Polymers

12 pages, 4623 KiB

Open AccessEditor’s ChoiceCommunication

Synthesis of Polyaniline/Scarlet 3R as a Conductive Polymer

by Takuya Yonehara and Hiromasa Goto

Polymers 2020, 12(3), 579; https://doi.org/10.3390/polym12030579 - 5 Mar 2020

Cited by 13 | Viewed by 3542

Polyaniline (PANI) was prepared in the presence of the acidic dye scarlet 3R. Color tuning was performed on PANI through doping–dedoping processes and by changing the solvent used during the optical absorption spectroscopic measurements. The chemical structure of the resulting polymer–dye composite was [...] Read more.

Polyaniline (PANI) was prepared in the presence of the acidic dye scarlet 3R. Color tuning was performed on PANI through doping–dedoping processes and by changing the solvent used during the optical absorption spectroscopic measurements. The chemical structure of the resulting polymer–dye composite was analyzed using infrared absorption spectroscopy, and it showed the occurrence of secondary doping in m-cresol. The shape of the UV–Vis optical absorption spectra for the composite solution is dependent on the types of organic solvents used during the analysis, which was influenced by the conformation of PANI and the ionic interactions between PANI and scarlet 3R. Full article

(This article belongs to the Section Polymer Chemistry)

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15 pages, 3985 KiB

Open AccessEditor’s ChoiceArticle

Investigating the Impact of Curing System on Structure-Property Relationship of Natural Rubber Modified with Brewery By-Product and Ground Tire Rubber

by Łukasz Zedler, Xavier Colom, Javier Cañavate, Mohammad Reza Saeb, Józef T. Haponiuk and Krzysztof Formela

Polymers 2020, 12(3), 545; https://doi.org/10.3390/polym12030545 - 3 Mar 2020

Cited by 31 | Viewed by 3852

Abstract

The application of wastes as a filler/reinforcement phase in polymers is a new strategy to modify the performance properties and reduce the price of biocomposites. The use of these fillers, coming from agricultural waste (cellulose/lignocellulose-based fillers) and waste rubbers, constitutes a method for [...] Read more.

The application of wastes as a filler/reinforcement phase in polymers is a new strategy to modify the performance properties and reduce the price of biocomposites. The use of these fillers, coming from agricultural waste (cellulose/lignocellulose-based fillers) and waste rubbers, constitutes a method for the management of post-consumer waste. In this paper, highly-filled biocomposites based on natural rubber (NR) and ground tire rubber (GTR)/brewers’ spent grain (BSG) hybrid reinforcements, were prepared using two different curing systems: (i) sulfur-based and (ii) dicumyl peroxide (DCP). The influence of the amount of fillers (in 100/0, 50/50, and 0/100 ratios in parts per hundred of rubber) and type of curing system on the final properties of biocomposites was evaluated by the oscillating disc rheometer, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, swelling behavior, tensile testing, and impedance tube measurements. The results show, that the scorch time and the optimum curing time values of sulfur cured biocomposites are affected by the change of the hybrid filler ratio while using the DCP curing system, and the obtained values do not show significant variations. The results conclude that the biocomposites cured with sulfur have better physico-mechanical and acoustic absorption, and that the type of curing system does not influence their thermal stability. The overall analysis indicates that the difference in final properties of highly filled biocomposites cured with two different systems is mainly affected by the: (i) cross-linking efficiency, (ii) partial absorption and reactions between fillers and used additives, and (iii) affinity of additives to applied fillers. Full article

(This article belongs to the Special Issue Environmentally-Friendly Polymeric Materials Based on Recycling and Bio-Based Components)

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20 pages, 5993 KiB

Open AccessEditor’s ChoiceReview

Solvent-Free Approaches for the Processing of Scaffolds in Regenerative Medicine

by Víctor Santos-Rosales, Ana Iglesias-Mejuto and Carlos A. García-González

Polymers 2020, 12(3), 533; https://doi.org/10.3390/polym12030533 - 2 Mar 2020

Cited by 35 | Viewed by 5357

Abstract

The regenerative medicine field is seeking novel strategies for the production of synthetic scaffolds that are able to promote the in vivo regeneration of a fully functional tissue. The choices of the scaffold formulation and the manufacturing method are crucial to determine the [...] Read more.

The regenerative medicine field is seeking novel strategies for the production of synthetic scaffolds that are able to promote the in vivo regeneration of a fully functional tissue. The choices of the scaffold formulation and the manufacturing method are crucial to determine the rate of success of the graft for the intended tissue regeneration process. On one hand, the incorporation of bioactive compounds such as growth factors and drugs in the scaffolds can efficiently guide and promote the spreading, differentiation, growth, and proliferation of cells as well as alleviate post-surgical complications such as foreign body responses and infections. On the other hand, the manufacturing method will determine the feasible morphological properties of the scaffolds and, in certain cases, it can compromise their biocompatibility. In the case of medicated scaffolds, the manufacturing method has also a key effect in the incorporation yield and retained activity of the loaded bioactive agents. In this work, solvent-free methods for scaffolds production, i.e., technological approaches leading to the processing of the porous material with no use of solvents, are presented as advantageous solutions for the processing of medicated scaffolds in terms of efficiency and versatility. The principles of these solvent-free technologies (melt molding, 3D printing by fused deposition modeling, sintering of solid microspheres, gas foaming, and compressed CO₂ and supercritical CO₂-assisted foaming), a critical discussion of advantages and limitations, as well as selected examples for regenerative medicine purposes are herein presented. Full article

(This article belongs to the Special Issue Bioactive Polymer Scaffolds and Thin Films for Biomedical Applications: State-of-the-Art and Challenges)

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17 pages, 9849 KiB

Open AccessEditor’s ChoiceArticle

Ammonium Polyphosphate with High Specific Surface Area by Assembling Zeolite Imidazole Framework in EVA Resin: Significant Mechanical Properties, Migration Resistance, and Flame Retardancy

by Jingyu Wang, Hui Shi, Pinlie Zhu, Yuanjie Wei and Jianwei Hao

Polymers 2020, 12(3), 534; https://doi.org/10.3390/polym12030534 - 2 Mar 2020

Cited by 16 | Viewed by 3941

Abstract

A zeolite imidazole framework (ZIF-67) was assembled onto the surface of ammonium polyphosphate (APP) for preparing a series multifunctional flame-retardant APP-ZIFs. The assembly mechanism, chemical structure, chemical compositions, morphology, and specific surface area of APP-ZIFs were characterized. The typical APPZ1 and APPZ4 were [...] Read more.

A zeolite imidazole framework (ZIF-67) was assembled onto the surface of ammonium polyphosphate (APP) for preparing a series multifunctional flame-retardant APP-ZIFs. The assembly mechanism, chemical structure, chemical compositions, morphology, and specific surface area of APP-ZIFs were characterized. The typical APPZ1 and APPZ4 were selected as intumescent flame retardants with dipentaerythritol (DPER) because of their superior unit catalytic efficiency of cobalt by thermogravimetric analysis. APPZ1 and APPZ4 possessed 6.8 and 92.1 times the specific surface area of untreated APP, which could significantly enhance the interfacial interaction, mechanical properties, and migration resistance when using in ethylene-vinyl acetate (EVA). With 25% loading, 25% APPZ4/DPER achieved a limiting oxygen index value of 29.4% and a UL 94 V-0 rating, whereas 25% APP/DPER achieved a limiting oxygen index value of only 26.2% and a V-2 rating, respectively. The peak of the heat release rate, smoke production rate, and CO production rate respectively decreased by 34.7%, 39.0%, and 40.1%, while the char residue increased by 91.7%. These significant improvements were attributed to the catalytic graphitization by nano cobalt phosphate and the formation of a more protective char barrier comprised of graphite-like carbon. Full article

(This article belongs to the Special Issue Flame Retarded Polymers and Composites)

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12 pages, 6667 KiB

Open AccessEditor’s ChoiceArticle

Enhanced Biocompatibility of Multi-Layered, 3D Bio-Printed Artificial Vessels Composed of Autologous Mesenchymal Stem Cells

by Eui Hwa Jang, Jung-Hwan Kim, Jun Hee Lee, Dae-Hyun Kim and Young-Nam Youn

Polymers 2020, 12(3), 538; https://doi.org/10.3390/polym12030538 - 2 Mar 2020

Cited by 30 | Viewed by 4457

Abstract

Artificial vessels capable of long-term patency are essential clinical tools in vascular surgery that involves small vessels. On-going attempts to develop artificial vessels that complements restenosis have not been entirely successful. Here, we report on the fabrication of small-sized artificial vessels using a [...] Read more.

Artificial vessels capable of long-term patency are essential clinical tools in vascular surgery that involves small vessels. On-going attempts to develop artificial vessels that complements restenosis have not been entirely successful. Here, we report on the fabrication of small-sized artificial vessels using a three-dimensional bio-printer. The fabrication employed biodegradable polycaprolactone and autologous MSCs harvested from the bone-marrow of canines. The MSCs were cultured and differentiated into endothelial-like cells. After confirming differentiation, artificial vessels comprising three-layers were constructed and implanted into the arteries of canines. The autologous MSCs printed on artificial vessels (cell-derived group) maintained a 64.3% patency (9 of 14 grafts) compared with artificial vessels without cells (control group, 54.5% patency (6 of 11 grafts)). The cell-derived vessels (61.9 cells/mm² ± 14.3) had more endothelial cells on their inner surfaces than the control vessels (21 cells/mm² ± 11.3). Moreover, the control vessels showed acute inflammation on the porous structures of the implanted artificial vessels, whereas the cell-derived vessels exhibited fibrinous clots with little to no inflammation. We concluded that the minimal rejection of these artificial vessels by the immune system was due to the use of autologous MSCs. We anticipate that this study will be of value in the field of tissue-engineering in clinical practice. Full article

(This article belongs to the Special Issue Biomimetic Polymer-Based Matrices for Regenerative Medicine)

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17 pages, 535 KiB

Open AccessEditor’s ChoiceReview

Studies of Cellulose and Starch Utilization and the Regulatory Mechanisms of Related Enzymes in Fungi

by Bao-Teng Wang, Shuang Hu, Xing-Ye Yu, Long Jin, Yun-Jia Zhu and Feng-Jie Jin

Polymers 2020, 12(3), 530; https://doi.org/10.3390/polym12030530 - 2 Mar 2020

Cited by 67 | Viewed by 6578

Abstract

Polysaccharides are biopolymers made up of a large number of monosaccharides joined together by glycosidic bonds. Polysaccharides are widely distributed in nature: Some, such as peptidoglycan and cellulose, are the components that make up the cell walls of bacteria and plants, and some, [...] Read more.

Polysaccharides are biopolymers made up of a large number of monosaccharides joined together by glycosidic bonds. Polysaccharides are widely distributed in nature: Some, such as peptidoglycan and cellulose, are the components that make up the cell walls of bacteria and plants, and some, such as starch and glycogen, are used as carbohydrate storage in plants and animals. Fungi exist in a variety of natural environments and can exploit a wide range of carbon sources. They play a crucial role in the global carbon cycle because of their ability to break down plant biomass, which is composed primarily of cell wall polysaccharides, including cellulose, hemicellulose, and pectin. Fungi produce a variety of enzymes that in combination degrade cell wall polysaccharides into different monosaccharides. Starch, the main component of grain, is also a polysaccharide that can be broken down into monosaccharides by fungi. These monosaccharides can be used for energy or as precursors for the biosynthesis of biomolecules through a series of enzymatic reactions. Industrial fermentation by microbes has been widely used to produce traditional foods, beverages, and biofuels from starch and to a lesser extent plant biomass. This review focuses on the degradation and utilization of plant homopolysaccharides, cellulose and starch; summarizes the activities of the enzymes involved and the regulation of the induction of the enzymes in well-studied filamentous fungi. Full article

(This article belongs to the Special Issue Main Applications of Plant, Fungal and Algal Polysaccharides: Current Vision and Future Horizon)

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19 pages, 4136 KiB

Open AccessEditor’s ChoiceArticle

Poly(vinyl alcohol)-Based Biofilms Plasticized with Polyols and Colored with Pigments Extracted from Tomato By-Products

by Laura Mitrea, Lavinia-Florina Călinoiu, Gheorghe-Adrian Martău, Katalin Szabo, Bernadette-Emoke Teleky, Vlad Mureșan, Alexandru-Vasile Rusu, Claudia-Terezia Socol and Dan-Cristian Vodnar

Polymers 2020, 12(3), 532; https://doi.org/10.3390/polym12030532 - 2 Mar 2020

Cited by 37 | Viewed by 7064

Abstract

In the current work the physicochemical features of poly(vinyl alcohol) (PVOH) biofilms, enriched with eco-friendly polyols and with carotenoid-rich extracts, were investigated. The polyols, such as glycerol (Gly), 1,3-propanediol (PDO), and 2,3-butanediol (BDO) were used as plasticizers and the tomato-based pigments (TP) as [...] Read more.

