Polymers

21 pages, 3034 KiB

Open AccessArticle

Comparative Analysis of Erosive Wear Behaviour of Epoxy, Polyester and Vinyl Esters Based Thermosetting Polymer Composites for Human Prosthetic Applications Using Taguchi Design

by Jeetendra Mohan Khare, Sanjeev Dahiya, Brijesh Gangil, Lalit Ranakoti, Shubham Sharma, Muhammad Roslim Muhammad Huzaifah, Rushdan Ahmad Ilyas, Shashi Prakash Dwivedi, Somnath Chattopadhyaya, Huseyin Cagan Kilinc and Changhe Li

Polymers 2021, 13(20), 3607; https://doi.org/10.3390/polym13203607 - 19 Oct 2021

Cited by 45 | Viewed by 3532

Abstract

In polymer composites, synthetic fibers are primarily used as a chief reinforcing material, with a wide range of applications, and are therefore essential to study. In the present work, we carried out the erosive wear of natural and synthetic fiber-based polymer composites. Glass [...] Read more.

In polymer composites, synthetic fibers are primarily used as a chief reinforcing material, with a wide range of applications, and are therefore essential to study. In the present work, we carried out the erosive wear of natural and synthetic fiber-based polymer composites. Glass fiber with jute and Grewia optiva fiber was reinforced in three different polymer resins: epoxy, vinyl ester and polyester. The hand lay-up method was used for the fabrication of composites. L₁₆ orthogonal array of Taguchi method used to identify the most significant parameters (impact velocity, fiber content, and impingement angle) in the analysis of erosive wear. ANOVA analysis revealed that the most influential parameter was in the erosive wear analysis was impact velocity followed by fiber content and impingement angle. It was also observed that polyester-based composites exhibited the highest erosive wear followed by vinyl ester-based composites, and epoxy-based composites showed the lowest erosive wear. From the present study, it may be attributed that the low hardness of the polyester resulting in low resistance against the impact of erodent particles. The SEM analysis furthermore illustrates the mechanism took place during the wear examination of all three types of composites at highest fiber loading. A thorough assessment uncovers brittle fractures in certain regions, implying that a marginal amount of impact forces was also acting on the fabricated samples. The developed fiber-reinforced polymer sandwich composite materials possess excellent biocompatibility, desirable promising properties for prosthetic, orthopaedic, and bone-fracture implant uses. Full article

(This article belongs to the Special Issue Bio and Synthetic Based Polymer Composite Materials)

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38 pages, 2960 KiB

Open AccessReview

Disposable Food Packaging and Serving Materials—Trends and Biodegradability

by Katarzyna Dybka-Stępień, Hubert Antolak, Magdalena Kmiotek, Dominik Piechota and Anna Koziróg

Polymers 2021, 13(20), 3606; https://doi.org/10.3390/polym13203606 - 19 Oct 2021

Cited by 58 | Viewed by 28593

Abstract

Food is an integral part of everyone’s life. Disposable food serving utensils and tableware are a very convenient solution, especially when the possibility of the use of traditional dishes and cutlery is limited (e.g., takeaway meals). As a result, a whole range of [...] Read more.

Food is an integral part of everyone’s life. Disposable food serving utensils and tableware are a very convenient solution, especially when the possibility of the use of traditional dishes and cutlery is limited (e.g., takeaway meals). As a result, a whole range of products is available on the market: plates, trays, spoons, forks, knives, cups, straws, and more. Both the form of the product (adapted to the distribution and sales system) as well as its ecological aspect (biodegradability and life cycle) should be of interest to producers and consumers, especially considering the clearly growing trend of “eco-awareness”. This is particularly important in the case of single-use products. The aim of the study was to present the current trends regarding disposable utensils intended for contact with food in the context of their biodegradability. This paper has summarized not only conventional polymers but also their modern alternatives gaining the attention of manufacturers and consumers of single-use products (SUPs). Full article

(This article belongs to the Special Issue Natural and Synthetic Polymers-Hopes and Fears in an Era of Ecological Modernization)

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18 pages, 6719 KiB

Open AccessArticle

Mechanical Properties and a Constitutive Model of 3D-Printed Copper Powder-Filled PLA Material

by Qing Ji, Zhijun Wang, Jianya Yi and Xuezhi Tang

Polymers 2021, 13(20), 3605; https://doi.org/10.3390/polym13203605 - 19 Oct 2021

Cited by 13 | Viewed by 3869

Abstract

Three-dimensional printing is becoming increasingly popular because of its extensive applicability. However, printing materials remain limited. To determine the mechanical properties of polylactic acid (PLA) and copper powder-filled polylactic acid (PLA-Cu) materials subjected to static and dynamic loading, stress–strain curves were obtained under [...] Read more.

Three-dimensional printing is becoming increasingly popular because of its extensive applicability. However, printing materials remain limited. To determine the mechanical properties of polylactic acid (PLA) and copper powder-filled polylactic acid (PLA-Cu) materials subjected to static and dynamic loading, stress–strain curves were obtained under the conditions of different strain rates using a universal material testing machine and a separated Hopkinson pressure bar experimental device. Scanning electron microscopy (SEM) was used to analyze the micro-morphology of the quasi-static compression fracture and dynamic impact sections. The results revealed that the yield stress and elastic modulus of the two materials increased with increasing strain rate. When the strain rate reached a critical point of 0.033 s⁻¹, the rate of crack propagation in the PLA samples increased, resulting in the material undergoing a change from ductile to brittle. The strength of the material subjected to dynamic loading was significantly higher than that subjected to quasi-static loading. The SEM image of the PLA-Cu material revealed that copper powder was evenly distributed throughout the 3D-printed sample and that stress initially began to concentrate at the defect site corresponding to the interface between the copper powder and PLA matrix; this resulted in comparatively lower toughness. This finding was consistent with the photographs captured via high-speed photography, which confirmed that the destruction of the specimen was accompanied by an explosive crushing process. Additionally, a Zhu–Wang–Tang constitutive model was used to fit the experimental results and establish a viscoelastic constitutive model of the material. By comparing the dynamic stress–strain curve to the theoretically predicted curve, we found that the established constitutive model could predict the mechanical properties of the PLA-Cu material with reasonable accuracy when the strain was below 7%. Full article

(This article belongs to the Special Issue Polymer Composites for 3D Printing)

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22 pages, 10025 KiB

Open AccessArticle

Flexural Behavior of Natural Hybrid FRP-Strengthened RC Beams and Strain Measurements Using BOTDA

by Krisada Chaiyasarn, Nazam Ali, Phatthanayu Phuphasuwan, Nakhorn Poovarodom, Panuwat Joyklad, Hisham Mohamad, Mingliang Zhou and Qudeer Hussain

Polymers 2021, 13(20), 3604; https://doi.org/10.3390/polym13203604 - 19 Oct 2021

Cited by 9 | Viewed by 2422

Abstract

Experimental and finite element analysis results of reinforced concrete beams under monotonic loading were presented in this study. In the experimental program, one beam was tested in an as-built condition. The other two beams were strengthened using natural hybrid FRP layers in different [...] Read more.

