Polymers

19 pages, 4065 KiB

Open AccessEditor’s ChoiceArticle

Micro-Clotting of Platelet-Rich Plasma Upon Loading in Hydrogel Microspheres Leads to Prolonged Protein Release and Slower Microsphere Degradation

by Miran Hannah Choi, Alexandra Blanco, Samuel Stealey, Xin Duan, Natasha Case, Scott Allen Sell, Muhammad Farooq Rai and Silviya Petrova Zustiak

Polymers 2020, 12(8), 1712; https://doi.org/10.3390/polym12081712 - 30 Jul 2020

Cited by 16 | Viewed by 4403

Abstract

Platelet-rich plasma (PRP) is an autologous blood product that contains a variety of growth factors (GFs) that are released upon platelet activation. Despite some therapeutic potential of PRP in vitro, in vivo data are not convincing. Bolus injection of PRP is cleared rapidly [...] Read more.

Platelet-rich plasma (PRP) is an autologous blood product that contains a variety of growth factors (GFs) that are released upon platelet activation. Despite some therapeutic potential of PRP in vitro, in vivo data are not convincing. Bolus injection of PRP is cleared rapidly from the body diminishing its therapeutic efficacy. This highlights a need for a delivery vehicle for a sustained release of PRP to improve its therapeutic effect. In this study, we used microfluidics to fabricate biodegradable PRP-loaded polyethylene glycol (PEG) microspheres. PRP was incorporated into the microspheres as a lyophilized PRP powder either as is (powder PRP) or first solubilized and pre-clotted to remove clots (liquid PRP). A high PRP loading of 10% w/v was achieved for both PRP preparations. We characterized the properties of the resulting PRP-loaded PEG microspheres including swelling, modulus, degradation, and protein release as a function of PRP loading and preparation. Overall, loading powder PRP into the PEG microspheres significantly affected the properties of microspheres, with the most pronounced effect noted in degradation. We further determined that microsphere degradation in the presence of powder PRP was affected by platelet aggregation and clotting. Platelet aggregation did not prevent but prolonged sustained PRP release from the microspheres. The delivery system developed and characterized herein could be useful for the loading and releasing of PRP to promote tissue regeneration and wound healing or to suppress tissue degeneration in osteoarthritis, and intervertebral disc degeneration. Full article

(This article belongs to the Special Issue Synthesis, Characterization and Biomedical Applications of Hydrogels)

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14 pages, 1423 KiB

Open AccessEditor’s ChoiceArticle

Copolymerized Natural Fibre from the Mesocarp of Orbignya phalerata (Babassu Fruit) as an Irrigating-Fertilizer for Growing Cactus Pears

by Ricardo Edvan, Mariane Sá, Regina Magalhães, Rafael Ratke, Heldeney R. Sousa, Lucas Mateus Lima Neri, Edson C. Silva-Filho, Jose Pereira Filho and Leilson Bezerra

Polymers 2020, 12(8), 1699; https://doi.org/10.3390/polym12081699 - 29 Jul 2020

Cited by 4 | Viewed by 2198

Abstract

Cactus pears face challenges due to global climate change, which is leading to in-depth research to monitor and increase their water activity. The objective of this study was to evaluate the use of the natural test hydrogel (TH) from Orbignya phalerata fibre as [...] Read more.

Cactus pears face challenges due to global climate change, which is leading to in-depth research to monitor and increase their water activity. The objective of this study was to evaluate the use of the natural test hydrogel (TH) from Orbignya phalerata fibre as nutrients and water for growing cactus pear genotypes (“Baiana” and “Doce” [Nopalea cochenillifera], ‘Gigante’ [Opuntia fícus-indica], and “Mexican Elephant Ear” [Opuntia stricta]) compared to the use of commercial hydrogel (CH), which is based on polymers composed of polyacrylamide, and a treatment without the use of hydrogel (WH). A completely randomized design was used, in a factorial scheme (4 × 3), with four genotypes of cactus pear and three forms of hydration, with five replications. The number and area of cladode was greatest (p < 0.01) in plants with CH and TH irrigation-fertilization in the ‘Doce’ cactus genotype. The dry biomass of the cladode and root in the ‘Gigante’ cactus genotype was greatest (p < 0.01) in the treatments with CH and TH irrigation-fertilisation. The ‘Baiana’, ‘Doce’, and ‘Gigante’ cactus genotypes exhibited more (p < 0.01) dry matter content with the TH irrigation-fertilisation. The highest (p < 0.01) neutral detergent fibre content was observed in the ‘Baiana’ and ‘Doce’ cactus genotypes when irrigation occurred with WH treatment, and the highest acid detergent fibre content in the ‘Gigante’ genotype. The copolymerized natural fibre from the mesocarp of Orbignya phalerata (babassu fruit) induced a better growth and chemical composition of cactus pear genotypes than the hydrogel based on polymers composed of polyacrylamide. Full article

(This article belongs to the Special Issue Advances in Polysaccharides)

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21 pages, 883 KiB

Open AccessEditor’s ChoiceReview

A Review on Citric Acid as Green Modifying Agent and Binder for Wood

by Seng Hua Lee, Paridah Md Tahir, Wei Chen Lum, Li Peng Tan, Paiman Bawon, Byung-Dae Park, Syeed SaifulAzry Osman Al Edrus and Ummi Hani Abdullah

Polymers 2020, 12(8), 1692; https://doi.org/10.3390/polym12081692 - 29 Jul 2020

Cited by 57 | Viewed by 9514

Abstract

Citric acid (CA) can be found naturally in fruits and vegetables, particularly citrus fruit. CA is widely used in many fields but its usage as a green modifying agent and binder for wood is barely addressed. Esterification is one of the most common [...] Read more.

Citric acid (CA) can be found naturally in fruits and vegetables, particularly citrus fruit. CA is widely used in many fields but its usage as a green modifying agent and binder for wood is barely addressed. Esterification is one of the most common chemical reactions applied in wood modification. CA contains three carboxyl groups, making it possible to attain at least two esterification reactions that are required for crosslinking when reacting with the hydroxyl groups of the cell wall polymers. In addition, the reaction could form ester linkages to bring adhesivity and good bonding characteristics, and therefore CA could be used as wood binder too. This paper presents a review concerning the usage of CA as a wood modifying agent and binder. For wood modification, the reaction mechanism between wood and CA and the pros and cons of using CA are discussed. CA and its combination with various reactants and their respective optimum parameters are also compiled in this paper. As for the major wood bonding component, the bonding mechanism and types of wood composites bonded with CA are presented. The best working conditions for the CA in the fabrication of wood-based panels are discussed. In addition, the environmental impacts and future outlook of CA-treated wood and bonded composite are also considered. Full article

(This article belongs to the Special Issue Recent Developments in Eco-Friendly Wood-Based Composites)

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15 pages, 4262 KiB

Open AccessEditor’s ChoiceArticle

New Insights into Crystallization of Heterophasic Isotactic Polypropylene by Fast Scanning Chip Calorimetry

by Daniela Mileva, Jingbo Wang, Markus Gahleitner, Katalee Jariyavidyanont and René Androsch

Polymers 2020, 12(8), 1683; https://doi.org/10.3390/polym12081683 - 28 Jul 2020

Cited by 12 | Viewed by 3260

Abstract

The crystallization kinetics of metallocene-catalyzed heterophasic isotactic polypropylene composed of a matrix of isotactic polypropylene (iPP) and rubbery particles made of random ethylene–propylene copolymers (EPC), often denoted as heterophasic iPP copolymers, was analyzed as a function of the cooling rate and supercooling in [...] Read more.

The crystallization kinetics of metallocene-catalyzed heterophasic isotactic polypropylene composed of a matrix of isotactic polypropylene (iPP) and rubbery particles made of random ethylene–propylene copolymers (EPC), often denoted as heterophasic iPP copolymers, was analyzed as a function of the cooling rate and supercooling in nonisothermal and isothermal crystallization experiments, respectively. Fast scanning chip calorimetry (FSC) allowed assessing crystallization at processing-relevant conditions, and variation of the content (0–39 wt %) and composition (0–35 wt % propylene counits) of the EPC particles revealed qualitatively new insight about mechanisms of heterogeneous crystal nucleation. For neat iPP homopolymer, the characteristic bimodal temperature dependence of the crystallization rate due to predominance of heterogeneous and homogeneous crystal nucleation at high and low temperatures, respectively, is reconfirmed. At high temperatures, in heterophasic iPP, the here studied ethylene-(C2)-rich EPC particles accelerate crystallization of the iPP-matrix, with the acceleration or nucleation efficacy correlating with the EPC-particle content. The crystallization time reduces by more than half in presence of 39 wt % EPC particles. An additional nucleating effect of the EPC particles on iPP-matrix crystallization is detected after their crystallization, suggesting that liquid/rubbery particles are less effective than solid/semicrystalline particles in affecting crystallization of the surrounding iPP-matrix. At low temperature, homogeneous crystal nucleation in the iPP-matrix outpaces all heterogeneous nucleation effects, and the matrix-crystallization rate is independent of the sample composition. The obtained results lead to the conclusion that the crystallization kinetics of iPP can be affected significantly by the content and composition of EPC particles, even towards superfast crystallizing iPP grades. Full article

(This article belongs to the Special Issue Recent Developments on Calorimetry and Thermal Analysis of Polymers and Nanocomposites)

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21 pages, 2677 KiB

Open AccessEditor’s ChoiceArticle

Nonlinear Optical Pigments. Two-Photon Absorption in Crosslinked Conjugated Polymers and Prospects for Remote Nonlinear Optical Thermometry

by Jan K. Zaręba, Marcin Nyk and Marek Samoć

Polymers 2020, 12(8), 1670; https://doi.org/10.3390/polym12081670 - 27 Jul 2020

Cited by 10 | Viewed by 2934

Abstract

Nonlinear optical (NLO) pigments are compounds insoluble in solvents that exhibit phenomena related to nonlinear optical susceptibilities (χ⁽ⁿ⁾ where n = 2,3,...), e.g., two-photon absorption (2PA) which is related to the imaginary part of χ⁽³⁾. Determination of spectrally-resolved 2PA properties [...] Read more.

Nonlinear optical (NLO) pigments are compounds insoluble in solvents that exhibit phenomena related to nonlinear optical susceptibilities (χ⁽ⁿ⁾ where n = 2,3,...), e.g., two-photon absorption (2PA) which is related to the imaginary part of χ⁽³⁾. Determination of spectrally-resolved 2PA properties for NLO pigments of macromolecular nature, such as coordination polymers or crosslinked polymers, has long been a challenging issue due to their particulate form, precluding characterizations with standard techniques such as Z-scan. In this contribution, we investigate thus far unknown spectrally-resolved 2PA properties of a new subclass of NLO pigments—crosslinked conjugated polymers. The studied compounds are built up from electron-donating (triphenylamine) and electron-withdrawing (2,2’-bipyridine) structural fragments joined by vinylene (Pol1) or vinyl(4-ethynylphenyl) (Pol2) aromatic bridges. 2PA properties of these polymers have been characterized in broad spectral range by specially modified two-photon excited fluorescence (TPEF) techniques: solid state TPEF (SSTPEF) and internal standard TPEF (ISTPEF). The impact of self-aggregation of aromatic backbones on the 2PA properties of the polymers has been evaluated through extended comparisons of NLO parameters, i.e., 2PA cross sections (σ₂) and molar-mass normalized 2PA merit factors (σ₂/M) with those of small-molecular model compounds: Mod1 and Mod2. By doing this, we found that the 2PA response of Pol1 and Pol2 is improved 2–3 times versus respective model compounds in the solid state form. Further comparisons with 2PA results collected for diluted solutions of Mod1 and Mod2 supports the notion that self-aggregated structure contributes to the observed enhancement of 2PA response. On the other hand, it is clear that Pol1 and Pol2 suffer from aggregation-caused quenching phenomenon, well reflected in time-resolved fluorescence properties as well as in relatively low values of quantum yield of fluorescence. Accordingly, despite improved intrinsic 2PA response, the effective intensity of two-photon excited emission for Pol1 and Pol2 is slightly lower relative to Mod1 and Mod2. Finally, we explore temperature-resolved luminescence properties under one- (377 nm), two- (820 nm), and three-photon excitation (1020 nm) conditions of postsynthetically Eu³⁺-functionalized material, Pol1-Eu, and discuss its suitability for temperature sensing applications. Full article

(This article belongs to the Special Issue Fluorescent Polymeric Probes)

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17 pages, 3339 KiB

Open AccessEditor’s ChoiceReview

Bio-Polyethylene (Bio-PE), Bio-Polypropylene (Bio-PP) and Bio-Poly(ethylene terephthalate) (Bio-PET): Recent Developments in Bio-Based Polymers Analogous to Petroleum-Derived Ones for Packaging and Engineering Applications

by Valentina Siracusa and Ignazio Blanco

Polymers 2020, 12(8), 1641; https://doi.org/10.3390/polym12081641 - 23 Jul 2020

Cited by 266 | Viewed by 40626

Abstract

In recent year, there has been increasing concern about the growing amount of plastic waste coming from daily life. Different kinds of synthetic plastics are currently used for an extensive range of needs, but in order to reduce the impact of petroleum-based plastics [...] Read more.