In the current work the physicochemical features of poly(vinyl alcohol) (PVOH) biofilms, enriched with eco-friendly polyols and with carotenoid-rich extracts, were investigated. The polyols, such as glycerol (Gly), 1,3-propanediol (PDO), and 2,3-butanediol (BDO) were used as plasticizers and the tomato-based pigments (TP) as coloring agents. The outcomes showed that β-carotene was the major carotenoid in the TP (1.605 mg β-carotene/100 DW), which imprinted the orange color to the biofilms. The flow behavior indicated that with the increase of shear rate the viscosity of biofilm solutions also increased until 50 s⁻¹, reaching values at 37 °C of approximately 9 ± 0.5 mPa·s for PVOH, and for PVOH+TP, 14 ± 0.5 mPa·s in combination with Gly, PDO, and BDO. The weight, thickness, and density of samples increased with the addition of polyols and TP. Biofilms with TP had lower transparency values compared with control biofilms (without vegetal pigments). The presence of BDO, especially, but also of PDO and glycerol in biofilms created strong bonds within the PVOH matrix by increasing their mechanical resistance. The novelty of the present approach relies on the replacement of synthetic colorants with natural pigments derived from agro-industrial by-products, and the use of a combination of biodegradable polymers and polyols, as an integrated solution for packaging application in the bioplastic industry. Full article

(This article belongs to the Special Issue Polymeric Materials for Food Engineering)

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19 pages, 10631 KiB

Open AccessEditor’s ChoiceArticle

Shape-Adaptive Metastructures with Variable Bandgap Regions by 4D Printing

by Reza Noroozi, Mahdi Bodaghi, Hamid Jafari, Ali Zolfagharian and Mohammad Fotouhi

Polymers 2020, 12(3), 519; https://doi.org/10.3390/polym12030519 - 1 Mar 2020

Cited by 98 | Viewed by 8421

Abstract

This article shows how four-dimensional (4D) printing technology can engineer adaptive metastructures that exploit resonating self-bending elements to filter vibrational and acoustic noises and change filtering ranges. Fused deposition modeling (FDM) is implemented to fabricate temperature-responsive shape-memory polymer (SMP) elements with self-bending features. [...] Read more.

This article shows how four-dimensional (4D) printing technology can engineer adaptive metastructures that exploit resonating self-bending elements to filter vibrational and acoustic noises and change filtering ranges. Fused deposition modeling (FDM) is implemented to fabricate temperature-responsive shape-memory polymer (SMP) elements with self-bending features. Experiments are conducted to reveal how the speed of the 4D printer head can affect functionally graded prestrain regime, shape recovery and self-bending characteristics of the active elements. A 3D constitutive model, along with an in-house finite element (FE) method, is developed to replicate the shape recovery and self-bending of SMP beams 4D-printed at different speeds. Furthermore, a simple approach of prestrain modeling is introduced into the commercial FE software package to simulate material tailoring and self-bending mechanism. The accuracy of the straightforward FE approach is validated against experimental observations and computational results from the in-house FE MATLAB-based code. Two periodic architected temperature-sensitive metastructures with adaptive dynamical characteristics are proposed to use bandgap engineering to forbid specific frequencies from propagating through the material. The developed computational tool is finally implemented to numerically examine how bandgap size and frequency range can be controlled and broadened. It is found out that the size and frequency range of the bandgaps are linked to changes in the geometry of self-bending elements printed at different speeds. This research is likely to advance the state-of-the-art 4D printing and unlock potentials in the design of functional metastructures for a broad range of applications in acoustic and structural engineering, including sound wave filters and waveguides. Full article

(This article belongs to the Special Issue Functional Polymers in Sensors and Actuators: Fabrication and Analysis)

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13 pages, 3627 KiB

Open AccessEditor’s ChoiceArticle

Study of UHMWPE Fiber Surface Modification and the Properties of UHMWPE/Epoxy Composite

by Lei Han, Haifeng Cai, Xu Chen, Cheng Zheng and Weihong Guo

Polymers 2020, 12(3), 521; https://doi.org/10.3390/polym12030521 - 1 Mar 2020

Cited by 40 | Viewed by 6595

Abstract

Ultra-high molecular weight polyethylene (UHMWPE)/epoxy composites with excellent adhesive properties were prepared by forming an interface membrane on the UHMWPE fiber surface. The interface membrane of the UHMWPE fiber and epoxy resin was polymerized by an aldol condensation between polyvinyl alcohol (PVA) and [...] Read more.

Ultra-high molecular weight polyethylene (UHMWPE)/epoxy composites with excellent adhesive properties were prepared by forming an interface membrane on the UHMWPE fiber surface. The interface membrane of the UHMWPE fiber and epoxy resin was polymerized by an aldol condensation between polyvinyl alcohol (PVA) and glutaraldehyde. Different surface treatment methods of UHMWPE fibers were optimized and the two-step PVA-glutaraldehyde condensation (Corona-PG-2S) method is the best. The interfacial adhesion between UHMWPE fiber and epoxy resin was enhanced, and the adhesive properties of the composite were improved. X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrum (EDS) results of the fiber treated by Corona-PG-2S shows that the surface oxygen content was up to 25.0 wt %, with an increase of 17.3 wt % compared with the surface oxygen content of unmodified UHMWPE fiber, which indicated that the surface polarity was greatly enhanced. The adhesive properties were improved by improving the polarity of the surface. The peel strength, ultimate cohesive force, tensile strength and flexural strength of the composite treated by Corona-PG-2S were greatly increased to 262.8%, 166.9%, 139.7%, 200.6% compared with those of unmodified samples. The composite prepared by Corona-PG-2S had excellent adhesive properties, demonstrating that the Corona-PG-2S method plays a major role in significantly improving the composite adhesive properties. Full article

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

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34 pages, 9037 KiB

Open AccessEditor’s ChoiceReview

Microscopic Techniques for the Analysis of Micro and Nanostructures of Biopolymers and Their Derivatives

by Abhilash Venkateshaiah, Vinod V.T. Padil, Malladi Nagalakshmaiah, Stanisław Waclawek, Miroslav Černík and Rajender S. Varma

Polymers 2020, 12(3), 512; https://doi.org/10.3390/polym12030512 - 27 Feb 2020

Cited by 65 | Viewed by 12473

Abstract

Natural biopolymers, a class of materials extracted from renewable sources, is garnering interest due to growing concerns over environmental safety; biopolymers have the advantage of biocompatibility and biodegradability, an imperative requirement. The synthesis of nanoparticles and nanofibers from biopolymers provides a green platform [...] Read more.

Natural biopolymers, a class of materials extracted from renewable sources, is garnering interest due to growing concerns over environmental safety; biopolymers have the advantage of biocompatibility and biodegradability, an imperative requirement. The synthesis of nanoparticles and nanofibers from biopolymers provides a green platform relative to the conventional methods that use hazardous chemicals. However, it is challenging to characterize these nanoparticles and fibers due to the variation in size, shape, and morphology. In order to evaluate these properties, microscopic techniques such as optical microscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM) are essential. With the advent of new biopolymer systems, it is necessary to obtain insights into the fundamental structures of these systems to determine their structural, physical, and morphological properties, which play a vital role in defining their performance and applications. Microscopic techniques perform a decisive role in revealing intricate details, which assists in the appraisal of microstructure, surface morphology, chemical composition, and interfacial properties. This review highlights the significance of various microscopic techniques incorporating the literature details that help characterize biopolymers and their derivatives. Full article

(This article belongs to the Special Issue Polymer Materials in Environmental Chemistry)

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30 pages, 10316 KiB

Open AccessEditor’s ChoiceReview

Carbon-Based Polymer Nanocomposite for High-Performance Energy Storage Applications

by Samarjeet Singh Siwal, Qibo Zhang, Nishu Devi and Vijay Kumar Thakur

Polymers 2020, 12(3), 505; https://doi.org/10.3390/polym12030505 - 26 Feb 2020

Cited by 150 | Viewed by 14139

Abstract

In recent years, numerous discoveries and investigations have been remarked for the development of carbon-based polymer nanocomposites. Carbon-based materials and their composites hold encouraging employment in a broad array of fields, for example, energy storage devices, fuel cells, membranes sensors, actuators, and electromagnetic [...] Read more.

In recent years, numerous discoveries and investigations have been remarked for the development of carbon-based polymer nanocomposites. Carbon-based materials and their composites hold encouraging employment in a broad array of fields, for example, energy storage devices, fuel cells, membranes sensors, actuators, and electromagnetic shielding. Carbon and its derivatives exhibit some remarkable features such as high conductivity, high surface area, excellent chemical endurance, and good mechanical durability. On the other hand, characteristics such as docility, lower price, and high environmental resistance are some of the unique properties of conducting polymers (CPs). To enhance the properties and performance, polymeric electrode materials can be modified suitably by metal oxides and carbon materials resulting in a composite that helps in the collection and accumulation of charges due to large surface area. The carbon-polymer nanocomposites assist in overcoming the difficulties arising in achieving the high performance of polymeric compounds and deliver high-performance composites that can be used in electrochemical energy storage devices. Carbon-based polymer nanocomposites have both advantages and disadvantages, so in this review, attempts are made to understand their synergistic behavior and resulting performance. The three electrochemical energy storage systems and the type of electrode materials used for them have been studied here in this article and some aspects for example morphology, exterior area, temperature, and approaches have been observed to influence the activity of electrochemical methods. This review article evaluates and compiles reported data to present a significant and extensive summary of the state of the art. Full article

(This article belongs to the Special Issue Carbon-Based Polymer Nanocomposites for High-Performance Applications)

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20 pages, 2446 KiB

Open AccessEditor’s ChoiceReview

Emerging Developments in the Use of Electrospun Fibers and Membranes for Protective Clothing Applications

by Avinash Baji, Komal Agarwal and Sruthi Venugopal Oopath

Polymers 2020, 12(2), 492; https://doi.org/10.3390/polym12020492 - 24 Feb 2020

Cited by 80 | Viewed by 9526

Abstract

There has been increased interest to develop protective fabrics and clothing for protecting the wearer from hazards such as chemical, biological, heat, UV, pollutants etc. Protective fabrics have been conventionally developed using a wide variety of techniques. However, these conventional protective fabrics lack [...] Read more.

There has been increased interest to develop protective fabrics and clothing for protecting the wearer from hazards such as chemical, biological, heat, UV, pollutants etc. Protective fabrics have been conventionally developed using a wide variety of techniques. However, these conventional protective fabrics lack breathability. For example, conventional protective fabrics offer good protection against water but have limited ability in removing the water vapor and moisture. Fibers and membranes fabricated using electrospinning have demonstrated tremendous potential to develop protective fabrics and clothing. These fabrics based on electrospun fibers and membranes have the potential to provide thermal comfort to the wearer and protect the wearer from wide variety of environmental hazards. This review highlights the emerging applications of electrospinning for developing such breathable and protective fabrics. Full article

(This article belongs to the Special Issue Electrospun Nanofibers: Theory and Its Applications)

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10 pages, 2698 KiB

Open AccessEditor’s ChoiceArticle

High-Conductivity, Flexible and Transparent PEDOT:PSS Electrodes for High Performance Semi-Transparent Supercapacitors

by Jiaxing Song, Guoqiang Ma, Fei Qin, Lin Hu, Bangwu Luo, Tiefeng Liu, Xinxing Yin, Zhen Su, Zhaobing Zeng, Youyu Jiang, Guannan Wang and Zaifang Li

Polymers 2020, 12(2), 450; https://doi.org/10.3390/polym12020450 - 14 Feb 2020

Cited by 59 | Viewed by 6350

Abstract

Herein, we report a flexible high-conductivity transparent electrode (denoted as S-PH1000), based on conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and itsapplication to flexible semi-transparentsupercapacitors. A high conductivity of 2673 S/cm was achieved for the S-PH1000 electrode on flexible plastic substrates via a H₂ [...] Read more.

