Polymers

11 pages, 3113 KB

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 112 | Viewed by 6667

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

► Show Figures

Figure 1

32 pages, 1569 KB

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 365 | Viewed by 21587

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

► Show Figures

Graphical abstract

45 pages, 5672 KB

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 102 | Viewed by 12307

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)

► Show Figures

Graphical abstract

25 pages, 2076 KB

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 384 | Viewed by 27628

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 Biobased and Biodegradable Polymers)

► Show Figures

Graphical abstract

17 pages, 4848 KB

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 76 | Viewed by 7468

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)

► Show Figures

Figure 1

28 pages, 6414 KB

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 60 | Viewed by 8506

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)

► Show Figures

Graphical abstract

21 pages, 2710 KB

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 100 | Viewed by 7827

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)

► Show Figures

Graphical abstract

16 pages, 3985 KB

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 61 | Viewed by 4865

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)

► Show Figures

Graphical abstract

20 pages, 4156 KB

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 68 | Viewed by 6384

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)

► Show Figures

Figure 1

18 pages, 6162 KB

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 46 | Viewed by 5656

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)

► Show Figures

Graphical abstract

14 pages, 5516 KB

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 22 | Viewed by 3875

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)

► Show Figures

Figure 1

12 pages, 3780 KB

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 74 | Viewed by 8510

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)

► Show Figures

Graphical abstract

17 pages, 3380 KB

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 118 | Viewed by 11949

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)

► Show Figures

Graphical abstract

27 pages, 5725 KB

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 56 | Viewed by 7689

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)

► Show Figures

Figure 1

12 pages, 3625 KB

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 28 | Viewed by 5174

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)

► Show Figures

Graphical abstract

28 pages, 2209 KB

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 472 | Viewed by 20843

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)

► Show Figures

Figure 1

25 pages, 7247 KB

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 179 | Viewed by 18916

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

► Show Figures

Figure 1

16 pages, 3183 KB

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 24 | Viewed by 5248

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)

► Show Figures

Graphical abstract

24 pages, 3616 KB

Open AccessEditor’s ChoiceArticle

Biodegradable, Flame-Retardant, and Bio-Based Rigid Polyurethane/Polyisocyanurate Foams for Thermal Insulation Application

by Marcin Borowicz, Joanna Paciorek-Sadowska, Jacek Lubczak and Bogusław Czupryński

Polymers 2019, 11(11), 1816; https://doi.org/10.3390/polym11111816 - 5 Nov 2019

Cited by 85 | Viewed by 5446

Abstract

This article raised the issue of studies on the use of new bio-polyol based on white mustard seed oil and 2,2’-thiodiethanol (3-thiapentane-1,5-diol) for the synthesis of rigid polyurethane/polyisocyanurate (RPU/PIR) foams. For this purpose, new formulations of polyurethane materials were prepared. Formulations contained bio-polyol [...] Read more.

This article raised the issue of studies on the use of new bio-polyol based on white mustard seed oil and 2,2’-thiodiethanol (3-thiapentane-1,5-diol) for the synthesis of rigid polyurethane/polyisocyanurate (RPU/PIR) foams. For this purpose, new formulations of polyurethane materials were prepared. Formulations contained bio-polyol content from 0 to 0.4 chemical equivalents of hydroxyl groups. An industrial flame retardant, tri(2-chloro-1-methylethyl) phosphate (Antiblaze TCMP), was added to half of the formulations. Basic foaming process parameters and functional properties, such as apparent density, compressive strength, brittleness, absorbability and water absorption, aging resistance, thermal conductivity coefficient λ, structure of materials, and flammability were examined. The susceptibility of the foams to biodegradation in soil was also examined. The increase in the bio-polyol content caused a slight increase in processing times. Also, it was noted that the use of bio-polyol had a positive effect on the functional properties of obtained RPU/PIR foams. Foams modified by bio-polyol based on mustard seed oil showed lower apparent density, brittleness, compressive strength, and absorbability and water absorption, as well as thermal conductivity, compared to the reference (unmodified) foams. Furthermore, the obtained materials were more resistant to aging and more susceptible to biodegradation. Full article

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

► Show Figures

Graphical abstract

12 pages, 3875 KB

Open AccessEditor’s ChoiceArticle

AgBr/BiOBr Nano-Heterostructure-Decorated Polyacrylonitrile Nanofibers: A Recyclable High-Performance Photocatalyst for Dye Degradation under Visible-Light Irradiation

by Mingyi Zhang, Ying Qi and Zhenyi Zhang

Polymers 2019, 11(10), 1718; https://doi.org/10.3390/polym11101718 - 19 Oct 2019

Cited by 40 | Viewed by 4480

Abstract

Macrostructural flexible photocatalysts have been proven to have desirable recyclable properties during the photocatalytic degradation of organic pollutants in water. However, the photocatalytic activities of these photocatalysts are often unsatisfactory due to the fast recombination of charge carriers and the limited surface active [...] Read more.

Macrostructural flexible photocatalysts have been proven to have desirable recyclable properties during the photocatalytic degradation of organic pollutants in water. However, the photocatalytic activities of these photocatalysts are often unsatisfactory due to the fast recombination of charge carriers and the limited surface active sites. Herein, we developed a novel flexible photocatalyst of AgBr/BiOBr/polyacrylonitrile (PAN) composite mats (CMs) through the controllable assembly of AgBr/BiOBr nano-heterostructures on electrospun polyacrylonitrile nanofibers (PAN NFs) via a three-step synthesis route. The component ratio of AgBr to BiOBr in the CMs could be easily adjusted by controlling the in situ ion exchange process. The charge–transfer process occurring at the interface of the AgBr/BiOBr nano-heterostructures strongly hindered the recombination of photoinduced electron–hole pairs, thereby effectively enhancing the photocatalytic activity of the AgBr/BiOBr/PAN CMs. Meanwhile, the unique hierarchical inorganic/organic heterostructure of the AgBr/BiOBr/PAN CMs not only led to good flexibility, but also provided an abundance of active sites for photocatalytic reactions. Upon visible-light irradiation, AgBr/BiOBr/PAN CMs with an optimal ratio of AgBr to BiOBr components exhibited both enhanced photocatalytic activity and excellent separability during the degradation of methyl orange in water compared to the BiOBr/PAN CMs. Full article