In recent year, there has been increasing concern about the growing amount of plastic waste coming from daily life. Different kinds of synthetic plastics are currently used for an extensive range of needs, but in order to reduce the impact of petroleum-based plastics and material waste, considerable attention has been focused on “green” plastics. In this paper, we present a broad review on the advances in the research and development of bio-based polymers analogous to petroleum-derived ones. The main interest for the development of bio-based materials is the strong public concern about waste, pollution and carbon footprint. The sustainability of those polymers, for general and specific applications, is driven by the great progress in the processing technologies that refine biomass feedstocks in order to obtain bio-based monomers that are used as building blocks. At the same time, thanks to the industrial progress, it is possible to obtain more versatile and specific chemical structures in order to synthetize polymers with ad-hoc tailored properties and functionalities, with engineering applications that include packaging but also durable and electronic goods. In particular, three types of polymers were described in this review: Bio-polyethylene (Bio-PE), bio-polypropylene (Bio-PP) and Bio-poly(ethylene terephthalate) (Bio-PET). The recent advances in their development in terms of processing technologies, product development and applications, as well as their advantages and disadvantages, are reported. Full article

(This article belongs to the Special Issue Biopolymer Modifications and Characterization)

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18 pages, 5197 KiB

Open AccessEditor’s ChoiceReview

Application of Synchrotron Radiation X-ray Scattering and Spectroscopy to Soft Matter

by Atsushi Takahara, Yuji Higaki, Tomoyasu Hirai and Ryohei Ishige

Polymers 2020, 12(7), 1624; https://doi.org/10.3390/polym12071624 - 21 Jul 2020

Cited by 16 | Viewed by 6117

Abstract

Light produced by synchrotron radiation (SR) is much brighter than that produced by conventional laboratory X-ray sources. The photon energy of SR X-ray ranges from soft and tender X-rays to hard X-rays. Moreover, X-rays become element sensitive with decreasing photon energy. By using [...] Read more.

Light produced by synchrotron radiation (SR) is much brighter than that produced by conventional laboratory X-ray sources. The photon energy of SR X-ray ranges from soft and tender X-rays to hard X-rays. Moreover, X-rays become element sensitive with decreasing photon energy. By using a wide energy range and high-quality light of SR, different scattering and spectroscopic methods were applied to various soft matters. We present five of our recent studies performed using specific light properties of a synchrotron facility, which are as follows: (1) In situ USAXS study to understand the deformation behavior of colloidal crystals during uniaxial stretching; (2) structure characterization of semiconducting polymer thin films along the film thickness direction by grazing-incidence wide-angle X-ray scattering using tender X-rays; (3) X-ray absorption fine structure (XAFS) analysis of the formation mechanism of poly(3-hexylthiophene) (P3HT); (4) soft X-ray absorption and emission spectroscopic analysis of water structure in polyelectrolyte brushes; and (5) X-ray photon correlation spectroscopic analysis of the diffusion behavior of polystyrene-grafted nanoparticles dispersed in a polystyrene matrix. Full article

(This article belongs to the Collection The Next Generation in Polymer Research)

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20 pages, 5179 KiB

Open AccessEditor’s ChoiceArticle

Synthetic Approaches for Poly(Phenylene) Block Copolymers via Nickel Coupling Reaction for Fuel Cell Applications

by Adam F. Nugraha, Songmi Kim, Farid Wijaya, Byungchan Bae and Dongwon Shin

Polymers 2020, 12(7), 1614; https://doi.org/10.3390/polym12071614 - 20 Jul 2020

Cited by 4 | Viewed by 4428

Abstract

Several methods to synthesize poly(phenylene) block copolymers through the nickel coupling reaction were attempted to reduce the use of expensive nickel catalysts in polymerization. The model reaction for poly(phenylene) having different types of dichlorobenzene derivative monomers illustrated the potential use of cost-effective catalysts, [...] Read more.

Several methods to synthesize poly(phenylene) block copolymers through the nickel coupling reaction were attempted to reduce the use of expensive nickel catalysts in polymerization. The model reaction for poly(phenylene) having different types of dichlorobenzene derivative monomers illustrated the potential use of cost-effective catalysts, such as NiBr₂ and NiCl₂, as alternatives to more expensive catalysts (e.g., bis(1,5-cyclooctadiene)nickel(0) (Ni(COD)₂)). By catalyzing the polymerization of multi-block poly(phenylene) with NiBr₂ and NiCl₂, random copolymers with similar molecular weights could be prepared. However, these catalysts did not result in a high-molecular-weight polymer, limiting their wide scale application. Further, the amount of Ni(COD)₂ could be reduced in this study by approximately 50% to synthesize poly(phenylene) multi-block copolymers, representing significant cost savings. Gel permeation chromatography and nuclear magnetic resonance results showed that the degree of polymerization and ion exchange capacity of the copolymers were almost the same as those achieved through conventional polymerization using 2.5 times as much Ni(COD)₂. The flexible quaternized membrane showed higher chloride ion conductivity than commercial Fumatech membranes with comparable water uptake and promising chemical stability. Full article

(This article belongs to the Special Issue Advanced Polymers for Electrochemical Applications)

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20 pages, 8186 KiB

Open AccessEditor’s ChoiceReview

Structural Polymorphism of Single pDNA Condensates Elicited by Cationic Block Polyelectrolytes

by Kensuke Osada

Polymers 2020, 12(7), 1603; https://doi.org/10.3390/polym12071603 - 19 Jul 2020

Cited by 8 | Viewed by 3677

Abstract

DNA folding is a core phenomenon in genome packaging within a nucleus. Such a phenomenon is induced by polyelectrolyte complexation between anionic DNA and cationic proteins of histones. In this regard, complexes formed between DNA and cationic polyelectrolytes have been investigated as models [...] Read more.

DNA folding is a core phenomenon in genome packaging within a nucleus. Such a phenomenon is induced by polyelectrolyte complexation between anionic DNA and cationic proteins of histones. In this regard, complexes formed between DNA and cationic polyelectrolytes have been investigated as models to gain insight into genome packaging. Upon complexation, DNA undergoes folding to reduce its occupied volume, which often results in multi-complex associated aggregates. However, when cationic copolymers comprising a polycation block and a neutral hydrophilic polymer block are used instead, DNA undergoes folding as a single molecule within a spontaneously formed polyplex micelle (PM), thereby allowing the observation of the higher-order structures that DNA forms. The DNA complex forms polymorphic structures, including globular, rod-shaped, and ring-shaped (toroidal) structures. This review focuses on the polymorphism of DNA, particularly, to elucidate when, how, and why DNA organizes into these structures with cationic copolymers. The interactions between DNA and the copolymers, and the specific nature of DNA in rigidity; i.e., rigid but foldable, play significant roles in the observed polymorphism. Moreover, PMs serve as potential gene vectors for systemic application. The significance of the controlled DNA folding for such an application is addressed briefly in the last part. Full article

(This article belongs to the Special Issue Bio-Based Polyelectrolytes: Development and Applications)

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14 pages, 2389 KiB

Open AccessEditor’s ChoiceArticle

Film Blowing of Linear and Long-Chain Branched Poly(ethylene terephthalate)

by Michael Härth and Andrea Dörnhöfer

Polymers 2020, 12(7), 1605; https://doi.org/10.3390/polym12071605 - 19 Jul 2020

Cited by 16 | Viewed by 5658

Abstract

Film blowing of Poly(ethylene terephthalate) (PET) is challenging due its inherently low melt viscosity and poor melt strength. In this study, it is shown how the rheological properties of a commercial PET can be altered by reactive extrusion using either pyromellitic dianhydride (PMDA) [...] Read more.

Film blowing of Poly(ethylene terephthalate) (PET) is challenging due its inherently low melt viscosity and poor melt strength. In this study, it is shown how the rheological properties of a commercial PET can be altered by reactive extrusion using either pyromellitic dianhydride (PMDA) or a multifunctional epoxy (Joncryl^® ADR 4368) as chain extender, in order to improve the processing behavior during film blowing. The modified materials were characterized by shear and elongation rheometry and relevant processing characteristics, like melt pressure, bubble stability, and film thickness uniformity, were used to assess the influence of the type of modifier on processing and product performance. It is shown that PMDA is useful to increase the melt strength which leads to an improved bubble stability, while epoxy modified PET shows a reduced drawability that can cause problems at high take-up ratios. On the other hand, the epoxy modifier indicates a pronounced strain hardening during elongational deformation, and therefore leads to a better film thickness uniformity compared to the neat PET and the PET modified with PMDA. The differences with respect to processing performance are discussed and ascribed to the molecular structure of the materials. Full article

(This article belongs to the Special Issue Extensional Rheology and Processing of Polymeric Materials)

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10 pages, 1939 KiB

Open AccessEditor’s ChoiceArticle

Engineering Graphene Oxide/Water Interface from First Principles to Experiments for Electrostatic Protective Composites

by Luca Valentini, Silvia Bittolo Bon and Giacomo Giorgi

Polymers 2020, 12(7), 1596; https://doi.org/10.3390/polym12071596 - 18 Jul 2020

Cited by 7 | Viewed by 3391

Abstract

From the global spread of COVID-19 we learned that SARS-CoV-2 virus can be transmitted via respiratory liquid droplets. In this study, we performed first-principles calculations suggesting that water molecules once in contact with the graphene oxide (GO) layer interact with its functional groups, [...] Read more.

From the global spread of COVID-19 we learned that SARS-CoV-2 virus can be transmitted via respiratory liquid droplets. In this study, we performed first-principles calculations suggesting that water molecules once in contact with the graphene oxide (GO) layer interact with its functional groups, therefore, developing an electric field induced by the heterostructure formation. Experiments on GO polymer composite film supports the theoretical findings, showing that the interaction with water aerosol generates a voltage output signal of up to −2 V. We then developed an electrostatic composite fiber by the coagulation method mixing GO with poly(methyl methacrylate) (PMMA). These findings could be used to design protective fabrics with antiviral activity against negatively charged spike proteins of airborne viruses. Full article

(This article belongs to the Special Issue Multifunctional Polymer Nanocomposites)

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16 pages, 5841 KiB

Open AccessEditor’s ChoiceArticle

Electron-Beam Irradiation of the PLLA/CMS/β-TCP Composite Nanofibers Obtained by Electrospinning

by Mohd Reusmaazran Yusof, Roslinda Shamsudin, Sarani Zakaria, Muhammad Azmi Abdul Hamid, Fatma Yalcinkaya, Yusof Abdullah and Norzita Yacob

Polymers 2020, 12(7), 1593; https://doi.org/10.3390/polym12071593 - 17 Jul 2020

Cited by 6 | Viewed by 2743

Abstract

Nanofibrous materials produced by electrospinning processes have potential advantages in tissue engineering because of their biocompatibility, biodegradability, biomimetic architecture, and excellent mechanical properties. The aim of the current work is to study the influence of the electron beam on the poly L-lactide acid/ [...] Read more.