Herein, we report a flexible high-conductivity transparent electrode (denoted as S-PH1000), based on conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and itsapplication to flexible semi-transparentsupercapacitors. A high conductivity of 2673 S/cm was achieved for the S-PH1000 electrode on flexible plastic substrates via a H₂SO₄ treatment with an optimized concentration of 80 wt.%. This is among the top electrical conductivities of PEDOT:PSS films processed on flexible substrates. As for the electrochemical properties,a high specific capacitance of 161F/g was obtained from the S-PH1000 electrode at a current density of 1 A/g. Excitingly, a specific capacitance of 121 F/g was retained even when the current density increased to 100 A/g, which demonstrates the high-rate property of this electrode. Flexible semi-transparent supercapacitors based on these electrodes demonstrate high transparency, over 60%, at 550 nm. A high power density value, over 19,200 W/kg,and energy density, over 3.40 Wh/kg, was achieved. The semi-transparent flexible supercapacitor was successfully applied topower a light-emitting diode. Full article

(This article belongs to the Special Issue Polymers for Energy Storage and Conversion)

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22 pages, 6123 KiB

Open AccessEditor’s ChoiceArticle

Polyurethane-Based Composites: Effects of Antibacterial Fillers on the Physical-Mechanical Behavior of Thermoplastic Polyurethanes

by Maurizio Villani, Roberto Consonni, Maurizio Canetti, Federico Bertoglio, Stefano Iervese, Giovanna Bruni, Livia Visai, Salvatore Iannace and Fabio Bertini

Polymers 2020, 12(2), 362; https://doi.org/10.3390/polym12020362 - 6 Feb 2020

Cited by 32 | Viewed by 5091

Abstract

The challenge to manufacture medical devices with specific antibacterial functions, and the growing demand for systems able to limit bacterial resistance growth, necessitates the development of new technologies which can be easily produced at an industrial level. The object of this work was [...] Read more.

The challenge to manufacture medical devices with specific antibacterial functions, and the growing demand for systems able to limit bacterial resistance growth, necessitates the development of new technologies which can be easily produced at an industrial level. The object of this work was the study and the development of silver, titanium dioxide, and chitosan composites for the realization and/or implementation of biomedical devices. Thermoplastic elastomeric polyurethane was selected and used as matrix for the various antibacterial functions introduced during the processing phase (melt compounding). This strategy was employed to directly incorporate antimicrobial agents into the main constituent material of the devices themselves. With the exception of the composite filled with titanium dioxide, all of the other tested composites were shown to possess satisfactory mechanical properties. The best antibacterial effects were obtained with all the composites against Staphylococcus aureus: viability was efficiently inhibited by the prepared materials in four different bacterial culture concentrations. Full article

(This article belongs to the Special Issue Eurofillers Polymer Blends)

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15 pages, 2918 KiB

Open AccessEditor’s ChoiceArticle

Beeswax-Modified Textiles: Method of Preparation and Assessment of Antimicrobial Properties

by Justyna Szulc, Waldemar Machnowski, Stanisława Kowalska, Anita Jachowicz, Tomasz Ruman, Aleksandra Steglińska and Beata Gutarowska

Polymers 2020, 12(2), 344; https://doi.org/10.3390/polym12020344 - 5 Feb 2020

Cited by 23 | Viewed by 8807

Abstract

In this work, beeswax was used for the first time for finishing polyester/Cotton/Viscose blend fabric and polyester fabric. The aims of the study were: (1) to characterize the composition of beeswax (using Gas Chromatography Mass Spectrometry, GC-MS and ¹⁰⁹AgNPET laser desorption/ionization mass [...] Read more.

In this work, beeswax was used for the first time for finishing polyester/Cotton/Viscose blend fabric and polyester fabric. The aims of the study were: (1) to characterize the composition of beeswax (using Gas Chromatography Mass Spectrometry, GC-MS and ¹⁰⁹AgNPET laser desorption/ionization mass spectrometry (LDI MS); (2) to develop a laboratory method for applying beeswax; (3) to assess the antimicrobial activity of beeswax fabrics against bacteria and fungi (AATCC 100–2004 test); and (4) to assess the properties of textiles modified by beeswax. Beeswax was composed of fatty acids, monoacyl esters, glyceride esters and more complex lipids. The bioactivity of modified fabrics was from −0.09 to 1.55. The highest biocidal activity (>1) was obtained for both fabrics against A. niger mold. The beeswax modification process neither affected the morphological structure of the fibers (the wax evenly covered the surface of the fibers) nor their color. The only statistically significant changes observed were in the mechanical properties of the fabrics. The results obtained indicate that modification of fabrics with beeswax may endow them with biocidal properties against molds, which has practical applications, for example, for the prevention of skin mycoses in health and social care facilities. Full article

(This article belongs to the Special Issue Current Trends in Antimicrobial Polymeric Materials)

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28 pages, 2602 KiB

Open AccessEditor’s ChoiceReview

Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) as a Promising Polymer Material for Biomedical Applications: A Concise Review

by Muzamil Hussain, Rizwan Ali Naqvi, Naseem Abbas, Shahzad Masood Khan, Saad Nawaz, Arif Hussain, Nida Zahra and Muhammad Waqas Khalid

Polymers 2020, 12(2), 323; https://doi.org/10.3390/polym12020323 - 4 Feb 2020

Cited by 115 | Viewed by 21566

Abstract

Ultra-High Molecular Weight Polyethylene (UHMWPE) is used in biomedical applications due to its high wear-resistance, ductility, and biocompatibility. A great deal of research in recent decades has focused on further improving its mechanical and tribological performances in order to provide durable implants in [...] Read more.

Ultra-High Molecular Weight Polyethylene (UHMWPE) is used in biomedical applications due to its high wear-resistance, ductility, and biocompatibility. A great deal of research in recent decades has focused on further improving its mechanical and tribological performances in order to provide durable implants in patients. Several methods, including irradiation, surface modifications, and reinforcements have been employed to improve the tribological and mechanical performance of UHMWPE. The effect of these modifications on tribological and mechanical performance was discussed in this review. Full article

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

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15 pages, 2614 KiB

Open AccessEditor’s ChoiceArticle

Poly(3,4-ethylenedioxythiophene) Based Solid-State Polymer Supercapacitor with Ionic Liquid Gel Polymer Electrolyte

by Haiyan Du, Zemin Wu, Yuyu Xu, Shaoze Liu and Huimin Yang

Polymers 2020, 12(2), 297; https://doi.org/10.3390/polym12020297 - 2 Feb 2020

Cited by 29 | Viewed by 4948

Abstract

In this work, solid-state polymer supercapacitor (SSC) was assembled using poly(3,4-ethylenedioxythiophene/carbon paper (PEDOT/CP) as an electrode and ionic liquid (1-butyl-3-methylimidazole tetrafluoroborate)/polyvinyl alcohol/sulfuric acid (IL/PVA/H₂SO₄) as a gel polymer electrolyte (GPE). The GPE was treated through freezing–thawing (F/T) cycles to [...] Read more.

In this work, solid-state polymer supercapacitor (SSC) was assembled using poly(3,4-ethylenedioxythiophene/carbon paper (PEDOT/CP) as an electrode and ionic liquid (1-butyl-3-methylimidazole tetrafluoroborate)/polyvinyl alcohol/sulfuric acid (IL/PVA/H₂SO₄) as a gel polymer electrolyte (GPE). The GPE was treated through freezing–thawing (F/T) cycles to improve the electrochemical properties of PEDOT SSC. Cyclic voltammetry (CV), galvanostatic charge–discharge measurements (GCD) and electrochemical impedance spectroscopy (EIS) techniques and conductivity were carried out to study the electrochemical performance. The results showed that the SSC based on ionic liquid GPE (SSC-IL/PVA/H₂SO₄) has a higher specific capacitance (with the value of 86.81 F/g at 1 mA/cm²) than the SSC-PVA/H₂SO₄.The number of F/T cycles has a great effect on the electrochemical performance of the device. The energy density of the SSC treated with 3 F/T cycles was significantly improved, reaching 176.90 Wh/kg. Compared with the traditional electrolytes, IL GPE has the advantages of high ionic conductivity, less volatility, non-flammability and wider potential window. Moreover, the IL GPE has excellent elastic recovery and self-healing performance, leading to its great potential applications in flexible or smart energy storage equipment. Full article

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21 pages, 4046 KiB

Open AccessEditor’s ChoiceReview

The Importance of Poly(ethylene glycol) Alternatives for Overcoming PEG Immunogenicity in Drug Delivery and Bioconjugation

by Thai Thanh Hoang Thi, Emily H. Pilkington, Dai Hai Nguyen, Jung Seok Lee, Ki Dong Park and Nghia P. Truong

Polymers 2020, 12(2), 298; https://doi.org/10.3390/polym12020298 - 2 Feb 2020

Cited by 394 | Viewed by 33057

Abstract

Poly(ethylene glycol) (PEG) is widely used as a gold standard in bioconjugation and nanomedicine to prolong blood circulation time and improve drug efficacy. The conjugation of PEG to proteins, peptides, oligonucleotides (DNA, small interfering RNA (siRNA), microRNA (miRNA)) and nanoparticles is a well-established [...] Read more.

Poly(ethylene glycol) (PEG) is widely used as a gold standard in bioconjugation and nanomedicine to prolong blood circulation time and improve drug efficacy. The conjugation of PEG to proteins, peptides, oligonucleotides (DNA, small interfering RNA (siRNA), microRNA (miRNA)) and nanoparticles is a well-established technique known as PEGylation, with PEGylated products have been using in clinics for the last few decades. However, it is increasingly recognized that treating patients with PEGylated drugs can lead to the formation of antibodies that specifically recognize and bind to PEG (i.e., anti-PEG antibodies). Anti-PEG antibodies are also found in patients who have never been treated with PEGylated drugs but have consumed products containing PEG. Consequently, treating patients who have acquired anti-PEG antibodies with PEGylated drugs results in accelerated blood clearance, low drug efficacy, hypersensitivity, and, in some cases, life-threatening side effects. In this succinct review, we collate recent literature to draw the attention of polymer chemists to the issue of PEG immunogenicity in drug delivery and bioconjugation, thereby highlighting the importance of developing alternative polymers to replace PEG. Several promising yet imperfect alternatives to PEG are also discussed. To achieve asatisfactory alternative, further joint efforts of polymer chemists and scientists in related fields are urgently needed to design, synthesize and evaluate new alternatives to PEG. Full article

(This article belongs to the Special Issue Biopolymers for Medical Applications)

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14 pages, 5322 KiB

Open AccessEditor’s ChoiceArticle

Degradable Controlled Release Fertilizer Composite Prepared via Extrusion: Fabrication, Characterization, and Release Mechanisms

by Siwen Bi, Vincenzo Barinelli and Margaret J. Sobkowicz

Polymers 2020, 12(2), 301; https://doi.org/10.3390/polym12020301 - 2 Feb 2020

Cited by 44 | Viewed by 7234

Abstract

In this work, biodegradable polymers were melt compounded with urea phosphate to fabricate “smart fertilizers” for sustainable agriculture. Urea phosphate (UP) is typically applied as a water-soluble fertilizer to treat phosphorus deficiency in high pH soils. Due to the low diffusion rate of [...] Read more.