(This article belongs to the Special Issue Polymer Adsorption at Interfaces)

► Show Figures

Graphical abstract

24 pages, 4966 KB

Open AccessEditor’s ChoiceArticle

Employing of Trukhan Model to Estimate Ion Transport Parameters in PVA Based Solid Polymer Electrolyte

by Shujahadeen B. Aziz, Rawezh B. Marif, M. A. Brza, M. H. Hamsan and M. F. Z. Kadir

Polymers 2019, 11(10), 1694; https://doi.org/10.3390/polym11101694 - 16 Oct 2019

Cited by 70 | Viewed by 5468

Abstract

In the current paper, ion transport parameters in poly (vinyl alcohol) (PVA) based solid polymer electrolyte were examined using Trukhan model successfully. The desired amount of lithium trifluoromethanesulfonate (LiCF₃SO₃) was dissolved in PVA host polymer to synthesis of solid [...] Read more.

In the current paper, ion transport parameters in poly (vinyl alcohol) (PVA) based solid polymer electrolyte were examined using Trukhan model successfully. The desired amount of lithium trifluoromethanesulfonate (LiCF₃SO₃) was dissolved in PVA host polymer to synthesis of solid polymer electrolytes (SPEs). Ion transport parameters such as mobility (μ), diffusion coefficient (D), and charge carrier number density (n) are investigated in detail using impedance spectroscopy. The data results from impedance plots illustrated a decrement of bulk resistance with an increase in temperature. Using electrical equivalent circuits (EEC), electrical impedance plots (ZivsZr) are fitted at various temperatures. The results of impedance study demonstrated that the resistivity of the sample decreases with increasing temperature. The decrease of resistance or impedance with increasing temperature distinguished from Bode plots. The dielectric constant and dielectric loss values increased with an increase in temperature. The loss tangent peaks shifted to higher frequency region and the intensity increased with an increase in temperature. In this contribution, ion transport as a complicated subject in polymer physics is studied. The conductivity versus reciprocal of temperature was found to obey Arrhenius behavior type. The ion transport mechanism is discussed from the tanδ spectra. The ion transport parameters at ambient temperature are found to be 9 × 10⁻⁸ cm²/s, 0.8 × 10¹⁷ cm⁻³, and 3 × 10⁻⁶ cm²/Vs for D, n, andμ respectively. All these parameters have shown increasing as temperature increased. The electric modulus parameters are studied in an attempt to understand the relaxation dynamics and to clarify the relaxation process and ion dynamics relationship. Full article

(This article belongs to the Special Issue Polyelectrolyte Complexes in Polymer Science and Technology)

► Show Figures

Graphical abstract

37 pages, 5930 KB

Open AccessEditor’s ChoiceReview

Fiber-Reinforced Polymer Composites: Manufacturing, Properties, and Applications

by Dipen Kumar Rajak, Durgesh D. Pagar, Pradeep L. Menezes and Emanoil Linul

Polymers 2019, 11(10), 1667; https://doi.org/10.3390/polym11101667 - 12 Oct 2019

Cited by 1288 | Viewed by 71022

Abstract

Composites have been found to be the most promising and discerning material available in this century. Presently, composites reinforced with fibers of synthetic or natural materials are gaining more importance as demands for lightweight materials with high strength for specific applications are growing [...] Read more.

Composites have been found to be the most promising and discerning material available in this century. Presently, composites reinforced with fibers of synthetic or natural materials are gaining more importance as demands for lightweight materials with high strength for specific applications are growing in the market. Fiber-reinforced polymer composite offers not only high strength to weight ratio, but also reveals exceptional properties such as high durability; stiffness; damping property; flexural strength; and resistance to corrosion, wear, impact, and fire. These wide ranges of diverse features have led composite materials to find applications in mechanical, construction, aerospace, automobile, biomedical, marine, and many other manufacturing industries. Performance of composite materials predominantly depends on their constituent elements and manufacturing techniques, therefore, functional properties of various fibers available worldwide, their classifications, and the manufacturing techniques used to fabricate the composite materials need to be studied in order to figure out the optimized characteristic of the material for the desired application. An overview of a diverse range of fibers, their properties, functionality, classification, and various fiber composite manufacturing techniques is presented to discover the optimized fiber-reinforced composite material for significant applications. Their exceptional performance in the numerous fields of applications have made fiber-reinforced composite materials a promising alternative over solitary metals or alloys. Full article

(This article belongs to the Collection Reinforced Polymer Composites)

► Show Figures

Graphical abstract

11 pages, 4281 KB

Open AccessEditor’s ChoiceCommunication

Stabilization of Electrospun Nanofiber Mats Used for Filters by 3D Printing

by Tomasz Kozior, Marah Trabelsi, Al Mamun, Lilia Sabantina and Andrea Ehrmann

Polymers 2019, 11(10), 1618; https://doi.org/10.3390/polym11101618 - 6 Oct 2019

Cited by 44 | Viewed by 7209

Abstract

Electrospinning is a well-known technology used to create nanofiber mats from diverse polymers and other materials. Due to their large surface-to-volume ratio, such nanofiber mats are often applied as air or water filters. Especially the latter, however, have to be mechanically highly stable, [...] Read more.

Electrospinning is a well-known technology used to create nanofiber mats from diverse polymers and other materials. Due to their large surface-to-volume ratio, such nanofiber mats are often applied as air or water filters. Especially the latter, however, have to be mechanically highly stable, which is challenging for common nanofiber mats. One of the approaches to overcome this problem is gluing them on top of more rigid objects, integrating them in composites, or reinforcing them using other technologies to avoid damage due to the water pressure. Here, we suggest another solution. While direct 3D printing with the fused deposition modeling (FDM) technique on macroscopic textile fabrics has been under examination by several research groups for years, here we report on direct FDM printing on nanofiber mats for the first time. We show that by choosing the proper height of the printing nozzle above the nanofiber mat, printing is possible for raw polyacrylonitrile (PAN) nanofiber mats, as well as for stabilized and even more brittle carbonized material. Under these conditions, the adhesion between both parts of the composite is high enough to prevent the nanofiber mat from being peeled off the 3D printed polymer. Abrasion tests emphasize the significantly increased mechanical properties, while contact angle examinations reveal a hydrophilicity between the original values of the electrospun and the 3D printed materials. Full article

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

► Show Figures

Graphical abstract

20 pages, 11731 KB

Open AccessEditor’s ChoiceArticle

Analysis of PLA Geometric Properties Processed by FFF Additive Manufacturing: Effects of Process Parameters and Plate-Extruder Precision Motion

by Eustaquio García Plaza, Pedro José Núñez López, Miguel Ángel Caminero Torija and Jesús Miguel Chacón Muñoz

Polymers 2019, 11(10), 1581; https://doi.org/10.3390/polym11101581 - 27 Sep 2019

Cited by 106 | Viewed by 6829

Abstract

The evolution of fused filament fabrication (FFF) technology, initially restricted to the manufacturing of prototypes, has led to its application in the manufacture of finished functional products with excellent mechanical properties. However, FFF technology entails drawbacks in aspects, such as dimensional and geometric [...] Read more.

