and location. We identified this as a function of the corresponding cell size, filler size, and the filler’s initial angle and location. We based the model’s development on the assumption that a polymer melt is incompressible during cell growth. The two-cell growth model is better than the one-cell growth model because it describes the filler’s movement in the cell wall between the two growing cells. The results revealed that the fillers near the cell were the ones most affected by the cell growth, while those at the midpoint between the two cells were the least affected. As a cell grows, its affected polymer area also increases. A dimensionless factor η was introduced to demonstrate the effects of the cell size and the filler length on the filler’s interconnectivity in the CPC foams. It is vital to keep the filler length comparable to the cell size when preparing CPC foams with the desired electrical conductivity. Our research provides a deeper understanding of the mechanism through which foaming influences the filler connections in CPC foams. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle Lipase-Catalyzed Synthesis, Properties Characterization, and Application of Bio-Based Dimer Acid Cyclocarbonate
Polymers 2018, 10(3), 262; doi:10.3390/polym10030262
Received: 6 February 2018 / Revised: 28 February 2018 / Accepted: 1 March 2018 / Published: 3 March 2018
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Abstract
Dimer acid cyclocarbonate (DACC) is synthesized from glycerol carbonate (GC) and Sapium sebiferum oil-derived dimer acid (DA, 9-[(Z)-non-3-enyl]-10-octylnonadecanedioic acid). Meanwhile, DACC can be used for synthetic materials of bio-based non-isocyanate polyurethane (bio-NIPU). In this study, DACC was synthesized by the esterification
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Dimer acid cyclocarbonate (DACC) is synthesized from glycerol carbonate (GC) and Sapium sebiferum oil-derived dimer acid (DA, 9-[(Z)-non-3-enyl]-10-octylnonadecanedioic acid). Meanwhile, DACC can be used for synthetic materials of bio-based non-isocyanate polyurethane (bio-NIPU). In this study, DACC was synthesized by the esterification of dimer acid and glycerol carbonate using Novozym 435 (Candida antarctica lipase B) as the biocatalyst. Via the optimizing reaction conditions, the highest yield of 76.00% and the lowest acid value of 43.82 mg KOH/g were obtained. The product was confirmed and characterized by Fourier transform-infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). Then, the synthetic DACC was further used to synthesize bio-NIPU, which was examined by FTIR, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC), indicating that it possesses very good physio-chemical properties and unique material quality with a potential prospect in applications. Full article
(This article belongs to the Special Issue Polymers from Renewable Resources)
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Open AccessArticle Enhanced Figures of Merit for a High-Performing Actuator in Electrostrictive Materials
Polymers 2018, 10(3), 263; doi:10.3390/polym10030263
Received: 8 February 2018 / Revised: 28 February 2018 / Accepted: 1 March 2018 / Published: 3 March 2018
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Abstract
The overall performance of an electrostrictive polymer is rated by characteristic numbers, such as its transverse strain, blocking force, and energy density, which are clearly limited by several parameters. Besides the geometrical impact, intrinsic material parameters, such as the permittivity coefficient as well
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The overall performance of an electrostrictive polymer is rated by characteristic numbers, such as its transverse strain, blocking force, and energy density, which are clearly limited by several parameters. Besides the geometrical impact, intrinsic material parameters, such as the permittivity coefficient as well as the Young’s modulus and the breakdown electric field, have strong influences on the actuation properties of an electroactive polymer and thus on the device’s overall behavior. As a result, an analysis of the figures of merit (FOMs) involving all relevant material parameters for the transverse strain, the blocking force, and the energy density was carried out, making it possible to determine the choice of polymer matrix in order to achieve a high actuator performance. Another purpose of this work was to demonstrate the possibility of accurately measuring the free deflection without the application of an external force and inversely measuring the blocking force under quasi-static displacement. The experimental results show good electrostrictive characteristics of the plasticized terpolymer under relatively low electric fields. Full article
(This article belongs to the Special Issue Fluorinated Polymers)
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Open AccessArticle Prestressed Unbonded Reinforcement System with Multiple CFRP Plates for Fatigue Strengthening of Steel Members
Polymers 2018, 10(3), 264; doi:10.3390/polym10030264
Received: 31 January 2018 / Revised: 28 February 2018 / Accepted: 2 March 2018 / Published: 4 March 2018
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Abstract
Carbon fiber reinforced polymer (CFRP) composites have exhibited a great potential for strengthening of steel structures. In the current study, an innovative prestressed unbonded reinforcement (PUR) system is introduced for fatigue strengthening of existing steel members. The system relies on a pair of
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Carbon fiber reinforced polymer (CFRP) composites have exhibited a great potential for strengthening of steel structures. In the current study, an innovative prestressed unbonded reinforcement (PUR) system is introduced for fatigue strengthening of existing steel members. The system relies on a pair of mechanical clamps; each holds multiple CFRP plates and anchors their prestressing forces to the steel substrate via friction. A finite element model was established to optimize the design of the required mechanical components of the system. A set of static and fatigue tests was conducted on the developed mechanical clamps as the key elements of the proposed PUR system. The performance of the PUR system was then evaluated using a set of fatigue tests on two precracked steel plate specimens, one without any strengthening system and the other one strengthened with the proposed PUR system. In the latter specimen, the CFRP plates were prestressed up to about 800 MPa (approximately 30% of the CFRP tensile strength), which resulted in a complete fatigue crack arrest in the precracked steel plate. Furthermore, neither slippage of the mechanical clamps nor any prestress loss in the CFRP plates was observed after 7.5 million fatigue cycles. Based on the promising experimental results, obtained from the sets of fatigue tests performed in the current study, it can be concluded that the proposed PUR system can be considered as an efficient alternative to the conventional bonded reinforcement solutions for fatigue strengthening of damaged steel members. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2017")
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Open AccessArticle Revealing the Interface Structure and Bonding Mechanism of Coupling Agent Treated WPC
Polymers 2018, 10(3), 266; doi:10.3390/polym10030266
Received: 27 January 2018 / Revised: 23 February 2018 / Accepted: 27 February 2018 / Published: 5 March 2018
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Abstract
This paper presents the interfacial optimisation of wood plastic composites (WPC) based on recycled wood flour and polyethylene by employing maleated and silane coupling agents. The effect of the incorporation of the coupling agents on the variation of chemical structure of the composites
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This paper presents the interfacial optimisation of wood plastic composites (WPC) based on recycled wood flour and polyethylene by employing maleated and silane coupling agents. The effect of the incorporation of the coupling agents on the variation of chemical structure of the composites were investigated by Attenuated total reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR) and Solid state 13C Nuclear Magnetic Resonance spectroscopy (NMR) analyses. The results revealed the chemical reactions that occurred between the coupling agents and raw materials, which thus contributed to the enhancement of compatibility and interfacial adhesion between the constituents of WPC. NMR results also indicated that there existed the transformation of crystalline cellulose to an amorphous state during the coupling agent treatments, reflecting the inferior resonance of crystalline carbohydrates. Fluorescence Microscope (FM) and Scanning Electron Microscope (SEM) analyses showed the improvements of wood particle dispersion and wettability, compatibility of the constituents, and resin penetration, and impregnation of the composites after the coupling agent treatments. The optimised interface of the composites was attributed to interdiffusion, electrostatic adhesion, chemical reactions, and mechanical interlocking bonding mechanisms. Full article
(This article belongs to the collection Polymeric Adhesives)
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Open AccessArticle Thickening Supercritical CO2 with π-Stacked Co-Polymers: Molecular Insights into the Role of Intermolecular Interaction
Polymers 2018, 10(3), 268; doi:10.3390/polym10030268
Received: 16 January 2018 / Revised: 23 February 2018 / Accepted: 1 March 2018 / Published: 6 March 2018
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Abstract
Vinyl Benzoate/Heptadecafluorodecyl acrylate (VBe/HFDA) co-polymers were synthesized and characterized as thickening agents for supercritical carbon dioxide (SC-CO2). The solubility and thickening capability of the co-polymer samples in SC-CO2 were evaluated by measuring cloud point pressure and relative viscosity. The molecular
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Vinyl Benzoate/Heptadecafluorodecyl acrylate (VBe/HFDA) co-polymers were synthesized and characterized as thickening agents for supercritical carbon dioxide (SC-CO2). The solubility and thickening capability of the co-polymer samples in SC-CO2 were evaluated by measuring cloud point pressure and relative viscosity. The molecular dynamics (MD) simulation for all atoms was employed to simulate the microscopic molecular behavior and the intermolecular interaction of co-polymer–CO2 systems. We found that the introduction of VBe group decreased the polymer–CO2 interaction and increased the polymer–polymer interaction, leading to a reduction in solubility of the co-polymers in SC-CO2. However, the co-polymer could generate more effective inter-chain interaction and generate more viscosity enhancement compared to the Poly(Heptadecafluorodecyl) (PHFDA) homopolymer due to the driving force provided by π-π stacking of the VBe groups. The optimum molar ratio value for VBe in co-polymers for the viscosity enhancement of SC-CO2 was found to be 0.33 in this work. The P(HFDA0.67-co-VBe0.33) was able to enhance the viscosity of SC-CO2 by 438 times at 5 wt. %. Less VBe content would result in a lack of intermolecular interaction, although excessive VBe content would generate more intramolecular π-π stacking and less intermolecular π-π stacking. Both conditions reduce the thickening capability of the P(HFDA-co-VBe) co-polymer. This work presented the relationship between structure and performance of the co-polymers in SC-CO2 by combining experiment and molecular simulations. Full article
(This article belongs to the Special Issue π-Stacked Polymers)
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Open AccessArticle Hyperthermia-Triggered Gemcitabine Release from Polymer-Coated Magnetite Nanoparticles
Polymers 2018, 10(3), 269; doi:10.3390/polym10030269
Received: 5 February 2018 / Revised: 27 February 2018 / Accepted: 3 March 2018 / Published: 6 March 2018
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Abstract
In this work a combined, multifunctional platform, which was devised for the simultaneous application of magnetic hyperthermia and the delivery of the antitumor drug gemcitabine, is described and tested in vitro. The system consists of magnetite particles embedded in a polymer envelope, designed