In this work, biodegradable polymers were melt compounded with urea phosphate to fabricate “smart fertilizers” for sustainable agriculture. Urea phosphate (UP) is typically applied as a water-soluble fertilizer to treat phosphorus deficiency in high pH soils. Due to the low diffusion rate of phosphate through slow-release fertilizer coatings, phosphate supply has been considered the “bottleneck” for nitrogen–phosphorous–potassium (NPK) nutrients supply. We study the influence of polymer matrix structure on release kinetics in deionized water using novel polyesters including poly (hexamethylene succinate) (PHS), poly (30% butylene succinate-co-70% hexamethylene succinate) (PBHS 30/70), and PBHS 70/30. Melt processed composites of UP and polyester were analyzed to determine UP loading efficiency and dispersion and distribution of the salt in the polymer matrix. A combined empirical model involving diffusion and erosion mechanisms was found have a good agreement with the experimental release curve. This work provides a solution for environmentally friendly controlled release phosphate fertilizer with good release performance using bio-based and biodegradable polymers. Full article

(This article belongs to the Special Issue Eco-Friendly Polymeric Materials: A New Chance for Our Future)

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10 pages, 1471 KiB

Open AccessEditor’s ChoiceArticle

Water Vapor Permeability through Porous Polymeric Membranes with Various Hydrophilicity as Synthetic and Natural Barriers

by Chalykh Anatoly, Zolotarev Pavel, Chalykh Tatiana, Rubtsov Alexei and Zolotova Svetlana

Polymers 2020, 12(2), 282; https://doi.org/10.3390/polym12020282 - 1 Feb 2020

Cited by 12 | Viewed by 4411

Abstract

The article is devoted to the analysis of sorption kinetics, permeability, and diffusion of water vapor in porous polymeric membranes of different hydrophilicities and through-porosities. The water transport measurement with a constant gradient of partial pressure allows the authors to obtain reliable characteristics [...] Read more.

The article is devoted to the analysis of sorption kinetics, permeability, and diffusion of water vapor in porous polymeric membranes of different hydrophilicities and through-porosities. The water transport measurement with a constant gradient of partial pressure allows the authors to obtain reliable characteristics for porous membranes, films, artificial leathers, and fabrics of various chemical natures (synthetic and bio-based) and phase structures. All the kinetic permeability curves were determined and effective diffusion coefficients, as well as their apparent activation energies, were calculated at the stationary and non-stationary stages of the mass transfer. The relationship between the sorption–diffusion characteristics of the polymer barriers and their vapor permeability is traced. Within the framework of a Zolotarev–Dubinin dual dispersive model, an analytical equation is obtained that relates permeability to diffusion coefficients of water vapor in the pore volume, polymer skeleton material using such characteristics as porosity and the solubility coefficient. It is proposed to use this equation to predict the sorption properties for barrier and porous materials of complex architecture specifically in food packaging. Full article

(This article belongs to the Special Issue Bio-Based and Biodegradable Plastics: From Passive Barrier to Active Packaging Behavior)

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15 pages, 3369 KiB

Open AccessEditor’s ChoiceArticle

Thermomechanical and Morphological Properties of Poly(ethylene terephthalate)/Anhydrous Calcium Terephthalate Nanocomposites

by Franco Dominici, Fabrizio Sarasini, Francesca Luzi, Luigi Torre and Debora Puglia

Polymers 2020, 12(2), 276; https://doi.org/10.3390/polym12020276 - 30 Jan 2020

Cited by 15 | Viewed by 3778

Abstract

Calcium terephthalate anhydrous salts (CATAS), synthetized by reaction of terephthalic acid with metal (Ca) oxide were incorporated at different weight contents (0–30 wt. %) in recycled Poly(ethylene terephthalate) (rPET) by melt processing. Their structure, morphology, thermal and mechanical properties (tensile and flexural behavior) [...] Read more.

Calcium terephthalate anhydrous salts (CATAS), synthetized by reaction of terephthalic acid with metal (Ca) oxide were incorporated at different weight contents (0–30 wt. %) in recycled Poly(ethylene terephthalate) (rPET) by melt processing. Their structure, morphology, thermal and mechanical properties (tensile and flexural behavior) were investigated. Results of tensile strength of the different formulations showed that when the CATAS content increased from 0.1 to 0.4 wt. %, tangible changes were observed (variation of tensile strength from 65.5 to 69.4 MPa, increasing value for E from 2887 up to 3131 MPa, respectively for neat rPET and rPET_0.4CATAS). A threshold weight amount (0.4 wt. %) of CATAS was also found, by formation at low loading, of a rigid amorphous fraction at the rPET/CATAS interface, due to the aromatic interactions (π−π conjugation) between the matrix and the filler. Above the threshold, a restriction of rPET/CATAS molecular chains mobility was detected, due to the formation of hybrid mechanical percolation networks. Additionally, enhanced thermal stability of CATAS filled rPET was registered at high content (T_max shift from 426 to 441 °C, respectively, for rPET and rPET_30CATAS), essentially due to chemical compatibility between terephthalate salts and polymer molecules, rich in stable aromatic rings. The singularity of a cold crystallization event, identified at the same loading level, confirmed the presence of an equilibrium state between nucleation and blocking effect of amorphous phase, basically related to the characteristic common terephthalate structure of synthetized Ca–Metal Organic Framework and the rPET matrix. Full article

(This article belongs to the Special Issue Advances in Manufacturing and Characterization of Functional Polyesters)

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29 pages, 1252 KiB

Open AccessEditor’s ChoiceReview

A Review on the Partial and Complete Dissolution and Fractionation of Wood and Lignocelluloses Using Imidazolium Ionic Liquids

by Hatem Abushammala and Jia Mao

Polymers 2020, 12(1), 195; https://doi.org/10.3390/polym12010195 - 11 Jan 2020

Cited by 79 | Viewed by 6686

Abstract

Ionic liquids have shown great potential in the last two decades as solvents, catalysts, reaction media, additives, lubricants, and in many applications such as electrochemical systems, hydrometallurgy, chromatography, CO₂ capture, etc. As solvents, the unlimited combinations of cations and anions have given [...] Read more.

Ionic liquids have shown great potential in the last two decades as solvents, catalysts, reaction media, additives, lubricants, and in many applications such as electrochemical systems, hydrometallurgy, chromatography, CO₂ capture, etc. As solvents, the unlimited combinations of cations and anions have given ionic liquids a remarkably wide range of solvation power covering a variety of organic and inorganic materials. Ionic liquids are also considered “green” solvents due to their negligible vapor pressure, which means no emission of volatile organic compounds. Due to these interesting properties, ionic liquids have been explored as promising solvents for the dissolution and fractionation of wood and cellulose for biofuel production, pulping, extraction of nanocellulose, and for processing all-wood and all-cellulose composites. This review describes, at first, the potential of ionic liquids and the impact of the cation/anion combination on their physiochemical properties and on their solvation power and selectivity to wood polymers. It also elaborates on how the dissolution conditions influence these parameters. It then discusses the different approaches, which are followed for the homogeneous and heterogeneous dissolution and fractionation of wood and cellulose using ionic liquids and categorize them based on the target application. It finally highlights the challenges of using ionic liquids for wood and cellulose dissolution and processing, including side reactions, viscosity, recyclability, and price. Full article

(This article belongs to the Special Issue Bio-Based Polymers for Engineered Green Materials)

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38 pages, 4008 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in Natural Gum-Based Biomaterials for Tissue Engineering and Regenerative Medicine: A Review

by Reza Mohammadinejad, Anuj Kumar, Marziyeh Ranjbar-Mohammadi, Milad Ashrafizadeh, Sung Soo Han, Gilson Khang and Ziba Roveimiab

Polymers 2020, 12(1), 176; https://doi.org/10.3390/polym12010176 - 9 Jan 2020

Cited by 134 | Viewed by 13472

Abstract

The engineering of tissues under a three-dimensional (3D) microenvironment is a great challenge and needs a suitable supporting biomaterial-based scaffold that may facilitate cell attachment, spreading, proliferation, migration, and differentiation for proper tissue regeneration or organ reconstruction. Polysaccharides as natural polymers promise great [...] Read more.

The engineering of tissues under a three-dimensional (3D) microenvironment is a great challenge and needs a suitable supporting biomaterial-based scaffold that may facilitate cell attachment, spreading, proliferation, migration, and differentiation for proper tissue regeneration or organ reconstruction. Polysaccharides as natural polymers promise great potential in the preparation of a three-dimensional artificial extracellular matrix (ECM) (i.e., hydrogel) via various processing methods and conditions. Natural polymers, especially gums, based upon hydrogel systems, provide similarities largely with the native ECM and excellent biological response. Here, we review the origin and physico-chemical characteristics of potentially used natural gums. In addition, various forms of scaffolds (e.g., nanofibrous, 3D printed-constructs) based on gums and their efficacy in 3D cell culture and various tissue regenerations such as bone, osteoarthritis and cartilage, skin/wound, retinal, neural, and other tissues are discussed. Finally, the advantages and limitations of natural gums are precisely described for future perspectives in tissue engineering and regenerative medicine in the concluding remarks. Full article

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45 pages, 23366 KiB

Open AccessEditor’s ChoiceReview

Machine-Learning-Assisted De Novo Design of Organic Molecules and Polymers: Opportunities and Challenges

by Guang Chen, Zhiqiang Shen, Akshay Iyer, Umar Farooq Ghumman, Shan Tang, Jinbo Bi, Wei Chen and Ying Li

Polymers 2020, 12(1), 163; https://doi.org/10.3390/polym12010163 - 8 Jan 2020

Cited by 106 | Viewed by 20099

Abstract

Organic molecules and polymers have a broad range of applications in biomedical, chemical, and materials science fields. Traditional design approaches for organic molecules and polymers are mainly experimentally-driven, guided by experience, intuition, and conceptual insights. Though they have been successfully applied to discover [...] Read more.

Organic molecules and polymers have a broad range of applications in biomedical, chemical, and materials science fields. Traditional design approaches for organic molecules and polymers are mainly experimentally-driven, guided by experience, intuition, and conceptual insights. Though they have been successfully applied to discover many important materials, these methods are facing significant challenges due to the tremendous demand of new materials and vast design space of organic molecules and polymers. Accelerated and inverse materials design is an ideal solution to these challenges. With advancements in high-throughput computation, artificial intelligence (especially machining learning, ML), and the growth of materials databases, ML-assisted materials design is emerging as a promising tool to flourish breakthroughs in many areas of materials science and engineering. To date, using ML-assisted approaches, the quantitative structure property/activity relation for material property prediction can be established more accurately and efficiently. In addition, materials design can be revolutionized and accelerated much faster than ever, through ML-enabled molecular generation and inverse molecular design. In this perspective, we review the recent progresses in ML-guided design of organic molecules and polymers, highlight several successful examples, and examine future opportunities in biomedical, chemical, and materials science fields. We further discuss the relevant challenges to solve in order to fully realize the potential of ML-assisted materials design for organic molecules and polymers. In particular, this study summarizes publicly available materials databases, feature representations for organic molecules, open-source tools for feature generation, methods for molecular generation, and ML models for prediction of material properties, which serve as a tutorial for researchers who have little experience with ML before and want to apply ML for various applications. Last but not least, it draws insights into the current limitations of ML-guided design of organic molecules and polymers. We anticipate that ML-assisted materials design for organic molecules and polymers will be the driving force in the near future, to meet the tremendous demand of new materials with tailored properties in different fields. Full article

(This article belongs to the Special Issue Artificial Intelligence in Polymer Science and Chemistry)

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28 pages, 4332 KiB

Open AccessEditor’s ChoiceArticle

New Monomer Based on Eugenol Methacrylate, Synthesis, Polymerization and Copolymerization with Methyl Methacrylate–Characterization and Thermal Properties

by Abdel-Basit Al-Odayni, Waseem Sharaf Saeed, Ahmed Yacine Badjah Hadj Ahmed, Ali Alrahlah, Abdullah Al-Kahtani and Taieb Aouak

Polymers 2020, 12(1), 160; https://doi.org/10.3390/polym12010160 - 8 Jan 2020

Cited by 26 | Viewed by 5786

Abstract

Poly(eugenyl-2-hydroxypropyl methacrylate) (PEUGMA), poly(methyl methacrylate) (PMMA) and poly(eugenyl-2-hydroxypropyl methacrylate-co-methyl methacrylate) (PEUGMA-co-MMA) were synthesized by a free radical polymerization route in the presence of azobisisobutyronitrile. EUGMA was synthesized by etherification of the eugenol phenolic hydroxyl group with glycidyl methacrylate. Polymers and copolymers were characterized [...] Read more.