The evolution of fused filament fabrication (FFF) technology, initially restricted to the manufacturing of prototypes, has led to its application in the manufacture of finished functional products with excellent mechanical properties. However, FFF technology entails drawbacks in aspects, such as dimensional and geometric precision, and surface finish. These aspects are crucial for the assembly and service life of functional parts, with geometric qualities lagging far behind the optimum levels obtained by conventional manufacturing processes. A further shortcoming is the proliferation of low cost FFF 3D printers with low quality mechanical components, and malfunctions that have a critical impact on the quality of finished products. FFF product quality is directly influenced by printer settings, material properties in terms of cured layers, and the functional mechanical efficiency of the 3D printer. This paper analyzes the effect of the build orientation (Bo), layer thickness (Lt), feed rate (Fr) parameters, and plate-extruder movements on the dimensional accuracy, flatness error, and surface texture of polylactic acid (PLA) using a low cost open-source FFF 3D printer. The mathematical modelling of geometric properties was performed using artificial neural networks (ANN). The results showed that thinner layer thickness generated lower dimensional deviations, and feed rate had a minor influence on dimensional accuracy. The flatness error and surface texture showed a quasi-linear behavior correlated to layer thickness and feed rate, with alterations produced by 3D printer malfunctions. The mathematical models provide a comprehensive analysis of the geometric behavior of PLA processing by FFF, in order to identify optimum print settings for the processing of functional components. Full article

(This article belongs to the Special Issue Polymer Materials with Advanced Functionalities for Additive Manufacturing)

► Show Figures

Graphical abstract

14 pages, 3827 KB

Open AccessEditor’s ChoiceArticle

Hybrid Nanocomposites of Cellulose/Carbon-Nanotubes/Polyurethane with Rapidly Water Sensitive Shape Memory Effect and Strain Sensing Performance

by Guanzheng Wu, Yanjia Gu, Xiuliang Hou, Ruiqing Li, Huizhen Ke and Xueliang Xiao

Polymers 2019, 11(10), 1586; https://doi.org/10.3390/polym11101586 - 27 Sep 2019

Cited by 55 | Viewed by 5604

Abstract

In this work, a fast water-responsive shape memory hybrid polymer based on thermoplastic polyurethane (TPU) was prepared by crosslinking with hydroxyethyl cotton cellulose nanofibers (CNF-C) and multi-walled carbon nanotubes (CNTs). The effect of CNTs content on the electrical conductivity of TPU/CNF-C/CNTs nanocomposite was [...] Read more.

In this work, a fast water-responsive shape memory hybrid polymer based on thermoplastic polyurethane (TPU) was prepared by crosslinking with hydroxyethyl cotton cellulose nanofibers (CNF-C) and multi-walled carbon nanotubes (CNTs). The effect of CNTs content on the electrical conductivity of TPU/CNF-C/CNTs nanocomposite was investigated for the feasibility of being a strain sensor. In order to know its durability, the mechanical and water-responsive shape memory effects were studied comprehensively. The results indicated good mechanical properties and sensing performance for the TPU matrix fully crosslinked with CNF-C and CNTs. The water-induced shape fixity ratio (R_f) and shape recovery ratio (R_r) were 49.65% and 76.64%, respectively, indicating that the deformed composite was able to recover its original shape under a stimulus. The TPU/CNF-C/CNTs samples under their fixed and recovered shapes were tested to investigate their sensing properties, such as periodicity, frequency, and repeatability of the sensor spline under different loadings. Results indicated that the hybrid composite can sense large strains accurately for more than 10³ times and water-induced shape recovery can to some extent maintain the sensing accuracy after material fatigue. With such good properties, we envisage that this kind of composite may play a significant role in developing new generations of water-responsive sensors or actuators. Full article

(This article belongs to the Special Issue Design and Manufacturing of Shape Memory Polymers and Active Structures)

► Show Figures

Figure 1

15 pages, 2536 KB

Open AccessEditor’s ChoiceArticle

Physical and Mechanical Properties of Thermally-Modified Beech Wood Impregnated with Silver Nano-Suspension and Their Relationship with the Crystallinity of Cellulose

by Siavash Bayani, Hamid R. Taghiyari and Antonios N. Papadopoulos

Polymers 2019, 11(10), 1538; https://doi.org/10.3390/polym11101538 - 20 Sep 2019

Cited by 39 | Viewed by 5151

Abstract

The aim of this study was to investigate the physical and mechanical properties of thermally modified beech wood impregnated with silver nano-suspension and to examine their relationship with the crystallinity of cellulose. Specimens were impregnated with a 400 ppm nanosilver suspension (NS); at [...] Read more.