Experimental and finite element analysis results of reinforced concrete beams under monotonic loading were presented in this study. In the experimental program, one beam was tested in an as-built condition. The other two beams were strengthened using natural hybrid FRP layers in different configurations. The natural hybrid FRP composite was developed by using natural jute FRP and basalt FRP. One of the most appealing advantages of natural fiber is its beneficial impact on the environment, which is necessary for the sustainability recognition as an alternative to synthetic FRP. The hybrid FRP was applied to the bottom concrete surface in one beam, while a U-shaped strengthening pattern was adopted for the other beam. The flexural behavior of each beam was assessed through strain measurements. Each beam was incorporated with conventional strain gages, as well as the Brillouin Optical Time Domain Analysis (BOTDA) technique. BOTDA has its exclusive advantages due to its simple system architecture, easy implementation, measurement speed, and cross-sensitivity. The experimental results revealed that the beam strengthened with the U-shaped hybrid FRP composite pattern had a better flexural response than the other counterpart beams did both in terms of peak loads and maximum bottom longitudinal steel bar strains. Beams B-01 and B-02 exhibited 20.5% and 28.4% higher energy dissipation capacities than the control beam did, respectively. The ultimate failure of the control beam was mainly due to the flexural cracks at very low loads, whereas the ultimate failure mode of FRP composite-strengthened beams was due to the rupture of the hybrid FRP composite. Further, strain measurements using BOTDA exhibited similar patterns as conventional strain gage measurements did. However, it was concluded that BOTDA measurements were substantially influenced by the bottom flexural cracks, ultimately resulting in shorter strain records than those of conventional strain gages. Nonlinear structural analysis of the beams was performed using the computer program ATENA. The analytical results for the control beam specimen showed a close match with the corresponding experimental results mainly in terms of maximum deflection. However, the analytical peak load was slightly higher than the corresponding experimental value. Full article

(This article belongs to the Special Issue Polymer Composites for Structural Applications)

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14 pages, 6076 KiB

Open AccessArticle

Quasi-Static Compression Properties of Bamboo and PVC Tube Reinforced Polymer Foam Structures

by J. J. N. Amelia, M. Y. M. Zuhri, Z. Leman, N. I. Zahari, A. As’arry and R. A. Ilyas

Polymers 2021, 13(20), 3603; https://doi.org/10.3390/polym13203603 - 19 Oct 2021

Cited by 8 | Viewed by 2080

Abstract

In recent years, there has been a growing interest for composite materials due to the superior capability to absorb energy and lightweight factor. These properties are compatible to be utilized in the development for transportation system as it can reduce the fuel consumption [...] Read more.

In recent years, there has been a growing interest for composite materials due to the superior capability to absorb energy and lightweight factor. These properties are compatible to be utilized in the development for transportation system as it can reduce the fuel consumption and also minimize the effect of crash to the passenger. Therefore, the aim for this project is to study the compression strength and energy absorbing capability for Polyvinyl chloride (PVC) and bamboo tubes reinforced with foam. Several parameters are being considered, these being the effect of single and multiple tube reinforced foam structure, foam density, diameter of the tube as well as effect of different crosshead speed. The results showed that increasing the relative foam density will led to an increase in the compression strength and specific energy absorption (SEA) values. Furthermore, a significant increase of compression strength can be seen when several tubes are introduced into the foam while SEA remained almost the same. Finally, the influence of crosshead below 20 mm/min did not vary significantly for both compression strength and SEA. Full article

(This article belongs to the Special Issue Bio and Synthetic Based Polymer Composite Materials)

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23 pages, 14729 KiB

Open AccessArticle

High Cyclability Energy Storage Device with Optimized Hydroxyethyl Cellulose-Dextran-Based Polymer Electrolytes: Structural, Electrical and Electrochemical Investigations

by Muhammad A. S. Azha, Elham M. A. Dannoun, Shujahadeen B. Aziz, Mohd F. Z. Kadir, Zaki Ismail Zaki, Zeinhom M. El-Bahy, Mazdida Sulaiman and Muaffaq M. Nofal

Polymers 2021, 13(20), 3602; https://doi.org/10.3390/polym13203602 - 19 Oct 2021

Cited by 8 | Viewed by 2331

Abstract

The preparation of a dextran (Dex)-hydroxyethyl cellulose (HEC) blend impregnated with ammonium bromide (NH₄Br) is done via the solution cast method. The phases due to crystalline and amorphous regions were separated and used to estimate the degree of crystallinity. The most [...] Read more.

The preparation of a dextran (Dex)-hydroxyethyl cellulose (HEC) blend impregnated with ammonium bromide (NH₄Br) is done via the solution cast method. The phases due to crystalline and amorphous regions were separated and used to estimate the degree of crystallinity. The most amorphous blend was discovered to be a blend of 40 wt% Dex and 60 wt% HEC. This polymer blend serves as the channel for ions to be conducted and electrodes separator. The conductivity has been optimized at (1.47 ± 0.12) × 10⁻⁴ S cm⁻¹ with 20 wt% NH₄Br. The EIS plots were fitted with EEC circuits. The DC conductivity against 1000/T follows the Arrhenius model. The highest conducting electrolyte possesses an ionic number density and mobility of 1.58 × 10²¹ cm⁻³ and 6.27 × 10⁻⁷ V⁻¹s⁻¹ cm², respectively. The TNM and LSV investigations were carried out on the highest conducting system. A non-Faradic behavior was predicted from the CV pattern. The fabricated electrical double layer capacitor (EDLC) achieved 8000 cycles, with a specific capacitance, internal resistance, energy density, and power density of 31.7 F g⁻¹, 80 Ω, 3.18 Wh kg⁻¹, and 922.22 W kg⁻¹, respectively. Full article

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

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10 pages, 1085 KiB

Open AccessArticle

Thermocontrolled Reversible Enzyme Complexation-Inactivation-Protection by Poly(N-acryloyl glycinamide)

by Pavel I. Semenyuk, Lidia P. Kurochkina, Lauri Mäkinen, Vladimir I. Muronetz and Sami Hietala

Polymers 2021, 13(20), 3601; https://doi.org/10.3390/polym13203601 - 19 Oct 2021

Cited by 6 | Viewed by 2543

Abstract

A prospective technology for reversible enzyme complexation accompanied with its inactivation and protection followed by reactivation after a fast thermocontrolled release has been demonstrated. A thermoresponsive polymer with upper critical solution temperature, poly(N-acryloyl glycinamide) (PNAGA), which is soluble in water at [...] Read more.

A prospective technology for reversible enzyme complexation accompanied with its inactivation and protection followed by reactivation after a fast thermocontrolled release has been demonstrated. A thermoresponsive polymer with upper critical solution temperature, poly(N-acryloyl glycinamide) (PNAGA), which is soluble in water at elevated temperatures but phase separates at low temperatures, has been shown to bind lysozyme, chosen as a model enzyme, at a low temperature (10 °C and lower) but not at room temperature (around 25 °C). The cooling of the mixture of PNAGA and lysozyme solutions from room temperature resulted in the capturing of the protein and the formation of stable complexes; heating it back up was accompanied by dissolving the complexes and the release of the bound lysozyme. Captured by the polymer, lysozyme was inactive, but a temperature-mediated release from the complexes was accompanied by its reactivation. Complexation also partially protected lysozyme from proteolytic degradation by proteinase K, which is useful for biotechnological applications. The obtained results are relevant for important medicinal tasks associated with drug delivery such as the delivery and controlled release of enzyme-based drugs. Full article

(This article belongs to the Special Issue Advances in Thermoresponsive Polymers)

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Graphical abstract

20 pages, 2710 KiB

Open AccessReview

Waste Natural Polymers as Potential Fillers for Biodegradable Latex-Based Composites: A Review

by D. N. Syuhada and A. R. Azura

Polymers 2021, 13(20), 3600; https://doi.org/10.3390/polym13203600 - 19 Oct 2021

Cited by 17 | Viewed by 3898

Abstract

In recent years, biodegradable composites have become important in various fields because of the increasing awareness of the global environment. Waste natural polymers have received much attention as renewable, biodegradable, non-toxic and low-cost filler in polymer composites. In order to exploit the high [...] Read more.