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In this work a combined, multifunctional platform, which was devised for the simultaneous application of magnetic hyperthermia and the delivery of the antitumor drug gemcitabine, is described and tested in vitro. The system consists of magnetite particles embedded in a polymer envelope, designed to make them biocompatible, thanks to the presence of poly (ethylene glycol) in the polymer shell. The commercial particles, after thorough cleaning, are provided with carboxyl terminal groups, so that at physiological pH they present negative surface charge. This was proved by electrophoresis, and makes it possible to electrostatically adsorb gemcitabine hydrochloride, which is the active drug of the resulting nanostructure. Both electrophoresis and infrared spectroscopy are used to confirm the adsorption of the drug. The gemcitabine-loaded particles are tested regarding their ability to release it while heating the surroundings by magnetic hyperthermia, in principle their chances as antitumor agents. The release, with first-order kinetics, is found to be faster when carried out in a thermostated bath at 43 °C than at 37 °C, as expected. But, the main result of this investigation is that while the particles retain their hyperthermia response, with reasonably high heating power, they release the drug faster and with zeroth-order kinetics when they are maintained at 43 °C under the action of the alternating magnetic field used for hyperthermia. Full article
(This article belongs to the Special Issue Selected Papers from "ECIS 2017")
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Open AccessArticle Nature-Inspired Green Procedure for Improving Performance of Protein-Based Nanocomposites via Introduction of Nanofibrillated Cellulose-Stablized Graphene/Carbon Nanotubes Hybrid
Polymers 2018, 10(3), 270; doi:10.3390/polym10030270
Received: 7 February 2018 / Revised: 28 February 2018 / Accepted: 2 March 2018 / Published: 6 March 2018
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Abstract
Soy protein isolate (SPI) provides a potential alternative biopolymer source to fossil fuels, but improving the mechanical properties and water resistance of SPI composites remains a huge challenge. Inspired by the synergistic effect of natural nacre, we developed a novel approach to fabricate
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Soy protein isolate (SPI) provides a potential alternative biopolymer source to fossil fuels, but improving the mechanical properties and water resistance of SPI composites remains a huge challenge. Inspired by the synergistic effect of natural nacre, we developed a novel approach to fabricate high-performance SPI nanocomposite films based on 2D graphene (G) nanosheets and 1D carbon nanotubes (CNTs) and nanofibrillated cellulose (NFC) using a casting method. The introduction of web-like NFC promoted the uniform dispersion of graphene/CNTs in the biopolymer matrix, as well as a high extent of cross-linkage combination between the fillers and SPI matrix. The laminated and cross-linked structures of the different nanocomposite films were observed by field-emission scanning electron microscope (FE-SEM) images. Due to the synergistic interactions of π–π stacking and hydrogen bonding between the nanofillers and SPI chains, the tensile strength of SPI/G/CNT/NFC film significantly increased by 78.9% and the water vapor permeability decreased by 31.76% in comparison to neat SPI film. In addition, the ultraviolet-visible (UV-vis) light barrier performance, thermal stability, and hydrophobicity of the films were significantly improved as well. This bioinspired synergistic reinforcing strategy opens a new path for constructing high-performance nanocomposites. Full article
(This article belongs to the Special Issue Polymer Hybrid Materials)
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Open AccessArticle Swelling Behaviour of Superabsorbent Polymers for Soil Amendment under Different Loads
Polymers 2018, 10(3), 271; doi:10.3390/polym10030271
Received: 6 January 2018 / Revised: 21 February 2018 / Accepted: 3 March 2018 / Published: 6 March 2018
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Abstract
One of the most important among the numerous applications of superabsorbent polymers (SAPs), also known as hydrogels, is soil improvement and supporting plant vegetation in agriculture and environmental engineering. Currently, when water scarcity involves water stress, they are becoming still more commonly used
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One of the most important among the numerous applications of superabsorbent polymers (SAPs), also known as hydrogels, is soil improvement and supporting plant vegetation in agriculture and environmental engineering. Currently, when water scarcity involves water stress, they are becoming still more commonly used for water retention in soil. As it turns out, one of the major factors influencing the superabsorbent polymers water retention capacity (WRC) is the load of soil. The study presents test results of absorbency under load (AUL) of SAPs. The object of the analysis was cross-linked copolymer of acrylamide and potassium acrylate, of a granulation of 0.50–3.15 mm. The authors analysed the water absorption capacity of the superabsorbent polymers under loads characteristic for 3 different densities of soil (1.3 g∙cm−3, 0.9 g∙cm−3, 0.5 g∙cm−3) and three different depths of application (10 cm, 20 cm, and 30 cm). Soil load and bulk densities were simulated by using weights. The experiments were conducted with a Mecmesin Multitest 2.5-xt apparatus. The obtained results demonstrate a very significant reduction in water absorption capacity by SAP under load. For a 30 cm deep layer of soil of bulk density of 1.3 g∙cm−3, after 1 h, this value amounted to 5.0 g∙g−1, and for the control sample without load, this value amounted to more than 200 g∙g−1. For the lowest load in the experiment, which was 0.49 kPa (10 cm deep layer of soil of a bulk density of 0.5 g∙cm−3), this value was 33.0 g∙g−1 after 60 min. Loads do not only limit the volume of the swelling superabsorbent polymer but they also prolong the swelling time. The soil load caused a decrease in the absorption capacity from 338.5 g∙g−1 to 19.3 g∙g−1, as well as a prolongation of the swelling time. The rate parameter (time required to reach 63% of maximum absorption capacity) increased from 63 min for the control sample to more than 300 min for the largest analysed load of 3.83 kPa. The implications of soil load on superabsorbent polymer swelling are crucial for its usage and thus for the soil system. This knowledge might be employed for the more effective usage of superabsorbent polymers in agriculture and environmental engineering, in which they are commonly used to retain water and to support plant growth. Full article
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Open AccessArticle ECM Decorated Electrospun Nanofiber for Improving Bone Tissue Regeneration
Polymers 2018, 10(3), 272; doi:10.3390/polym10030272
Received: 25 January 2018 / Revised: 23 February 2018 / Accepted: 26 February 2018 / Published: 6 March 2018
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Abstract
Optimization of nanofiber surface properties can lead to enhanced tissue regeneration outcomes in the context of bone tissue engineering. Herein, we developed a facile strategy to decorate elctrospun nanofibers using extracellular matrix (ECM) in order to improve their performance for bone tissue engineering.
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Optimization of nanofiber surface properties can lead to enhanced tissue regeneration outcomes in the context of bone tissue engineering. Herein, we developed a facile strategy to decorate elctrospun nanofibers using extracellular matrix (ECM) in order to improve their performance for bone tissue engineering. Electrospun PLLA nanofibers (PLLA NF) were seeded with MC3T3-E1 cells and allowed to grow for two weeks in order to harvest a layer of ECM on nanofiber surface. After decellularization, we found that ECM was successfully preserved on nanofiber surface while maintaining the nanostructure of electrospun fibers. ECM decorated on PLLA NF is biologically active, as evidenced by its ability to enhance mouse bone marrow stromal cells (mBMSCs) adhesion, support cell proliferation and promote early stage osteogenic differentiation of mBMSCs. Compared to PLLA NF without ECM, mBMSCs grown on ECM/PLLA NF exhibited a healthier morphology, faster proliferation profile, and more robust osteogenic differentiation. Therefore, our study suggests that ECM decoration on electrospun nanofibers could serve as an efficient approach to improving their performance for bone tissue engineering. Full article
(This article belongs to the Special Issue Polymer Scaffolds for Biomedical Application)
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Open AccessArticle The Anomalies of Hyaluronan Structures in Presence of Surface Active Phospholipids—Molecular Mass Dependence
Polymers 2018, 10(3), 273; doi:10.3390/polym10030273
Received: 1 February 2018 / Revised: 2 March 2018 / Accepted: 4 March 2018 / Published: 6 March 2018
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Abstract
Interactions between hyaluronan (A-) and phospholipids play a key role in many systems in the human body. One example is the articular cartilage system, where the synergistic effect of such interactions supports nanoscale lubrication. A molecular dynamics simulation has been performed to understand
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Interactions between hyaluronan (A-) and phospholipids play a key role in many systems in the human body. One example is the articular cartilage system, where the synergistic effect of such interactions supports nanoscale lubrication. A molecular dynamics simulation has been performed to understand the process of formation of hydrogen bonds inside the hyaluronan network, both in the presence and absence of phospholipids. Additionally, the effect of the molecular mass of (A-) was analyzed. The main finding of this work is a robust demonstration of the optimal parameters (H-bond energy, molecular mass) influencing the facilitated lubrication mechanism of the articular cartilage system. Simulation results show that the presence of phospholipids has the greatest influence on hyaluronan at low molecular mass. We also show the specific sites of H-bonding between chains. Simulation results can help to understand how hyaluronan and phospholipids interact at several levels of articular cartilage system functioning. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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Open AccessArticle Two Chemically Stable Cd(II) Polymers as Fluorescent Sensor and Photocatalyst for Aromatic Dyes
Polymers 2018, 10(3), 274; doi:10.3390/polym10030274
Received: 24 January 2018 / Revised: 22 February 2018 / Accepted: 23 February 2018 / Published: 7 March 2018
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Abstract
Two new 2D Cd(II)-based coordination polymers (CPs), viz. [Cd2(H2L)2(2,2’-bipy)2] (1) and [Cd(L)0.5(phen)·0.5H2O] (2), have been constructed using ethylene glycol ether bridging tetracarboxylate ligand 5,5′(4,4′-phenylenebis(methyleneoxy)) diisophthalic acid (H
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Two new 2D Cd(II)-based coordination polymers (CPs), viz. [Cd2(H2L)2(2,2’-bipy)2] (1) and [Cd(L)0.5(phen)·0.5H2O] (2), have been constructed using ethylene glycol ether bridging tetracarboxylate ligand 5,5′(4,4′-phenylenebis(methyleneoxy)) diisophthalic acid (H4L). Both CPs behaved as profound fluorescent sensor for Fe3+ ion and nitro-aromatics (NACs), specifically 2,4,6-trinitrophenol (TNP). The stability at elevated temperature and photocatalytic behaviors of both 1 and 2 for photo-decomposition of aromatic dyes have also been explored. An attempt has been made to explore the plausible mechanism related with the decrease in fluorescence intensity of 1 and 2 in presence of NACs using theoretical calculations. Additionally, the probable mechanism of photo catalysis by 1 and 2 to photo-degrade aromatic dyes has been explained using density of states (DOS) calculations. Full article
(This article belongs to the Special Issue Coordination Polymer)