The aim of this study was to investigate the physical and mechanical properties of thermally modified beech wood impregnated with silver nano-suspension and to examine their relationship with the crystallinity of cellulose. Specimens were impregnated with a 400 ppm nanosilver suspension (NS); at least, 90% of silver nano-particles ranged between 20 and 100 nano-meters. Heat treatment took place in a laboratory oven at three temperatures, namely 145, 165, and 185 °C. Physical properties and mechanical properties of treated wood demonstrated statistically insignificant fluctuations at low temperatures compared to control specimens. On the other hand, an increase of temperature to 185 °C had a significant effect on all properties. Physical properties (volumetric swelling and water absorption) and mechanical properties (MOR and MOE) of treated wood demonstrated statistically insignificant fluctuations at low temperatures compared to control specimens. This degradation ultimately resulted in significant decrease in MOR, impact strength, and physical properties. However, thermal modification at 185 °C did not seem to cause significant fluctuations in MOE and compression strength parallel to grain. As a consequence of the thermal modification, part of amorphous cellulose was changed to crystalline cellulose. At low temperatures an increased crystallinity caused some of the properties to be improved. Crystallinity also demonstrated a decrease in NS-HT185 in comparison to HT185 treatment. TCr indices in specimens thermally treated at 145 °C revealed a significant increase as a result of impregnation with nanosilver suspension. This improvement in TCr index resulted in a noticeable increase in MOR and MOE values. Other properties did not show significant fluctuations, suggesting that the effect of the increased crystallinity and cross-linking in lignin was more than the negative effect of the low cell-wall polymer degradation caused by thermal modification. Change of amorphous cellulose to crystalline cellulose, as well as cross-linking in lignin, partially ameliorated the negative effects of thermal degradation at higher temperatures and therefore, compression parallel to grain and modulus of elasticity did not decrease significantly. Overall, it can be concluded that increased crystallinity and cross-linking in lignin can compensate for some decreased properties caused by thermal modification, but it would be significantly dependent on the temperature under which modification is carried out. Impregnating specimens with silver nano-suspension prior to thermal modification enhanced the effects of thermal modification as a result of improved thermal conductivity. Full article

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

► Show Figures

Figure 1

21 pages, 5824 KB

Open AccessEditor’s ChoiceArticle

Fabrication and Evaluation of a Novel Non-Invasive Stretchable and Wearable Respiratory Rate Sensor Based on Silver Nanoparticles Using Inkjet Printing Technology

by Ala’aldeen Al-Halhouli, Loiy Al-Ghussain, Saleem El Bouri, Haipeng Liu and Dingchang Zheng

Polymers 2019, 11(9), 1518; https://doi.org/10.3390/polym11091518 - 18 Sep 2019

Cited by 45 | Viewed by 6269

Abstract

The respiration rate (RR) is a key vital sign that links to adverse clinical outcomes and has various important uses. However, RR signals have been neglected in many clinical practices for several reasons and it is still difficult to develop low-cost RR sensors [...] Read more.

The respiration rate (RR) is a key vital sign that links to adverse clinical outcomes and has various important uses. However, RR signals have been neglected in many clinical practices for several reasons and it is still difficult to develop low-cost RR sensors for accurate, automated, and continuous measurement. This study aims to fabricate, develop and evaluate a novel stretchable and wearable RR sensor that is low-cost and easy to use. The sensor is fabricated using the soft lithography technique of polydimethylsiloxane substrates (PDMS) for the stretchable sensor body and inkjet printing technology for creating the conductive circuit by depositing the silver nanoparticles on top of the PDMS substrates. The inkjet-printed (IJP) PDMS-based sensor was developed to detect the inductance fluctuations caused by respiratory volumetric changes. The output signal was processed in a Wheatstone bridge circuit to derive the RR. Six different patterns for a IJP PDMS-based sensor were carefully designed and tested. Their sustainability (maximum strain during measurement) and durability (the ability to go bear axial cyclic strains) were investigated and compared on an automated mechanical stretcher. Their repeatability (output of the sensor in repeated tests under identical condition) and reproducibility (output of different sensors with the same design under identical condition) were investigated using a respiratory simulator. The selected optimal design pattern from the simulator evaluation was used in the fabrication of the IJP PDMS-based sensor where the accuracy was inspected by attaching it to 37 healthy human subjects (aged between 19 and 34 years, seven females) and compared with the reference values from e-Health nasal sensor. Only one design survived the inspection procedures where design #6 (array consists of two horseshoe lines) indicated the best sustainability and durability, and went through the repeatability and reproducibility tests. Based on the best pattern, the developed sensor accurately measured the simulated RR with an error rate of 0.46 ± 0.66 beats per minute (BPM, mean ± SD). On human subjects, the IJP PDMS-based sensor and the reference e-Health sensor showed the same RR value, without any observable differences. The performance of the sensor was accurate with no apparent error compared with the reference sensor. Considering its low cost, good mechanical property, simplicity, and accuracy, the IJP PDMS-based sensor is a promising technique for continuous and wearable RR monitoring, especially under low-resource conditions. Full article

(This article belongs to the Special Issue Polymer-Based Flexible Printed Electronics and Sensors)

► Show Figures

Graphical abstract

17 pages, 4076 KB

Open AccessEditor’s ChoiceArticle

Boron Removal from Aqueous Solutions by Using a Novel Alginate-Based Sorbent: Comparison with Al₂O₃ Particles

by Hary Demey, Jesus Barron-Zambrano, Takoua Mhadhbi, Hafida Miloudi, Zhen Yang, Montserrat Ruiz and Ana Maria Sastre

Polymers 2019, 11(9), 1509; https://doi.org/10.3390/polym11091509 - 16 Sep 2019

Cited by 39 | Viewed by 6069

Abstract

Boron removal was evaluated in the present work by using calcium alginate beads (CA) and a novel composite based on alginate–alumina (CAAl) as sorbents in a batch system. The effects of different parameters such as pH, temperature, contact time, and composition of alginate [...] Read more.

Boron removal was evaluated in the present work by using calcium alginate beads (CA) and a novel composite based on alginate–alumina (CAAl) as sorbents in a batch system. The effects of different parameters such as pH, temperature, contact time, and composition of alginate (at different concentrations of guluronic and mannuronic acids) on boron sorption were investigated. The results confirm that calcium alginate beads (CA) exhibited a better adsorption capacity in a slightly basic medium, and the composite alginate–alumina (CAAl) exhibited improved boron removal at neutral pH. Sorption isotherm studies were performed and the Langmuir isotherm model was found to fit the experimental data. The maximum sorption capacities were 4.5 mmol g⁻¹ and 5.2 mmol g⁻¹, using CA and CAAl, respectively. Thermodynamic parameters such as change in free energy (ΔG⁰), enthalpy (ΔH⁰), and entropy (ΔS⁰) were also determined. The pseudo-first-order and pseudo-second-order rate equations (PFORE and PSORE, respectively) were tested to fit the kinetic data; the experimental results can be better described with PSORE. The regeneration of the loaded sorbents was demonstrated by using dilute HCl solution (distilled water at pH 3) as eluent for metal recovery. Full article