Nanofibrous materials produced by electrospinning processes have potential advantages in tissue engineering because of their biocompatibility, biodegradability, biomimetic architecture, and excellent mechanical properties. The aim of the current work is to study the influence of the electron beam on the poly L-lactide acid/ carboxy-methyl starch/β-tricalcium phosphate (PLLA/CMS/β-TCP) composite nanofibers for potential applications as bone-tissue scaffolds. The composite nanofibers were prepared by electrospinning in the combination of 5% v/v carboxy-methyl starch (CMS) and 0.25 wt% of β-TCP with the PLLA as a matrix component. The composites nanofibers were exposed under 5, 30, and 100 kGy of irradiation dose. The electron-beam irradiation showed no morphological damage to the fibers, and slight reduction in the water-contact angle and mechanical strength at the higher-irradiation doses. The chain scission was found to be a dominant effect; the higher doses of electron-beam irradiation thus increased the in vitro degradation rate of the composite nanofibers. The chemical interaction due to irradiation was indicated by the Fourier transform infrared (FTIR) spectrum and thermal behavior was investigated by a differential scanning calorimeter (DSC). The results showed that the electron-beam-induced poly L-lactide acid/carboxy-methyl starch/β-tricalcium phosphate (PLLA/CMS/β-TCP) composite nanofibers may have great potential for bone-tissue engineering. Full article

(This article belongs to the Special Issue Electrospinning of Biopolymer Nanofibers)

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20 pages, 7261 KiB

Open AccessEditor’s ChoiceArticle

A Case Study of Polyetheretherketone (II): Playing with Oxygen Concentration and Modeling Thermal Decomposition of a High-Performance Material

by Aditya Ramgobin, Gaëlle Fontaine and Serge Bourbigot

Polymers 2020, 12(7), 1577; https://doi.org/10.3390/polym12071577 - 16 Jul 2020

Cited by 10 | Viewed by 2849

Abstract

Kinetic decomposition models for the thermal decomposition of a high-performance polymeric material (polyetheretherketone, PEEK) were determined from specific techniques. Experimental data from thermogravimetric analysis (TGA) and previously elucidated decomposition mechanisms were combined with a numerical simulating tool to establish a comprehensive kinetic model [...] Read more.

Kinetic decomposition models for the thermal decomposition of a high-performance polymeric material (polyetheretherketone, PEEK) were determined from specific techniques. Experimental data from thermogravimetric analysis (TGA) and previously elucidated decomposition mechanisms were combined with a numerical simulating tool to establish a comprehensive kinetic model for the decomposition of PEEK under three atmospheres: nitrogen, 2% oxygen, and synthetic air. Multistepped kinetic models with subsequent and competitive reactions were established by taking into consideration the different types of reactions that may occur during the thermal decomposition of the material (chain scission, thermo-oxidation, char formation). The decomposition products and decomposition mechanism of PEEK which were established in our previous report allowed for the elucidation of the kinetic decomposition models. A three-stepped kinetic thermal decomposition pathway was a good fit to model the thermal decomposition of PEEK under nitrogen. The kinetic model involved an autocatalytic type of reaction followed by competitive and successive nth order reactions. Such types of models were set up for the evaluation of the kinetics of the thermal decomposition of PEEK under 2% oxygen and in air, leading to models with satisfactory fidelity. Full article

(This article belongs to the Collection Fire and Polymers)

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9 pages, 5661 KiB

Open AccessEditor’s ChoiceArticle

High Refractive-Index Hybrids Consisting of Water-Soluble Matrices with Bipyridine-Modified Polyhedral Oligomeric Silsesquioxane and Lanthanoid Cations

by Kazunari Ueda, Takahiro Kakuta, Kazuo Tanaka and Yoshiki Chujo

Polymers 2020, 12(7), 1560; https://doi.org/10.3390/polym12071560 - 14 Jul 2020

Cited by 4 | Viewed by 2727

Abstract

We report high refractive-index (RI) films composed of polyhedral oligomeric silsesquioxane (SSQ) matrices and various lanthanoid cations. The SSQ matrices were constructed from octaammonium SSQ by connecting with bipyridine dicarboxylic acid, which is expected to capture cations. By modulating the feed ratio between [...] Read more.

We report high refractive-index (RI) films composed of polyhedral oligomeric silsesquioxane (SSQ) matrices and various lanthanoid cations. The SSQ matrices were constructed from octaammonium SSQ by connecting with bipyridine dicarboxylic acid, which is expected to capture cations. By modulating the feed ratio between SSQ and dicarboxylic acid, the series of the SSQ matrices were obtained with variable cross-linking ratios among the SSQ units. Thin transparent films were able to be prepared through the drop-casting method with the aqueous mixtures containing SSQ matrices and various kinds of lanthanoid salts up to 40 wt %. From RI measurements, it was revealed that the increase of the amount of the metal ion can significantly lift up the RI values. In particular, critical losses of Abbe numbers, which theoretically have the trade-off relationship toward increases in RI values, were hardly detected. This effect could be obtained by cation assembly in local spots that are assisted by SSQ. Full article

(This article belongs to the Special Issue Silsesquioxane (POSS) Polymers, Copolymers and Nanoparticles)

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29 pages, 13876 KiB

Open AccessEditor’s ChoiceReview

Separation of Semiconducting Carbon Nanotubes Using Conjugated Polymer Wrapping

by Jingyi Wang and Ting Lei

Polymers 2020, 12(7), 1548; https://doi.org/10.3390/polym12071548 - 13 Jul 2020

Cited by 36 | Viewed by 6732

Abstract

In the past two decades, single-walled carbon nanotubes (SWNTs) have been explored for electronic applications because of their high charge carrier mobility, low-temperature solution processability and mechanical flexibility. Semiconducting SWNTs (s-SWNTs) are also considered an alternative to traditional silicon-based semiconductors. However, large-scale, as-produced [...] Read more.

In the past two decades, single-walled carbon nanotubes (SWNTs) have been explored for electronic applications because of their high charge carrier mobility, low-temperature solution processability and mechanical flexibility. Semiconducting SWNTs (s-SWNTs) are also considered an alternative to traditional silicon-based semiconductors. However, large-scale, as-produced SWNTs have poor solubility, and they are mixtures of metallic SWNTs (m-SWNTs) and s-SWNTs, which limits their practical applications. Conjugated polymer wrapping is a promising method to disperse and separate s-SWNTs, due to its high selectivity, high separation yield and simplicity of operation. In this review, we summarize the recent progress of the conjugated polymer wrapping method, and discuss possible separation mechanisms for s-SWNTs. We also discuss various parameters that may affect the selectivity and sorting yield. Finally, some electronic applications of polymer-sorted s-SWNTs are introduced. The aim of this review is to provide polymer chemist a basic concept of polymer based SWNT separation, as well as some polymer design strategies, influential factors and potential applications. Full article

(This article belongs to the Special Issue Conjugated Polymers and Polymer Networks with Unconventional Structural and Functional Features)

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42 pages, 12062 KiB

Open AccessEditor’s ChoiceReview

FDM-Based 3D Printing of Polymer and Associated Composite: A Review on Mechanical Properties, Defects and Treatments

by Sachini Wickramasinghe, Truong Do and Phuong Tran

Polymers 2020, 12(7), 1529; https://doi.org/10.3390/polym12071529 - 10 Jul 2020

Cited by 496 | Viewed by 34214

Abstract

Fused deposition modelling (FDM) is one of the fastest-growing additive manufacturing methods used in printing fibre-reinforced composites (FRC). The performances of the resulting printed parts are limited compared to those by other manufacturing methods due to their inherent defects. Hence, the effort to [...] Read more.

Fused deposition modelling (FDM) is one of the fastest-growing additive manufacturing methods used in printing fibre-reinforced composites (FRC). The performances of the resulting printed parts are limited compared to those by other manufacturing methods due to their inherent defects. Hence, the effort to develop treatment methods to overcome these drawbacks has accelerated during the past few years. The main focus of this study is to review the impact of those defects on the mechanical performance of FRC and therefore to discuss the available treatment methods to eliminate or minimize them in order to enhance the functional properties of the printed parts. As FRC is a combination of polymer matrix material and continuous or short reinforcing fibres, this review will thoroughly discuss both thermoplastic polymers and FRCs printed via FDM technology, including the effect of printing parameters such as layer thickness, infill pattern, raster angle and fibre orientation. The most common defects on printed parts, in particular, the void formation, surface roughness and poor bonding between fibre and matrix, are explored. An inclusive discussion on the effectiveness of chemical, laser, heat and ultrasound treatments to minimize these drawbacks is provided by this review. Full article

(This article belongs to the Section Polymer Processing and Engineering)

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24 pages, 4634 KiB

Open AccessEditor’s ChoiceArticle

Biodegradation of Crystalline Cellulose Nanofibers by Means of Enzyme Immobilized-Alginate Beads and Microparticles

by Arnaud Kamdem Tamo, Ingo Doench, Aliuska Morales Helguera, Daniel Hoenders, Andreas Walther and Anayancy Osorio Madrazo

Polymers 2020, 12(7), 1522; https://doi.org/10.3390/polym12071522 - 9 Jul 2020

Cited by 39 | Viewed by 5301

Abstract

Recent advances in nanocellulose technology have revealed the potential of crystalline cellulose nanofibers to reinforce materials which are useful for tissue engineering, among other functions. However, the low biodegradability of nanocellulose can possess some problems in biomedical applications. In this work, alginate particles [...] Read more.

Recent advances in nanocellulose technology have revealed the potential of crystalline cellulose nanofibers to reinforce materials which are useful for tissue engineering, among other functions. However, the low biodegradability of nanocellulose can possess some problems in biomedical applications. In this work, alginate particles with encapsulated enzyme cellulase extracted from Trichoderma reesei were prepared for the biodegradation of crystalline cellulose nanofibers, which carrier system could be incorporated in tissue engineering biomaterials to degrade the crystalline cellulose nanoreinforcement in situ and on-demand during tissue regeneration. Both alginate beads and microparticles were processed by extrusion-dropping and inkjet-based methods, respectively. Processing parameters like the alginate concentration, concentration of ionic crosslinker Ca²⁺, hardening time, and ionic strength of the medium were varied. The hydrolytic activity of the free and encapsulated enzyme was evaluated for unmodified (CNFs) and TEMPO-oxidized cellulose nanofibers (TOCNFs) in suspension (heterogeneous conditions); in comparison to solubilized cellulose derivatives (homogeneous conditions). The enzymatic activity was evaluated for temperatures between 25–75 °C, pH range from 3.5 to 8.0 and incubation times until 21 d. Encapsulated cellulase in general displayed higher activity compared to the free enzyme over wider temperature and pH ranges and for longer incubation times. A statistical design allowed optimizing the processing parameters for the preparation of enzyme-encapsulated alginate particles presenting the highest enzymatic activity and sphericity. The statistical analysis yielded the optimum particles characteristics and properties by using a formulation of 2% (w/v) alginate, a coagulation bath of 0.2 M CaCl₂ and a hardening time of 1 h. In homogeneous conditions the highest catalytic activity was obtained at 55 °C and pH 4.8. These temperature and pH values were considered to study the biodegradation of the crystalline cellulose nanofibers in suspension. The encapsulated cellulase preserved its activity for several weeks over that of the free enzyme, which latter considerably decreased and practically showed deactivation after just 10 d. The alginate microparticles with their high surface area-to-volume ratio effectively allowed the controlled release of the encapsulated enzyme and thereby the sustained hydrolysis of the cellulose nanofibers. The relative activity of cellulase encapsulated in the microparticles leveled-off at around 60% after one day and practically remained at that value for three weeks. Full article

(This article belongs to the Special Issue Natural Polymer Based Micro and Nanoparticles)

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18 pages, 3146 KiB

Open AccessEditor’s ChoiceReview

Present Status in Polymeric Mouthguards. A Future Area for Additive Manufacturing?

by Ana M. Sousa, Ana C. Pinho, Ana Messias and Ana P. Piedade

Polymers 2020, 12(7), 1490; https://doi.org/10.3390/polym12071490 - 3 Jul 2020

Cited by 23 | Viewed by 9314

Abstract

Athletes from contact sports are more prone to orofacial injuries because of the exposure to possible shocks and collisions derived from physical proximity. The use of protector polymeric mouthguards proved to be useful in the prevention of the described injuries. There are different [...] Read more.