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Open AccessArticle Co-Deposition of a Hydrogel/Calcium Phosphate Hybrid Layer on 3D Printed Poly(Lactic Acid) Scaffolds via Dip Coating: Towards Automated Biomaterials Fabrication
Polymers 2018, 10(3), 275; doi:10.3390/polym10030275
Received: 23 October 2017 / Revised: 16 February 2018 / Accepted: 28 February 2018 / Published: 7 March 2018
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Abstract
The article describes the surface modification of 3D printed poly(lactic acid) (PLA) scaffolds with calcium phosphate (CP)/gelatin and CP/chitosan hybrid coating layers. The presence of gelatin or chitosan significantly enhances CP co-deposition and adhesion of the mineral layer on the PLA scaffolds. The
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The article describes the surface modification of 3D printed poly(lactic acid) (PLA) scaffolds with calcium phosphate (CP)/gelatin and CP/chitosan hybrid coating layers. The presence of gelatin or chitosan significantly enhances CP co-deposition and adhesion of the mineral layer on the PLA scaffolds. The hydrogel/CP coating layers are fairly thick and the mineral is a mixture of brushite, octacalcium phosphate, and hydroxyapatite. Mineral formation is uniform throughout the printed architectures and all steps (printing, hydrogel deposition, and mineralization) are in principle amenable to automatization. Overall, the process reported here therefore has a high application potential for the controlled synthesis of biomimetic coatings on polymeric biomaterials. Full article
(This article belongs to the Special Issue Bio-inspired and Bio-based Polymers)
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Open AccessArticle Morphological Structure, Rheological Behavior, Mechanical Properties and Sound Insulation Performance of Thermoplastic Rubber Composites Reinforced by Different Inorganic Fillers
Polymers 2018, 10(3), 276; doi:10.3390/polym10030276
Received: 13 February 2018 / Revised: 1 March 2018 / Accepted: 2 March 2018 / Published: 7 March 2018
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Abstract
The application area of a sound insulation material is highly dependent on the technology adopted for its processing. In this study, thermoplastic rubber (TPR, polypropylene/ethylene propylene diene monomer) composites were simply prepared via an extrusion method. Two microscale particles, CaCO3 and hollow
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The application area of a sound insulation material is highly dependent on the technology adopted for its processing. In this study, thermoplastic rubber (TPR, polypropylene/ethylene propylene diene monomer) composites were simply prepared via an extrusion method. Two microscale particles, CaCO3 and hollow glass microspheres (HGW) were chosen to not only enhance the sound insulation but also reinforced the mechanical properties. Meanwhile, the processing capability of composites was confirmed. SEM images showed that the CaCO3 was uniformly dispersed in TPR matrix with ~3 μm scale aggregates, while the HGM was slightly aggregated to ~13 μm scale. The heterogeneous dispersion of micro-scale fillers strongly affected the sound transmission loss (STL) value of composites. The STL values of TPR composites with 40 wt % CaCO3 and 20 wt % HGM composites were about 12 dB and 7 dB higher than that of pure TPR sample, respectively. The improved sound insulation performances of the composites have been attributed to the enhanced reflection and dissipate sound energy in the heterogeneous composite. Moreover, the mechanical properties were also enhanced. The discontinued sound impedance and reinforced stiffness were considered as crucial for the sound insulation. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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Open AccessArticle Thermoconductive Thermosetting Composites Based on Boron Nitride Fillers and Thiol-Epoxy Matrices
Polymers 2018, 10(3), 277; doi:10.3390/polym10030277
Received: 6 February 2018 / Revised: 28 February 2018 / Accepted: 4 March 2018 / Published: 7 March 2018
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Abstract
In this work, the effect of the addition of boron nitride (BN) fillers in a thiol-cycloaliphatic epoxy formulation has been investigated. Calorimetric studies put into evidence that the kinetics of the curing has been scarcely affected and that the addition of particles does
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In this work, the effect of the addition of boron nitride (BN) fillers in a thiol-cycloaliphatic epoxy formulation has been investigated. Calorimetric studies put into evidence that the kinetics of the curing has been scarcely affected and that the addition of particles does not affect the final structure of the network. Rheologic studies have shown the increase in the viscoelastic properties on adding the filler and allow the percolation threshold to be calculated, which was found to be 35.5%. The use of BN agglomerates of bigger size increases notably the viscosity of the formulation. Glass transition temperatures are not affected by the filler added, but Young’s modulus and hardness have been notably enhanced. Thermal conductivity of the composites prepared shows a linear increase with the proportion of BN particle sheets added, reaching a maximum of 0.97 W/K·m. The addition of 80 μm agglomerates, allowed to increase this value until 1.75 W/K·m. Full article
(This article belongs to the Special Issue Hybrid Materials Based on Thermosets)
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Open AccessArticle Effect of Cationic Surface Modification on the Rheological Behavior and Microstructure of Nanocrystalline Cellulose
Polymers 2018, 10(3), 278; doi:10.3390/polym10030278
Received: 4 February 2018 / Revised: 23 February 2018 / Accepted: 5 March 2018 / Published: 7 March 2018
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Abstract
In the present work, the microstructure and rheological behavior of nanocrystalline cellulose (NCC) and cationically modified NCC (CNCC) were comparatively studied. The resultant CNCC generally showed improved dispersion and higher thermal stability in comparison to the un-modified NCC. The rheological behavior demonstrated that
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In the present work, the microstructure and rheological behavior of nanocrystalline cellulose (NCC) and cationically modified NCC (CNCC) were comparatively studied. The resultant CNCC generally showed improved dispersion and higher thermal stability in comparison to the un-modified NCC. The rheological behavior demonstrated that the viscosity of the NCC suspension substantially decreased with the increasing shear rate (0.01–100 s−1), showing the typical characteristics of a pseudoplastic fluid. In contrast, the CNCC suspensions displayed a typical three-region behavior, regardless of changes in pH, temperature, and concentration. Moreover, the CNCC suspensions exhibited higher shear stress and viscosity at a given shear rate (0.01–100 s−1) than the NCC suspension. Meanwhile, the dynamic viscoelasticity measurements revealed that the CNCC suspensions possessed a higher elastic (G′) and loss modulus (G″) than NCC suspensions over the whole frequency range (0.1–500 rad·s−1), providing evidence that the surface cationization of NCC makes it prone to behave as a gel-like structure. Full article
(This article belongs to the Special Issue Surface Modification and Functional Coatings for Polymers)
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Open AccessFeature PaperArticle Bioactive Sr(II)/Chitosan/Poly(ε-caprolactone) Scaffolds for Craniofacial Tissue Regeneration. In Vitro and In Vivo Behavior
Polymers 2018, 10(3), 279; doi:10.3390/polym10030279
Received: 31 January 2018 / Revised: 23 February 2018 / Accepted: 2 March 2018 / Published: 7 March 2018
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Abstract
In craniofacial tissue regeneration, the current gold standard treatment is autologous bone grafting, however, it presents some disadvantages. Although new alternatives have emerged there is still an urgent demand of biodegradable scaffolds to act as extracellular matrix in the regeneration process. A potentially
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In craniofacial tissue regeneration, the current gold standard treatment is autologous bone grafting, however, it presents some disadvantages. Although new alternatives have emerged there is still an urgent demand of biodegradable scaffolds to act as extracellular matrix in the regeneration process. A potentially useful element in bone regeneration is strontium. It is known to promote stimulation of osteoblasts while inhibiting osteoclasts resorption, leading to neoformed bone. The present paper reports the preparation and characterization of strontium (Sr) containing hybrid scaffolds formed by a matrix of ionically cross-linked chitosan and microparticles of poly(ε-caprolactone) (PCL). These scaffolds of relatively facile fabrication were seeded with osteoblast-like cells (MG-63) and human bone marrow mesenchymal stem cells (hBMSCs) for application in craniofacial tissue regeneration. Membrane scaffolds were prepared using chitosan:PCL ratios of 1:2 and 1:1 and 5 wt % Sr salts. Characterization was performed addressing physico-chemical properties, swelling behavior, in vitro biological performance and in vivo biocompatibility. Overall, the composition, microstructure and swelling degree (≈245%) of scaffolds combine with the adequate dimensional stability, lack of toxicity, osteogenic activity in MG-63 cells and hBMSCs, along with the in vivo biocompatibility in rats allow considering this system as a promising biomaterial for the treatment of craniofacial tissue regeneration. Full article
(This article belongs to the Special Issue Advances in Chitin/Chitosan Characterization and Applications)
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Open AccessArticle Multidimensional Nanocomposites of Epoxy Reinforced with 1D and 2D Carbon Nanostructures for Improve Fracture Resistance
Polymers 2018, 10(3), 281; doi:10.3390/polym10030281
Received: 6 February 2018 / Revised: 1 March 2018 / Accepted: 2 March 2018 / Published: 8 March 2018
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Abstract
A hybrid nanocomposites based on epoxy reinforced with a combination of 1D and 2D carbon nanomaterials for improving impact resistance are reported. Multi-walled carbon nanotubes and oxidized-multi-walled carbon nanotubes are used as 1D nanoreinforcements, and graphene derivative materials such as graphene oxide and
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A hybrid nanocomposites based on epoxy reinforced with a combination of 1D and 2D carbon nanomaterials for improving impact resistance are reported. Multi-walled carbon nanotubes and oxidized-multi-walled carbon nanotubes are used as 1D nanoreinforcements, and graphene derivative materials such as graphene oxide and reduced graphene oxide are utilized as 2D nanoreinforcements. In this research, the impact resistance of epoxy matrix reinforced with 1D or 2D and the mixture of both nanomaterials is studied. The research is focused on evaluation of the influence of adding different combinations of nanomaterials into epoxy resin and their Izod impact response. Moreover, fracture surface of nanocomposites is observed by scanning electron microscopy. Images show differences between the surfaces of brittle nature on thermoset epoxy polymer and tough nanocomposites. Synergy created with 1D and 2D nanomaterials produces stable dispersions in the processing, reflected in the interface. The interactions in nanocomposites are evidenced by infrared spectra, principally on the peaks related to oxygenated functional groups present in nanomaterials and absent in polymer matrix. Consequently, an increase of 138% in fracture strength of nanocomposites is exhibited, in comparison to the neat epoxy matrix. In addition, hybrid nanocomposites were synthesized in two different methods to evaluate the influence of manufacturing method on final properties of nanocomposites. Full article
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Open AccessArticle Mechanocatalytic Solvent-Free Esterification of Sugarcane Bagasse
Polymers 2018, 10(3), 282; doi:10.3390/polym10030282
Received: 17 January 2018 / Revised: 17 February 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
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Abstract