(This article belongs to the Special Issue Algae-Based Polymers: Current Trends and Emerging Opportunities)

► Show Figures

Graphical abstract

14 pages, 11746 KB

Open AccessEditor’s ChoiceArticle

Effect of Porosity and Crystallinity on 3D Printed PLA Properties

by Yuhan Liao, Chang Liu, Bartolomeo Coppola, Giuseppina Barra, Luciano Di Maio, Loredana Incarnato and Khalid Lafdi

Polymers 2019, 11(9), 1487; https://doi.org/10.3390/polym11091487 - 12 Sep 2019

Cited by 178 | Viewed by 12487

Abstract

Additive manufacturing (AM) is a promising technology for the rapid tooling and fabrication of complex geometry components. Among all AM techniques, fused filament fabrication (FFF) is the most widely used technique for polymers. However, the consistency and properties control of the FFF product [...] Read more.

Additive manufacturing (AM) is a promising technology for the rapid tooling and fabrication of complex geometry components. Among all AM techniques, fused filament fabrication (FFF) is the most widely used technique for polymers. However, the consistency and properties control of the FFF product remains a challenging issue. This study aims to investigate physical changes during the 3D printing of polylactic acid (PLA). The correlations between the porosity, crystallinity and mechanical properties of the printed parts were studied. Moreover, the effects of the build-platform temperature were investigated. The experimental results confirmed the anisotropy of printed objects due to the occurrence of orientation phenomena during the filament deposition and the formation both of ordered and disordered crystalline forms (α and δ, respectively). A heat treatment post-3D printing was proposed as an effective method to improve mechanical properties by optimizing the crystallinity (transforming the δ form into the α one) and overcoming the anisotropy of the 3D printed object. Full article

► Show Figures

Graphical abstract

13 pages, 6259 KB

Open AccessEditor’s ChoiceArticle

A Modular and Practical Synthesis of Zwitterionic Hydrogels through Sequential Amine-Epoxy “Click” Chemistry and N-Alkylation Reaction

by Junki Oh, Kevin Injoe Jung, Hyun Wook Jung and Anzar Khan

Polymers 2019, 11(9), 1491; https://doi.org/10.3390/polym11091491 - 12 Sep 2019

Cited by 22 | Viewed by 5841

Abstract

In this work, the amine-epoxy “click” reaction is shown to be a valuable general tool in the synthesis of reactive hydrogels. The practicality of this reaction arises due to its catalyst-free nature, its operation in water, and commercial availability of a large variety [...] Read more.

In this work, the amine-epoxy “click” reaction is shown to be a valuable general tool in the synthesis of reactive hydrogels. The practicality of this reaction arises due to its catalyst-free nature, its operation in water, and commercial availability of a large variety of amine and epoxide molecules that can serve as hydrophilic network precursors. Therefore, hydrogels can be prepared in a modular fashion through a simple mixing of the precursors in water and used as produced (without requiring any post-synthesis purification step). The gelation behavior and final hydrogel properties depend upon the molecular weight of the precursors and can be changed as per the requirement. A post-synthesis modification through alkylation at the nitrogen atom of the newly formed β-hydroxyl amine linkages allows for functionalizing the hydrogels. For example, ring-opening reaction of cyclic sulfonic ester gives rise to surfaces with a zwitterionic character. Finally, the established gelation chemistry can be combined with soft lithography techniques such as micromolding in capillaries (MIMIC) to obtain hydrogel microstructures. Full article

(This article belongs to the Section Polymer Chemistry)

► Show Figures

Graphical abstract

21 pages, 2237 KB

Open AccessEditor’s ChoiceArticle

Accelerated Weathering of Polylactide-Based Composites Filled with Linseed Cake: The Influence of Time and Oil Content within the Filler

by Olga Mysiukiewicz, Mateusz Barczewski, Katarzyna Skórczewska, Joanna Szulc and Arkadiusz Kloziński

Polymers 2019, 11(9), 1495; https://doi.org/10.3390/polym11091495 - 12 Sep 2019

Cited by 29 | Viewed by 4173

Abstract

This paper presents the effects of accelerated weathering on the properties of polylactide (PLA) composites filled with linseed cake. The particle-shaped waste filler with different linseed oil content (0.9–39.8 wt %) was incorporated with constant amount of 10 wt % to a polymeric [...] Read more.

This paper presents the effects of accelerated weathering on the properties of polylactide (PLA) composites filled with linseed cake. The particle-shaped waste filler with different linseed oil content (0.9–39.8 wt %) was incorporated with constant amount of 10 wt % to a polymeric matrix and subjected to accelerated weathering tests with different exposition times. The structure of the composites, their mechanical, thermal, and thermo-mechanical properties were evaluated by means of scanning electron microscopy, tensile test, dynamic mechanical thermal analysis, and differential scanning calorimetry prior to and after weathering. The results of the measurements were analyzed in reference to the amount of crude oil contained in the filler. The behavior of the multiphase composite during weathering was described. It was found that the oil-rich samples during the first stage of the process showed increased resistance to hydrolytic degradation due to their relatively high crystallinity. The presence of water and elevated temperatures caused swelling of the filler and cracking of the polymeric matrix. Those discontinuities enabled the plasticizing oil to be rinsed out of the composite and thus water penetrated into the samples. As a result, the PLA-based composites containing oil-rich linseed cake were found to be more vulnerable to hydrolytic degradation in a longer time. Full article

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

► Show Figures

Graphical abstract

31 pages, 4001 KB

Open AccessEditor’s ChoiceReview

Bone Repair and Regenerative Biomaterials: Towards Recapitulating the Microenvironment

by Neda Aslankoohi, Dibakar Mondal, Amin S. Rizkalla and Kibret Mequanint

Polymers 2019, 11(9), 1437; https://doi.org/10.3390/polym11091437 - 2 Sep 2019

Cited by 67 | Viewed by 7701

Abstract

Biomaterials and tissue engineering scaffolds play a central role to repair bone defects. Although ceramic derivatives have been historically used to repair bone, hybrid materials have emerged as viable alternatives. The rationale for hybrid bone biomaterials is to recapitulate the native bone composition [...] Read more.