In recent years, biodegradable composites have become important in various fields because of the increasing awareness of the global environment. Waste natural polymers have received much attention as renewable, biodegradable, non-toxic and low-cost filler in polymer composites. In order to exploit the high potential for residual natural loading in latex composites, different types of surface modification techniques have been applied. This review discusses the preparation and characterization of the modified waste natural fillers for latex-based composites. The potency of the waste natural filler for the latex-based composites was explored with a focus on the mechanical, thermal, biodegradability and filler–latex interaction. This review also offers an update on the possible application of the waste natural filler towards the biodegradability of the latex-based composites for a more sustainable future. Full article

(This article belongs to the Special Issue Advances in Bio-Based and Biodegradable Polymeric Composites)

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20 pages, 2049 KiB

Open AccessArticle

Pre-Heating Effect on Monomer Elution and Degree of Conversion of Contemporary and Thermoviscous Bulk-Fill Resin-Based Dental Composites

by Dóra Kincses, Katalin Böddi, Zsuzsanna Őri, Bálint Viktor Lovász, Sára Jeges, József Szalma, Sándor Kunsági-Máté and Edina Lempel

Polymers 2021, 13(20), 3599; https://doi.org/10.3390/polym13203599 - 19 Oct 2021

Cited by 15 | Viewed by 3556

Abstract

Detection of unreacted monomers from pre-heated resin-based dental composites (RBC) is not a well-investigated topic so far. The objectives were to determine the temperature changes during the application and polymerization, the degree of conversion (DC) and unreacted monomer elution of room temperature (RT), [...] Read more.

Detection of unreacted monomers from pre-heated resin-based dental composites (RBC) is not a well-investigated topic so far. The objectives were to determine the temperature changes during the application and polymerization, the degree of conversion (DC) and unreacted monomer elution of room temperature (RT), and pre-heated thermoviscous [VisCalor Bulk(VCB)] and high-viscosity full-body contemporary [Filtek One Bulk(FOB)] bulk-fill RBCs. The RBCs’ temperatures during the sample preparation were recorded with a K-type thermocouple. The DC at the top and bottom was measured with micro-Raman spectroscopy and the amounts of eluted BisGMA, UDMA, DDMA, and TEGDMA were assessed with High-Performance Liquid Chromatography. The temperatures of the pre-heated RBCs decreased rapidly during the manipulation phase. The temperature rise during photopolymerization reflects the bottom DCs. The differences in DC% between the top and the bottom were significant. RT VCB had a lower DC% compared to FOB. Pre-heating did not influence the DC, except on the bottom surface of FOB where a significant decrease was measured. Pre-heating significantly decreased the elution of BisGMA, UDMA, DDMA in the case of FOB, meanwhile, it had no effect on monomer release from VCB, except TEGDMA, which elution was decreased. In comparison, RBC composition had a stronger influence on DC and monomer elution, than pre-cure temperature. Full article

(This article belongs to the Special Issue Polymer Composites for Structural Applications)

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19 pages, 3289 KiB

Open AccessArticle

Cellulosic/Polyvinyl Alcohol Composite Hydrogel: Synthesis, Characterization and Applications in Tissue Engineering

by Mathilde Stricher, Claude-Olivier Sarde, Erwann Guénin, Christophe Egles and Frédéric Delbecq

Polymers 2021, 13(20), 3598; https://doi.org/10.3390/polym13203598 - 19 Oct 2021

Cited by 6 | Viewed by 3864

Abstract

The biomedical field still requires composite materials for medical devices and tissue engineering model design. As part of the pursuit of non-animal and non-proteic scaffolds, we propose here a cellulose-based material. In this study, 9%, 18% and 36% dialdehyde-functionalized microcrystalline celluloses (DAC) were [...] Read more.

The biomedical field still requires composite materials for medical devices and tissue engineering model design. As part of the pursuit of non-animal and non-proteic scaffolds, we propose here a cellulose-based material. In this study, 9%, 18% and 36% dialdehyde-functionalized microcrystalline celluloses (DAC) were synthesized by sodium periodate oxidation. The latter was subsequently coupled to PVA at ratios 1:2, 1:1 and 2:1 by dissolving in N-methyl pyrrolidone and lithium chloride. Moulding and successive rehydration in ethanol and water baths formed soft hydrogels. While oxidation effectiveness was confirmed by dialdehyde content determination for all DAC, we observed increasing hydrolysis associated with particle fragmentation. Imaging, FTIR and XDR analysis highlighted an intertwined DAC/PVA network mainly supported by electrostatic interactions, hemiacetal and acetal linkage. To meet tissue engineering requirements, an interconnected porosity was optimized using 0–50 µm salts. While the role of DAC in strengthening the hydrogel was identified, the oxidation ratio of DAC showed no distinct trend. DAC 9% material exhibited the highest indirect and direct cytocompatibility creating spheroid-like structures. DAC/PVA hydrogels showed physical stability and acceptability in vivo that led us to propose our DAC 9%/PVA based material for soft tissue graft application. Full article

(This article belongs to the Special Issue Intrinsically Biocompatible Polymer Systems II)

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12 pages, 4643 KiB

Open AccessArticle

Injection Molding of Low-Density Polyethylene (LDPE) as a Model Polymer: Effect of Molding Parameters on the Microstructure and Crystallinity

by César Leyva-Porras, Andrea Balderrama-Aguilar, Yael Estrada-Ávila, Iñaki Espelosín-Gómez, Mónica Mendoza-Duarte, Claudia Piñón-Balderrama, María Zenaida Saavedra-Leos and Iván Estrada-Moreno

Polymers 2021, 13(20), 3597; https://doi.org/10.3390/polym13203597 - 19 Oct 2021

Cited by 5 | Viewed by 4911

Abstract

Due to its relatively simple structure, low-density polyethylene (LDPE) can be considered as a model polymer for the study of its properties. Herein, the effect of processing variables on the microstructure and crystallinity of injection-molded LDPE specimens was quantitatively determined. The polymer was [...] Read more.

Due to its relatively simple structure, low-density polyethylene (LDPE) can be considered as a model polymer for the study of its properties. Herein, the effect of processing variables on the microstructure and crystallinity of injection-molded LDPE specimens was quantitatively determined. The polymer was injected at different temperature conditions in the barrel and the mold. The specimens were characterized by scanning electron microscopy and X-ray diffraction. With the data obtained, an analysis of variance (ANOVA) was carried out, and response surface graphs (SRP) were constructed to quantify and to observe the behavior of the processing variables, respectively. Different models were obtained to predict the effect of the experimental factors on the response variables. The results showed that the interaction of the two temperatures has the greatest effect on the size of the spherulite, while the temperature of the mold affects the crystallinity. The SRP showed different behaviors: for the spherulite, the size increases with the mold temperature, while for the crystallinity, higher values were observed at an intermediate mold temperature and a low melt temperature. The results presented herein are valuable for setting empirical relations between the microstructure, crystallinity, and the molding conditions of LDPE. Full article

(This article belongs to the Special Issue Polymer Composites for Structural Applications)

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19 pages, 10966 KiB

Open AccessEditor’s ChoiceArticle

Preliminary Study for the Preparation of Transmucosal or Transdermal Patches with Acyclovir and Lidocaine

by Cristina-Adela Marioane, Mădălin Bunoiu, Mădălina Mateescu, Paula Sfîrloagă, Gabriela Vlase and Titus Vlase

Polymers 2021, 13(20), 3596; https://doi.org/10.3390/polym13203596 - 19 Oct 2021

Cited by 9 | Viewed by 2686

Abstract

The present study aimed to prepare and evaluate patches for the controlled release of lidocaine/acyclovir and the binary mixture between lidocaine: acyclovir in the oral cavity. Mucoside adhesive patches containing 12.5 mg/cm² lidocaine/acyclovir or binary mixture base were developed by a solvent [...] Read more.