Athletes from contact sports are more prone to orofacial injuries because of the exposure to possible shocks and collisions derived from physical proximity. The use of protector polymeric mouthguards proved to be useful in the prevention of the described injuries. There are different types of mouthguards with varying ranges of protection and prices, but they are all made from polymers and share the same propose: to absorb and dissipate the impact energy resulting from the shocks. As they are used inside the mouth, they should not impair breathing and speaking nor compromise the comfort of the athlete. However, the ideal mouthguard is yet to be created. The choice of the most appropriate polymeric material and the standard required properties have not yet been reported. Regardless of the numerous studies in this field, normalized control parameters for both material characterization and mouthguard fabrication are absent. This paper aims to present a review of the current types of available mouthguards and their properties/characteristics. Moreover, a detailed description of the most common polymers for the fabrication of mouthguards, together with the manufacturing techniques, are discussed. Full article

(This article belongs to the Special Issue Polymer Connect: Polymer Science and Composite Materials)

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11 pages, 5405 KiB

Open AccessEditor’s ChoiceArticle

Internal Residual Strain Measurements in Carbon Fiber-Reinforced Polymer Laminates Curing Process Using Embedded Tilted Fiber Bragg Grating Sensor

by Ke-Ping Ma, Chao-Wei Wu, Yao-Tung Tsai, Ya-Chun Hsu and Chia-Chin Chiang

Polymers 2020, 12(7), 1479; https://doi.org/10.3390/polym12071479 - 1 Jul 2020

Cited by 6 | Viewed by 2671

Abstract

Carbon fiber reinforced plastics (CFRP) have many mechanical properties that are superior to those of conventional structural materials and are becoming more and more widely used. Monitoring the curing process used to produce such composite material is important to ensure the quality of [...] Read more.

Carbon fiber reinforced plastics (CFRP) have many mechanical properties that are superior to those of conventional structural materials and are becoming more and more widely used. Monitoring the curing process used to produce such composite material is important to ensure the quality of the process, especially for the characterization of residual strains after the material has been manufactured. In this study, we present a tilted fiber Bragg grating (TFBG) sensor used to monitor the curing of CFRP composite materials. The TFBG sensor was embedded into the layers of CFRP laminates to study the curing residual strain of the laminates. The experimental results showed that the curing residual stress was about −22.25 MPa, the axial residual strain was −281.351 με, and lateral residual strain of 89.91 με. The TFBG sensor was found to be sensitive to the curing residual strain of the CFRP, meaning that it has potential for use in applications involving composite curing processes. Moreover, it is indeed possible to improve the properties of composite materials via the optimization and monitoring of their curing parameters. Full article

(This article belongs to the Special Issue Selected Papers from IMETI 2021)

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15 pages, 3804 KiB

Open AccessEditor’s ChoiceArticle

Reinforcement of Epoxy Composites with Application of Finely-ground Ochre and Electrophysical Method of the Composition Modification

by Amirbek Bekeshev, Anton Mostovoy, Lyazzat Tastanova, Yulia Kadykova, Svetlana Kalganova and Marina Lopukhova

Polymers 2020, 12(7), 1437; https://doi.org/10.3390/polym12071437 - 27 Jun 2020

Cited by 30 | Viewed by 3609

Abstract

The conducted studies have proven the possibility of the directed control of operational properties of epoxy composites, due to the addition of finely-ground ocher into their composition, and the use of microwave modification of the epoxy composition. The rational content of ocher as [...] Read more.

The conducted studies have proven the possibility of the directed control of operational properties of epoxy composites, due to the addition of finely-ground ocher into their composition, and the use of microwave modification of the epoxy composition. The rational content of ocher as a modifying additive (0.5 parts by mass) and a filler (75 parts by mass) of the epoxy composition has been selected, which ensures the improvement of the studied complex of physical-mechanical properties. It has been proven that ocher affects the structure formation processes and the structure of the epoxy composite, thus increasing its thermal, heat and fire resistance. During the research, the application efficiency has been proven, and the optimal parameters of the microwave modification (power—350 W; duration—30 s) of epoxy compositions filled with ocher, which increase physical-mechanical characteristics of composites, have been selected. Full article

(This article belongs to the Special Issue Epoxy Resins and Composites)

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15 pages, 4949 KiB

Open AccessEditor’s ChoiceArticle

Effects of a Reactive Phosphorus–Sulfur Containing Flame-Retardant Monomer on the Flame Retardancy and Thermal and Mechanical Properties of Unsaturated Polyester Resin

by Kang Dai, Zhenzhen Deng, Guyue Liu, Yutong Wu, Wenbin Xu and Yuan Hu

Polymers 2020, 12(7), 1441; https://doi.org/10.3390/polym12071441 - 27 Jun 2020

Cited by 17 | Viewed by 3648

Abstract

A novel reactive phosphorus and sulfur-containing monomer (bis(acryloxyethyldiphenylphosphate)sulfone, BADPS) was synthesized to enhance the comprehensive performance of unsaturated polyester resin (UPR), and corresponding flame-retardant unsaturated polyester resins (FR-UPRs) with various amounts of BADPS were prepared by radical bulk polymerization. The flame retardancy and [...] Read more.

A novel reactive phosphorus and sulfur-containing monomer (bis(acryloxyethyldiphenylphosphate)sulfone, BADPS) was synthesized to enhance the comprehensive performance of unsaturated polyester resin (UPR), and corresponding flame-retardant unsaturated polyester resins (FR-UPRs) with various amounts of BADPS were prepared by radical bulk polymerization. The flame retardancy and thermal and mechanical properties of the UPR samples were investigated by limiting oxygen index (LOI) measurements, cone calorimetry, differential scanning calorimetry (DSC), a thermogravimetric analysis (TGA), and a tension test. The results showed that the introduction of BADPS remarkably enhanced the flame resistance and high-temperature stability, as well as the tensile performance of UPR. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and Raman spectroscopy studies revealed that BADPS can efficaciously promote the formation of UPR char residue with an improved microstructure and increased graphitization degree, which enhancedthe high-temperature stability and char yield of UPR. Additionally, a thermogravimetry-Fourier transform infrared (TG-FTIR) analysis corroborated that the evolution of combustible volatiles from UPR decomposition was substantially restrained by the incorporation of BADPS, which is beneficial for the suppression of fire hazards in UPR. Full article

(This article belongs to the Collection Fire and Polymers)

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12 pages, 924 KiB

Open AccessEditor’s ChoiceArticle

Potential Use of Wollastonite as a Filler in UF Resin Based Medium-Density Fiberboard (MDF)

by Hamid R. Taghiyari, Ayoub Esmailpour, Roya Majidi, Jeffrey J. Morrell, Mohammad Mallaki, Holger Militz and Antonios N. Papadopoulos

Polymers 2020, 12(7), 1435; https://doi.org/10.3390/polym12071435 - 27 Jun 2020

Cited by 23 | Viewed by 3624

Abstract

Urea-formaldehyde (UF) resins are primary petroleum-based, increasing their potential environmental footprint. Identifying additives to reduce the total amount of resin needed without adversely affecting the panel properties could reduce these impacts. Wollastonite is a mineral containing calcium and silica that has been used [...] Read more.

Urea-formaldehyde (UF) resins are primary petroleum-based, increasing their potential environmental footprint. Identifying additives to reduce the total amount of resin needed without adversely affecting the panel properties could reduce these impacts. Wollastonite is a mineral containing calcium and silica that has been used as an additive in a variety of materials and may be useful as a resin extender. Nanoscale wollastonite has been shown to enhance the panel properties but is costly. Micron-scale wollastonite may be a less costly alternative. Medium-density fiberboards were produced by blending a hardwood furnish with UF alone, micron-sized wollastonite alone, or a 9:1 ratio of UF to wollastonite. Panels containing of only wollastonite had poor properties, but the properties of panels with 9:1 UF/wollastonite were similar to the UF-alone panels, except for the internal bond strength. The results suggest that small amounts of micron-sized wollastonite could serve as a resin extender. Further studies are suggested to determine if the micron-sized material has similar positive effects on the resin curing rate. Full article

(This article belongs to the Special Issue Recent Developments in Eco-Friendly Wood-Based Composites)

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15 pages, 3374 KiB

Open AccessEditor’s ChoiceArticle

A Highly Sensitive and Flexible Capacitive Pressure Sensor Based on a Porous Three-Dimensional PDMS/Microsphere Composite

by Young Jung, Wookjin Lee, Kyungkuk Jung, Byunggeon Park, Jinhyoung Park, Jongsoo Ko and Hanchul Cho

Polymers 2020, 12(6), 1412; https://doi.org/10.3390/polym12061412 - 24 Jun 2020

Cited by 74 | Viewed by 6901

Abstract

In recent times, polymer-based flexible pressure sensors have been attracting a lot of attention because of their various applications. A highly sensitive and flexible sensor is suggested, capable of being attached to the human body, based on a three-dimensional dielectric elastomeric structure of [...] Read more.

In recent times, polymer-based flexible pressure sensors have been attracting a lot of attention because of their various applications. A highly sensitive and flexible sensor is suggested, capable of being attached to the human body, based on a three-dimensional dielectric elastomeric structure of polydimethylsiloxane (PDMS) and microsphere composite. This sensor has maximal porosity due to macropores created by sacrificial layer grains and micropores generated by microspheres pre-mixed with PDMS, allowing it to operate at a wider pressure range (~150 kPa) while maintaining a sensitivity (of 0.124 kPa⁻¹ in a range of 0~15 kPa) better than in previous studies. The maximized pores can cause deformation in the structure, allowing for the detection of small changes in pressure. In addition to exhibiting a fast rise time (~167 ms) and fall time (~117 ms), as well as excellent reproducibility, the fabricated pressure sensor exhibits reliability in its response to repeated mechanical stimuli (2.5 kPa, 1000 cycles). As an application, we develop a wearable device for monitoring repeated tiny motions, such as the pulse on the human neck and swallowing at the Adam’s apple. This sensory device is also used to detect movements in the index finger and to monitor an insole system in real-time. Full article

(This article belongs to the Section Polymer Composites and Nanocomposites)

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16 pages, 1853 KiB

Open AccessEditor’s ChoiceArticle

An Innovative Method for the Recycling of Waste Carbohydrate-Based Flours

by Carola Esposito Corcione, Raffaella Striani, Francesca Ferrari, Paolo Visconti, Daniela Rizzo and Antonio Greco

Polymers 2020, 12(6), 1414; https://doi.org/10.3390/polym12061414 - 24 Jun 2020

Cited by 10 | Viewed by 2523

Abstract

This work represents an innovative study that, for the first time, explores the possibility to use waste flours to produce thermoplastic polymeric bio-films. To the best of our knowledge, this is the first time that waste flours, derived from bakeries, pizzerias or pasta [...] Read more.

This work represents an innovative study that, for the first time, explores the possibility to use waste flours to produce thermoplastic polymeric bio-films. To the best of our knowledge, this is the first time that waste flours, derived from bakeries, pizzerias or pasta factories, have been proposed for the production of bio-polymers, as a replacement of neat starch. To this aim, durum waste flour derived from a pasta factory, soft waste flour derived from pizzerias and neat maize starch used as control material were firstly analyzed from dimensional, morphological and chemical points of view. Afterwards, waste flour films were produced by the addition of a nature-based plasticizer, glycerol. Mechanical characterization of the plasticized thermoplastic films, produced by compression molding, evidenced low performances, even in the case of the neat maize starch. In order to improve the mechanical properties, the possibility to include polylactic acid and cardanol-based plasticizer was also investigated. Mass transport properties of all the produced bio-films were investigated by measuring their water vapor permeability and hygroscopic absorption. The durability properties of the bio-films were assessed by accelerated ageing tests, while the bio-degradability of the waste-based films was evaluated by measuring the solubility and the degradation in water. The physicochemical analyses of the novel bio-films evidenced good mechanical properties; specifically, the waste-based films showed a lower hygroscopic absorption and water solubility than those of the blends containing neat starch. Full article

(This article belongs to the Special Issue Eco-Innovative Engineering of the Polymer Material’s Life Cycle)

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14 pages, 3754 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Transdermal Composite Microneedle Composed of Mesoporous Iron Oxide Nanoraspberry and PVA for Androgenetic Alopecia Treatment

by Jen-Hung Fang, Che-Hau Liu, Ru-Siou Hsu, Yin-Yu Chen, Wen-Hsuan Chiang, Hui-Min David Wang and Shang-Hsiu Hu

Polymers 2020, 12(6), 1392; https://doi.org/10.3390/polym12061392 - 22 Jun 2020

Cited by 45 | Viewed by 6094

Abstract

The transdermal delivery of therapeutic agents amplifying a local concentration of active molecules have received considerable attention in wide biomedical applications, especially in vaccine development and medical beauty. Unlike oral or subcutaneous injections, this approach can not only avoid the loss of efficacy [...] Read more.