Biomaterials and tissue engineering scaffolds play a central role to repair bone defects. Although ceramic derivatives have been historically used to repair bone, hybrid materials have emerged as viable alternatives. The rationale for hybrid bone biomaterials is to recapitulate the native bone composition to which these materials are intended to replace. In addition to the mechanical and dimensional stability, bone repair scaffolds are needed to provide suitable microenvironments for cells. Therefore, scaffolds serve more than a mere structural template suggesting a need for better and interactive biomaterials. In this review article, we aim to provide a summary of the current materials used in bone tissue engineering. Due to the ever-increasing scientific publications on this topic, this review cannot be exhaustive; however, we attempted to provide readers with the latest advance without being redundant. Furthermore, every attempt is made to ensure that seminal works and significant research findings are included, with minimal bias. After a concise review of crystalline calcium phosphates and non-crystalline bioactive glasses, the remaining sections of the manuscript are focused on organic-inorganic hybrid materials. Full article

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

► Show Figures

Graphical abstract

21 pages, 3171 KB

Open AccessEditor’s ChoiceArticle

The Use of Waste from the Production of Rapeseed Oil for Obtaining of New Polyurethane Composites

by Joanna Paciorek-Sadowska, Marcin Borowicz, Marek Isbrandt, Bogusław Czupryński and Łukasz Apiecionek

Polymers 2019, 11(9), 1431; https://doi.org/10.3390/polym11091431 - 31 Aug 2019

Cited by 63 | Viewed by 6061

Abstract

This article presents the results of research on obtaining new polyurethane materials modified by a by-product from vegetable oils industry—rapeseed cake. The chemical composition of rapeseed cake was examined. Rigid polyurethane-polyisocyanurate (RPU/PIR) foams containing a milled rapeseed cake in their composition were obtained [...] Read more.

This article presents the results of research on obtaining new polyurethane materials modified by a by-product from vegetable oils industry—rapeseed cake. The chemical composition of rapeseed cake was examined. Rigid polyurethane-polyisocyanurate (RPU/PIR) foams containing a milled rapeseed cake in their composition were obtained as part of the conducted research. Biofiller was added in amount of 30 wt.% up to 60 wt.%. Effects of rapeseed cake on the foaming process, cell structure and selected properties of foams, such as apparent density, compressive strength, brittleness, flammability, absorbability, water absorption, thermal resistance and thermal conductivity are described. The foaming process of RPU/PIR foams modified by rapeseed cake was characterized by a lower reactivity, lower foaming temperature and decrease in dielectric polarization. This resulted in a slowed formation of the polyurethane matrix. Apparent density of RPU/PIR foams with biofiller was higher than in unmodified foam. Addition of rapeseed cake did not have a significant influence on the thermal conductivity of obtained materials. However, we observed a tendency for opening the cells of modified foams and obtaining a smaller cross-sectional area of cells. This led to an increase of absorbability and water absorption of obtained materials. However, an advantageous effect of using rapeseed cake in polyurethane formulations was noted. Modified RPU/PIR foams had higher compressive strength, lower brittleness and lower flammability than reference foam. Full article

(This article belongs to the Special Issue Environmentally Sustainable Polymers)

► Show Figures

Graphical abstract

17 pages, 7056 KB

Open AccessEditor’s ChoiceArticle

Poly(Lactic Acid)/ZnO Bionanocomposite Films with Positively Charged ZnO as Potential Antimicrobial Food Packaging Materials

by Insoo Kim, Karthika Viswanathan, Gopinath Kasi, Kambiz Sadeghi, Sarinthip Thanakkasaranee and Jongchul Seo

Polymers 2019, 11(9), 1427; https://doi.org/10.3390/polym11091427 - 30 Aug 2019

Cited by 129 | Viewed by 9979

Abstract

A series of PLA/ZnO bionanocomposite films were prepared by introducing positively surface charged zinc oxide nanoparticles (ZnO NPs) into biodegradable poly(lactic acid) (PLA) by the solvent casting method, and their physical properties and antibacterial activities were evaluated. The physical properties and antibacterial efficiencies [...] Read more.

A series of PLA/ZnO bionanocomposite films were prepared by introducing positively surface charged zinc oxide nanoparticles (ZnO NPs) into biodegradable poly(lactic acid) (PLA) by the solvent casting method, and their physical properties and antibacterial activities were evaluated. The physical properties and antibacterial efficiencies of the bionanocomposite films were strongly dependent on the ZnO NPs content. The bionanocomposite films with over 3% ZnO NPs exhibited a rough surface, poor dispersion, hard agglomerates, and voids, leading to a reduction in the crystallinity and morphological defects. With the increasing ZnO NPs content, the thermal stability and barrier properties of the PLA/ZnO bionanocomposite films were decreased while their hydrophobicity increased. The bionanocomposite films showed appreciable antimicrobial activity against Staphylococcus aureus and Escherichia coli. Especially, the films with over 3% of ZnO NPs exhibited a complete growth inhibition of E. coli. The strong interactions between the positively charged surface ZnO NPs and negatively charged surface of the bacterial membrane led to the production of reactive oxygen species (ROS) and eventually bacterial cell death. Consequently, these PLA/ZnO bionanocomposite films can potentially be used as a food packaging material with excellent UV protective and antibacterial properties. Full article

► Show Figures

Graphical abstract

14 pages, 1093 KB

Open AccessEditor’s ChoiceArticle

High-Temperature Performance of Polymer-Modified Asphalt Mixes: Preliminary Evaluation of the Usefulness of Standard Technical Index in Polymer-Modified Asphalt

by Kezhen Yan, Lingyun You and Daocheng Wang

Polymers 2019, 11(9), 1404; https://doi.org/10.3390/polym11091404 - 27 Aug 2019

Cited by 38 | Viewed by 5900

Abstract

The objectives of this study are to evaluate the high-temperature performance of polymer-modified asphalt and asphalt mixtures, and to investigate if the standard technical indexes are useful in the performance evaluation of the polymer-modified asphalt. There are four typically used polymer-modified asphalt types [...] Read more.