Poly(eugenyl-2-hydroxypropyl methacrylate) (PEUGMA), poly(methyl methacrylate) (PMMA) and poly(eugenyl-2-hydroxypropyl methacrylate-co-methyl methacrylate) (PEUGMA-co-MMA) were synthesized by a free radical polymerization route in the presence of azobisisobutyronitrile. EUGMA was synthesized by etherification of the eugenol phenolic hydroxyl group with glycidyl methacrylate. Polymers and copolymers were characterized using size exclusion chromatography, Fourier transform infrared, and nuclear magnetic resonance. The effects of the encumbering substituent on the thermal behavior of the polymers and copolymers were studied by differential scanning calorimetry, thermogravimetry (TG) and direct analysis, using real-time, time-of-flight mass spectroscopy (DART-ToF-MS) methods. The results obtained revealed that for PEUGMA, the average molecular weight was 1.08 × 10⁵, and increased slowly with the decrease in the EUGMA content in the copolymer. The order of the distribution of dyads comonomer units in the copolymer chains estimated by the Igarashi method based on the reactivity ratio does reveal a random distribution with a tendency toward alternation. The glass transition temperature of PEUGMA (46 °C) increased with the MMA content in the copolymer, and those of the copolymer fit well with the Johnston’s linearized expression. The TG analysis of pure PEUGMA revealed a significantly high thermal stability compared to that of PMMA. During its degradation, the preliminary decomposition was at 340 °C, and decreased as the MMA units increased in the copolymer. The DART-ToF-MS analysis revealed that the isothermal decomposition of PEUGMA led to a regeneration of raw materials such as EUGMA, GMA and EUG, in which the maximum amount was achieved at 450 °C. Full article

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25 pages, 2958 KiB

Open AccessEditor’s ChoiceReview

Piezoelectric Scaffolds as Smart Materials for Neural Tissue Engineering

by Angelika Zaszczynska, Paweł Sajkiewicz and Arkadiusz Gradys

Polymers 2020, 12(1), 161; https://doi.org/10.3390/polym12010161 - 8 Jan 2020

Cited by 97 | Viewed by 9541

Abstract

Injury to the central or peripheral nervous systems leads to the loss of cognitive and/or sensorimotor capabilities, which still lacks an effective treatment. Tissue engineering in the post-injury brain represents a promising option for cellular replacement and rescue, providing a cell scaffold for [...] Read more.

Injury to the central or peripheral nervous systems leads to the loss of cognitive and/or sensorimotor capabilities, which still lacks an effective treatment. Tissue engineering in the post-injury brain represents a promising option for cellular replacement and rescue, providing a cell scaffold for either transplanted or resident cells. Tissue engineering relies on scaffolds for supporting cell differentiation and growth with recent emphasis on stimuli responsive scaffolds, sometimes called smart scaffolds. One of the representatives of this material group is piezoelectric scaffolds, being able to generate electrical charges under mechanical stimulation, which creates a real prospect for using such scaffolds in non-invasive therapy of neural tissue. This paper summarizes the recent knowledge on piezoelectric materials used for tissue engineering, especially neural tissue engineering. The most used materials for tissue engineering strategies are reported together with the main achievements, challenges, and future needs for research and actual therapies. This review provides thus a compilation of the most relevant results and strategies and serves as a starting point for novel research pathways in the most relevant and challenging open questions. Full article

(This article belongs to the Special Issue Biodegradable Polymer Scaffolds for Tissue Engineering)

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19 pages, 2424 KiB

Open AccessEditor’s ChoiceReview

Research Progress on Polymer Solar Cells Based on PEDOT:PSS Electrodes

by Lin Hu, Jiaxing Song, Xinxing Yin, Zhen Su and Zaifang Li

Polymers 2020, 12(1), 145; https://doi.org/10.3390/polym12010145 - 7 Jan 2020

Cited by 87 | Viewed by 13628

Abstract

Solution-processed polymer solar cells (PSCs) have attracted dramatically increasing attention over the past few decades owing to their advantages of low cost, solution processability, light weight, and excellent flexibility. Recent progress in materials synthesis and devices engineering has boosted the power conversion efficiency [...] Read more.

Solution-processed polymer solar cells (PSCs) have attracted dramatically increasing attention over the past few decades owing to their advantages of low cost, solution processability, light weight, and excellent flexibility. Recent progress in materials synthesis and devices engineering has boosted the power conversion efficiency (PCE) of single-junction PSCs over 17%. As an emerging technology, it is still a challenge to prepare solution-processed flexible electrodes for attractive flexible PSCs. Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is one of the most promising candidates for electrodes due to its high conductivity (>4000 S/cm), excellent transmittance (>90%), intrinsically high work function (W_F > 5.0 eV), and aqueous solution processability. To date, a great number of single-junction PSCs based on PEDOT:PSS electrodes have realized a PCE over 12%. In this review, we introduce the current research on the conductive complex PEDOT:PSS as well as trace the development of PEDOT:PSS used in electrodes for high performance PSCs and perovskite solar cells. We also discuss and comment on the aspects of conductivity, transmittance, work-function adjustment, film preparing methods, and device fabrications. A perspective on the challenges and future directions in this field is be offered finally. Full article

(This article belongs to the Special Issue Polymer-Based Solar Cells)

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27 pages, 2707 KiB

Open AccessEditor’s ChoiceReview

A Comprehensive Review on Water Diffusion in Polymers Focusing on the Polymer–Metal Interface Combination

by Chao Yang, Xiao Xing, Zili Li and Shouxin Zhang

Polymers 2020, 12(1), 138; https://doi.org/10.3390/polym12010138 - 6 Jan 2020

Cited by 73 | Viewed by 8777

Abstract

Water diffusion in polymers is relevant to a broad range of physicochemical phenomena and technological processes. Although many fields contributed to rapid progress in the fundamental knowledge of water–polymer interactions, detailed understandings come mainly from interpreting numerous experiments. These studies showed that a [...] Read more.

Water diffusion in polymers is relevant to a broad range of physicochemical phenomena and technological processes. Although many fields contributed to rapid progress in the fundamental knowledge of water–polymer interactions, detailed understandings come mainly from interpreting numerous experiments. These studies showed that a remarkably rich variety of diffusion forms between water and even seemingly simple polymers. In this review, focusing on the gravimetric and capacitance method, we discuss contradictions and problems existing for water diffusion in polymers in detail from perspectives of experiments and models, focusing on the analysis of error derived from widely used methods, especially for the Brasher–Kingsbury equation. We also provide a perspective on outstanding problems, challenges, and open questions, including water clusters, relaxation, and electrochemical reactions at the metal/polymer interface, as well as expanding the theoretical prospective. Full article

(This article belongs to the Special Issue Polymer Structures in Solution)

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18 pages, 2061 KiB

Open AccessEditor’s ChoiceReview

Degradation of Plastics under Anaerobic Conditions: A Short Review

by Xochitl Quecholac-Piña, María del Consuelo Hernández-Berriel, María del Consuelo Mañón-Salas, Rosa María Espinosa-Valdemar and Alethia Vázquez-Morillas

Polymers 2020, 12(1), 109; https://doi.org/10.3390/polym12010109 - 5 Jan 2020

Cited by 84 | Viewed by 17890

Abstract

Plastic waste is an issue of global concern because of the environmental impact of its accumulation in waste management systems and ecosystems. Biodegradability was proposed as a solution to overcome this problem; however, most biodegradable plastics were designed to degrade under aerobic conditions, [...] Read more.

Plastic waste is an issue of global concern because of the environmental impact of its accumulation in waste management systems and ecosystems. Biodegradability was proposed as a solution to overcome this problem; however, most biodegradable plastics were designed to degrade under aerobic conditions, ideally fulfilled in a composting plant. These new plastics could arrive to anaerobic environments, purposely or frequently, because of their mismanagement at the end of their useful life. This review analyzes the behavior of biodegradable and conventional plastics under anaerobic conditions, specifically in anaerobic digestion systems and landfills. A review was performed in order to identify: (a) the environmental conditions found in anaerobic digestion processes and landfills, as well as the mechanisms for degradation in those environments; (b) the experimental methods used for the assessment of biodegradation in anaerobic conditions; and (c) the extent of the biodegradation process for different plastics. Results show a remarkable variability of the biodegradation rate depending on the type of plastic and experimental conditions, with clearly better performance in anaerobic digestion systems, where temperature, water content, and inoculum are strictly controlled. The majority of the studied plastics showed that thermophilic conditions increase degradation. It should not be assumed that plastics designed to be degraded aerobically will biodegrade under anaerobic conditions, and an exact match must be done between the specific plastics and the end of life options that they will face. Full article

(This article belongs to the Special Issue Recent Advances in Bioplastics II)

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24 pages, 2136 KiB

Open AccessEditor’s ChoiceReview

Challenges with Verifying Microbial Degradation of Polyethylene

by Zahra Montazer, Mohammad B. Habibi Najafi and David B. Levin

Polymers 2020, 12(1), 123; https://doi.org/10.3390/polym12010123 - 5 Jan 2020

Cited by 192 | Viewed by 21990

Abstract

Polyethylene (PE) is the most abundant synthetic, petroleum-based plastic materials produced globally, and one of the most resistant to biodegradation, resulting in massive accumulation in the environment. Although the microbial degradation of polyethylene has been reported, complete biodegradation of polyethylene has not been [...] Read more.

Polyethylene (PE) is the most abundant synthetic, petroleum-based plastic materials produced globally, and one of the most resistant to biodegradation, resulting in massive accumulation in the environment. Although the microbial degradation of polyethylene has been reported, complete biodegradation of polyethylene has not been achieved, and rapid degradation of polyethylene under ambient conditions in the environment is still not feasible. Experiments reported in the literature suffer from a number of limitations, and conclusive evidence for the complete biodegradation of polyethylene by microorganisms has been elusive. These limitations include the lack of a working definition for the biodegradation of polyethylene that can lead to testable hypotheses, a non-uniform description of experimental conditions used, and variations in the type(s) of polyethylene used, leading to a profound limitation in our understanding of the processes and mechanisms involved in the microbial degradation of polyethylene. The objective of this review is to outline the challenges in polyethylene degradation experiments and clarify the parameters required to achieve polyethylene biodegradation. This review emphasizes the necessity of developing a biochemically-based definition for the biodegradation of polyethylene (and other synthetic plastics) to simplify the comparison of results of experiments focused for the microbial degradation of polyethylene. Full article

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17 pages, 3564 KiB

Open AccessEditor’s ChoiceArticle

Study on the Moisture Absorption and Thermal Properties of Hygroscopic Exothermic Fibers and Related Interactions with Water Molecules

by Yi Cui, Shuyi Gao, Ruiyun Zhang, Longdi Cheng and Jianyong Yu

Polymers 2020, 12(1), 98; https://doi.org/10.3390/polym12010098 - 4 Jan 2020

Cited by 31 | Viewed by 4935

Abstract

The aim of this paper is to study the hygroscopic behavior of hygroscopic exothermic fiber-based materials and to obtain a better understanding of the thermal performance of these fibers during the moisture absorption process. The temperature distribution of different kinds of hygroscopic exothermic [...] Read more.