The transdermal delivery of therapeutic agents amplifying a local concentration of active molecules have received considerable attention in wide biomedical applications, especially in vaccine development and medical beauty. Unlike oral or subcutaneous injections, this approach can not only avoid the loss of efficacy of oral drugs due to the liver’s first-pass effect but also reduce the risk of infection by subcutaneous injection. In this study, a magneto-responsive transdermal composite microneedle (MNs) with a mesoporous iron oxide nanoraspberry (MIO), that can improve the drug delivery efficiency, was fabricated by using a 3D printing-molding method. With loading of Minoxidil (Mx, a medication commonly used to slow the progression of hair loss and speed the process of hair regrowth), MNs can break the barrier of the stratum corneum through the puncture ability, and control the delivery dose for treating androgenetic alopecia (AGA). By 3D printing process, the sizes and morphologies of MNs is able to be, easily, architected. The MIOs were embedded into the tip of MNs which can deliver Mx as well as generate mild heating for hair growth, which is potentially attributed by the expansion of hair follicle and drug penetration. Compared to the mice without any treatments, the hair density of mice exhibited an 800% improvement after being treated by MNs with MF at 10-days post-treatment. Full article

(This article belongs to the Special Issue Advanced Polymer Nanocomposites)

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45 pages, 3261 KiB

Open AccessEditor’s ChoiceReview

Stimuli-Responsive Polymeric Nanocarriers for Drug Delivery, Imaging, and Theragnosis

by Sabya Sachi Das, Priyanshu Bharadwaj, Muhammad Bilal, Mahmood Barani, Abbas Rahdar, Pablo Taboada, Simona Bungau and George Z. Kyzas

Polymers 2020, 12(6), 1397; https://doi.org/10.3390/polym12061397 - 22 Jun 2020

Cited by 298 | Viewed by 15481

Abstract

In the past few decades, polymeric nanocarriers have been recognized as promising tools and have gained attention from researchers for their potential to efficiently deliver bioactive compounds, including drugs, proteins, genes, nucleic acids, etc., in pharmaceutical and biomedical applications. Remarkably, these polymeric nanocarriers [...] Read more.

In the past few decades, polymeric nanocarriers have been recognized as promising tools and have gained attention from researchers for their potential to efficiently deliver bioactive compounds, including drugs, proteins, genes, nucleic acids, etc., in pharmaceutical and biomedical applications. Remarkably, these polymeric nanocarriers could be further modified as stimuli-responsive systems based on the mechanism of triggered release, i.e., response to a specific stimulus, either endogenous (pH, enzymes, temperature, redox values, hypoxia, glucose levels) or exogenous (light, magnetism, ultrasound, electrical pulses) for the effective biodistribution and controlled release of drugs or genes at specific sites. Various nanoparticles (NPs) have been functionalized and used as templates for imaging systems in the form of metallic NPs, dendrimers, polymeric NPs, quantum dots, and liposomes. The use of polymeric nanocarriers for imaging and to deliver active compounds has attracted considerable interest in various cancer therapy fields. So-called smart nanopolymer systems are built to respond to certain stimuli such as temperature, pH, light intensity and wavelength, and electrical, magnetic and ultrasonic fields. Many imaging techniques have been explored including optical imaging, magnetic resonance imaging (MRI), nuclear imaging, ultrasound, photoacoustic imaging (PAI), single photon emission computed tomography (SPECT), and positron emission tomography (PET). This review reports on the most recent developments in imaging methods by analyzing examples of smart nanopolymers that can be imaged using one or more imaging techniques. Unique features, including nontoxicity, water solubility, biocompatibility, and the presence of multiple functional groups, designate polymeric nanocues as attractive nanomedicine candidates. In this context, we summarize various classes of multifunctional, polymeric, nano-sized formulations such as liposomes, micelles, nanogels, and dendrimers. Full article

(This article belongs to the Special Issue Polymeric Materials for Drug Delivery Application)

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15 pages, 2720 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of a 2,3-Dialkoxynaphthalene-Based Conjugated Copolymer via Direct Arylation Polymerization (DAP) for Organic Electronics

by Ignacio A. Jessop, Aylin Chong, Linda Graffo, María B. Camarada, Catalina Espinoza, Felipe A. Angel, Cesar Saldías, Alain Tundidor-Camba and Claudio A. Terraza

Polymers 2020, 12(6), 1377; https://doi.org/10.3390/polym12061377 - 19 Jun 2020

Cited by 10 | Viewed by 2928

Abstract

Poly[(5,5’-(2,3-bis(2-ethylhexyloxy)naphthalene-1,4-diyl)bis(thiophene-2,2′-diyl))-alt-(2,1,3-benzothiadiazole-4,7-diyl)] (PEHONDTBT) was synthesized for the first time and through direct arylation polymerization (DAP) for use as p-donor material in organic solar cells. Optimized reaction protocol leads to a donor-acceptor conjugated polymer in good yield, with less structural defects than its [...] Read more.

Poly[(5,5’-(2,3-bis(2-ethylhexyloxy)naphthalene-1,4-diyl)bis(thiophene-2,2′-diyl))-alt-(2,1,3-benzothiadiazole-4,7-diyl)] (PEHONDTBT) was synthesized for the first time and through direct arylation polymerization (DAP) for use as p-donor material in organic solar cells. Optimized reaction protocol leads to a donor-acceptor conjugated polymer in good yield, with less structural defects than its analog obtained from Suzuki polycondensation, and with similar or even higher molecular weight than other previously reported polymers based on the 2,3-dialkoxynaphthalene monomer. The batch-to-batch repeatability of the optimized DAP conditions for the synthesis of PEHONDTBT was proved, showing the robustness of the synthetic strategy. The structure of PEHONDTBT was corroborated by NMR, exhibiting good solubility in common organic solvents, good film-forming ability, and thermal stability. PEHONDTBT film presented an absorption band centered at 498 nm, a band gap of 2.15 eV, and HOMO and LUMO energy levels of −5.31 eV and −3.17 eV, respectively. Theoretical calculations were performed to understand the regioselectivity in the synthesis of PEHONDTBT and to rationalize its optoelectronic properties. Bilayer heterojunction organic photovoltaic devices with PEHONDTBT as the donor layer were fabricated to test their photovoltaic performance, affording low power-conversion efficiency in the preliminary studies. Full article

(This article belongs to the Section Polymer Chemistry)

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14 pages, 2915 KiB

Open AccessEditor’s ChoiceArticle

Light Processable Starch Hydrogels

by Camilla Noè, Chiara Tonda-Turo, Annalisa Chiappone, Marco Sangermano and Minna Hakkarainen

Polymers 2020, 12(6), 1359; https://doi.org/10.3390/polym12061359 - 17 Jun 2020

Cited by 47 | Viewed by 7784

Abstract

Light processable hydrogels were successfully fabricated by utilizing maize starch as raw material. To render light processability, starch was gelatinized and methacrylated by simple reaction with methacrylic anhydride. The methacrylated starch was then evaluated for its photocuring reactivity and 3D printability by digital [...] Read more.

Light processable hydrogels were successfully fabricated by utilizing maize starch as raw material. To render light processability, starch was gelatinized and methacrylated by simple reaction with methacrylic anhydride. The methacrylated starch was then evaluated for its photocuring reactivity and 3D printability by digital light processing (DLP). Hydrogels with good mechanical properties and biocompatibility were obtained by direct curing from aqueous solution containing lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) as photo-initiator. The properties of the hydrogels were tunable by simply changing the concentration of starch in water. Photo-rheology showed that the formulations with 10 or 15 wt% starch started curing immediately and reached G’ plateau after only 60 s, while it took 90 s for the 5 wt% formulation. The properties of the photocured hydrogels were further characterized by rheology, compressive tests, and swelling experiments. Increasing the starch content from 10 to 15 wt% increased the compressive stiffness from 13 to 20 kPa. This covers the stiffness of different body tissues giving promise for the use of the hydrogels in tissue engineering applications. Good cell viability with human fibroblast cells was confirmed for all three starch hydrogel formulations indicating no negative effects from the methacrylation or photo-crosslinking reaction. Finally, the light processability of methacrylated starch by digital light processing (DLP) 3D printing directly from aqueous solution was successfully demonstrated. Altogether the results are promising for future application of the hydrogels in tissue engineering and as cell carriers Full article

(This article belongs to the Collection Sustainable Polymeric Materials from Renewable Resources)

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22 pages, 4131 KiB

Open AccessEditor’s ChoiceReview

Solar Cells for Indoor Applications: Progress and Development

by Swarup Biswas and Hyeok Kim

Polymers 2020, 12(6), 1338; https://doi.org/10.3390/polym12061338 - 12 Jun 2020

Cited by 77 | Viewed by 8265

Abstract

The Internet of things (IoT) has been rapidly growing in the past few years. IoT connects numerous devices, such as wireless sensors, actuators, and wearable devices, to optimize and monitor daily activities. Most of these devices require power in the microwatt range and [...] Read more.

The Internet of things (IoT) has been rapidly growing in the past few years. IoT connects numerous devices, such as wireless sensors, actuators, and wearable devices, to optimize and monitor daily activities. Most of these devices require power in the microwatt range and operate indoors. To this end, a self-sustainable power source, such as a photovoltaic (PV) cell, which can harvest low-intensity indoor light, is appropriate. Recently, the development of highly efficient PV cells for indoor applications has attracted tremendous attention. Therefore, different types of PV materials, such as inorganic, dye-sensitized, organic, and perovskite materials, have been employed for harvesting low-intensity indoor light energy. Although considerable efforts have been made by researchers to develop low-cost, stable, and efficient PV cells for indoor applications, Extensive investigation is necessary to resolve some critical issues concerning PV cells, such as environmental stability, lifetime, large-area fabrication, mechanical flexibility, and production cost. To address these issues, a systematic review of these aspects will be highly useful to the research community. This study discusses the current status of the development of indoor PV cells based on previous reports. First, we have provided relevant background information. Then, we have described the different indoor light sources, and subsequently critically reviewed previous reports regarding indoor solar cells based on different active materials such as inorganic, dye-sensitized, organic, and perovskite. Finally, we have placed an attempt to provide insight into factors needed to further improve the feasibility of PV technology for indoor applications. Full article

(This article belongs to the Special Issue Photovoltaic Semiconductor Materials)

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14 pages, 1439 KiB

Open AccessEditor’s ChoiceReview

The Modelling of Extrusion Processes for Polymers—A Review

by Marko Hyvärinen, Rowshni Jabeen and Timo Kärki

Polymers 2020, 12(6), 1306; https://doi.org/10.3390/polym12061306 - 8 Jun 2020

Cited by 68 | Viewed by 17701

Abstract

Extrusion processes are widely used in industries that aim to produce advanced solutions for increasingly sophisticated demands in the plastic, food, and pharmaceutical sectors. Though the process has been in use since the 1930s, limited information is available on the analytical computation of [...] Read more.

Extrusion processes are widely used in industries that aim to produce advanced solutions for increasingly sophisticated demands in the plastic, food, and pharmaceutical sectors. Though the process has been in use since the 1930s, limited information is available on the analytical computation of extrusion. Generally, production has been carried out based on empirical experience and trial-and-error approaches. The development of industrial operations is, however, best addressed by modelling the processes involved, and the flow of polymer melts and fibers in extruders has been subjected to some previous studies. Also included an overview of design of a die as well as challenges in sheet/film production. This article systematically and critically reviews the literature related to the process design, machine design, process parameters, flow models, and flow analysis of extrusion with a focus on modelling the extrusion of composite materials. Full article

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19 pages, 4217 KiB

Open AccessEditor’s ChoiceArticle

Mechanical Behavior of Melt-Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites

by Karolina Gaska, Georgia C. Manika, Thomas Gkourmpis, Davide Tranchida, Antonis Gitsas and Roland Kádár

Polymers 2020, 12(6), 1309; https://doi.org/10.3390/polym12061309 - 8 Jun 2020

Cited by 14 | Viewed by 3323

Abstract

The mechanical properties of novel low percolation melt-mixed 3D hierarchical graphene/polypropylene nanocomposites are analyzed in this study. The analysis spans a broad range of techniques and time scales, from impact to tensile, dynamic mechanical behavior, and creep. The applicability of the time–temperature superposition [...] Read more.