The objectives of this study are to evaluate the high-temperature performance of polymer-modified asphalt and asphalt mixtures, and to investigate if the standard technical indexes are useful in the performance evaluation of the polymer-modified asphalt. There are four typically used polymer-modified asphalt types employed in the study. The standard high-temperature rheological test, such as the temperature sweep test, was used to express the high-temperature performance of the polymer-modified asphalt. Also, considering the non-Newtonian fluid properties of the polymer-modified asphalt, the multiple stress creep recovery (MSCR) and zero-shear viscosity (ZSV) tests were employed for the characterizations. Besides, based on the mixture design of SMA-13, the high temperature of the polymer-modified asphalt mixture was evaluated via Marshall stability and rutting tests. The test results concluded that the ranking of the four kinds of polymer-modified asphalt was different in various laboratory tests. The TB-APAO has the best technical indexes in MSCR and ZSV tests, while the WTR-APAO performed best in the temperature sweep test. In addition, the correlation between the polymer-modified asphalt and the asphalt mixture was very poor. Thus, the present standard technical indexes for the profoundly polymer-modified asphalt mixtures are no longer suitable. Full article

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

► Show Figures

Graphical abstract

23 pages, 10984 KB

Open AccessEditor’s ChoiceArticle

Effect of Fibers Configuration and Thickness on Tensile Behavior of GFRP Laminates Exposed to Harsh Environment

by Milad Bazli, Hamed Ashrafi, Armin Jafari, Xiao-Ling Zhao, R.K. Singh Raman and Yu Bai

Polymers 2019, 11(9), 1401; https://doi.org/10.3390/polym11091401 - 26 Aug 2019

Cited by 52 | Viewed by 6120

Abstract

The present study indicates the importance of using glass fiber reinforced polymer (GFRP) laminates with appropriate thickness and fibers orientation when exposed to harsh environmental conditions. The effect of different environmental conditions on tensile properties of different GFRP laminates is investigated. Laminates were [...] Read more.

The present study indicates the importance of using glass fiber reinforced polymer (GFRP) laminates with appropriate thickness and fibers orientation when exposed to harsh environmental conditions. The effect of different environmental conditions on tensile properties of different GFRP laminates is investigated. Laminates were exposed to three environmental conditions: (1) Freeze/thaw cycles without the presence of moisture, (2) freeze/thaw cycles with the presence of moisture and (3) UV radiation and water vapor condensation cycles. The effect of fiber configuration and laminate thickness were investigated by considering three types of fiber arrangement: (1) Continuous unidirectional, (2) continuous woven and (3) chopped strand mat and two thicknesses (2 and 5 mm). Microstructure and tensile properties of the laminates after exposure to different periods of conditioning (0, 750, 1250 and 2000 h) were studied using SEM and tensile tests. Statistical analyses were used to quantify the obtained results and propose prediction models. The results showed that the condition comprising UV radiation and moisture condition was the most aggressive, while dry freeze/thaw environment was the least. Furthermore, the laminates with chopped strand mat and continuous unidirectional fibers respectively experienced the highest and the lowest reductions properties in all environmental conditions. The maximum reductions in tensile strength for chopped strand mat laminates were about 7%, 32%, and 42% in the dry freeze/thaw, wet freeze/thaw and UV with moisture environments, respectively. The corresponding decreases in the tensile strength for unidirectional laminates were negligible, 17% and 23%, whereas those for the woven laminates were and 7%, 24%, and 34%. Full article

(This article belongs to the Special Issue Degradation and Stabilization of Polymer-Based Materials)

► Show Figures

Graphical abstract

17 pages, 2664 KB

Open AccessEditor’s ChoiceArticle

The Effect of Bulky Substituents on Two π-Conjugated Mesogenic Fluorophores. Their Organic Polymers and Zinc-Bridged Luminescent Networks

by Rosita Diana, Barbara Panunzi, Simona Concilio, Francesco Marrafino, Rafi Shikler, Tonino Caruso and Ugo Caruso

Polymers 2019, 11(9), 1379; https://doi.org/10.3390/polym11091379 - 22 Aug 2019

Cited by 28 | Viewed by 3491

Abstract

From a dicyano-phenylenevinylene (PV) and an azobenzene (AB) skeleton, two new symmetrical salen dyes were obtained. Terminal bulky substituents able to reduce intermolecular interactions and flexible tails to guarantee solubility were added to the fluorogenic cores. Photochemical performances were investigated on the small [...] Read more.

From a dicyano-phenylenevinylene (PV) and an azobenzene (AB) skeleton, two new symmetrical salen dyes were obtained. Terminal bulky substituents able to reduce intermolecular interactions and flexible tails to guarantee solubility were added to the fluorogenic cores. Photochemical performances were investigated on the small molecules in solution, as neat crystals and as dopants in polymeric matrixes. High fluorescence quantum yield in the orange-red region was observed for the brightest emissive films (88% yield). The spectra of absorption and fluorescence were predicted by Density Functional Theory (DFT) calculations. The predicted energy levels of the frontier orbitals are in good agreement with voltammetry and molecular spectroscopy measures. Employing the two dyes as dopants of a nematic polymer led to remarkable orange or yellow luminescence, which dramatically decreases in on-off switch mode after liquid crystal (LC) order was lost. The fluorogenic cores were also embedded in organic polymers and self-assembly zinc coordination networks to transfer the emission properties to a macro-system. The final polymers emit from red to yellow both in solution and in the solid state and their photoluminescence (PL) performance are, in some cases, enhanced when compared to the fluorogenic cores. Full article

► Show Figures

Graphical abstract

18 pages, 14113 KB

Open AccessEditor’s ChoiceArticle

Effect of Graphene Oxide Coating on Natural Fiber Composite for Multilayered Ballistic Armor

by Ulisses Oliveira Costa, Lucio Fabio Cassiano Nascimento, Julianna Magalhães Garcia, Sergio Neves Monteiro, Fernanda Santos da Luz, Wagner Anacleto Pinheiro and Fabio da Costa Garcia Filho

Polymers 2019, 11(8), 1356; https://doi.org/10.3390/polym11081356 - 16 Aug 2019

Cited by 92 | Viewed by 8351

Abstract

Composites with sustainable natural fibers are currently experiencing remarkably diversified applications, including in engineering industries, owing to their lower cost and density as well as ease in processing. Among the natural fibers, the fiber extracted from the leaves of the Amazonian curaua plant [...] Read more.