Esterification is a versatile way to produce the derivatives of lignocellulose with developed properties. However, the traditional heterogeneous esterification of lignocellulose suffered from the drawbacks of low efficiency, additional reaction medium and heating. In the present study, an efficient method was developed to
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Esterification is a versatile way to produce the derivatives of lignocellulose with developed properties. However, the traditional heterogeneous esterification of lignocellulose suffered from the drawbacks of low efficiency, additional reaction medium and heating. In the present study, an efficient method was developed to produce the functionalized sugarcane bagasse (SCB) by ball milling without any additional solvents and heating. The effects of pulverization time, rotation speed, the kind of linear chain anhydrides, the ratio of anhydrides to SCB, with or without pyridine catalyst and the dosage of catalyst were investigated on weight percent gain (WPG) of SCB esters. The results indicated that the high efficiency of this mechanocatalystic esterification was probably due to the destroyed crystalline structure and the promoted penetration of the esterifying reagent onto SCB bulk caused by ball milling. The maximum WPG of SCB acetate, propionate and butyrate reached 33.3%, 33.6% and 32.4%, respectively. The physicochemical structure of the esterified SCB was characterized with Fourier transform infrared spectra (FT-IR), solid state cross-polarized magic angle spinning 13C nuclear magnetic resonance (CP/MAS 13C-NMR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The direct evidence of the esterification occurrence was provided with FT-IR and solid-state CP/MAS 13C-NMR. The thermal stability of SCB increased upon the mechanocatalytic esterification. The results implied that the relatively homogeneous modification was achieved with this semi-homogeneous esterification method by ball milling. Full article
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Open AccessArticle Thermo-Responsive Fluorescent Polymers with Diverse LCSTs for Ratiometric Temperature Sensing through FRET
Polymers 2018, 10(3), 283; doi:10.3390/polym10030283
Received: 30 January 2018 / Revised: 21 February 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
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Abstract
Temperature is a significant parameter to regulate biological reactions and functions inside cells. Sensing the intracellular temperature with a competent method is necessary to understand life science. In this work, an energy-transfer polymeric thermometer was designed for temperature sensing. The thermometer was prepared
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Temperature is a significant parameter to regulate biological reactions and functions inside cells. Sensing the intracellular temperature with a competent method is necessary to understand life science. In this work, an energy-transfer polymeric thermometer was designed for temperature sensing. The thermometer was prepared from two thermo-responsive polymers with different lower critical solution temperatures (LCSTs) of 31.1 °C and 48.6 °C, coupling with blue and red fluorescent molecules, respectively, developed for ratiometric temperature sensing based on the Förster resonance energy transfer (FRET) mechanism. The polymers were synthesized from two monomers, N-isopropylacrylamide (NIPA) and N-isopropylmethacrylamide (NIPmA), which provided different temperature responses. The fluorescent intensity of each polymer (peaked at 436 and 628 nm, respectively) decreased upon the heating of the polymer aqueous solution. While these two polymer aqueous solutions were mixed, the fluorescent intensity decrease at 436 nm and substantial fluorescence enhancement at 628 nm was observed with the increasing temperature due to FRET effect. The cell imaging of HeLa cells by these thermo-responsive polymers was explored. The difference of LCSTs resulting in ratiometric fluorescence change would have a potential impact on the various biomedical applications. Full article
(This article belongs to the Special Issue Nanoparticle-Reinforced Polymers)
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Open AccessArticle Humidity-Induced Phase Transitions of Surfactants Embedded in Latex Coatings Can Drastically Alter Their Water Barrier and Mechanical Properties
Polymers 2018, 10(3), 284; doi:10.3390/polym10030284
Received: 18 February 2018 / Revised: 2 March 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
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Abstract
Latex coatings are environmentally friendly i.e., they are formed from aqueous polymer dispersions, are cheap to produce and provide exceptional mechanical properties. Therefore, they are ubiquitous and can be found in a wide range of different applications such as paints and varnishes, pressure-sensitive
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Latex coatings are environmentally friendly i.e., they are formed from aqueous polymer dispersions, are cheap to produce and provide exceptional mechanical properties. Therefore, they are ubiquitous and can be found in a wide range of different applications such as paints and varnishes, pressure-sensitive adhesives, textiles, construction materials, paper coatings and inks. However, they also have weaknesses and their surfactant content is among them. Surfactants are often needed to stabilize polymer particles in the aqueous latex dispersions. These surfactants also form part of the coatings formed from these dispersions, and it is well-known that they can lower their performance. This work further explores this aspect and focuses on the role that embedded surfactant domains play in the response of latex coatings to humid environments. For this purpose, we made use of several experimental techniques where humidity control was implemented: quartz crystal microbalance with dissipation, atomic force microscopy and differential scanning calorimetry. By means of this multimethodological approach, we report that surfactants embedded in latex coatings can undergo humidity-induced transitions towards more hydrated and softer phases, and that this results in a drastic decrease of the mechanical and water barrier properties of the whole coatings. Subsequently, this work highlights the potential of taking into account the phase behavior of surfactants when choosing which ones to use in the synthesis of latex dispersions as this would help in predicting their performance under different environmental conditions. Full article
(This article belongs to the Special Issue Selected Papers from "ECIS 2017")
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Open AccessArticle Mechanical Properties of Rice Husk Biochar Reinforced High Density Polyethylene Composites
Polymers 2018, 10(3), 286; doi:10.3390/polym10030286
Received: 22 February 2018 / Revised: 4 March 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
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Abstract
Rice husk biochar was utilized to reinforce high-density polyethylene (HDPE) and to prepare biochar/plastic composites (BPC) by the extrusion method. Morphologies, non-isothermal crystallization behavior, and mechanical properties of the composites were investigated. The SEM (scanning electron microscope) showed that HDPE was embedded into
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Rice husk biochar was utilized to reinforce high-density polyethylene (HDPE) and to prepare biochar/plastic composites (BPC) by the extrusion method. Morphologies, non-isothermal crystallization behavior, and mechanical properties of the composites were investigated. The SEM (scanning electron microscope) showed that HDPE was embedded into the holes of the rice husk biochar. The DSC (differential scanning calorimeter) showed that biochar could reduce the crystallization rate and the higher the content of rice husk biochar, the slower the crystallization rate. Significantly, the bending and tensile strength of BPC could reach 53.7 and 20 MPa, far beyond WPC (wood plastic composites). With the increase of filler content, BPC were still stronger than WPC, although the impact strength of BPC and WPC all showed a general decline in the trend. The strong interaction was achieved by the utilization of rice husk biochar to reinforce HDPE. Full article
(This article belongs to the Special Issue Mechanics of Emerging Polymers with Unprecedented Networks)
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Open AccessArticle Evaluation of Strength Properties of Sand Modified with Organic Polymers
Polymers 2018, 10(3), 287; doi:10.3390/polym10030287
Received: 27 January 2018 / Revised: 1 March 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
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Abstract
Due to weak physical properties of sand, chemical reinforcement methods are widely used to improve sand properties to meet the engineering requirements. However, most of the traditional additives cause environmental problems. Therefore, non-traditional additives such as liquid polymers, enzymes, ions, and lignin derivatives
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Due to weak physical properties of sand, chemical reinforcement methods are widely used to improve sand properties to meet the engineering requirements. However, most of the traditional additives cause environmental problems. Therefore, non-traditional additives such as liquid polymers, enzymes, ions, and lignin derivatives have been studied extensively. In this study, organic polymer is used as a soil stabilizer to reinforce the sand. To evaluate the effectiveness of the organic polymer as soil stabilizer, a series of unconfined compression strength (UCS) tests, direct shear tests, and tensile tests were carried out on reinforced sand with different polymer concentrations and dry densities of sand. The reinforcement mechanism was analysed with scanning electron microscopy (SEM) images. The results indicated that the polymer concentration and dry density of sand had significant effects on the strength characteristics of reinforced sand specimens. The unconfined compressive strength, cohesion, and tensile strength of specimens with the same dry density increased with the increasing polymer concentration. The polymer membranes—formed by the mixture of polymer and water—enwrap the sand particles and interlink them to form a stable structure. The efficiency of this stabilization changed with dry sand density. Full article
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Open AccessArticle Tube Expansion Deformation Enables In Situ Synchrotron X-ray Scattering Measurements during Extensional Flow-Induced Crystallization of Poly l-Lactide Near the Glass Transition
Polymers 2018, 10(3), 288; doi:10.3390/polym10030288
Received: 11 February 2018 / Revised: 4 March 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
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Abstract
Coronary Heart Disease (CHD) is one of the leading causes of death worldwide, claiming over seven million lives each year. Permanent metal stents, the current standard of care for CHD, inhibit arterial vasomotion and induce serious complications such as late stent thrombosis. Bioresorbable
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Coronary Heart Disease (CHD) is one of the leading causes of death worldwide, claiming over seven million lives each year. Permanent metal stents, the current standard of care for CHD, inhibit arterial vasomotion and induce serious complications such as late stent thrombosis. Bioresorbable vascular scaffolds (BVSs) made from poly l-lactide (PLLA) overcome these complications by supporting the occluded artery for 3–6 months and then being completely resorbed in 2–3 years, leaving behind a healthy artery. The BVS that recently received clinical approval is, however, relatively thick (~150 µm, approximately twice as thick as metal stents ~80 µm). Thinner scaffolds would facilitate implantation and enable treatment of smaller arteries. The key to a thinner scaffold is careful control of the PLLA microstructure during processing to confer greater strength in a thinner profile. However, the rapid time scales of processing (~1 s) defy prediction due to a lack of structural information. Here, we present a custom-designed instrument that connects the strain-field imposed on PLLA during processing to in situ development of microstructure observed using synchrotron X-ray scattering. The connection between deformation, structure and strength enables processing–structure–property relationships to guide the design of thinner yet stronger BVSs. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle Preparation and Characterization of Self-Colored Waterborne Polyurethane and Its Application in Eco-Friendly Manufacturing of Microfiber Synthetic Leather Base