The mechanical properties of novel low percolation melt-mixed 3D hierarchical graphene/polypropylene nanocomposites are analyzed in this study. The analysis spans a broad range of techniques and time scales, from impact to tensile, dynamic mechanical behavior, and creep. The applicability of the time–temperature superposition principle and its limitations in the construction of the master curve for the isotactic polypropylene (iPP)-based graphene nanocomposites has been verified and presented. The Williams–Landel–Ferry method has been used to evaluate the dynamics and also Cole–Cole curves were presented to verify the thermorheological character of the nanocomposites. Short term (quasi-static) tensile tests, creep, and impact strength measurements were used to evaluate the load transfer efficiency. A significant increase of Young’s modulus with increasing filler content indicates reasonably good dispersion and adhesion between the iPP and the filler. The Young’s modulus results were compared with predicted modulus values using Halpin–Tsai model. An increase in brittleness resulting in lower impact strength values has also been recorded. Full article

(This article belongs to the Special Issue Polymer Nanocomposite Interfaces; Fabrication, Properties and Simulations)

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23 pages, 6201 KiB

Open AccessEditor’s ChoiceArticle

Design of Waterborne Asymmetric Block Copolymers as Thermoresponsive Materials

by Gordana Siljanovska Petreska, Christof van Sluijs, Clemens Auschra and Maria Paulis

Polymers 2020, 12(6), 1253; https://doi.org/10.3390/polym12061253 - 30 May 2020

Viewed by 2848

Abstract

AB diblock waterborne copolymers made of styrene (St) and 2-ethylhexyl acrylate (2EHA) were synthesized by means of two-step reversible addition fragmentation chain transfer (RAFT) (mini)emulsion polymerization. Monofunctional asymmetric RAFT agent was used to initiate the polymerization. The hard polystyrene “A” block was synthesized [...] Read more.

AB diblock waterborne copolymers made of styrene (St) and 2-ethylhexyl acrylate (2EHA) were synthesized by means of two-step reversible addition fragmentation chain transfer (RAFT) (mini)emulsion polymerization. Monofunctional asymmetric RAFT agent was used to initiate the polymerization. The hard polystyrene “A” block was synthesized via miniemulsion polymerization followed by 2EHA pre-emulsion feeding to form the soft “B” block. Polymerization kinetics and the evolution of the molecular weight distribution were followed during synthesis of both initial and final block copolymers. DSC measurements of the block copolymers revealed the existence of two glass transition temperatures (Tgs) and thus the occurrence of two-phase systems. Microscopic techniques (atomic force microscopy (AFM) and transmission electron microscopy (TEM)) were used to study the phase separation within the particles in the latex form, after film formation at room temperature cast directly from the latex and after different post-treatments well above the Tg of the hard-polystyrene domains, when complete particle coalescence had occurred. The morphological differences observed after different annealing temperatures were correlated with the mechanical properties analyzed by DMTA measurements. Finally, the differences found in the mechanical properties of the block copolymers annealed at different temperatures were correlated to their heat seal application results. Full article

(This article belongs to the Special Issue Advanced Polymeric Functional Materials Using Reversible Deactivation Radical Polymerization Techniques)

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18 pages, 4701 KiB

Open AccessEditor’s ChoiceArticle

Designing Imidazolium Poly(amide-amide) and Poly(amide-imide) Ionenes and Their Interactions with Mono- and Tris(imidazolium) Ionic Liquids

by Kathryn E. O’Harra, Danielle M. Noll, Irshad Kammakakam, Emily M. DeVriese, Gala Solis, Enrique M. Jackson and Jason E. Bara

Polymers 2020, 12(6), 1254; https://doi.org/10.3390/polym12061254 - 30 May 2020

Cited by 7 | Viewed by 3936

Abstract

Here we introduce the synthesis and thermal properties of a series of sophisticated imidazolium ionenes with alternating amide-amide or amide-imide backbone functionality, and investigate the structural effects of mono(imidazolium) and unprecedented tris(imidazolium) ionic liquids (ILs) in these ionenes. The new set of poly(amide-amide) [...] Read more.

Here we introduce the synthesis and thermal properties of a series of sophisticated imidazolium ionenes with alternating amide-amide or amide-imide backbone functionality, and investigate the structural effects of mono(imidazolium) and unprecedented tris(imidazolium) ionic liquids (ILs) in these ionenes. The new set of poly(amide-amide) (PAA) and poly(amide-imide) (PAI) ionenes represent the intersection of conventional high-performance polymers with the ionene archetype–presenting polymers with alternating functional and ionic elements precisely sequenced along the backbone. The effects of polymer composition on the thermal properties and morphology were analyzed. Five distinct polymer backbones were synthesized and combined with a stoichiometric equivalent of the IL 1-benzyl-3-methylimidazolium bistriflimide ([Bnmim][Tf₂N]), which were studied to probe the self-assembly, structuring, and contributions of intermolecular forces when IL is added. Furthermore, three polyamide (PA) or polyimide (PI) ionenes with simpler xylyl linkages were interfaced with [Bnmim][Tf₂N] as well as a novel amide-linked tris(imidazolium) IL, to demonstrate the structural changes imparted by the inclusion of functional, ionic additives dispersed within the ionene matrix. This work highlights the possibilities for utilizing concepts from small molecules which exhibit supramolecular self-assembly to guide creative design and manipulate the structuring of ionenes. Full article

(This article belongs to the Special Issue Innovative Polymer Electrolytes)

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19 pages, 6844 KiB

Open AccessEditor’s ChoiceArticle

Calorimetric and Dielectric Study of Renewable Poly(hexylene 2,5-furan-dicarboxylate)-Based Nanocomposites In Situ Filled with Small Amounts of Graphene Platelets and Silica Nanoparticles

by Olawale Monsur Sanusi, Lazaros Papadopoulos, Panagiotis A. Klonos, Zoi Terzopoulou, Nourredine Aït Hocine, Abdelkibir Benelfellah, George Z. Papageorgiou, Apostolos Kyritsis and Dimitrios N. Bikiaris

Polymers 2020, 12(6), 1239; https://doi.org/10.3390/polym12061239 - 29 May 2020

Cited by 25 | Viewed by 3615

Abstract

Poly(hexylene 2,5 furan-dicarboxylate) (PHF) is a relatively new biobased polyester prepared from renewable resources, which is targeted for use in food packaging applications, owing to its great mechanical and gas barrier performance. Since both properties are strongly connected to crystallinity, the latter is [...] Read more.

Poly(hexylene 2,5 furan-dicarboxylate) (PHF) is a relatively new biobased polyester prepared from renewable resources, which is targeted for use in food packaging applications, owing to its great mechanical and gas barrier performance. Since both properties are strongly connected to crystallinity, the latter is enhanced here by the in situ introduction in PHF of graphene nanoplatelets and fumed silica nanoparticles, as well as mixtures of both, at low amounts. For this investigation, we employed Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and dielectric spectroscopy (BDS). The fillers were found to improve crystallization in both the rate (increasing T_c) and fraction (CF), which was rationalized via the concept of fillers acting as crystallization agents. This action was found stronger in the case of graphene as compared to silica. BDS allowed the detection of local and segmental dynamics, in particular in PHF for the first time. The glass transition dynamics in both BDS (α relaxation) and DSC (T_g) are mainly dominated by the relatively high CF, whereas in the PHF filled uniquely with silica strong spatial confinement effects due to crystals were revealed. Finally, all samples demonstrated the segmental-like dynamics above T_g, which screens the global chain dynamics (normal mode). Full article

(This article belongs to the Special Issue Recent Developments on Calorimetry and Thermal Analysis of Polymers and Nanocomposites)

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15 pages, 3326 KiB

Open AccessEditor’s ChoiceArticle

Controlled Synthesis of Poly(pentafluorostyrene-ran-methyl methacrylate) Copolymers by Nitroxide Mediated Polymerization and Their Use as Dielectric Layers in Organic Thin-film Transistors

by Alexander J. Peltekoff, Mathieu N. Tousignant, Victoria E. Hiller, Owen A. Melville and Benoît H. Lessard

Polymers 2020, 12(6), 1231; https://doi.org/10.3390/polym12061231 - 29 May 2020

Cited by 11 | Viewed by 4321

Abstract

A library of statistically random pentafluorostyrene (PFS) and methyl methacrylate (MMA) copolymers with narrow molecular weight distributions was produced, using nitroxide mediated polymerization (NMP) to study the effect of polymer composition on the performance of bottom-gate top-contact organic thin-film transistors, when utilized as [...] Read more.

A library of statistically random pentafluorostyrene (PFS) and methyl methacrylate (MMA) copolymers with narrow molecular weight distributions was produced, using nitroxide mediated polymerization (NMP) to study the effect of polymer composition on the performance of bottom-gate top-contact organic thin-film transistors, when utilized as the dielectric medium. Contact angle measurements confirmed the ability to tune the surface properties of copolymer thin films through variation of its PFS/MMA composition, while impedance spectroscopy determined the effect of this variation on dielectric properties. Bottom-gate, top-contact copper phthalocyanine (CuPc) based organic thin-film transistors were fabricated using the random copolymers as a dielectric layer. We found that increasing the PFS content led to increased field-effect mobility, until a point after which the CuPc no longer adhered to the polymer dielectric. Full article

(This article belongs to the Special Issue Controlled Polymerization)

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13 pages, 4976 KiB

Open AccessEditor’s ChoiceArticle

Development of Poly(l-Lactic Acid)-Based Bending Actuators

by Daniela M. Correia, Liliana C. Fernandes, Bárbara D.D. Cruz, Gabriela Botelho, Verónica de Zea Bermudez and Senentxu Lanceros-Méndez

Polymers 2020, 12(5), 1187; https://doi.org/10.3390/polym12051187 - 22 May 2020

Cited by 9 | Viewed by 3553

Abstract

This work reports on the development of bending actuators based on poly(l-lactic acid) (PLLA)/ionic liquid (IL) blends, through the incorporation of 40% wt. of the 1-ethyl-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][TFSI]) IL. The films, obtained by solvent casting at room temperature and 50 °C, [...] Read more.

This work reports on the development of bending actuators based on poly(l-lactic acid) (PLLA)/ionic liquid (IL) blends, through the incorporation of 40% wt. of the 1-ethyl-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][TFSI]) IL. The films, obtained by solvent casting at room temperature and 50 °C, were subjected to several post-thermal treatments at 70, 90, 120 and 140 °C, in order to modify the crystallinity of the films. The influence of the drying temperature and of [Emim][TFSI] blending on the morphological, structural, mechanical and electrical properties of the composite materials were studied. The IL induced the formation of a porous surface independently of the processing conditions. Moreover, the [Emim][TFSI] dopant and the post-thermal treatments at 70 °C promoted an increase of the degree of crystallinity of the samples. No significant changes were observed in the degree of crystallinity and Young Modulus for samples with thermal treatment between 70 and 140 °C. The viability of the developed high ionic conductive blends for applications as soft actuators was evaluated. A maximum displacement of 1.7 mm was achieved with the PLLA/[Emim][TFSI] composite prepared at 50 °C and thermally treated at 140 °C, for an applied voltage of 10 Vpp, at a frequency of 100 mHz. This work highlights interesting avenues for the use of PLLA in the field of actuators. Full article

(This article belongs to the Special Issue Conducting Polymers for Advanced Applications)

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24 pages, 3183 KiB

Open AccessEditor’s ChoiceReview

Chitosan-Based Drug Delivery System: Applications in Fish Biotechnology

by Yuanbing Wu, Ania Rashidpour, María Pilar Almajano and Isidoro Metón

Polymers 2020, 12(5), 1177; https://doi.org/10.3390/polym12051177 - 21 May 2020

Cited by 67 | Viewed by 7843

Abstract

Chitosan is increasingly used for safe nucleic acid delivery in gene therapy studies, due to well-known properties such as bioadhesion, low toxicity, biodegradability and biocompatibility. Furthermore, chitosan derivatization can be easily performed to improve the solubility and stability of chitosan–nucleic acid polyplexes, and [...] Read more.