The present study aimed to prepare and evaluate patches for the controlled release of lidocaine/acyclovir and the binary mixture between lidocaine: acyclovir in the oral cavity. Mucoside adhesive patches containing 12.5 mg/cm² lidocaine/acyclovir or binary mixture base were developed by a solvent casting method using sodium alginate, polyvinylpyrrolidone (PVP), glycerol (Gly), polyvinyl alcohol (PVA), and Span 80 (S). Binary mixtures between all components were prepared before the patches’ formulation in order to be able to check the substance compatibility. All formulated patches were analyzed by FT-IR spectroscopy, UV-Vis analysis, thermogravimetry (TGA), and scanning electron microscopy (SEM). FT-IR and TGA analyses were also used to check compatibility between binary mixtures. The study establishes which membranes are indicated in the controlled release of lidocaine/acyclovir and those membranes that contain both active principles. Membranes based on alginate, PVP, and PVA can be used to release the active substance. Simultaneously, membranes with SPAN used as a gelling agent were excluded due to the interaction with the active substance. The following membranes composition have been chosen for lidocaine release: Alginate:Gly and Alginate:Gly:PVP. At the same time, the following membrane compositions were chosen for acyclovir membranes: Alginate:Gly:PVP and Alginate:PVA:Gly. Both active substances could be included to obtain a homogeneous distribution only in the membrane based on alginate, PVA, and Gly. Full article

(This article belongs to the Special Issue Functional Alginate-Based Materials)

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11 pages, 1458 KiB

Open AccessArticle

Coaxial Electrospun PLLA Fibers Modified with Water-Soluble Materials for Oligodendrocyte Myelination

by Zhepeng Liu, Jing Wang, Haini Chen, Guanyu Zhang, Zhuman Lv, Yijun Li, Shoujin Zhao and Wenlin Li

Polymers 2021, 13(20), 3595; https://doi.org/10.3390/polym13203595 - 19 Oct 2021

Cited by 3 | Viewed by 2431

Abstract

Myelin sheaths are essential in maintaining the integrity of axons. Development of the platform for in vitro myelination would be especially useful for demyelinating disease modeling and drug screening. In this study, a fiber scaffold with a core–shell structure was prepared in one [...] Read more.

Myelin sheaths are essential in maintaining the integrity of axons. Development of the platform for in vitro myelination would be especially useful for demyelinating disease modeling and drug screening. In this study, a fiber scaffold with a core–shell structure was prepared in one step by the coaxial electrospinning method. A high-molecular-weight polymer poly-L-lactic acid (PLLA) was used as the core, while the shell was a natural polymer material such as hyaluronic acid (HA), sodium alginate (SA), or chitosan (CS). The morphology, differential scanning calorimetry (DSC), Fourier transform infrared spectra (FTIR), contact angle, viability assay, and in vitro myelination by oligodendrocytes were characterized. The results showed that such fibers are bead-free and continuous, with an average size from 294 ± 53 to 390 ± 54 nm. The DSC and FTIR curves indicated no changes in the phase state of coaxial brackets. Hyaluronic acid/PLLA coaxial fibers had the minimum contact angle (53.1° ± 0.24°). Myelin sheaths were wrapped around a coaxial electrospun scaffold modified with water-soluble materials after a 14-day incubation. All results suggest that such a scaffold prepared by coaxial electrospinning potentially provides a novel platform for oligodendrocyte myelination. Full article

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

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21 pages, 9119 KiB

Open AccessArticle

Fabrication and Characterization of Electrospun Folic Acid/Hybrid Fibers: In Vitro Controlled Release Study and Cytocompatibility Assays

by Fatma Nur Parin, Sana Ullah, Kenan Yildirim, Motahira Hashmi and Ick-Soo Kim

Polymers 2021, 13(20), 3594; https://doi.org/10.3390/polym13203594 - 19 Oct 2021

Cited by 29 | Viewed by 2949

Abstract

The fabrication of skin-care products with therapeutic properties has been significant for human health trends. In this study, we developed efficient hydrophilic composite nanofibers (NFs) loaded with the folic acid (FA) by electrospinning and electrospraying processes for tissue engineering or wound healing cosmetic [...] Read more.

The fabrication of skin-care products with therapeutic properties has been significant for human health trends. In this study, we developed efficient hydrophilic composite nanofibers (NFs) loaded with the folic acid (FA) by electrospinning and electrospraying processes for tissue engineering or wound healing cosmetic applications. The morphological, chemical and thermal characteristics, in vitro release properties, and cytocompatibility of the resulting composite fibers with the same amount of folic acid were analyzed. The SEM micrographs indicate that the obtained nanofibers were in the nanometer range, with an average fiber diameter of 75–270 nm and a good porosity ratio (34–55%). The TGA curves show that FA inhibits the degradation of the polymer and acts as an antioxidant at high temperatures. More physical interaction between FA and matrices has been shown to occur in the electrospray process than in the electrospinning process. A UV-Vis in vitro study of FA-loaded electrospun fibers for 8 h in artificial acidic (pH 5.44) and alkaline (pH 8.04) sweat solutions exhibited a rapid release of FA-loaded electrospun fibers, showing the effect of polymer matrix–FA interactions and fabrication processes on their release from the nanofibers. PVA-CHi/FA webs have the highest release value, with 95.2% in alkaline media. In acidic media, the highest release (92%) occurred on the PVA-Gel–CHi/sFA sample, and this followed first-order and Korsmeyer–Peppas kinetic models. Further, the L929 cytocompatibility assay results pointed out that all NFs (with/without FA) generated had no cell toxicity; on the contrary, the FA in the fibers facilitates cell growth. Therefore, the nanofibers are a potential candidate material in skin-care and tissue engineering applications. Full article

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

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15 pages, 75932 KiB

Open AccessArticle

Preparation of Biomimetic 3D Gastric Model with Photo-Curing Resin and Evaluation the Growth of Helicobacter pylori

by Yu-Tung Hsu, Ming-Hu Ho, Shiao-Pieng Lee and Chen-Yu Kao

Polymers 2021, 13(20), 3593; https://doi.org/10.3390/polym13203593 - 19 Oct 2021

Cited by 1 | Viewed by 2180

Abstract

Three-dimensional (3D) printing technology is now widely used in biomedical developments. Especially, photo-curing systems provide high resolution and precision. The current goal of biomedical 3D printing technology is the printing of human organs, but the current commercial photo-curable materials generally have high mechanical [...] Read more.