The aim of this paper is to study the hygroscopic behavior of hygroscopic exothermic fiber-based materials and to obtain a better understanding of the thermal performance of these fibers during the moisture absorption process. The temperature distribution of different kinds of hygroscopic exothermic fibers in the process of moisture absorption, observed by infrared camera, demonstrated two types of heating performance of these fibers, which might be related to its hygroscopic behavior. Based on the sorption isotherms, a Guggenheim-Anderson-de Boer (GAB) multi-layer adsorption model was selected as the optimal moisture absorption fitting model to describe the moisture absorption process of these fibers, which illustrated that water sorption capacity and the water–fiber/water–water interaction had a significant influence on its heating performance. The net isosteric heats of sorption decreased with an increase of moisture content, which further explained the main factor affecting the heat dissipation of fibers under different moisture contents. The state of adsorbed water and water vapor interaction on the fiber surface were studied by simultaneous thermal analysis (TGA-DSC) measurement. The percentage of bound and unbound water formation at low and high humidity had a profound effect on the thermal performance of fibers. It can therefore be concluded that the content of tightly bound water a strong water–fiber interaction was the main factor affecting the heating performance of fibers at low moisture content, and the content of loosely bound water reflected that water sorption capacity was the main factor affecting the heating performance of fibers at high moisture content. This was further proven by the heat of desorption. Full article

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23 pages, 4287 KiB

Open AccessEditor’s ChoiceReview

Lignin-Based Hydrogels: Synthesis and Applications

by Diana Rico-García, Leire Ruiz-Rubio, Leyre Pérez-Alvarez, Saira L. Hernández-Olmos, Guillermo L. Guerrero-Ramírez and José Luis Vilas-Vilela

Polymers 2020, 12(1), 81; https://doi.org/10.3390/polym12010081 - 3 Jan 2020

Cited by 133 | Viewed by 15876

Abstract

Polymers obtained from biomass are an interesting alternative to petro-based polymers due to their low cost of production, biocompatibility, and biodegradability. This is the case of lignin, which is the second most abundant biopolymer in plants. As a consequence, the exploitation of lignin [...] Read more.

Polymers obtained from biomass are an interesting alternative to petro-based polymers due to their low cost of production, biocompatibility, and biodegradability. This is the case of lignin, which is the second most abundant biopolymer in plants. As a consequence, the exploitation of lignin for the production of new materials with improved properties is currently considered as one of the main challenging issues, especially for the paper industry. Regarding its chemical structure, lignin is a crosslinked polymer that contains many functional hydrophilic and active groups, such as hydroxyls, carbonyls and methoxyls, which provides a great potential to be employed in the synthesis of biodegradable hydrogels, materials that are recognized for their interesting applicability in biomedicine, soil and water treatment, and agriculture, among others. This work describes the main methods for the preparation of lignin-based hydrogels reported in the last years, based on the chemical and/or physical interaction with polymers widely used in hydrogels formulations. Furthermore, herein are also reviewed the current applications of lignin hydrogels as stimuli-responsive materials, flexible supercapacitors, and wearable electronics for biomedical and water remediation applications. Full article

(This article belongs to the Special Issue Properties, Applications and Perspectives of Lignin)

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11 pages, 3113 KiB

Open AccessEditor’s ChoiceArticle

Modification of Renewable Cardanol onto Carbon Fiber for the Improved Interfacial Properties of Advanced Polymer Composites

by Yawen Zheng, Lei Chen, Xiaoyun Wang and Guangshun Wu

Polymers 2020, 12(1), 45; https://doi.org/10.3390/polym12010045 - 28 Dec 2019

Cited by 100 | Viewed by 5947

Abstract

A facile in situ polymerization was developed for grafting renewable cardanol onto the carbon fiber (CF) surfaces to strengthen the fiber–matrix interface. CFs were chemically modified with hydroxyl groups by using an aryl diazonium reaction, and then copolymerized in situ with hexachlorocyclotriphosphazene (HCCP) [...] Read more.

A facile in situ polymerization was developed for grafting renewable cardanol onto the carbon fiber (CF) surfaces to strengthen the fiber–matrix interface. CFs were chemically modified with hydroxyl groups by using an aryl diazonium reaction, and then copolymerized in situ with hexachlorocyclotriphosphazene (HCCP) and cardanol to build cardanol-modified fibers (CF-cardanol). The cardanol molecules were successfully introduced, as confirmed using Raman spectra and X-ray photoelectron spectroscopy (XPS); the cardanol molecules were found to increase the surface roughness, energy, interfacial wettability, and activity with the matrix resin. As a result, the interlaminar shear strength (ILSS) of CF-cardanol composites increased from 48.2 to 68.13 MPa. In addition, the anti-hydrothermal ageing properties of the modified composites were significantly increased. The reinforcing mechanisms of the fiber–matrix interface were also studied. Full article

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32 pages, 1569 KiB

Open AccessEditor’s ChoiceReview

Application of Protein-Based Films and Coatings for Food Packaging: A Review

by Hongbo Chen, Jingjing Wang, Yaohua Cheng, Chuansheng Wang, Haichao Liu, Huiguang Bian, Yiren Pan, Jingyao Sun and Wenwen Han

Polymers 2019, 11(12), 2039; https://doi.org/10.3390/polym11122039 - 9 Dec 2019

Cited by 270 | Viewed by 16649

Abstract

As the IV generation of packaging, biopolymers, with the advantages of biodegradability, process ability, combination possibilities and no pollution to food, have become the leading food packaging materials. Biopolymers can be directly extracted from biomass, synthesized from bioderived monomers and produced directly by [...] Read more.

As the IV generation of packaging, biopolymers, with the advantages of biodegradability, process ability, combination possibilities and no pollution to food, have become the leading food packaging materials. Biopolymers can be directly extracted from biomass, synthesized from bioderived monomers and produced directly by microorganisms which are all abundant and renewable. The raw materials used to produce biopolymers are low-cost, some even coming from agrion dustrial waste. This review summarized the advances in protein-based films and coatings for food packaging. The materials studied to develop protein-based packaging films and coatings can be divided into two classes: plant proteins and animal proteins. Parts of proteins are referred in this review, including plant proteins i.e., gluten, soy proteins and zein, and animal proteins i.e., casein, whey and gelatin. Films and coatings based on these proteins have excellent gas barrier properties and satisfactory mechanical properties. However, the hydrophilicity of proteins makes the protein-based films present poor water barrier characteristics. The application of plasticizers and the corresponding post-treatments can make the properties of the protein-based films and coatings improved. The addition of active compounds into protein-based films can effectively inhibit or delay the growth of microorganisms and the oxidation of lipids. The review also summarized the research about the storage requirements of various foods that can provide corresponding guidance for the preparation of food packaging materials. Numerous application examples of protein-based films and coatings in food packaging also confirm their important role in food packaging materials. Full article

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45 pages, 5672 KiB

Open AccessEditor’s ChoiceReview

Core–Shell Fibers: Design, Roles, and Controllable Release Strategies in Tissue Engineering and Drug Delivery

by Muhammad Faiq Abdullah, Tamrin Nuge, Andri Andriyana, Bee Chin Ang and Farina Muhamad

Polymers 2019, 11(12), 2008; https://doi.org/10.3390/polym11122008 - 4 Dec 2019

Cited by 77 | Viewed by 10141

Abstract

The key attributes of core–shell fibers are their ability to preserve bioactivity of incorporated-sensitive biomolecules (such as drug, protein, and growth factor) and subsequently control biomolecule release to the targeted microenvironments to achieve therapeutic effects. Such qualities are highly favorable for tissue engineering [...] Read more.

The key attributes of core–shell fibers are their ability to preserve bioactivity of incorporated-sensitive biomolecules (such as drug, protein, and growth factor) and subsequently control biomolecule release to the targeted microenvironments to achieve therapeutic effects. Such qualities are highly favorable for tissue engineering and drug delivery, and these features are not able to be offered by monolithic fibers. In this review, we begin with an overview on design requirement of core–shell fibers, followed by the summary of recent preparation methods of core–shell fibers, with focus on electrospinning-based techniques and other newly discovered fabrication approaches. We then highlight the importance and roles of core–shell fibers in tissue engineering and drug delivery, accompanied by thorough discussion on controllable release strategies of the incorporated bioactive molecules from the fibers. Ultimately, we touch on core–shell fibers-related challenges and offer perspectives on their future direction towards clinical applications. Full article

(This article belongs to the Special Issue Advances in Polymer Nanofibers)

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25 pages, 2076 KiB

Open AccessEditor’s ChoiceReview

Silk Fibroin-Based Biomaterials for Biomedical Applications: A Review

by Thang Phan Nguyen, Quang Vinh Nguyen, Van-Huy Nguyen, Thu-Ha Le, Vu Quynh Nga Huynh, Dai-Viet N. Vo, Quang Thang Trinh, Soo Young Kim and Quyet Van Le

Polymers 2019, 11(12), 1933; https://doi.org/10.3390/polym11121933 - 24 Nov 2019

Cited by 292 | Viewed by 20870

Abstract

Since it was first discovered, thousands of years ago, silkworm silk has been known to be an abundant biopolymer with a vast range of attractive properties. The utilization of silk fibroin (SF), the main protein of silkworm silk, has not been limited to [...] Read more.

Since it was first discovered, thousands of years ago, silkworm silk has been known to be an abundant biopolymer with a vast range of attractive properties. The utilization of silk fibroin (SF), the main protein of silkworm silk, has not been limited to the textile industry but has been further extended to various high-tech application areas, including biomaterials for drug delivery systems and tissue engineering. The outstanding mechanical properties of SF, including its facile processability, superior biocompatibility, controllable biodegradation, and versatile functionalization have allowed its use for innovative applications. In this review, we describe the structure, composition, general properties, and structure-properties relationship of SF. In addition, the methods used for the fabrication and modification of various materials are briefly addressed. Lastly, recent applications of SF-based materials for small molecule drug delivery, biological drug delivery, gene therapy, wound healing, and bone regeneration are reviewed and our perspectives on future development of these favorable materials are also shared. Full article

(This article belongs to the Section Biomacromolecules, Biobased and Biodegradable Polymers)

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17 pages, 4848 KiB

Open AccessEditor’s ChoiceArticle

Development of Coffee Biochar Filler for the Production of Electrical Conductive Reinforced Plastic

by Mauro Giorcelli and Mattia Bartoli

Polymers 2019, 11(12), 1916; https://doi.org/10.3390/polym11121916 - 21 Nov 2019

Cited by 64 | Viewed by 6383

Abstract

In this work we focused our attention on an innovative use of food residual biomasses. In particular, we produced biochar from coffee waste and used it as filler in epoxy resin composites with the aim to increase their electrical properties. Electrical conductivity was [...] Read more.

In this work we focused our attention on an innovative use of food residual biomasses. In particular, we produced biochar from coffee waste and used it as filler in epoxy resin composites with the aim to increase their electrical properties. Electrical conductivity was studied for the biochar and biochar-based composite in function of pressure applied. The results obtained were compared with carbon black and carbon black composites. We demonstrated that, even if the coffee biochar had less conductivity compared with carbon black in powder form, it created composites with better conductivity in comparison with carbon black composites. In addition, composite mechanical properties were tested and they generally improved with respect to neat epoxy resin. Full article

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

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28 pages, 6414 KiB

Open AccessEditor’s ChoiceReview

Cellulose in Ionic Liquids and Alkaline Solutions: Advances in the Mechanisms of Biopolymer Dissolution and Regeneration

by Omar A. El Seoud, Marc Kostag, Kerstin Jedvert and Naved I. Malek

Polymers 2019, 11(12), 1917; https://doi.org/10.3390/polym11121917 - 21 Nov 2019

Cited by 43 | Viewed by 6635

Abstract

This review is focused on assessment of solvents for cellulose dissolution and the mechanism of regeneration of the dissolved biopolymer. The solvents of interest are imidazole-based ionic liquids, quaternary ammonium electrolytes, salts of super-bases, and their binary mixtures with molecular solvents. We briefly [...] Read more.