Chitosan is increasingly used for safe nucleic acid delivery in gene therapy studies, due to well-known properties such as bioadhesion, low toxicity, biodegradability and biocompatibility. Furthermore, chitosan derivatization can be easily performed to improve the solubility and stability of chitosan–nucleic acid polyplexes, and enhance efficient target cell drug delivery, cell uptake, intracellular endosomal escape, unpacking and nuclear import of expression plasmids. As in other fields, chitosan is a promising drug delivery vector with great potential for the fish farming industry. This review highlights state-of-the-art assays using chitosan-based methodologies for delivering nucleic acids into cells, and focuses attention on recent advances in chitosan-mediated gene delivery for fish biotechnology applications. The efficiency of chitosan for gene therapy studies in fish biotechnology is discussed in fields such as fish vaccination against bacterial and viral infection, control of gonadal development and gene overexpression and silencing for overcoming metabolic limitations, such as dependence on protein-rich diets and the low glucose tolerance of farmed fish. Finally, challenges and perspectives on the future developments of chitosan-based gene delivery in fish are also discussed. Full article

(This article belongs to the Special Issue Functional Chitosan-Based Composites)

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11 pages, 1953 KiB

Open AccessEditor’s ChoiceArticle

Correlation between Mechanical Properties and Processing Conditions in Rubber-Toughened Wood Polymer Composites

by Valentina Mazzanti, Lorenzo Malagutti, Andrea Santoni, Francesca Sbardella, Andrea Calzolari, Fabrizio Sarasini and Francesco Mollica

Polymers 2020, 12(5), 1170; https://doi.org/10.3390/polym12051170 - 20 May 2020

Cited by 17 | Viewed by 2989

Abstract

The use of wood fibers is a deeply investigated topic in current scientific research and one of their most common applications is as filler for thermoplastic polymers. The resulting material is a biocomposite, known as a Wood Polymer Composite (WPC). For increasing the [...] Read more.

The use of wood fibers is a deeply investigated topic in current scientific research and one of their most common applications is as filler for thermoplastic polymers. The resulting material is a biocomposite, known as a Wood Polymer Composite (WPC). For increasing the sustainability and reducing the cost, it is convenient to increase the wood fiber content as much as possible, so that the polymeric fraction within the composite is thereby reduced. On the other hand, this is often thwarted by a sharp decrease in toughness and processability—a disadvantage that could be overcome by compounding the material with a toughening agent. This work deals with the mechanical properties in tension and impact of polypropylene filled with 50 wt.% wood flour, toughened with different amounts (0%, 10%, and 20%) of a polypropylene-based thermoplastic vulcanizate (TPV). Such properties are also investigated as a function of extrusion processing variables, such as the feeding mode (i.e., starve vs. flood feeding) and screw speed. It is found that the mechanical properties do depend on the processing conditions: the best properties are obtained either in starve feeding conditions, or in flood feeding conditions, but at a low screw speed. The toughening effect of TPV is significant when its content reaches 20 wt.%. For this percentage, the processing conditions are less relevant in governing the final properties of the composites in terms of the stiffness and strength. Full article

(This article belongs to the Special Issue Wood Plastic Composites)

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11 pages, 2565 KiB

Open AccessEditor’s ChoiceArticle

Optimization and Quality Evaluation of the Interlayer Bonding Performance of Additively Manufactured Polymer Structures

by Patrick Striemann, Daniel Hülsbusch, Michael Niedermeier and Frank Walther

Polymers 2020, 12(5), 1166; https://doi.org/10.3390/polym12051166 - 19 May 2020

Cited by 25 | Viewed by 3025

Abstract

The application of additive manufacturing changes from prototypes to series production. In order to fulfill all requirements of series production, the process and the material characteristics must be known. The machine operator of additive manufacturing systems is both a component and a material [...] Read more.

The application of additive manufacturing changes from prototypes to series production. In order to fulfill all requirements of series production, the process and the material characteristics must be known. The machine operator of additive manufacturing systems is both a component and a material producer. Nevertheless, there is no standardized procedure for the manufacturing or testing of such materials. This includes the high degree of anisotropy of additively manufactured polymers via material extrusion. The interlayer bonding performance between two layers in the manufacturing direction z is the obvious weakness that needs to be improved. By optimizing this interlayer contact zone, the overall performance of the additively manufactured polymer is increased. This was achieved by process modification with an infrared preheating system (IPS) to keep the temperature of the interlayer contact zone above the glass transition temperature during the manufacturing process. Combining destructive and non-destructive testing methods, the process modification IPS was determined and evaluated by a systematic approach for characterizing the interlayer bonding performance. Thereby, tensile tests under quasi-static and cyclic loading were carried out on short carbon fiber-reinforced polyamide (SCFRP). In addition, micro-computed tomography and microscopic investigations were used to determine the process quality. The IPS increases the ultimate interlayer tensile strength by approx. 15% and shows a tendency to significantly improved the fatigue properties. Simultaneously, the analysis of the micro-computed tomography data shows a homogenization of the void distribution by using the IPS. Full article

(This article belongs to the Special Issue Functional Polymers in Additive Manufacturing)

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10 pages, 648 KiB

Open AccessEditor’s ChoiceReview

Lignin as a UV Light Blocker—A Review

by Hasan Sadeghifar and Arthur Ragauskas

Polymers 2020, 12(5), 1134; https://doi.org/10.3390/polym12051134 - 15 May 2020

Cited by 203 | Viewed by 12494

Abstract

Lignin is the by-product of pulp and paper industries and bio-refining operations. It is available as the leading natural phenolic biopolymer in the market. It has chromophore functional groups and can absorb a broad spectrum of UV light in range of 250–400 nm. [...] Read more.

Lignin is the by-product of pulp and paper industries and bio-refining operations. It is available as the leading natural phenolic biopolymer in the market. It has chromophore functional groups and can absorb a broad spectrum of UV light in range of 250–400 nm. Using lignin as a natural ingredient in sunscreen cream, transparent film, paints, varnishes and microorganism protection has been actively investigated. Both in non-modified and modified forms, lignin provides enhancing UV protection of commercial products with less than a 10% blend with other material. In mixtures with other synthetic UV blockers, lignin indicated synergic effects and increased final UV blocking potential in compare with using only synthetic UV blocker or lignin. However, using lignin as a UV blocker is also challenging due to its complex structure, polydispersity in molecular weight, brownish color and some impurities that require more research in order to make it an ideal bio-based UV blocker. Full article

(This article belongs to the Special Issue Progress in Lignin Value-Added Polymers)

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22 pages, 2905 KiB

Open AccessEditor’s ChoiceReview

Production of Sustainable and Biodegradable Polymers from Agricultural Waste

by Chrysanthos Maraveas

Polymers 2020, 12(5), 1127; https://doi.org/10.3390/polym12051127 - 14 May 2020

Cited by 197 | Viewed by 24129

Abstract

Agro-wastes are derived from diverse sources including grape pomace, tomato pomace, pineapple, orange, and lemon peels, sugarcane bagasse, rice husks, wheat straw, and palm oil fibers, among other affordable and commonly available materials. The carbon-rich precursors are used in the production bio-based polymers [...] Read more.

Agro-wastes are derived from diverse sources including grape pomace, tomato pomace, pineapple, orange, and lemon peels, sugarcane bagasse, rice husks, wheat straw, and palm oil fibers, among other affordable and commonly available materials. The carbon-rich precursors are used in the production bio-based polymers through microbial, biopolymer blending, and chemical methods. The Food and Agriculture Organization (FAO) estimates that 20–30% of fruits and vegetables are discarded as waste during post-harvest handling. The development of bio-based polymers is essential, considering the scale of global environmental pollution that is directly linked to the production of synthetic plastics such as polypropylene (PP) and polyethylene (PET). Globally, 400 million tons of synthetic plastics are produced each year, and less than 9% are recycled. The optical, mechanical, and chemical properties such as ultraviolet (UV) absorbance, tensile strength, and water permeability are influenced by the synthetic route. The production of bio-based polymers from renewable sources and microbial synthesis are scalable, facile, and pose a minimal impact on the environment compared to chemical synthesis methods that rely on alkali and acid treatment or co-polymer blending. Despite the development of advanced synthetic methods and the application of biofilms in smart/intelligent food packaging, construction, exclusion nets, and medicine, commercial production is limited by cost, the economics of production, useful life, and biodegradation concerns, and the availability of adequate agro-wastes. New and cost-effective production techniques are critical to facilitate the commercial production of bio-based polymers and the replacement of synthetic polymers. Full article

(This article belongs to the Special Issue Biodegradable and Sustainable Polymers)

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14 pages, 2228 KiB

Open AccessEditor’s ChoiceArticle

Graphene Oxide Composite for Selective Recognition, Capturing, Photothermal Killing of Bacteria over Mammalian Cells

by Gang Ma, Junjie Qi, Qifan Cui, Xueying Bao, Dong Gao and Chengfen Xing

Polymers 2020, 12(5), 1116; https://doi.org/10.3390/polym12051116 - 13 May 2020

Cited by 25 | Viewed by 4142

Abstract

The multifunctional photothermal therapy (PTT) platform with the ability to selectively kill bacteria over mammalian cells has received widespread attention recently. Herein, we prepared graphene oxide-amino(polyethyleneglycol) (GO-PEG-NH₂) while using the hydrophobic interaction between heptadecyl end groups of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethyleneglycol)] (DSPE-PEG-NH₂) [...] Read more.

The multifunctional photothermal therapy (PTT) platform with the ability to selectively kill bacteria over mammalian cells has received widespread attention recently. Herein, we prepared graphene oxide-amino(polyethyleneglycol) (GO-PEG-NH₂) while using the hydrophobic interaction between heptadecyl end groups of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethyleneglycol)] (DSPE-PEG-NH₂) and graphene oxide (GO). Based on GO-PEG-NH₂, the versatile PTT system was constructed with simultaneous selective recognition, capturing, and photothermal killing of bacteria. When the cells undergo bacterial infection, owing to the poly(ethylene glycol) (PEG) chains and positively charged amino groups, GO-PEG-NH₂ can specifically recognize and capture bacteria in the presence of cells. Meanwhile, the stable photothermal performance of GO-PEG-NH₂ enables the captured bacteria to be efficiently photothermally ablated upon the irradiation of 808 nm laser. Besides, the GO-PEG-NH₂ is highly stable in various biological media and it exhibits low cytotoxicity, suggesting that it holds great promise for biological applications. This work provides new insight into graphene-based materials as a PTT agent for the development of new therapeutic platforms. Full article

(This article belongs to the Special Issue Polymeric and Polymer Nanocomposite Materials for Photonic Applications)

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28 pages, 3967 KiB

Open AccessEditor’s ChoiceReview

A Review on Barrier Properties of Poly(Lactic Acid)/Clay Nanocomposites

by Shuvra Singha and Mikael S. Hedenqvist

Polymers 2020, 12(5), 1095; https://doi.org/10.3390/polym12051095 - 11 May 2020

Cited by 66 | Viewed by 7020

Abstract

Poly(lactic acid) (PLA) is considered to be among the best biopolymer substitutes for the existing petroleum-based polymers in the field of food packaging owing to its renewability, biodegradability, non-toxicity and mechanical properties. However, PLA displays only moderate barrier properties to gases, vapors and [...] Read more.