Three-dimensional (3D) printing technology is now widely used in biomedical developments. Especially, photo-curing systems provide high resolution and precision. The current goal of biomedical 3D printing technology is the printing of human organs, but the current commercial photo-curable materials generally have high mechanical strength that cannot meet the mechanical properties of the object to be printed. In this research, a gastric model was printed using a photo-curing 3D printing technique. To mimic the wrinkle pattern of human gastric tissue, cis-1,4 polyisoprene with different reactive diluents was mixed and identified a formulation that produced a print with human gastric softness. This research discussed the effect of the Young’s modulus of the material and elucidated the relationship between the degree of conversion rate and viscosity. After modifying the cis-1,4 polyisoprene surface from hydrophobic to hydrophilic, we then evaluated its adhesion efficiency for gastric mucin and the gastrointestinal-inhabiting bacterium Helicobacter pylori. Full article

(This article belongs to the Section Polymer Applications)

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15 pages, 3859 KiB

Open AccessArticle

Polyethylenimine-Modified Bombyx mori Silk Fibroin as a Delivery Carrier of the ING4-IL-24 Coexpression Plasmid

by Longxing Niu, Guo Chen, Yanfei Feng, Xueping Liu, Peng Pan, Linling Huang, Ying Guo and Mingzhong Li

Polymers 2021, 13(20), 3592; https://doi.org/10.3390/polym13203592 - 19 Oct 2021

Cited by 12 | Viewed by 2696

Abstract

One of the major challenges for lung cancer gene therapy is to find a gene delivery vector with high efficiency and low toxicity. In this study, low-molecular-weight polyethyleneimine (PEI, 1.8 kDa) was grafted onto the side chains of Bombyx mori silk fibroin (BSF) [...] Read more.

One of the major challenges for lung cancer gene therapy is to find a gene delivery vector with high efficiency and low toxicity. In this study, low-molecular-weight polyethyleneimine (PEI, 1.8 kDa) was grafted onto the side chains of Bombyx mori silk fibroin (BSF) to prepare cationized BSF (CBSF), which was used to package the plasmid DNA (pDNA) encoded by the inhibitor of growth 4 (ING4) and interleukin-24 (IL-24). FTIR and ¹H-NMR spectra demonstrated that PEI was effectively coupled to the side chains of BSF by amino bonds. The results of the trinitrobenzene sulfonic acid method and zeta potential showed that the free amino group content on BSF increased from 125.1 ± 1.2 µmol/mL to 153.5 ± 2.2 µmol/mL, the isoelectric point increased from 3.68 to 8.82, and the zeta potential reversed from − 11.8 ± 0.1 mV to + 12.4 ± 0.3 mV after PEI grafting. Positively charged CBSF could package pDNA to form spherical CBSF/pDNA complexes. In vitro, human lung adenocarcinoma A549 cells and human embryonic lung fibroblast WI-38 cells were transfected with CBSF/pDNA complexes. Confocal laser scanning microscopy analysis and flow cytometry tests showed that CBSF/pDNA complexes can effectively transfect A549 cells, and the transfection efficiency was higher than that of 25 kDa PEI/pDNA complexes. CCK-8 assay results showed that CBSF/pDNA complexes significantly inhibited the proliferation of A549 cells but had no significant effect on WI-38 cells and exhibited lower cytotoxicity to WI-38 cells than 25 kDa PEI. Therefore, a gene delivery system, constructed with the low-molecular-weight PEI-modified silk fibroin protein and the ING4-IL-24 double gene coexpression plasmid has potential applications in gene therapy for lung cancer. Full article

(This article belongs to the Special Issue Biomaterials in Medical Applications)

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10 pages, 3387 KiB

Open AccessArticle

Effect of Process Control Parameters on the Filtration Performance of PAN–CTAB Nanofiber/Nanonet Web Combined with Meltblown Nonwoven

by Hyo Kyoung Kang, Hyun Ju Oh, Jung Yeon Kim, Hak Yong Kim and Yeong Og Choi

Polymers 2021, 13(20), 3591; https://doi.org/10.3390/polym13203591 - 19 Oct 2021

Cited by 10 | Viewed by 2617

Abstract

Nanofibers have potential applications as filters for particles with diameters <10 μm owing to their large specific surface area, macropores, and controllable geometry or diameter. The filtration efficiency can be increased by creating nanonets (<50 nm) whose diameter is smaller than that of [...] Read more.

Nanofibers have potential applications as filters for particles with diameters <10 μm owing to their large specific surface area, macropores, and controllable geometry or diameter. The filtration efficiency can be increased by creating nanonets (<50 nm) whose diameter is smaller than that of nanofibers. This study investigates the effect of process conditions on the generation of nanonet structures from a polyacrylonitrile (PAN) solution containing cation surfactants; in addition, the filtration performance is analyzed. The applied electrospinning voltage and the electrostatic treatment of meltblown polypropylene (used as a substrate) are the most influential process parameters of nanonet formation. Electrospun polyacrylonitrile–cetylmethylammonium bromide (PAN–CTAB) showed a nanofiber/nanonet structure and improved thermal and mechanical properties compared with those of the electrospun PAN. The pore size distribution and filter efficiency of the PAN nanofiber web and PAN–CTAB nanofiber/nanonet web with meltblown were measured. The resulting PAN–CTAB nanofiber/nanonet air filter showed a high filtration efficiency of 99% and a low pressure drop of 7.7 mmH₂O at an air flow rate of 80 L/min. The process control methods for the nanonet structures studied herein provide a new approach for developing functional materials for air-filtration applications. Full article

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

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17 pages, 6328 KiB

Open AccessArticle

Electrospun Polyacrylonitrile/Lignin/Poly(Ethylene Glycol)-Based Porous Activated Carbon Nanofiber for Removal of Nickel(II) Ion from Aqueous Solution

by Aiza Farhani Zakaria, Sazlinda Kamaruzaman and Norizah Abdul Rahman

Polymers 2021, 13(20), 3590; https://doi.org/10.3390/polym13203590 - 19 Oct 2021

Cited by 12 | Viewed by 3063

Abstract

The issue of heavy metal contamination has caused a great deal of concern among water quality experts today, as it contributes to water pollution. Activated carbon nanofibers (ACNFs) showed a significant ability in removing heavy metals from the wastewater. In this study, polyacrylonitrile [...] Read more.

The issue of heavy metal contamination has caused a great deal of concern among water quality experts today, as it contributes to water pollution. Activated carbon nanofibers (ACNFs) showed a significant ability in removing heavy metals from the wastewater. In this study, polyacrylonitrile (PAN) was blended and electrospun with an abundant and inexpensive biopolymer, lignin and a water soluble polymer, poly(ethylene glycol) (PEG), by using an electrospinning technique to form nanofibers. The electrospun nanofibers were then investigated as a precursor for the production of porous ACNFs to study the removal of nickel(II) ions by adsorption technique. PEG was added to act as a porogen and to create the porous structure of carbon nanofibers (CNFs). CNFs were prepared by thermal treatment of the electrospun nanofibers and followed by activation of CNFs by thermal and acid treatment on CNFs. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectral analysis of the ACNFs showed a strong absorption peak of the C-O functional group, indicating the increase in the oxygenated compound. Field emission scanning electron microscopy (FESEM) images concluded that the ACNFs have more porous and compact fibers with a smaller fiber diameter of 263 ± 11 nm, while the CNFs are less compact and have slightly larger fiber diameter of 323 ± 6 nm. The adsorption study showed that the ACNFs possessed a much higher adsorption capacity of 18.09 mg/g compared with the CNFs, which the amount adsorbed was achieved only at 2.7 mg/g. The optimum adsorption conditions that gave the highest percentage of 60% for nickel(II) ions removal were 50 mg of adsorbent dosage, 100 ppm of nickel(II) solution, pH 3, and a contact time of 60 min. The study demonstrated that the fabrication of ACNFs from PAN/lignin/PEG electrospun nanofibers have potential as adsorbents for the removal of heavy metal contaminants. Full article

(This article belongs to the Special Issue Development in Carbon Based Polymer Materials: Structure, Processing, Properties and Applications)

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8 pages, 2227 KiB

Open AccessArticle

Effect of Multiple Enamel Surface Treatments on Micro-Shear Bond Strength

by René Daher, Ivo Krejci, Mustapha Mekki, Charlotte Marin, Enrico Di Bella and Stefano Ardu

Polymers 2021, 13(20), 3589; https://doi.org/10.3390/polym13203589 - 18 Oct 2021

Cited by 8 | Viewed by 2195

Abstract

Objectives: The aim of this study was to evaluate the effect of different enamel surface treatments on the micro-shear bond strength. Materials and methods: Sixty-four approximal surfaces from freshly extracted molars were randomly assigned to eight groups, according to combinations of [...] Read more.