Polymers 2018, 10(3), 289; doi:10.3390/polym10030289
Received: 5 February 2018 / Revised: 27 February 2018 / Accepted: 5 March 2018 / Published: 8 March 2018
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Abstract
A novel self-colored waterborne polyurethane (SCPU) was synthesized and used in the preparation of a microfiber synthetic leather (MS-Leather) base in order to reduce the pollution caused by N,N-dimethylformamide (DMF) and dyes. The SCPU was prepared using the reaction of
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A novel self-colored waterborne polyurethane (SCPU) was synthesized and used in the preparation of a microfiber synthetic leather (MS-Leather) base in order to reduce the pollution caused by N,N-dimethylformamide (DMF) and dyes. The SCPU was prepared using the reaction of a reactive brilliant red K-2G with a waterborne polyurethane which was then extended via a first generation of hyperbranched poly(amine-ester). With the introduction of the dye, new absorption peaks at 1118 cm−1 [S=O], 1413 cm−1 [N=N], and 1635 cm−1 [C=N] appeared in the Fourier transform infrared (FTIR) spectrum of SCPU, and SCPU mean particle size increased to 162 nm. The X-ray diffraction (XRD) peak intensity of SCPU at 19.27° was 1310 cts. The thermal stability of SCPU at 200–280 °C was inferior to that of the control sample; however, it improved at temperatures above 360 °C. Finally, a free-dyeing MS-Leather base prepared by using SCPU without DMF was manufactured. It was found that the dyes were distributed mainly in the polyurethane matrix rather than in the microfibers. Moreover, the color changes of the base before and after being washed in both a water and a soap solution were 0.93 and 4.21, respectively. This indicated that the base’s washing color fastness to water was better than to a soap solution. Full article
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Open AccessArticle Correlation between Solubility Parameters and Properties of Alkali Lignin/PVA Composites
Polymers 2018, 10(3), 290; doi:10.3390/polym10030290
Received: 20 January 2018 / Revised: 21 February 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
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Abstract
Although lignin blending with thermoplastic polymers has been widely studied, the usefulness of the lignin–polymer composites is limited by the poor compatibility of the two components. In the present study, alkali lignin/PVA composite membranes were prepared by incorporating 10%, 15%, 20% and 25%
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Although lignin blending with thermoplastic polymers has been widely studied, the usefulness of the lignin–polymer composites is limited by the poor compatibility of the two components. In the present study, alkali lignin/PVA composite membranes were prepared by incorporating 10%, 15%, 20% and 25% alkali lignin into the composites. The thermodynamic parameters of the composites were measured using inverse gas chromatography (IGC). Composite membranes with 10%, 15%, 20%, and 25% alkali lignin had solubility parameters of 17.51, 18.70, 16.64 and 16.38 (J/cm3)0.5, respectively, indicating that the solubility parameter firstly increased, and then decreased, with increasing proportions of alkali lignin. When the alkali lignin content was 15%, the composites had the largest solubility parameters. The composite membrane with an alkali lignin content of 15% had a tensile strength of 18.86 MPa and a hydrophilic contact angle of 89°. We have shown that the solubility parameters of blends were related to mechanical and hydrophilic properties of the composites and the relationships have been verified experimentally and theoretically. Full article
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Open AccessArticle Development of Crystalline Morphology and Its Relationship with Mechanical Properties of PP/PET Microfibrillar Composites Containing POE and POE-g-MA
Polymers 2018, 10(3), 291; doi:10.3390/polym10030291
Received: 9 February 2018 / Revised: 2 March 2018 / Accepted: 5 March 2018 / Published: 8 March 2018
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Abstract
The main goal of this research is to study the development of crystalline morphology and compare it to various mechanical properties of microfibrillar composites (MFCs) based on polypropylene (PP) and poly(ethylene terephthalate) (PET), by adding a functional compatibilizer and a non-functional rubber in
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The main goal of this research is to study the development of crystalline morphology and compare it to various mechanical properties of microfibrillar composites (MFCs) based on polypropylene (PP) and poly(ethylene terephthalate) (PET), by adding a functional compatibilizer and a non-functional rubber in two different steps in the processing sequence. The MFCs were prepared at a weight ratio of 80/20 PP/PET by twin screw extrusion followed by cold drawing and injection moulding. The non-functionalized polyolefin-based elastomer (POE) and the functional compatibilizer (i.e., POE grafted with maleic anhydride (POE-g-MA)) were added in a fixed weight percentage at two stages: during extrusion or during injection moulding. The morphology observations showed differences in crystalline structure, and the PP spherulite size was reduced in all MFCs due to the presence of PET fibrils. Their relationship with the mechanical performances of the composite was studied by tensile and impact tests. Adding the functional compatibilizer during extrusions showed better mechanical properties compared to MFCs. Overall, a clear relationship was identified between processing, structure and properties. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle Extraction Optimization, Purification, Antioxidant Activity, and Preliminary Structural Characterization of Crude Polysaccharide from an Arctic Chlorella sp.
Polymers 2018, 10(3), 292; doi:10.3390/polym10030292
Received: 16 January 2018 / Revised: 2 March 2018 / Accepted: 4 March 2018 / Published: 9 March 2018
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Abstract
The arctic strain of Chlorella sp. (Chlorella-Arc) exists in the coldest and driest arctic ecosystems, and it is a new resource of active polysaccharides. The extraction of crude polysaccharide from Chlorella-Arc was optimized using the response surface methodology. A crude
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The arctic strain of Chlorella sp. (Chlorella-Arc) exists in the coldest and driest arctic ecosystems, and it is a new resource of active polysaccharides. The extraction of crude polysaccharide from Chlorella-Arc was optimized using the response surface methodology. A crude polysaccharide yield of approximately 9.62 ± 0.11% dry weight was obtained under these optimized conditions. Three fractions (P-I, P-II, and P-III) were present after purification by 2-diethylaminoethanol Sepharose Fast Flow and Sephadex G-100 chromatography. The P-IIa fraction demonstrated significant antioxidant activities. Moreover, P-IIa was an α- and β-type heteropolysaccharide with a pyran group and contained variable amounts of rhamnose, arabinose, glucose, and galactose based on fourier-transform infrared spectroscopy, high-performance liquid chromatography, and 1H and 13C nuclear magnetic resonance imaging. Production of high amounts of polysaccharide may allow further exploration of the microalgae Chlorella-Arc as a natural antioxidant. Full article
(This article belongs to the Special Issue Polysaccharides)
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Open AccessArticle Multi-Responsive Behaviors of Copolymers Bearing N-Isopropylacrylamide with or without Phenylboronic Acid in Aqueous Solution
Polymers 2018, 10(3), 293; doi:10.3390/polym10030293
Received: 30 January 2018 / Revised: 27 February 2018 / Accepted: 6 March 2018 / Published: 9 March 2018
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Abstract
Continuing efforts to develop novel smart materials are anticipated to upgrade the quality of life of humans. Thermo-responsive poly(N-isopropylacrylamide) and glucose-responsive phenylboronic acid—typical representatives—are often integrated as multi-stimuli-sensitive materials, but few are available for side-by-side comparisons with their properties. In this
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Continuing efforts to develop novel smart materials are anticipated to upgrade the quality of life of humans. Thermo-responsive poly(N-isopropylacrylamide) and glucose-responsive phenylboronic acid—typical representatives—are often integrated as multi-stimuli-sensitive materials, but few are available for side-by-side comparisons with their properties. In this study, both copolymers bearing N-isopropylacrylamide (NIPAAm), with or without 3-acrylamidophenylboronic acid (AAPBA), were synthesized by free radical polymerization, and characterized by Fourier transform infrared spectrometry, nuclear magnetic resonance hydrogen spectroscopy and gel permeation chromatography. Dynamic light scattering was used to analyze and compare the responsive behaviors of the copolymers in different aqueous solutions. Atomic force microscopy was also employed to investigate the apparent morphology changes with particle sizes. The results demonstrated that the introduction of NIPAAm endowed the composite materials with thermosensitivity, whereas the addition of AAPBA lowered the molecular weight of the copolymers, intensified the intermolecular aggregation of the nanoparticles, reduced the lower critical solution temperature (LCST) of the composites, and accordingly allowed the copolymers to respond to glucose. It was also concluded that the responding of smart copolymers to operating parameters can be activated only under special conditions, and copolymer dimension and conformation were affected by inter/intramolecular interactions. Full article
(This article belongs to the Special Issue Smart Polymers)
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Open AccessArticle 60Co γ-ray Irradiation Crosslinking of Chitosan/Graphene Oxide Composite Film: Swelling, Thermal Stability, Mechanical, and Antibacterial Properties
Polymers 2018, 10(3), 294; doi:10.3390/polym10030294
Received: 13 February 2018 / Revised: 4 March 2018 / Accepted: 5 March 2018 / Published: 9 March 2018
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Abstract
In this paper, chitosan (CS)/graphene oxide (GO) composite films were prepared, and the effect of γ-ray irradiation on the properties of composite films was investigated. The irradiation crosslinking reaction occurred in composite films with the existence of acetic acid, and the properties changed
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In this paper, chitosan (CS)/graphene oxide (GO) composite films were prepared, and the effect of γ-ray irradiation on the properties of composite films was investigated. The irradiation crosslinking reaction occurred in composite films with the existence of acetic acid, and the properties changed upon the various irradiation dose. The swelling degree of the composite film with 0 wt % GO decreased with the increasing of the irradiation dose, but the swelling degree of which with GO increased instead. The thermal stability increased with the increasing of the irradiation dose, but the effect of the irradiation on the thermal stability weakened as the increasing of the content of GO, due to the enhanced irradiation resistance performance. The tensile strength increased firstly and decreased subsequently with the increasing of the irradiation dose and the content of GO. Composite films showed the enhanced antibacterial activity against Bacillus subtilis, compared to Escherichia coli and Staphylococcus aureus. The antibacterial activity weakened with the increasing of the content of GO. The antibacterial activity was relatively stronger when the irradiation dose was 20 KGy. In addition, the structural, crystal, and morphological properties of composite films were characterized by FT-IR, XRD, and SEM. It is worth noting that the GO was pre-functionalized via KH560 for the better compatibility with CS matrix. Full article