Poly(lactic acid) (PLA) is considered to be among the best biopolymer substitutes for the existing petroleum-based polymers in the field of food packaging owing to its renewability, biodegradability, non-toxicity and mechanical properties. However, PLA displays only moderate barrier properties to gases, vapors and organic compounds, which can limit its application as a packaging material. Hence, it becomes essential to understand the mass transport properties of PLA and address the transport challenges. Significant improvements in the barrier properties can be achieved by incorporating two-dimensional clay nanofillers, the planes of which create tortuosity to the diffusing molecules, thereby increasing the effective length of the diffusion path. This article reviews the literature on barrier properties of PLA/clay nanocomposites. The important PLA/clay nanocomposite preparation techniques, such as solution intercalation, melt processing and in situ polymerization, are outlined followed by an extensive account of barrier performance of nanocomposites drawn from the literature. Fundamentals of mass transport phenomena and the factors affecting mass transport are also presented. Furthermore, mathematical models that have been proposed/used to predict the permeability in polymer/clay nanocomposites are reviewed and the extent to which the models are validated in PLA/clay composites is discussed. Full article

(This article belongs to the Special Issue Performance and Application of Novel Biocomposites)

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20 pages, 2506 KiB

Open AccessEditor’s ChoiceReview

Functional Micro- and Nanofibers Obtained by Nonwoven Post-Modification

by Tomasz Kowalczyk

Polymers 2020, 12(5), 1087; https://doi.org/10.3390/polym12051087 - 10 May 2020

Cited by 23 | Viewed by 3767

Abstract

Micro- and nanofibers are historically-known materials that are continuously reinvented due to their valuable properties. They display promise for applications in many fields, from tissue engineering to catalysis or sensors. In the first application, micro- and nanofibers are mainly produced from a limited [...] Read more.

Micro- and nanofibers are historically-known materials that are continuously reinvented due to their valuable properties. They display promise for applications in many fields, from tissue engineering to catalysis or sensors. In the first application, micro- and nanofibers are mainly produced from a limited library of biomaterials with properties that need alteration before use. Post-modification is a very effective method for attaining on-demand features and functions of nonwovens. This review summarizes and presents methods of functionalization of nonwovens produced by electrostatic means. The reviewed modifications are grouped into physical methods, chemical modification, and mixed methods. Full article

(This article belongs to the Special Issue Functional Electrospun Nanofibers)

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14 pages, 11699 KiB

Open AccessEditor’s ChoiceArticle

Poly (vinyl alcohol)/β-Cyclodextrin Composite Fiber with Good Flame Retardant and Super-Smoke Suppression Properties

by Cheng-Yuan Xing, Shi-Lin Zeng, Shi-Kai Qi, Meng-Jin Jiang, Long Xu, Li Chen, Sheng Zhang and Bang-Jing Li

Polymers 2020, 12(5), 1078; https://doi.org/10.3390/polym12051078 - 8 May 2020

Cited by 16 | Viewed by 3723

Abstract

Fibers with good flame retardant (FR) and smoke suppression performances are highly desirable for the purpose of eliminating fire hazard. This study developed a novel FR fiber by wet-spinning poly (vinyl alcohol)/β-cyclodextrin (PVA/βCD) composite fiber and crosslinking it with hexamethylene diisocyanate (HDI). βCDs [...] Read more.

Fibers with good flame retardant (FR) and smoke suppression performances are highly desirable for the purpose of eliminating fire hazard. This study developed a novel FR fiber by wet-spinning poly (vinyl alcohol)/β-cyclodextrin (PVA/βCD) composite fiber and crosslinking it with hexamethylene diisocyanate (HDI). βCDs showed good compatibility with PVA matrix, and the resulting PVA/CD/HDI fibers showed mechanical strength at the same level as natural cotton fiber. The PVA/CD/HDI fibers also showed excellent flame retardance (the LOI value of PVA/CD/HDI could reach 41.7%, and their peak of heat release (PHRR) could be reduced by up to 77.7% by neat PVA), and super-smoke suppression (the value of total smoke production (TSP) was only 28.6% compared to PVA). These dramatic reductions of fire hazard were ascribed to the char formation of βCD and crosslinking structure of PVA/CD/HDI, which formed a compact char layer during combustion, thus preventing heat transmission and smoke release. Full article

(This article belongs to the Special Issue Advances in Flame Retardant Polymeric Materials)

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23 pages, 2446 KiB

Open AccessEditor’s ChoiceReview

Activation Energies and Temperature Dependencies of the Rates of Crystallization and Melting of Polymers

by Sergey Vyazovkin

Polymers 2020, 12(5), 1070; https://doi.org/10.3390/polym12051070 - 7 May 2020

Cited by 60 | Viewed by 8041

Abstract

The objective of this review paper is to survey the phase transition kinetics with a focus on the temperature dependence of the rates of crystallization and melting, as well as on the activation energies of these processes obtained via the Arrhenius kinetic treatment, [...] Read more.

The objective of this review paper is to survey the phase transition kinetics with a focus on the temperature dependence of the rates of crystallization and melting, as well as on the activation energies of these processes obtained via the Arrhenius kinetic treatment, including the treatment by isoconversional methods. The literature is analyzed to track the development of the basic models and their underlying concepts. The review presents both theoretical and practical considerations regarding the kinetic analysis of crystallization and melting. Both processes are demonstrated to be kinetically complex, and this is revealed in the form of nonlinear Arrhenius plots and/or the variation of the activation energy with temperature. Principles which aid one to understand and interpret such results are discussed. An emphasis is also put on identifying proper computational methods and experimental data that can lead to meaningful kinetic interpretation. Full article

(This article belongs to the Special Issue Recent Developments on Calorimetry and Thermal Analysis of Polymers and Nanocomposites)

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30 pages, 7109 KiB

Open AccessEditor’s ChoiceReview

Water-Soluble Photoinitiators in Biomedical Applications

by Wiktoria Tomal and Joanna Ortyl

Polymers 2020, 12(5), 1073; https://doi.org/10.3390/polym12051073 - 7 May 2020

Cited by 151 | Viewed by 24777

Abstract

Light-initiated polymerization processes are currently an important tool in various industrial fields. The advancement of technology has resulted in the use of photopolymerization in various biomedical applications, such as the production of 3D hydrogel structures, the encapsulation of cells, and in drug delivery [...] Read more.

Light-initiated polymerization processes are currently an important tool in various industrial fields. The advancement of technology has resulted in the use of photopolymerization in various biomedical applications, such as the production of 3D hydrogel structures, the encapsulation of cells, and in drug delivery systems. The use of photopolymerization processes requires an appropriate initiating system that, in biomedical applications, must meet additional criteria such as high water solubility, non-toxicity to cells, and compatibility with visible low-power light sources. This article is a literature review on those compounds that act as photoinitiators of photopolymerization processes in biomedical applications. The division of initiators according to the method of photoinitiation was described and the related mechanisms were discussed. Examples from each group of photoinitiators are presented, and their benefits, limitations, and applications are outlined. Full article

(This article belongs to the Special Issue Biomedical Polymer Materials II)

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25 pages, 4090 KiB

Open AccessEditor’s ChoiceReview

Potential Natural Fiber Polymeric Nanobiocomposites: A Review

by K. M. Faridul Hasan, Péter György Horváth and Tibor Alpár

Polymers 2020, 12(5), 1072; https://doi.org/10.3390/polym12051072 - 7 May 2020

Cited by 157 | Viewed by 15807

Abstract

Composite materials reinforced with biofibers and nanomaterials are becoming considerably popular, especially for their light weight, strength, exceptional stiffness, flexural rigidity, damping property, longevity, corrosion, biodegradability, antibacterial, and fire-resistant properties. Beside the traditional thermoplastic and thermosetting polymers, nanoparticles are also receiving attention in [...] Read more.

Composite materials reinforced with biofibers and nanomaterials are becoming considerably popular, especially for their light weight, strength, exceptional stiffness, flexural rigidity, damping property, longevity, corrosion, biodegradability, antibacterial, and fire-resistant properties. Beside the traditional thermoplastic and thermosetting polymers, nanoparticles are also receiving attention in terms of their potential to improve the functionality and mechanical performances of biocomposites. These remarkable characteristics have made nanobiocomposite materials convenient to apply in aerospace, mechanical, construction, automotive, marine, medical, packaging, and furniture industries, through providing environmental sustainability. Nanoparticles (TiO₂, carbon nanotube, rGO, ZnO, and SiO₂) are easily compatible with other ingredients (matrix polymer and biofibers) and can thus form nanobiocomposites. Nanobiocomposites are exhibiting a higher market volume with the expansion of new technology and green approaches for utilizing biofibers. The performances of nanobiocomposites depend on the manufacturing processes, types of biofibers used, and the matrix polymer (resin). An overview of different natural fibers (vegetable/plants), nanomaterials, biocomposites, nanobiocomposites, and manufacturing methods are discussed in the context of potential application in this review. Full article

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15 pages, 3442 KiB

Open AccessEditor’s ChoiceArticle

Effect of Bis (2-Aminoethyl) Adipamide/Adipic Acid Segment on Polyamide 6: Crystallization Kinetics Study

by Yu-Hao Chen, Palraj Ranganathan, Chin-Wen Chen, Yi-Huan Lee and Syang-Peng Rwei

Polymers 2020, 12(5), 1067; https://doi.org/10.3390/polym12051067 - 6 May 2020

Cited by 12 | Viewed by 3512

Abstract

The crystallization behavior of novel polyamide 6 (PA6) copolyamides with different amounts of bis (2-aminoethyl) adipamide/adipic acid (BAEA/AA) segment was investigated. The wide-angle X-ray diffraction (WAXD) results showed that as the amount of BAEA/AA segment increased to 10 mole%, the crystalline forms of [...] Read more.

The crystallization behavior of novel polyamide 6 (PA6) copolyamides with different amounts of bis (2-aminoethyl) adipamide/adipic acid (BAEA/AA) segment was investigated. The wide-angle X-ray diffraction (WAXD) results showed that as the amount of BAEA/AA segment increased to 10 mole%, the crystalline forms of all PA6 copolyamide were transferred from the stable α-form to the unstable γ-form because of the complex polymer structure. According to studies of crystallization kinetics, the Avrami exponent (n) values for all copolyamide samples ranged from 1.43 to 3.67 under isothermal conditions, implying that the crystallization is involved in the two- to three-dimensional growth at a high temperature of isothermal condition. The copolyamides provided a slower crystallization rate and higher crystallization activation energy (ΔE_a) than neat PA6. Polyamide containing 10 mole% of BEAE/AA content exhibited a unique crystallization behavior in the coexistence of the α and γ forms. These results deepen our understanding of the relationship between BAEA/AA content, crystal structure, and its crystallization behavior in low-melting PA6, and they make these types of copolyamides useful for their practical application. Full article

(This article belongs to the Special Issue Thermal Analysis of Polymer Materials)

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15 pages, 3999 KiB

Open AccessEditor’s ChoiceArticle

Preparation of Tri(alkenyl)functional Open-Cage Silsesquioxanes as Specific Polymer Modifiers

by Katarzyna Mituła, Michał Dutkiewicz, Julia Duszczak, Monika Rzonsowska and Beata Dudziec

Polymers 2020, 12(5), 1063; https://doi.org/10.3390/polym12051063 - 6 May 2020

Cited by 7 | Viewed by 2991

Abstract

The scientific reports on polyhedral oligomeric silsesquioxanes are mostly focused on the formation of completely condensed T₈ cubic type structures and recently so-called double-decker derivatives. Herein, we report on efficient synthetic routes leading to trifunctionalized, open-cage silsesquioxanes with alkenyl groups of varying [...] Read more.

The scientific reports on polyhedral oligomeric silsesquioxanes are mostly focused on the formation of completely condensed T₈ cubic type structures and recently so-called double-decker derivatives. Herein, we report on efficient synthetic routes leading to trifunctionalized, open-cage silsesquioxanes with alkenyl groups of varying chain lengths from -vinyl to -dec-9-enyl and two types of inert groups (iBu, Ph) at the silsesquioxane core. The presented methodology was focused on hydrolytic condensation reaction and it enabled obtaining titled compounds with high yields and purity. A parallel synthetic methodology that was based on the hydrosilylation reaction was also studied. Additionally, a thorough characterization of the obtained compounds was performed, also in terms of their thermal stability, melting and crystallization temperatures (TGA and DSC) in order to show the changes in the abovementioned parameters dependent on the type of reactive as well as inert groups at Si-O-Si core. The presence of unsaturated alkenyl groups has a profound impact on the application potential of these systems, i.e., as modifiers or comonomers for copolymerization reaction. Full article

(This article belongs to the Special Issue Silsesquioxane (POSS) Polymers, Copolymers and Nanoparticles)

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