Objectives: The aim of this study was to evaluate the effect of different enamel surface treatments on the micro-shear bond strength. Materials and methods: Sixty-four approximal surfaces from freshly extracted molars were randomly assigned to eight groups, according to combinations of the following enamel surface treatments: ground or unground, 37.5% phosphoric acid etching time of 15 or 30 s, and with or without primer application. The same bonding agent (Optibond FL™ Adhesive, Kerr) was then used for all groups, and a 1.8 mm diameter resin composite (Harmonize™, Kerr) cylinder was built up on the bonded surface. Samples underwent a shear force test at a crosshead speed of 1 mm/min until failure. Bond strength was calculated, and failure modes were inspected under an optical microscope. Results: Bond-strength values ranged from 8.2 MPa for 15 s etched unground enamel with primer application to 19.6 MPa for 30 s etched ground enamel without primer application. ANOVA and Fisher’s LSD post hoc tests revealed significant differences between the groups. Conclusions: Etching time and grinding have a statistically significant effect on the micro-shear bond strength of a three-step etch-and-rinse adhesive system on enamel. Primer application does not seem to be beneficial for enamel adhesion. Full article

(This article belongs to the Special Issue Advanced Polymeric Composites in Dentistry: Synthesis, Properties, and Applications)

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13 pages, 4951 KiB

Open AccessArticle

Experimental Investigation of the Wear Behaviour of Coated Polymer Gears

by Brigita Polanec, Franc Zupanič, Tonica Bončina, Frančišek Tašner and Srečko Glodež

Polymers 2021, 13(20), 3588; https://doi.org/10.3390/polym13203588 - 18 Oct 2021

Cited by 13 | Viewed by 2768

Abstract

A comprehensive experimental investigation of the wear behaviour of coated spur polymer gears made of POM is performed in this study. The three physical vapour deposition (PVD) coatings investigated were aluminium (Al), chromium (Cr), and chromium nitrite (CrN). Al was deposited in three [...] Read more.

A comprehensive experimental investigation of the wear behaviour of coated spur polymer gears made of POM is performed in this study. The three physical vapour deposition (PVD) coatings investigated were aluminium (Al), chromium (Cr), and chromium nitrite (CrN). Al was deposited in three process steps: By plasma activation, metallisation of Al by the magnetron sputtering process, and by plasma polymerisation. Cr deposition was performed in only one step, namely, the metallization of Cr by the magnetron sputtering process. The deposition of CrN was carried out in two steps: the first involved the metallization of Cr by the magnetron sputtering process while the second step, vapour deposition, involved the reactive metallisation of Cr with nitrogen, also by the magnetron sputtering process. The gears were tested on an in-house developed testing rig for different torques (16, 20, 24 and 30 Nm) and rotational speed of 1000 rpm. The duration of the experiments was set to 13 h, when the tooth thickness, and, consequently, the wear of the tooth flank was recorded. The experimental results showed that the influence of metallisation with aluminium, chromium, and chromium nitrite surface coatings on the wear behaviour of the analysed polymer gear is not significant. This is probably due to the fact that the analysed coatings were, in all cases, very thin (less than 500 nm), and therefore did not influence the wear resistance significantly. In that respect, an additional testing using thicker coatings should be applied in the further research work. Full article

(This article belongs to the Special Issue Polymer Gears, Mechanisms and Transmissions)

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13 pages, 15895 KiB

Open AccessArticle

Detection of Barely Visible Impact Damage in Polymeric Laminated Composites Using a Biomimetic Tactile Whisker

by Sakineh Fotouhi, Saber Khayatzadeh, Wei Xia Pui, Mahdi Damghani, Mahdi Bodaghi and Mohamad Fotouhi

Polymers 2021, 13(20), 3587; https://doi.org/10.3390/polym13203587 - 18 Oct 2021

Cited by 13 | Viewed by 3357

Abstract

This is a novel investigation on the possibility of detecting barely visible impact damage (BVID) in composite materials by whisking across the surface via tactile whisker sensors that resemble rats’ whiskers. A series of drop tower low-velocity impact tests were performed on quasi-isotropic [...] Read more.

This is a novel investigation on the possibility of detecting barely visible impact damage (BVID) in composite materials by whisking across the surface via tactile whisker sensors that resemble rats’ whiskers. A series of drop tower low-velocity impact tests were performed on quasi-isotropic composite plates. The plates were made from unidirectional T800 carbon/MTM49-3 epoxy prepregs with the stacking sequence of [45/0/90/−45]_4S. Investigating the specimens’ surface by the naked eye does not reveal any significant damage, rather than a small dent on the surface, with no tangible difference in the different impact energy levels. Ultrasonic C-scan observations showed the existence of BVID in all the impact energy levels, with an increasing trend in the damage size by increasing the impact energy level. The collected data from whisker sensors were analyzed using the support vector machine classifier, based on their vibrational properties, to identify the impacted region and classify the impact severity. It was observed that after training for 13 whisker contacts, the BVID severity can be classified with an accuracy of 100%. This is offering a new BVID detection technique, with a high potential for automation and high reliability that can be used as an alternative or combined with available inspection systems. Full article

(This article belongs to the Special Issue Multifunctional Smart Polymers and Polymeric Composites)

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29 pages, 2714 KiB

Open AccessReview

Regenerated Cellulose Products for Agricultural and Their Potential: A Review

by Nur Amira Zainul Armir, Amalia Zulkifli, Shamini Gunaseelan, Swarna Devi Palanivelu, Kushairi Mohd Salleh, Muhamad Hafiz Che Othman and Sarani Zakaria

Polymers 2021, 13(20), 3586; https://doi.org/10.3390/polym13203586 - 18 Oct 2021

Cited by 45 | Viewed by 8174

Abstract

Cellulose is one of the most abundant natural polymers with excellent biocompatibility, non-toxicity, flexibility, and renewable source. Regenerated cellulose (RC) products result from the dissolution-regeneration process risen from solvent and anti-solvent reagents, respectively. The regeneration process changes the cellulose chain conformation from cellulose [...] Read more.

Cellulose is one of the most abundant natural polymers with excellent biocompatibility, non-toxicity, flexibility, and renewable source. Regenerated cellulose (RC) products result from the dissolution-regeneration process risen from solvent and anti-solvent reagents, respectively. The regeneration process changes the cellulose chain conformation from cellulose I to cellulose II, leads the structure to have more amorphous regions with improved crystallinity, and inclines towards extensive modification on the RC products such as hydrogel, aerogel, cryogel, xerogel, fibers, membrane, and thin film. Recently, RC products are accentuated to be used in the agriculture field to develop future sustainable agriculture as alternatives to conventional agriculture systems. However, different solvent types and production techniques have great influences on the end properties of RC products. Besides, the fabrication of RC products from solely RC lacks excellent mechanical characteristics. Thus, the flexibility of RC has allowed it to be homogenously blended with other materials to enhance the final products’ properties. This review will summarize the properties and preparation of potential RC-based products that reflect its application to replace soil the plantation medium, govern the release of the fertilizer, provide protection on crops and act as biosensors. Full article

(This article belongs to the Special Issue Biopolymers Characterisation)

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12 pages, 22870 KiB

Open AccessArticle

Dielectric Barrier Discharge Plasma Jet (DBDjet) Processed Reduced Graphene Oxide/Polypyrrole/Chitosan Nanocomposite Supercapacitors

by Chen Liu, Cheng-Wei Hung, I-Chung Cheng, Cheng-Che Hsu, I-Chun Cheng and Jian-Zhang Chen

Polymers 2021, 13(20), 3585; https://doi.org/10.3390/polym13203585 - 18 Oct 2021

Cited by 18 | Viewed by 3228

Abstract

Reduced graphene oxide (rGO) and/or polypyrrole (PPy) are mixed with chitosan (CS) binder materials for screen-printing supercapacitors (SCs) on arc atmospheric-pressure plasma jet (APPJ)-treated carbon cloth. The performance of gel-electrolyte rGO/CS, PPy/CS, and rGO/PPy/CS SCs processed by a dielectric barrier discharge plasma jet [...] Read more.