(This article belongs to the Special Issue Polymer Hybrid Materials)
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Open AccessArticle Computer Modeling for Single-Screw Extrusion of Wood–Plastic Composites
Polymers 2018, 10(3), 295; doi:10.3390/polym10030295
Received: 9 February 2018 / Revised: 3 March 2018 / Accepted: 6 March 2018 / Published: 9 March 2018
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Abstract
Experimental and theoretical studies have been performed on the single-screw extrusion of wood–plastics composites. Experimental research has been carried out on the flow and melting of polypropylene (PP)-based composites with different wood flour (WF) content in the single-screw extruder. Based on these experimental
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Experimental and theoretical studies have been performed on the single-screw extrusion of wood–plastics composites. Experimental research has been carried out on the flow and melting of polypropylene (PP)-based composites with different wood flour (WF) content in the single-screw extruder. Based on these experimental observations, elementary models of the process phenomena have been proposed and a global model of the process has been developed. This global computer model includes the models of solid conveying, melting dependent on the wood flour content, melt flow in the screw, and melt flow in the die. 3-D non-Newtonian finite element method (FEM) screw pumping characteristics have been applied to model the melt flow in the metering section of the screw. The model predicts the extrusion output, pressure and temperature profiles, melting profile, and power consumption. The model has been validated experimentally. An effect of material slip on the extruder operation has been discussed including both slipping in the screw/barrel surfaces and in the extruding die. Full article
(This article belongs to the Special Issue Model-Based Polymer Processing)
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Open AccessArticle Structural Investigation of Poly(ethylene furanoate) Polymorphs
Polymers 2018, 10(3), 296; doi:10.3390/polym10030296
Received: 26 January 2018 / Revised: 6 March 2018 / Accepted: 7 March 2018 / Published: 9 March 2018
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Abstract
α and β crystalline phases of poly(ethylene furanoate) (PEF) were determined using X-ray powder diffraction by structure resolution in direct space and Rietveld refinement. Moreover, the α’ structure of a PEF sample was refined from data previously reported for PEF fiber. Triclinic α-PEF
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α and β crystalline phases of poly(ethylene furanoate) (PEF) were determined using X-ray powder diffraction by structure resolution in direct space and Rietveld refinement. Moreover, the α’ structure of a PEF sample was refined from data previously reported for PEF fiber. Triclinic α-PEF a = 5.729 Å, b = 7.89 Å, c = 9.62 Å, α = 98.1°, β = 65.1°, γ = 101.3°; monoclinic α’-PEF a = 5.912 Å, b = 6.91 Å, c = 19.73 Å, α = 90°, β = 90°, γ = 104.41°; and monoclinic β-PEF a = 5.953 Å, b = 6.60 Å, c = 10.52 Å, α = 90°, β = 107.0°, γ = 90° were determined as the best fitting of X-ray diffraction (XRD) powder patterns. Final atomic coordinates are reported for all polymorphs. In all cases PEF chains adopted an almost planar configuration. Full article
(This article belongs to the Special Issue Polymers from Renewable Resources)
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Open AccessArticle The Discovery of an Iridium(III) Dimer Complex as a Potent Antibacterial Agent against Non-Replicating Mycobacterium smegmatis
Polymers 2018, 10(3), 297; doi:10.3390/polym10030297
Received: 12 February 2018 / Revised: 4 March 2018 / Accepted: 6 March 2018 / Published: 9 March 2018
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Abstract
Novel agents are urgently needed to rapidly kill drug-resistant Mycobacterium tuberculosis. Noble metal complexes, particularly polypyridyl iridium complexes serving as therapeutic agents, have attracted considerable interest recently, due to their significant cytotoxic or antimicrobial activities. Here, we reported an polypyridyl iridium dimer
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Novel agents are urgently needed to rapidly kill drug-resistant Mycobacterium tuberculosis. Noble metal complexes, particularly polypyridyl iridium complexes serving as therapeutic agents, have attracted considerable interest recently, due to their significant cytotoxic or antimicrobial activities. Here, we reported an polypyridyl iridium dimer complex [Ir(ppy)2Cl]2 (3), with ppy = phenylpyridine, which was found to be active against both exponential growing and non-replicating M. smegmatis, with minimum inhibitory concentration values of 2 μg/mL, and exhibited rapid bactericidal kinetics, killing pathogens within 30–60 min. Moreover, 3 was demonstrated to generate a large amount of reactive oxygen species and to be effective in drug-resistant strains. Taken together, the selectively active iridium(III) dimer complex showed promise for use as a novel drug candidate for the treatment of M. tuberculosis infection. Full article
(This article belongs to the Special Issue Antimicrobial Polymers)
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Open AccessArticle Preparation of Molecularly Imprinted Mesoporous Materials for Highly Enhancing Adsorption Performance of Cytochrome C
Polymers 2018, 10(3), 298; doi:10.3390/polym10030298
Received: 15 February 2018 / Revised: 8 March 2018 / Accepted: 9 March 2018 / Published: 10 March 2018
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Abstract
Molecularly imprinted mesoporous materials (MIMs) were synthesized to improve the adsorption performance of Cytochrome c (Cyt c) by using an imidazolium-based amphiphilic ionic liquid 1-octadecyl-3-methylimidazolium chloride (C18MIMCl) as surfactant in aqueous solution via the epitope imprinting approach. The surface-exposed C-terminus nonapeptide
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Molecularly imprinted mesoporous materials (MIMs) were synthesized to improve the adsorption performance of Cytochrome c (Cyt c) by using an imidazolium-based amphiphilic ionic liquid 1-octadecyl-3-methylimidazolium chloride (C18MIMCl) as surfactant in aqueous solution via the epitope imprinting approach. The surface-exposed C-terminus nonapeptide of Cyt c (residues 96–104, AYLKKATNE) was utilized as the imprinted template. The nitrogen adsorption-desorption, thermo-gravimetric analysis, and transmission electron microscopy verified the successful preparation of MIMs with ordered mesoporous structure. The adsorption isotherm studies showed that the obtained MIMs exhibited superior adsorption capacity toward Cyt c of 86.47 mg·g−1 because of the high specific surface areas of 824 m2·g−1, and the appropriate pore size promoted the mass transfer of Cyt c, causing a rapid adsorption equilibrium within 20 min. Furthermore, these MIMs still remained excellent selectivity and recognition ability according to the selective as well as the competitive adsorption studies, suggesting that the molecularly imprinted mesoporous materials is expected to be used in the field of highly efficient separation and enrichment of proteins. Full article
(This article belongs to the Special Issue Molecularly Imprinted Polymers)
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Open AccessArticle Orthogonal Templating Control of the Crystallisation of Poly(ε-Caprolactone)
Polymers 2018, 10(3), 300; doi:10.3390/polym10030300
Received: 8 January 2018 / Revised: 27 February 2018 / Accepted: 2 March 2018 / Published: 11 March 2018
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Abstract
The crystal growth of poly(ε-caprolactone) can be very effectively directed through the use of small amounts of dibenzylidene sorbitol in conjunction with modest flow fields to yield extremely high levels of the preferred polymer crystal orientation. We show that by introducing small quantities
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The crystal growth of poly(ε-caprolactone) can be very effectively directed through the use of small amounts of dibenzylidene sorbitol in conjunction with modest flow fields to yield extremely high levels of the preferred polymer crystal orientation. We show that by introducing small quantities of a terpolymer, based on polyvinyl butyral we can switch the symmetry axis of the final lamellar orientation from parallel to perpendicular to the melt flow direction. During shear flow of the polymer melt, the dibenzylidene sorbitol forms highly extended nanoparticles which adopt a preferred alignment with respect to the flow field and on cooling, polymer crystallisation is directed by these particles. The presence of the terpolymer, based on polyvinyl butyral, limits the aspect ratio of the dibenzylidene sorbitol (DBS) particles, such that the preferred orientation of the particles in the polymer melt changes from parallel to normal to the flow direction. The alignment of lamellar crystals perpendicular to the flow direction has important implications for applications such as scaffolds for tissue engineering and for barrier film properties. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle Ultrasound- and Thermo-Responsive Ionic Liquid Polymers
Polymers 2018, 10(3), 301; doi:10.3390/polym10030301
Received: 24 February 2018 / Revised: 9 March 2018 / Accepted: 9 March 2018 / Published: 11 March 2018
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Abstract
Poly(sodium 2-acrylamido-2-methylpropanesulfonate) (PAMPSNa) was prepared via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. An ionic liquid polymer (PAMPSP4448) was then prepared by exchanging the pendant counter cation from sodium (Na+) to tributyl-n-octylphosphonium (P4448+). We
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Poly(sodium 2-acrylamido-2-methylpropanesulfonate) (PAMPSNa) was prepared via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. An ionic liquid polymer (PAMPSP4448) was then prepared by exchanging the pendant counter cation from sodium (Na+) to tributyl-n-octylphosphonium (P4448+). We studied the ultrasound- and thermo-responsive behaviors of PAMPSP4448 in water. When the aqueous PAMPSP4448 solution was heated from 5 to 50 °C, the solution was always transparent with 100% transmittance. Unimers and interpolymer aggregates coexisted in water in the temperature range 5–50 °C. Generally, hydrogen bonding interactions are broken as the temperature increases due to increased molecular motion. Above 25 °C, the size of the interpolymer aggregates decreased, because hydrophobic interactions inside them were strengthened by dehydration accompanying cleavage of hydrogen bonds between water molecules and the pendant amide or sulfonate groups in PAMPSP4448. Above 25 °C, sonication of the aqueous solution induced an increase in the collision frequency of the aggregates. This promoted hydrophobic interactions between the aggregates to form larger aggregates, and the aqueous solution became turbid. When the temperature was decreased below 8 °C, hydrogen bonds reformed between water molecules and the pendant amide or sulfonate groups, allowing PAMPSP4448 to redissolve in water to form a transparent solution. The solution could be repeatedly controlled between turbidity and transparency by sonication and cooling, respectively. Full article
(This article belongs to the Special Issue Stimuli Responsive Polymers)
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Open AccessArticle Holographic Lenses in an Environment-Friendly Photopolymer
Polymers 2018, 10(3), 302; doi:10.3390/polym10030302
Received: 7 February 2018 / Revised: 6 March 2018 / Accepted: 7 March 2018 / Published: 11 March 2018
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Abstract
In this paper, we theoretically and experimentally evaluated the quality of volume phase transmission lenses stored in an environmentally friendly photopolymer. Holographic lenses (HLs) were obtained using symmetrical and asymmetrical experimental setups with the same positive and negative focal length and pupil diameter.