This review is focused on assessment of solvents for cellulose dissolution and the mechanism of regeneration of the dissolved biopolymer. The solvents of interest are imidazole-based ionic liquids, quaternary ammonium electrolytes, salts of super-bases, and their binary mixtures with molecular solvents. We briefly discuss the mechanism of cellulose dissolution and address the strategies for assessing solvent efficiency, as inferred from its physico-chemical properties. In addition to the favorable effect of lower cellulose solution rheology, microscopic solvent/solution properties, including empirical polarity, Lewis acidity, Lewis basicity, and dipolarity/polarizability are determinants of cellulose dissolution. We discuss how these microscopic properties are calculated from the UV-Vis spectra of solvatochromic probes, and their use to explain the observed solvent efficiency order. We dwell briefly on use of other techniques, in particular NMR and theoretical calculations for the same purpose. Once dissolved, cellulose is either regenerated in different physical shapes, or derivatized under homogeneous conditions. We discuss the mechanism of, and the steps involved in cellulose regeneration, via formation of mini-sheets, association into “mini-crystals”, and convergence into larger crystalline and amorphous regions. We discuss the use of different techniques, including FTIR, X-ray diffraction, and theoretical calculations to probe the forces involved in cellulose regeneration. Full article

(This article belongs to the Special Issue Cellulose and Renewable Materials)

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21 pages, 2710 KiB

Open AccessEditor’s ChoiceArticle

Study of the Influence of the Reprocessing Cycles on the Final Properties of Polylactide Pieces Obtained by Injection Molding

by Angel Agüero, Maria del Carmen Morcillo, Luis Quiles-Carrillo, Rafael Balart, Teodomiro Boronat, Diego Lascano, Sergio Torres-Giner and Octavio Fenollar

Polymers 2019, 11(12), 1908; https://doi.org/10.3390/polym11121908 - 20 Nov 2019

Cited by 78 | Viewed by 6512

Abstract

This research work aims to study the influence of the reprocessing cycles on the mechanical, thermal, and thermomechanical properties of polylactide (PLA). To this end, PLA was subjected to as many as six extrusion cycles and the resultant pellets were shaped into pieces [...] Read more.

This research work aims to study the influence of the reprocessing cycles on the mechanical, thermal, and thermomechanical properties of polylactide (PLA). To this end, PLA was subjected to as many as six extrusion cycles and the resultant pellets were shaped into pieces by injection molding. Mechanical characterization revealed that the PLA pieces presented relatively similar properties up to the third reprocessing cycle, whereas further cycles induced an intense reduction in ductility and toughness. The effect of the reprocessing cycles was also studied by the changes in the melt fluidity, which showed a significant increase after four reprocessing cycles. An increase in the bio-polyester chain mobility was also attained with the number of the reprocessing cycles that subsequently favored an increase in crystallinity of PLA. A visual inspection indicated that PLA developed certain yellowing and the pieces also became less transparent with the increasing number of reprocessing cycles. Therefore, the obtained results showed that PLA suffers a slight degradation after one or two reprocessing cycles whereas performance impairment becomes more evident above the fourth reprocessing cycle. This finding suggests that the mechanical recycling of PLA for up to three cycles of extrusion and subsequent injection molding is technically feasible. Full article

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

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16 pages, 3985 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of Sucrose and Ammonium Dihydrogen Phosphate (SADP) Adhesive for Plywood

by Zhongyuan Zhao, Shijing Sun, Di Wu, Min Zhang, Caoxing Huang, Kenji Umemura and Qiang Yong

Polymers 2019, 11(12), 1909; https://doi.org/10.3390/polym11121909 - 20 Nov 2019

Cited by 52 | Viewed by 3920

Abstract

The development of eco-friendly adhesives for wood composite products has been a major topic in the field of wood science and product engineering. Although the research on tannin-based and soybean protein-based adhesives has already reached, or at least nears, industrial implementation, we also [...] Read more.

The development of eco-friendly adhesives for wood composite products has been a major topic in the field of wood science and product engineering. Although the research on tannin-based and soybean protein-based adhesives has already reached, or at least nears, industrial implementation, we also face a variety of remaining challenges with regards to the push for sustainable adhesives. First, petroleum-derived substances remain a pre-requisite for utilization of said adhesive systems, and also the viscosity of these novel adhesives continues to limit its ability to serve as a drop-in substitute. Within this study, we focus upon the development of an eco-friendly plywood adhesive that does not require any addition of petroleum derived reagents, and the resultant liquid adhesive has both high solid contents as well as a manageably low viscosity at processing temperatures. Specifically, a system based on sucrose and ammonium dihydrogen phosphate (ADP) was synthesized into an adhesive with ~80% solid content and with viscosities ranging from 480–1270 mPa·s. The bonding performance of all adhesive-bound veneer specimens satisfied GB/T 9846-2015 standard at 170 °C hot pressing temperature. To better explain the system’s efficiency, in-depth chemical analysis was performed in an effort to understand the chemical makeup of the cured adhesives as well as the components over the time course of curing. Several new structures involving the fixation of nitrogen speak to a novel adhesive molecular network. This research provides a possibility of synthesizing an eco-friendly wood adhesive with a high solid content and a low viscosity by renewable materials, and this novel adhesive system has the potential to be widely utilized in the wood industry. Full article

(This article belongs to the Section Polymer Applications)

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20 pages, 4156 KiB

Open AccessEditor’s ChoiceArticle

Transferrin-Conjugated Docetaxel–PLGA Nanoparticles for Tumor Targeting: Influence on MCF-7 Cell Cycle

by Sajan Jose, Thomas A. Cinu, Rosmy Sebastian, M. H. Shoja, N. A. Aleykutty, Alessandra Durazzo, Massimo Lucarini, Antonello Santini and Eliana B. Souto

Polymers 2019, 11(11), 1905; https://doi.org/10.3390/polym11111905 - 19 Nov 2019

Cited by 56 | Viewed by 5372

Abstract

Targeted drug delivery systems are commonly used to improve the therapeutic index of anti-cancer drugs by increasing their selectivity and reducing systemic distribution and toxicity. Ligand-conjugated nanoparticles (NPs) can be effectively applied for active chemotherapeutic targeting to overexpressed receptors of tumor cells. In [...] Read more.

Targeted drug delivery systems are commonly used to improve the therapeutic index of anti-cancer drugs by increasing their selectivity and reducing systemic distribution and toxicity. Ligand-conjugated nanoparticles (NPs) can be effectively applied for active chemotherapeutic targeting to overexpressed receptors of tumor cells. In this study, transferrin (Tf) was successfully conjugated with poly-l-lactic-co-glycolic acid (PLGA) using ethylene diamine confirmed by NMR, for the loading of docetaxel trihydrate (DCT) into PLGA nanoparticles (NPs). The DCT-loaded Tf-conjugated PLGA NPs were produced by an emulsion-solvent evaporation technique, and a 3² full factorial design was used to optimize the nanoparticle formulations. The DCT-loaded Tf-conjugated PLGA NPs were characterized by FTIR spectroscopy, differential scanning calorimetry, powder X-ray diffraction (PXRD), TEM, particle size, and zeta potential analysis. In vitro release kinetics confirmed that release of DCT from the designed formulations followed a zero-order kinetics and a diffusion controlled non-Fickian release profile. The DCT-loaded Tf-conjugated PLGA NPs were evaluated in vitro in MCF-7 cells for bioactivity assessment. Cytotoxicity studies confirmed that the Tf-conjugated PLGA NPs were more active than the non-conjugated counterparts. Cell uptake studies re-confirmed the ligand-mediated active targeting of the formulated NPs. From the cell cycle analysis, the anti-cancer activity of DCT-loaded Tf-conjugated PLGA NPs was shown to occur by arresting the G₂/M phase. Full article

(This article belongs to the Special Issue Biopolymers for Medical Applications)

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14 pages, 5516 KiB

Open AccessEditor’s ChoiceArticle

Mechanical and Physical Properties of Oriented Strand Lumber (OSL): The Effect of Fortification Level of Nanowollastonite on UF Resin

by Vahid Hassani, Hamid R. Taghiyari, Olaf Schmidt, Sadegh Maleki and Antonios N. Papadopoulos

Polymers 2019, 11(11), 1884; https://doi.org/10.3390/polym11111884 - 14 Nov 2019

Cited by 20 | Viewed by 3268

Abstract

The aim of this work is to investigate the effect of the fortification level of nanowollastonite on urea-formaldehyde resin (UF) and its effect on mechanical and physical properties of oriented strand lumbers (OSL). Two resin contents are applied, namely, 8% and 10%. Nanowollastonite [...] Read more.

The aim of this work is to investigate the effect of the fortification level of nanowollastonite on urea-formaldehyde resin (UF) and its effect on mechanical and physical properties of oriented strand lumbers (OSL). Two resin contents are applied, namely, 8% and 10%. Nanowollastonite is mixed with the resin at two levels (10% and 20%). It is found that the fortification of UF resin with 10% nanowollastonite can be considered as an optimum level. When nanowollastonite content is higher (that is, 20%), higher volume of UF resin is left over from the process of sticking the strips together, and therefore is absorbed by wollastonite nanofibers. The mechanism involved in the fortification of UF resin with nanowollastonite, which results in an improvement of thickness swelling values, can be attributed to the following two main factors: (i) nanowollastonite compounds making active bonds with the cellulose hydroxyl groups, putting them out of reach for bonding with the water molecules and (ii) high thermal conductivity coefficient of wollastonite improving the transfer of heat to different layers of the OSL mat, facilitating better and more complete resin curing. Since nanowollastonite contributes to making bonds between the wood strips, which consequently improves physical and mechanical properties, its use can be safely recommended in the OSL production process to improve the physical and mechanical properties of the panel. Full article

(This article belongs to the Special Issue Advances in Wood Composites)

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18 pages, 6162 KiB

Open AccessEditor’s ChoiceArticle

Injection Molding of Highly Filled Polypropylene-based Biocomposites. Buckwheat Husk and Wood Flour Filler: A Comparison of Agricultural and Wood Industry Waste Utilization

by Jacek Andrzejewski, Mateusz Barczewski and Marek Szostak

Polymers 2019, 11(11), 1881; https://doi.org/10.3390/polym11111881 - 14 Nov 2019

Cited by 38 | Viewed by 4759

Abstract

The study presents a comparative analysis for two types of polymer fillers used during the processing of polypropylene by the injection molding technique. The aim of the study was to assess the usefulness of buckwheat husk waste as an alternative to the widely [...] Read more.

The study presents a comparative analysis for two types of polymer fillers used during the processing of polypropylene by the injection molding technique. The aim of the study was to assess the usefulness of buckwheat husk waste as an alternative to the widely used wood fiber fillers. For this purpose, we prepared composite samples containing 10, 30 and 50 wt % of the filler, which were subjected to mechanical tests, thermal analysis, and structural observations in order to evaluate and compare their properties. Additionally, we evaluated the effectiveness of the composite system’s compatibility by using maleic anhydride grafted polypropylene (PP-g-MA). The results of mechanical tests confirmed a more effective reinforcement mechanism for wood fibers; however, with the addition of PP-g-MA compatibilizer, these differences were significantly reduced: we observed a 14% drop for tensile modulus and 5% for strength. This suggests high susceptibility to this type of adhesion promoter, also confirmed by SEM observations. The paper also discusses rheological measurements conducted on a rotational rheometer, which allowed to confirm more favorable flow characteristics for composites based on buckwheat husks. Full article

(This article belongs to the Special Issue Environmentally-Friendly Polymeric Materials Based on Recycling and Bio-Based Components)

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12 pages, 3780 KiB

Open AccessEditor’s ChoiceArticle

Flexure Behaviors of ABS-Based Composites Containing Carbon and Kevlar Fibers by Material Extrusion 3D Printing

by Kui Wang, Shixian Li, Yanni Rao, Yiyun Wu, Yong Peng, Song Yao, Honghao Zhang and Said Ahzi

Polymers 2019, 11(11), 1878; https://doi.org/10.3390/polym11111878 - 13 Nov 2019

Cited by 62 | Viewed by 7380

Abstract

Short-fiber-reinforced thermoplastics are popular for improving the mechanical properties exhibited by pristine thermoplastic materials. Due to the inherent conflict between strength and ductility, there are only a few successful cases of simultaneous enhancement of these two properties in polymer composite components. The objective [...] Read more.