Reduced graphene oxide (rGO) and/or polypyrrole (PPy) are mixed with chitosan (CS) binder materials for screen-printing supercapacitors (SCs) on arc atmospheric-pressure plasma jet (APPJ)-treated carbon cloth. The performance of gel-electrolyte rGO/CS, PPy/CS, and rGO/PPy/CS SCs processed by a dielectric barrier discharge plasma jet (DBDjet) was assessed and compared. DBDjet processing improved the hydrophilicity of these three nanocomposite electrode materials. Electrochemical measurements including electrical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charging-discharging (GCD) were used to evaluate the performance of the three types of SCs. The Trasatti method was used to evaluate the electric-double layer capacitance (EDLC) and pseudocapacitance (PC) of the capacitance. The energy and power density of the three types of SCs were illustrated and compared using Ragone plots. Our experiments verify that, with the same weight of active materials, the combined use of rGO and PPy in SCs can significantly increase the capacitance and improve the operation stability. Full article

(This article belongs to the Special Issue Plasma Processes for Polymers II)

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17 pages, 6071 KiB

Open AccessArticle

Microstructure Formation of Cement Mortars Modified by Superabsorbent Polymers

by Jan Fořt, Jiří Šál, Martin Böhm, María Jesús Morales-Conde, Manuel Alejandro Pedreño-Rojas and Robert Černý

Polymers 2021, 13(20), 3584; https://doi.org/10.3390/polym13203584 - 18 Oct 2021

Cited by 3 | Viewed by 2263

Abstract

The utilization of superabsorbent polymers (SAPs) in cement-based materials has been found to be a promising means of mitigating the autogenous propagation of shrinkage and cracks. On the other hand, the undesired effects of SAPs’ application on functional properties, including mechanical strength, microstructure [...] Read more.

The utilization of superabsorbent polymers (SAPs) in cement-based materials has been found to be a promising means of mitigating the autogenous propagation of shrinkage and cracks. On the other hand, the undesired effects of SAPs’ application on functional properties, including mechanical strength, microstructure formation, and the evolution of hydration heat are not properly understood, given the variety in SAPs’ characteristics. To contribute to the present state-of-the-art, cement mortars, modified with two grades of SAPs by dosages of 0.3%, 0.6%, and 0.9%, were designed and studied with emphasis on the relationship between the materials’ porosities and mechanical strengths. The obtained results are interpreted by scanning electron microscopy analysis and hydration heat evolution to elucidate the major changes and their driving factors. Besides the benefits associated with the mitigation of autogenous shrinkage, the achieved results point to an adverse effect of supplementation with SAP on mechanical strength at an early age, and an even more pronounced increase at a later age. The employed scanning electron microscopy images, together with mercury-intrusion porosimetry data, depict distortion in the material porosity as a result of the filling of formed voids and the closing of open ends by swelled hydrogels. Only the minor benefit of a greater cross-linking density was obtained by the formation of dense structures and the gains in mechanical strength therefrom. Full article

(This article belongs to the Special Issue Application of Polymeric Materials in the Building Industry)

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14 pages, 3075 KiB

Open AccessArticle

Heterogeneous Hybrid Nanocomposite Based on Chitosan/Magnesia Hybrid Films: Ecofriendly and Recyclable Solid Catalysts for Organic Reactions

by Metwally Madkour, Khaled D. Khalil and Fakhreia A. Al-Sagheer

Polymers 2021, 13(20), 3583; https://doi.org/10.3390/polym13203583 - 17 Oct 2021

Cited by 8 | Viewed by 2292

Abstract

Chitosan/magnesia hybrid films (CS-Mg) have been prepared via sol-gel process and employed as heterogeneous catalysts. An in situ generation of a magnesia network in the chitosan matrix was performed through hydrolysis/condensation reactions of magnesium ethoxide. The synthesized hybrid films were characterized using various [...] Read more.

Chitosan/magnesia hybrid films (CS-Mg) have been prepared via sol-gel process and employed as heterogeneous catalysts. An in situ generation of a magnesia network in the chitosan matrix was performed through hydrolysis/condensation reactions of magnesium ethoxide. The synthesized hybrid films were characterized using various analytical techniques, such as X-ray photo-electron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The hybrid films display excellent catalytic activities in Michael and Knoevenagel reactions via one pot or solvent-free approaches under microwave irradiation conditions. Chitosan/magnesia hybrid films, catalysed pyrimidine, benzochromene, coumarin and arylidene-malononitriles derivatives formation reactions occurred with highly efficient yields of 97%, 92%, 86% and 95% respectively. Due to the fact that the films are durable and insoluble in common organic solvents, they were easily separated and can be recycled up to five times without a considerable loss of their catalytic activity. Full article

(This article belongs to the Special Issue Biobased Materials for Emerging Applications)

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12 pages, 5288 KiB

Open AccessEditor’s ChoiceArticle

Rheological Properties of Aqueous Sodium Alginate Slurries for LTO Battery Electrodes

by Christina Toigo, Milan Kracalik, Elke Bradt, Karl-Heinz Pettinger and Catia Arbizzani

Polymers 2021, 13(20), 3582; https://doi.org/10.3390/polym13203582 - 17 Oct 2021

Cited by 8 | Viewed by 3586

Abstract

Rheological properties of electrode slurries have been intensively studied for manifold different combinations of active materials and binders. Standardly, solvent-based systems are under use, but a trend towards water-based electrode manufacturing is becoming more and more important. The different solvent is beneficial in [...] Read more.

Rheological properties of electrode slurries have been intensively studied for manifold different combinations of active materials and binders. Standardly, solvent-based systems are under use, but a trend towards water-based electrode manufacturing is becoming more and more important. The different solvent is beneficial in terms of sustainability and process safety but is also accompanied by some disadvantages such as extraction of residual humidity and a higher complexity concerning slurry stability. Li₄Ti₅O₁₂ (LTO) active material provides good long-term stability and can be processed in aqueous solutions. Combining the LTO active material with sodium alginate (SA) as a promising biobased polymer binder reveals good electrochemical properties but suffers from bad slurry stability. In this work, we present a comprehensive rheological study on material interactions in anode slurries consisting of LTO and SA, based on a complex interaction of differentially sized materials. The use of two different surfactants—namely, an anionic and non-ionic one, to enhance slurry stability, compared with surfactant-free slurry. Full article

(This article belongs to the Special Issue Functional Alginate-Based Materials)

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14 pages, 2715 KiB

Open AccessArticle

Autogenous Cross-Linking of Recycled Keratin from Poultry-Feather Waste to Hydrogels for Plant-Growth Media

by Markus Brenner and Oliver Weichold

Polymers 2021, 13(20), 3581; https://doi.org/10.3390/polym13203581 - 17 Oct 2021

Cited by 8 | Viewed by 2625

Abstract

The global rise in atmospheric temperature is leading to an increasing spread of semi-arid and arid regions and is accompanied by a deterioration of arable land. Polymers can help in a number of ways, but they must not be a burden to the [...] Read more.