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In this paper, we theoretically and experimentally evaluated the quality of volume phase transmission lenses stored in an environmentally friendly photopolymer. Holographic lenses (HLs) were obtained using symmetrical and asymmetrical experimental setups with the same positive and negative focal length and pupil diameter. The image quality was evaluated from the calculation of the modulation transfer function (MTF) by capturing the point spread function (PSF) with a charge-coupled device (CCD). A maximum frequency of 14 L/mm, reaching an MTF value of 0.1, was obtained for a negative asymmetrically recorded HL, evaluated at 473 nm wavelength. A theoretical study of aberrations was carried out to qualitatively evaluate the experimental results obtained. Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications)
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Open AccessFeature PaperArticle Minimizing the Strong Screening Effect of Polyhedral Oligomeric Silsesquioxane Nanoparticles in Hydrogen-Bonded Random Copolymers
Polymers 2018, 10(3), 303; doi:10.3390/polym10030303
Received: 21 February 2018 / Revised: 8 March 2018 / Accepted: 9 March 2018 / Published: 11 March 2018
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Abstract
A series of poly(vinylphenol-co-methacryisobutyl polyhedral oligomeric silsesquioxane) (PVPh-co-PMAPOSS) random copolymers have been synthesized through free radical copolymerizations of acetoxystyrene with methacryisobutyl POSS monomer and subsequent hydrazine monohydrate-mediated hydrolysis of the acetoxyl units. These random copolymers were characterized using nuclear
[...] Read more.
A series of poly(vinylphenol-co-methacryisobutyl polyhedral oligomeric silsesquioxane) (PVPh-co-PMAPOSS) random copolymers have been synthesized through free radical copolymerizations of acetoxystyrene with methacryisobutyl POSS monomer and subsequent hydrazine monohydrate-mediated hydrolysis of the acetoxyl units. These random copolymers were characterized using nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC), which revealed that the POSS content in the random copolymers could be varied by changing the POSS monomer feed ratio by 1H NMR analyses. This molecular design approach allowed us to investigate the thermal properties and hydrogen bonding interactions of these PVPh-co-PMAPOSS random copolymers in comparison with those of PVPh/PMAPOSS blend systems. Hydrogen bonding interactions were absent in the PVPh/PMAPOSS blend system, because of a strong screening effect; in contrast, the PVPh-co-PMAPOSS random copolymers experienced enhanced intramolecular hydrogen bonding that minimized the strong screening effect of the POSS nanoparticles. Full article
(This article belongs to the Special Issue Phase Behavior in Polymers)
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Open AccessArticle Cost-Effective Double-Layer Hydrogel Composites for Wound Dressing Applications
Polymers 2018, 10(3), 305; doi:10.3390/polym10030305
Received: 20 February 2018 / Revised: 7 March 2018 / Accepted: 8 March 2018 / Published: 12 March 2018
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Abstract
Although poly vinyl alcohol-poly acrylic acid (PVA-PAA) composites have been widely used for biomedical applications, their incorporation into double-layer assembled thin films has been limited because the interfacial binding materials negatively influence the water uptake capacity of PVA. To minimize the effect of
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Although poly vinyl alcohol-poly acrylic acid (PVA-PAA) composites have been widely used for biomedical applications, their incorporation into double-layer assembled thin films has been limited because the interfacial binding materials negatively influence the water uptake capacity of PVA. To minimize the effect of interfacial binding, a simple method for the fabrication of a double-layered PVA-PAA hydrogel was introduced, and its biomedical properties were evaluated in this study. Our results revealed that the addition of PAA layers on the surface of PVA significantly increased the swelling properties. Compared to PVA, the equilibrium swelling ratio of the PVA-PAA hydrogel increased (p = 0.035) and its water vapour permeability significantly decreased (p = 0.04). Statistical analysis revealed that an increase in pH value from 7 to 10 as well as the addition of PAA at pH = 7 significantly increased the adhesion force (p < 0.04). The mechanical properties—including ultimate tensile strength, modulus, and elongation at break—remained approximately untouched compared to PVA. A significant increase in biocompatibility was found after day 7 (p = 0.016). A higher release rate for tetracycline was found at pH = 8 compared to neutral pH. Full article
(This article belongs to the Special Issue Smart and Modern Thermoplastic Polymer Materials)
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Open AccessArticle Morphology, Mechanical Properties and Dimensional Stability of Biomass Particles/High Density Polyethylene Composites: Effect of Species and Composition
Polymers 2018, 10(3), 308; doi:10.3390/polym10030308
Received: 1 February 2018 / Revised: 10 March 2018 / Accepted: 11 March 2018 / Published: 13 March 2018
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Abstract
The utilization of four types of biomass particles, including hardwood (poplar), softwood (radiata pine), crop (wheat straw) and bamboo (moso bamboo), as reinforcing fillers in preparing high density polyethylene (HDPE) based composites was studied. To improve interfacial compatibility, maleic anhydride grafted polyethylene (MAPE)
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The utilization of four types of biomass particles, including hardwood (poplar), softwood (radiata pine), crop (wheat straw) and bamboo (moso bamboo), as reinforcing fillers in preparing high density polyethylene (HDPE) based composites was studied. To improve interfacial compatibility, maleic anhydride grafted polyethylene (MAPE) was applied as the coupling agent. The effects of the biomass species on the mechanical and water absorption properties of the resulting composites were evaluated based on chemical composition analysis. A creep-recovery test was conducted in single cantilever mode using a dynamic mechanical analyzer. Results show that the four types of biomass particles had similar chemical compositions but different composition contents. Poplar particles with high cellulose content loading in the HDPE matrix exhibited higher tensile and flexure properties and creep resistance. Fracture morphology analysis indicated a weak particle-matrix interface in wheat straw based composites. Given the high crystallinity and minimum hemicellulose content, the moso bamboo reinforced composite showed high impact strength and better water resistance. Full article
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Open AccessArticle Synthesis, Characterization and Drug Loading of Multiresponsive p[NIPAm-co-PEGMA] (core)/p[NIPAm-co-AAc] (Shell) Nanogels with Monodisperse Size Distributions
Polymers 2018, 10(3), 309; doi:10.3390/polym10030309
Received: 19 February 2018 / Revised: 8 March 2018 / Accepted: 12 March 2018 / Published: 13 March 2018
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Abstract
We report the synthesis and properties of temperature- and pH-responsive p([NIPAm-co-PEGMA] (core)/[NIPAm-co-AAc] (shell)) nanogels with narrow size distributions, tunable sizes and increased drug loading efficiencies. The core-shell nanogels were synthesized using an optimized two-stage seeded polymerization methodology. The
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We report the synthesis and properties of temperature- and pH-responsive p([NIPAm-co-PEGMA] (core)/[NIPAm-co-AAc] (shell)) nanogels with narrow size distributions, tunable sizes and increased drug loading efficiencies. The core-shell nanogels were synthesized using an optimized two-stage seeded polymerization methodology. The core-shell nanogels show a narrow size distribution and controllable physico-chemical properties. The hydrodynamic sizes, charge distributions, temperature-induced volume phase transition behaviors, pH-responsive behaviors and drug loading capabilities of the core-shell nanogels were investigated using transmission electron microscopy, zeta potential measurements, dynamic light scattering and UV-Vis spectroscopy. The size of the core-shell nanogels was controlled by polymerizing NIPAm with crosslinker poly(ethylene glycol) dimethacrylate (PEGDMA) of different molecular weights (Mn-200, 400, 550 and 750 g/mol) during the core synthesis. It was found that the swelling/deswelling kinetics of the nanogels was sharp and reversible; with its volume phase transition temperature in the range of 40–42 °C. Furthermore, the nanogels loaded with l-3,4-dihydroxyphenylalanine (L-DOPA), using a modified breathing-in mechanism, showed high loading and encapsulation efficiencies, providing potential possibilities of such nanogels for biomedical applications. Full article
(This article belongs to the Special Issue Core-Shell Structured Polymers)
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Open AccessArticle Reusable Xerogel Containing Quantum Dots with High Fluorescence Retention
Polymers 2018, 10(3), 310; doi:10.3390/polym10030310
Received: 27 November 2017 / Revised: 2 March 2018 / Accepted: 7 March 2018 / Published: 13 March 2018
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Abstract
Although various analytical methods have been established based on quantum dots (QDs), most were conducted in solution, which is inadequate for storage/transportation and rapid analysis. Moreover, the potential environmental problems caused by abandoned QDs cannot be ignored. In this paper, a reusable xerogel