Short-fiber-reinforced thermoplastics are popular for improving the mechanical properties exhibited by pristine thermoplastic materials. Due to the inherent conflict between strength and ductility, there are only a few successful cases of simultaneous enhancement of these two properties in polymer composite components. The objective of this work was to explore the feasibility of simultaneous enhancement of strength and ductility in ABS-based composites with short-carbon and Kevlar fiber reinforcement by material extrusion 3D printing (ME3DP). Microstructure characterization and measurement of thermal and mechanical properties were conducted to evaluate the fiber-reinforced ABS. The influence of printing raster orientation and build direction on the mechanical properties of material extrusion of 3D-printed composites was analyzed. Experimental results demonstrated that the reinforcement of the ABS-based composites by short-carbon and Kevlar fibers under optimized 3D-printing conditions led to balanced flexural strength and ductility. The ABS-based composites with a raster orientation of ±45° and side build direction presented the highest flexural behaviors among the samples in the current study. The main reason was attributed to the printed contour layers and the irregular zigzag paths, which could delay the initiation and propagation of microcracks. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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17 pages, 3380 KiB

Open AccessEditor’s ChoiceReview

Review of Polymeric Materials in 4D Printing Biomedical Applications

by Ming-You Shie, Yu-Fang Shen, Suryani Dyah Astuti, Alvin Kai-Xing Lee, Shu-Hsien Lin, Ni Luh Bella Dwijaksara and Yi-Wen Chen

Polymers 2019, 11(11), 1864; https://doi.org/10.3390/polym11111864 - 12 Nov 2019

Cited by 102 | Viewed by 10534

Abstract

The purpose of 4D printing is to embed a product design into a deformable smart material using a traditional 3D printer. The 3D printed object can be assembled or transformed into intended designs by applying certain conditions or forms of stimulation such as [...] Read more.

The purpose of 4D printing is to embed a product design into a deformable smart material using a traditional 3D printer. The 3D printed object can be assembled or transformed into intended designs by applying certain conditions or forms of stimulation such as temperature, pressure, humidity, pH, wind, or light. Simply put, 4D printing is a continuum of 3D printing technology that is now able to print objects which change over time. In previous studies, many smart materials were shown to have 4D printing characteristics. In this paper, we specifically review the current application, respective activation methods, characteristics, and future prospects of various polymeric materials in 4D printing, which are expected to contribute to the development of 4D printing polymeric materials and technology. Full article

(This article belongs to the Special Issue 3D and 4D Printing of (Bio)Materials)

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27 pages, 5725 KiB

Open AccessEditor’s ChoiceArticle

Flat Die Extruded Biocompatible Poly(Lactic Acid) (PLA)/Poly(Butylene Succinate) (PBS) Based Films

by Vito Gigante, Maria-Beatrice Coltelli, Alessandro Vannozzi, Luca Panariello, Alessandra Fusco, Luisa Trombi, Giovanna Donnarumma, Serena Danti and Andrea Lazzeri

Polymers 2019, 11(11), 1857; https://doi.org/10.3390/polym11111857 - 11 Nov 2019

Cited by 44 | Viewed by 6571

Abstract

Biodegradable polymers are promising materials for films and sheets used in many widely diffused applications like packaging, personal care products and sanitary products, where the synergy of high biocompatibility and reduced environmental impact can be particularly significant. Plasticized poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) [...] Read more.

Biodegradable polymers are promising materials for films and sheets used in many widely diffused applications like packaging, personal care products and sanitary products, where the synergy of high biocompatibility and reduced environmental impact can be particularly significant. Plasticized poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) blend-based films, showing high cytocompatibility and improved flexibility than pure PLA, were prepared by laboratory extrusion and their processability was controlled by the use of a few percent of a commercial melt strength enhancer, based on acrylic copolymers and micro-calcium carbonate. The melt strength enhancer was also found effective in reducing the crystallinity of the films. The process was upscaled by producing flat die extruded films in which elongation at break and tear resistance were improved than pure PLA. The in vitro biocompatibility, investigated through the contact of flat die extruded films with cells, namely, keratinocytes and mesenchymal stromal cells, resulted improved with respect to low density polyethylene (LDPE). Moreover, the PLA-based materials were able to affect immunomodulatory behavior of cells and showed a slight indirect anti-microbial effect. These properties could be exploited in several applications, where the contact with skin and body is relevant. Full article

(This article belongs to the Special Issue Eurofillers Polymer Blends)

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12 pages, 3625 KiB

Open AccessEditor’s ChoiceArticle

Dual-Layer Approach toward Self-Healing and Self-Cleaning Polyurethane Thermosets

by Muhammad Naveed, Muhammad Rabnawaz, Ajmir Khan and Mohammad O. Tuhin

Polymers 2019, 11(11), 1849; https://doi.org/10.3390/polym11111849 - 9 Nov 2019

Cited by 24 | Viewed by 4421

Abstract

There is an urgent need for coatings that exhibit both self-healing as well as self-cleaning properties as they can be used for a wide range of applications. Herein we report a novel approach toward fabricating polyurethane thermosets possessing both self-cleaning and self-healing properties. [...] Read more.

There is an urgent need for coatings that exhibit both self-healing as well as self-cleaning properties as they can be used for a wide range of applications. Herein we report a novel approach toward fabricating polyurethane thermosets possessing both self-cleaning and self-healing properties. The desired coating was achieved via casting a bottom layer of self-healable polyurethanes comprised of reversible phenolic urethane bonds followed by a subsequent dip-coating of the prepared layer in a solution of bis(3-aminopropyl)-terminated polydimethylsiloxane (PDMS-NH₂). The PDMS was used to impart self-cleaning properties to the coating. While the self-healing behavior of the bottom polyurethane layer is achieved through phenolic urethane chemistry, via the exchange of phenolic urethane moieties. The prepared coatings were tested for their optical, mechanical, self-healing, and self-cleaning properties using a variety of characterization methods, which confirmed the successful fabrication of novel self-cleaning and self-healing clear urethane coatings. Full article

(This article belongs to the Special Issue Polymeric Self-Healing Materials)

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28 pages, 2209 KiB

Open AccessEditor’s ChoiceReview

The Use of Chitosan, Alginate, and Pectin in the Biomedical and Food Sector—Biocompatibility, Bioadhesiveness, and Biodegradability

by Gheorghe Adrian Martău, Mihaela Mihai and Dan Cristian Vodnar

Polymers 2019, 11(11), 1837; https://doi.org/10.3390/polym11111837 - 8 Nov 2019

Cited by 369 | Viewed by 16940

Abstract

Nowadays, biopolymers as intelligent and active biopolymer systems in the food and pharmaceutical industry are of considerable interest in their use. With this association in view, biopolymers such as chitosan, alginate, pectin, cellulose, agarose, guar gum, agar, carrageenan, gelatin, dextran, xanthan, and other [...] Read more.

Nowadays, biopolymers as intelligent and active biopolymer systems in the food and pharmaceutical industry are of considerable interest in their use. With this association in view, biopolymers such as chitosan, alginate, pectin, cellulose, agarose, guar gum, agar, carrageenan, gelatin, dextran, xanthan, and other polymers have received significant attention in recent years due to their abundance and natural availability. Furthermore, their versatile properties such as non-toxicity, biocompatibility, biodegradability, and flexibility offer significant functionalities with multifunctional applications. The purpose of this review is to summarize the most compatible biopolymers such as chitosan, alginate, and pectin, which are used for application in food, biotechnological processes, and biomedical applications. Therefore, chitosan, alginate, and pectin are biopolymers (used in the food industry as a stabilizing, thickening, capsular agent, and packaging) with great potential for future developments. Moreover, this review highlights their characteristics, with a particular focus on their potential for biocompatibility, biodegradability, bioadhesiveness, and their limitations on certain factors in the human gastrointestinal tract. Full article

(This article belongs to the Special Issue Polymeric Materials for Food Engineering)

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25 pages, 7247 KiB

Open AccessEditor’s ChoiceReview

Viologen-Based Electrochromic Materials: From Small Molecules, Polymers and Composites to Their Applications

by Kwok Wei Shah, Su-Xi Wang, Debbie Xiang Yun Soo and Jianwei Xu

Polymers 2019, 11(11), 1839; https://doi.org/10.3390/polym11111839 - 8 Nov 2019

Cited by 138 | Viewed by 14542

Abstract

Organic materials have gained considerable attention for electrochromic (EC) applications owing to improved EC performance and good processability. As a class of well-recognized organic EC materials, viologens have received persistent attention due to the structural versatility and property tunability, and are major active [...] Read more.

Organic materials have gained considerable attention for electrochromic (EC) applications owing to improved EC performance and good processability. As a class of well-recognized organic EC materials, viologens have received persistent attention due to the structural versatility and property tunability, and are major active EC components for most of the marketed EC devices. Over the past two decades, extensive efforts have been made to design and synthesize different types of viologen-based materials with enhanced EC properties. This review summarizes chemical structures, preparation and EC properties of various latest viologen-based electrochromes, including small viologen derivatives, main-chain viologen-based polymers, conjugated polymers with viologen side-chains and viologen-based organic/inorganic composites. The performance enhancement mechanisms are concisely discussed. The current marketed viologens-based electrochromic devices (ECDs) are briefly introduced and an outlook on the challenges and future exploration directions for viologen-based materials and their ECDs are also proposed. Full article

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16 pages, 3183 KiB

Open AccessEditor’s ChoiceArticle

Dual-Wavelength (UV and Blue) Controlled Photopolymerization Confinement for 3D-Printing: Modeling and Analysis of Measurements

by Jui-Teng Lin, Da-Chuan Cheng, Kuo-Ti Chen and Hsia-Wei Liu

Polymers 2019, 11(11), 1819; https://doi.org/10.3390/polym11111819 - 6 Nov 2019

Cited by 25 | Viewed by 4588

Abstract

The kinetics and modeling of dual-wavelength (UV and blue) controlled photopolymerization confinement (PC) are presented and measured data are analyzed by analytic formulas and numerical data. The UV-light initiated inhibition effect is strongly monomer-dependent due to different C=C bond rate constants and conversion [...] Read more.

The kinetics and modeling of dual-wavelength (UV and blue) controlled photopolymerization confinement (PC) are presented and measured data are analyzed by analytic formulas and numerical data. The UV-light initiated inhibition effect is strongly monomer-dependent due to different C=C bond rate constants and conversion efficacies. Without the UV-light, for a given blue-light intensity, higher initiator concentration (C₁₀) and rate constant (k’) lead to higher conversion, as also predicted by analytic formulas, in which the total conversion rate (R_T) is an increasing function of C₁ and k’R, which is proportional to k’[gB₁C₁]^0.5. However, the coupling factor B₁ plays a different role that higher B₁ leads to higher conversion only in the transient regime; whereas higher B₁ leads to lower steady-state conversion. For a fixed initiator concentration C₁₀, higher inhibitor concentration (C₂₀) leads to lower conversion due to a stronger inhibition effect. However, same conversion reduction was found for the same H-factor defined by H₀ = [b₁C₁₀ − b₂C₂₀]. Conversion of blue-only are much higher than that of UV-only and UV-blue combined, in which high C₂₀ results a strong reduction of blue-only-conversion, such that the UV-light serves as the turn-off (trigger) mechanism for the purpose of spatial confirmation within the overlap area of UV and blue light. For example, UV-light controlled methacrylate conversion of a glycidyl dimethacrylate resin is formulated with a tertiary amine co-initiator, and butyl nitrite. The system is subject to a continuous exposure of a blue light, but an on-off exposure of a UV-light. Finally, we developed a theoretical new finding for the criterion of a good material/candidate governed by a double ratio of light-intensity and concentration, [I₂₀C₂₀]/[I₁₀C₁₀]. Full article

(This article belongs to the Special Issue Functionally Responsive Polymeric Materials II)

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