The global rise in atmospheric temperature is leading to an increasing spread of semi-arid and arid regions and is accompanied by a deterioration of arable land. Polymers can help in a number of ways, but they must not be a burden to the environment. In this context, we present herein a method by which goose feathers, representative of keratin waste in general, can be transformed into hydrogels for use as a plant growth medium. The treatment of shredded feathers in Na₂S solution at ambient conditions dissolves approx. 80% of the keratin within 30 min. During evaporation, the thiol groups of cysteine reoxidise to disulphide bridges. Additionally, the protein chains form β-sheets. Both act as cross-links that enables the formation of gels. The drying conditions were found to be crucial as slower evaporation affords gels with higher degrees of swelling at the cost of reduced gel yields. The cress germination test indicated the absence of toxic substances in the gel, which strongly adheres to the roots. Thereby, the plants are protected from drought stress as long as the gel still contains moisture. Full article

(This article belongs to the Special Issue Polymers for Soil in Agriculture and Urban Landscaping)

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14 pages, 3411 KiB

Open AccessArticle

Biopolymer Hydrogel Scaffolds Containing Doxorubicin as A Localized Drug Delivery System for Inhibiting Lung Cancer Cell Proliferation

by Chuda Chittasupho, Jakrapong Angklomklew, Thanu Thongnopkoon, Wongwit Senavongse, Pensak Jantrawut and Warintorn Ruksiriwanich

Polymers 2021, 13(20), 3580; https://doi.org/10.3390/polym13203580 - 17 Oct 2021

Cited by 10 | Viewed by 2766

Abstract

A hydrogel scaffold is a localized drug delivery system that can maintain the therapeutic level of drug concentration at the tumor site. In this study, the biopolymer hydrogel scaffold encapsulating doxorubicin was fabricated from gelatin, sodium carboxymethyl cellulose, and gelatin/sodium carboxymethyl cellulose mixture [...] Read more.

A hydrogel scaffold is a localized drug delivery system that can maintain the therapeutic level of drug concentration at the tumor site. In this study, the biopolymer hydrogel scaffold encapsulating doxorubicin was fabricated from gelatin, sodium carboxymethyl cellulose, and gelatin/sodium carboxymethyl cellulose mixture using a lyophilization technique. The effects of a crosslinker on scaffold morphology and pore size were determined using scanning electron microscopy. The encapsulation efficiency and the release profile of doxorubicin from the hydrogel scaffolds were determined using UV-Vis spectrophotometry. The anti-proliferative effect of the scaffolds against the lung cancer cell line was investigated using an MTT assay. The results showed that scaffolds made from different types of natural polymer had different pore configurations and pore sizes. All scaffolds had high encapsulation efficiency and drug-controlled release profiles. The viability and proliferation of A549 cells, treated with gelatin, gelatin/SCMC, and SCMC scaffolds containing doxorubicin significantly decreased compared with control. These hydrogel scaffolds might provide a promising approach for developing a superior localized drug delivery system to kill lung cancer cells. Full article

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

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17 pages, 4750 KiB

Open AccessArticle

Organosilica-Modified Multiblock Copolymers for Membrane Gas Separation

by Ilsiya M. Davletbaeva, Alexander Yu. Alentiev, Zulfiya Z. Faizulina, Ilnaz I. Zaripov, Roman Yu. Nikiforov, Victor V. Parfenov and Alexander V. Arkhipov

Polymers 2021, 13(20), 3579; https://doi.org/10.3390/polym13203579 - 17 Oct 2021

Cited by 5 | Viewed by 2109

Abstract

Organosubstituted silica derivatives were synthesized and investigated as modifiers of block copolymers based on macroinitiator and 2,4-toluene diisocyanate. A peculiarity of the modified block copolymers is the existence in their structure of coplanar rigid polyisocyanate blocks of acetal nature (O-polyisocyanates). Organosubstituted silica derivatives [...] Read more.

Organosubstituted silica derivatives were synthesized and investigated as modifiers of block copolymers based on macroinitiator and 2,4-toluene diisocyanate. A peculiarity of the modified block copolymers is the existence in their structure of coplanar rigid polyisocyanate blocks of acetal nature (O-polyisocyanates). Organosubstituted silica derivatives have a non-additive effect on high-temperature relaxation and α-transitions of modified polymers and exhibit the ability to influence the supramolecular structure of block copolymers. The use of the developed modifiers leads to a change in the gas transport properties of block copolymers. The increase of the permeability coefficients is due to the increase of the diffusion coefficients. At the same time, the gas solubility coefficients do not change. An increase in the ideal selectivity for a number of gas pairs is observed. An increase in the selectivity for the CO₂/N₂ gas pair (from 25 to 39) by 1.5 times demonstrates the promising use of this material for flue gases separation. Full article

(This article belongs to the Special Issue Self-Assembly of Block Copolymers: Experiment and Modelling)

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17 pages, 5917 KiB

Open AccessArticle

Interaction Insight of Pullulan-Mediated Gamma-Irradiated Silver Nanoparticle Synthesis and Its Antibacterial Activity

by Mohd Shahrul Nizam Salleh, Roshafima Rasit Ali, Kamyar Shameli, Mohd Yusof Hamzah, Rafiziana Md Kasmani and Mohamed Mahmoud Nasef

Polymers 2021, 13(20), 3578; https://doi.org/10.3390/polym13203578 - 17 Oct 2021

Cited by 17 | Viewed by 2771

Abstract

The production of pure silver nanoparticles (Ag-NPs) with unique properties remains a challenge even today. In the present study, the synthesis of silver nanoparticles (Ag-NPs) from natural pullulan (PL) was carried out using a radiation-induced method. It is known that pullulan is regarded [...] Read more.

The production of pure silver nanoparticles (Ag-NPs) with unique properties remains a challenge even today. In the present study, the synthesis of silver nanoparticles (Ag-NPs) from natural pullulan (PL) was carried out using a radiation-induced method. It is known that pullulan is regarded as a microbial polysaccharide, which renders it suitable to act as a reducing and stabilizing agent during the production of Ag-NPs. Pullulan-assisted synthesis under gamma irradiation was successfully developed to obtain Ag-NPs, which was characterized by UV-Vis, XRD, TEM, and Zeta potential analysis. Pullulan was used as a stabilizer and template for the growth of silver nanoparticles, while gamma radiation was modified to be selective to reduce silver ions. The formation of Ag-NPs was confirmed using UV–Vis spectra by showing a surface plasmon resonance (SPR) band in the region of 410–420 nm. As observed by TEM images, it can be said that by increasing the radiation dose, the particle size decreases, resulting in a mean diameter of Ag-NPs ranging from 40.97 to 3.98 nm. The XRD analysis confirmed that silver metal structures with a face-centered cubic (FCC) crystal were present, while TEM images showed a spherical shape with smooth edges. XRD also demonstrated that increasing the dose of gamma radiation increases the crystallinity at a high purity of Ag-NPs. As examined by zeta potential, the synthesized Ag-NP/PL was negatively charged with high stability. Ag-NP/PL was then analysed for antimicrobial activity against Staphylococcus aureus, and it was found that it had high antibacterial activity. It is found that the adoption of radiation doses results in a stable and green reduction process for silver nanoparticles. Full article

(This article belongs to the Special Issue Polymer Nanoparticles: Synthesis and Applications)

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Polymers, Volume 13, Issue 20 (October-2 2021) – 155 articles

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