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Although various analytical methods have been established based on quantum dots (QDs), most were conducted in solution, which is inadequate for storage/transportation and rapid analysis. Moreover, the potential environmental problems caused by abandoned QDs cannot be ignored. In this paper, a reusable xerogel containing CdTe with strong emission is established by introducing host–guest interactions between QDs and polymer matrix. This xerogel shows high QDs loading capacity without decrease or redshift in fluorescence (the maximum of loading is 50 wt % of the final xerogel), which benefits from the steric hindrance of β-cyclodextrin (βCD) molecules. Host–guest interactions immobilize QDs firmly, resulting in the excellent fluorescence retention of the xerogel. The good detecting performance and reusability mean this xerogel could be employed as a versatile analysis platform (for quantitative and qualitative analyses). In addition, the xerogel can be self-healed by the aid of water. Full article
(This article belongs to the Special Issue Host-Guest Polymer Complexes)
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Open AccessArticle Enantiopure Chiral Coordination Polymers Based on Polynuclear Paddlewheel Helices and Arsenyl Tartrate
Polymers 2018, 10(3), 311; doi:10.3390/polym10030311
Received: 17 February 2018 / Revised: 9 March 2018 / Accepted: 11 March 2018 / Published: 13 March 2018
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Abstract
Herein, we report the preparation of chiral, one-dimensional coordination polymers based on trinuclear paddlewheel helices [M3(dpa)4]2+ (M = Co(II) and Ni(II); dpa = the anion of 2,2′-dipyridylamine). Enantiomeric resolution of a racemic mixture of [M3(dpa)4
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Herein, we report the preparation of chiral, one-dimensional coordination polymers based on trinuclear paddlewheel helices [M3(dpa)4]2+ (M = Co(II) and Ni(II); dpa = the anion of 2,2′-dipyridylamine). Enantiomeric resolution of a racemic mixture of [M3(dpa)4]2+ complexes was achieved by chiral recognition of the respective enantiomer by [Δ-As2(tartrate)2]2− or [Λ-As2(tartrate)2]2− in N,N-dimethylformamide (DMF), affording crystalline coordination polymers formed from [(Δ-Co3(dpa)4)(Λ-As2(tartrate)2)]·3DMF (Δ-1), [(Λ-Co3(dpa)4)(Δ-As2(tartrate)2)]·3DMF (Λ-1), [(Δ-Ni3(dpa)4)(Λ-As2(tartrate)2)]·(4 − n)DMF∙nEt2O (Δ-2) or [(Λ-Ni3(dpa)4)(Δ-As2(tartrate)2)]·(4 − n)DMF∙nEt2O (Λ-2) repeating units. UV-visible circular dichroism spectra of the complexes in DMF solutions demonstrate the efficient isolation of optically active species. The helicoidal [M3(dpa)4]2+ units that were obtained display high stability towards racemization as shown by the absence of an evolution of the dichroic signals after several days at room temperature and only a small decrease of the signal after 3 h at 80 °C. Full article
(This article belongs to the Special Issue Coordination Polymer)
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Open AccessArticle Structure and Properties Study of PA6 Nanocomposites Flame Retarded by Aluminium Salt of Diisobutylphosphinic Acid and Different Organic Montmorillonites
Polymers 2018, 10(3), 312; doi:10.3390/polym10030312
Received: 9 January 2018 / Revised: 5 March 2018 / Accepted: 6 March 2018 / Published: 13 March 2018
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Abstract
Two different types of organic montmorillonite, namely quaternary ammonium salt intercalated MMT (CMMT) and quaternary phosphonium salt intercalated MMT (PMMT) were used as fillers in the flame-retardant polyamide (PA6) based on aluminium salts of diisobutylphosphinic acid (ABPA). The influence of different types of
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Two different types of organic montmorillonite, namely quaternary ammonium salt intercalated MMT (CMMT) and quaternary phosphonium salt intercalated MMT (PMMT) were used as fillers in the flame-retardant polyamide (PA6) based on aluminium salts of diisobutylphosphinic acid (ABPA). The influence of different types of organic montmorillonite (OMMT) on the structure and properties of flame-retardant PA6 nanocomposites were systematically investigated. The X-ray diffraction and transmission electron microscopy results suggested that the introduction of OMMT improved the dispersion of the flame retardant particles independently of the type of OMMT. The derivative thermogravimetry (DTG) curve transformed to one peak from two peaks (representing the degradation of ABPA and PA6, respectively) after incorporation of the OMMT, which further confirmed better ABPA dispersion. Viscoelastic measurements demonstrated that a mechanically stable network structure was formed with the introduction of OMMT or ABPA and OMMT, while PA6/ABPA/PMMT presented the highest storage modulus and viscosity, suggesting a more efficient network structure. From UL-94 and limited oxygen index (LOI) tests, PA6/ABPA/PMMT presented the best flame performance, with a UL-94 of V-0 and a LOI of 33%. In addition, the PA6/ABPA/PMMT presented the lowest peak heat release rate (pHRR) among the investigated samples. Combined with the char layer analysis, it can be deduced that the introduction of PMMT improved the dispersion of ABPA, and promoted the formation of more efficient network structure, before promoting more compact char structures, which finally resulted in improved flame retardancy. Full article
(This article belongs to the Special Issue Polymer-Clay (Nano)Composites)
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Open AccessArticle Strength of PLA Components Fabricated with Fused Deposition Technology Using a Desktop 3D Printer as a Function of Geometrical Parameters of the Process
Polymers 2018, 10(3), 313; doi:10.3390/polym10030313
Received: 5 February 2018 / Revised: 19 February 2018 / Accepted: 9 March 2018 / Published: 13 March 2018
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Abstract
The current paper studies the influence of geometrical parameters of the fused deposition modeling (FDM)—fused filament fabrication (FFF) 3D printing process on printed part strength for open source desktop 3D printers and the most popular material used for that purpose—i.e., polylactic acid (PLA).
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The current paper studies the influence of geometrical parameters of the fused deposition modeling (FDM)—fused filament fabrication (FFF) 3D printing process on printed part strength for open source desktop 3D printers and the most popular material used for that purpose—i.e., polylactic acid (PLA). The study was conducted using a set of different nozzles (0.4, 0.6, and 0.8 mm) and a range of layer heights from the minimum to maximum physical limits of the machine. To assess print strength, a novel assessment method is proposed. A tubular sample is loaded in the weakest direction (across layers) in a three-point bending fixture. Mesostructure evaluation through scanning electronic microscopy (SEM) scans of the samples was used to explain the obtained results. We detected a significant influence of geometric process parameters on sample mesostructure, and consequently, on sample strength. Full article
(This article belongs to the Special Issue Polymers for Modern and Advanced Engineering Applications)
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Open AccessArticle 3D Printable Filaments Made of Biobased Polyethylene Biocomposites
Polymers 2018, 10(3), 314; doi:10.3390/polym10030314
Received: 21 February 2018 / Revised: 9 March 2018 / Accepted: 10 March 2018 / Published: 13 March 2018
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Abstract
Two different series of biobased polyethylene (BioPE) were used for the manufacturing of biocomposites, complemented with thermomechanical pulp (TMP) fibers. The intrinsic hydrophilic character of the TMP fibers was previously modified by grafting hydrophobic compounds (octyl gallate and lauryl gallate) by means of
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Two different series of biobased polyethylene (BioPE) were used for the manufacturing of biocomposites, complemented with thermomechanical pulp (TMP) fibers. The intrinsic hydrophilic character of the TMP fibers was previously modified by grafting hydrophobic compounds (octyl gallate and lauryl gallate) by means of an enzymatic-assisted treatment. BioPE with low melt flow index (MFI) yielded filaments with low void fraction and relatively low thickness variation. The water absorption of the biocomposites was remarkably improved when the enzymatically-hydrophobized TMP fibers were used. Importantly, the 3D printing of BioPE was improved by adding 10% and 20% TMP fibers to the composition. Thus, 3D printable biocomposites with low water uptake can be manufactured by using fully biobased materials and environmentally-friendly processes. Full article
(This article belongs to the Special Issue Polymers from Renewable Resources)
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Open AccessArticle Photo-Polymerization in Chiral Dopant Liquid Crystal Cells via Holographic Exposure to Fabricate Polarization-Independent Phase Modulator with Fast Optical Response
Polymers 2018, 10(3), 315; doi:10.3390/polym10030315
Received: 21 January 2018 / Revised: 12 March 2018 / Accepted: 12 March 2018 / Published: 14 March 2018
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Abstract
Small liquid crystal domains with random director distributions were obtained to show novel optical isotropy using a holographic exposure processes to treat chiral dopant liquid crystal cells in the isotropic phase (i.e., polymer-stabilized isotropic liquid crystal cells). The cells used to fabricate phase
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Small liquid crystal domains with random director distributions were obtained to show novel optical isotropy using a holographic exposure processes to treat chiral dopant liquid crystal cells in the isotropic phase (i.e., polymer-stabilized isotropic liquid crystal cells). The cells used to fabricate phase modulators showed unique performances, including low light scattering, polarization-independence, and fast optical response. Furthermore, an extra fluoro-surfactant dopant in cells showed that the phase modulators retained their performance but with considerable reduction of operating voltages, from 180 Vrms to 100 Vrms. Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications)
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Open AccessArticle Comparative Study of Ex Vivo Transmucosal Permeation of Pioglitazone Nanoparticles for the Treatment of Alzheimer’s Disease
Polymers 2018, 10(3), 316; doi:10.3390/polym10030316
Received: 27 February 2018 / Revised: 11 March 2018 / Accepted: 13 March 2018 / Published: 14 March