Composites with sustainable natural fibers are currently experiencing remarkably diversified applications, including in engineering industries, owing to their lower cost and density as well as ease in processing. Among the natural fibers, the fiber extracted from the leaves of the Amazonian curaua plant (Ananas erectifolius) is a promising strong candidate to replace synthetic fibers, such as aramid (Kevlar™), in multilayered armor system (MAS) intended for ballistic protection against level III high velocity ammunition. Another remarkable material, the graphene oxide is attracting considerable attention for its properties, especially as coating to improve the interfacial adhesion in polymer composites. Thus, the present work investigates the performance of graphene oxide coated curaua fiber (GOCF) reinforced epoxy composite, as a front ceramic MAS second layer in ballistic test against level III 7.62 mm ammunition. Not only GOCF composite with 30 vol% fibers attended the standard ballistic requirement with 27.4 ± 0.3 mm of indentation comparable performance to Kevlar™ 24 ± 7 mm with same thickness, but also remained intact, which was not the case of non-coated curaua fiber similar composite. Mechanisms of ceramic fragments capture, curaua fibrils separation, curaua fiber pullout, composite delamination, curaua fiber braking, and epoxy matrix rupture were for the first time discussed as a favorable combination in a MAS second layer to effectively dissipate the projectile impact energy. Full article

(This article belongs to the Special Issue Natural Fibres and their Composites)

► Show Figures

Figure 1

15 pages, 6159 KB

Open AccessEditor’s ChoiceArticle

Structure–Property Relationships in Polyethylene-Based Composites Filled with Biochar Derived from Waste Coffee Grounds

by Rossella Arrigo, Pravin Jagdale, Mattia Bartoli, Alberto Tagliaferro and Giulio Malucelli

Polymers 2019, 11(8), 1336; https://doi.org/10.3390/polym11081336 - 12 Aug 2019

Cited by 64 | Viewed by 7131

Abstract

In this work, biochar (BC) derived from spent coffee grounds has been incorporated into high density polyethylene (PE) through melt mixing. The influence of the filler content on the rheological and thermal behavior of the obtained composites was assessed. In particular, a rheological [...] Read more.

In this work, biochar (BC) derived from spent coffee grounds has been incorporated into high density polyethylene (PE) through melt mixing. The influence of the filler content on the rheological and thermal behavior of the obtained composites was assessed. In particular, a rheological study was performed systematically using different flow fields, including linear and nonlinear dynamic shear flow, revealing that the dynamics of PE macromolecules in the composite materials are slowed down because of the confinement of the polymer chains onto the filler surface and/or within the BC porous structure. Oscillatory amplitude sweep tests indicated that composites show weak strain overshoot behavior in the nonlinear regime: This finding clearly proves the formation of weak structural complexes, which cause a retardation of the macromolecular chains dynamics. Furthermore, the embedded BC particles were able to improve the thermo-oxidative stability of PE-based composites, remarkably increasing the PE decomposition temperatures. Full article

► Show Figures

Graphical abstract

35 pages, 11117 KB

Open AccessEditor’s ChoiceReview

A Review on Porous Polymeric Membrane Preparation. Part II: Production Techniques with Polyethylene, Polydimethylsiloxane, Polypropylene, Polyimide, and Polytetrafluoroethylene

by XueMei Tan and Denis Rodrigue

Polymers 2019, 11(8), 1310; https://doi.org/10.3390/polym11081310 - 5 Aug 2019

Cited by 168 | Viewed by 17088

Abstract

The development of porous polymeric membranes is an important area of application in separation technology. This article summarizes the development of porous polymers from the perspectives of materials and methods for membrane production. Polymers such as polyethylene, polydimethylsiloxane, polypropylene, polyimide, and polytetrafluoroethylene are [...] Read more.

The development of porous polymeric membranes is an important area of application in separation technology. This article summarizes the development of porous polymers from the perspectives of materials and methods for membrane production. Polymers such as polyethylene, polydimethylsiloxane, polypropylene, polyimide, and polytetrafluoroethylene are reviewed due to their outstanding thermal stability, chemical resistance, mechanical strength, and low cost. Six different methods for membrane fabrication are critically reviewed, including thermally induced phase separation, melt-spinning and cold-stretching, phase separation micromolding, imprinting/soft molding, manual punching, and three-dimensional printing. Each method is described in details related to the strategy used to produce the porous polymeric membranes with a specific morphology and separation performances. The key factors associated with each method are presented, including solvent/non-solvent system type and composition, polymer solution composition and concentration, processing parameters, and ambient conditions. Current challenges are also described, leading to future development and innovation to improve these membranes in terms of materials, fabrication equipment, and possible modifications. Full article

(This article belongs to the Collection Silicon-Containing Polymeric Materials)

► Show Figures

Figure 1

16 pages, 2937 KB

Open AccessEditor’s ChoiceReview

Cationic Polymers with Tailored Structures for Rendering Polysaccharide-Based Materials Antimicrobial: An Overview

by Yuanfeng Pan, Qiuyang Xia and Huining Xiao

Polymers 2019, 11(8), 1283; https://doi.org/10.3390/polym11081283 - 1 Aug 2019

Cited by 62 | Viewed by 9947

Abstract

Antimicrobial polymers have attracted substantial interest due to high demands on improving the health of human beings via reducing the infection caused by various bacteria. The review presented herein focuses on rendering polysaccharides, mainly cellulosic-based materials and starch to some extent, antimicrobial via [...] Read more.

Antimicrobial polymers have attracted substantial interest due to high demands on improving the health of human beings via reducing the infection caused by various bacteria. The review presented herein focuses on rendering polysaccharides, mainly cellulosic-based materials and starch to some extent, antimicrobial via incorporating cationic polymers, guanidine-based types in particular. Extensive review on synthetic antimicrobial materials or plastic/textile has been given in the past. However, few review reports have been presented on antimicrobial polysaccharide, cellulosic-based materials, or paper packaging, especially. The current review fills the gap between synthetic materials and natural polysaccharides (cellulose, starch, and cyclodextrin) as substrates or functional additives for different applications. Among various antimicrobial polymers, particular attention in this review is paid to guanidine-based polymers and their derivatives, including copolymers, star polymer, and nanoparticles with core-shell structures. The review has also been extended to gemini surfactants and polymers. Cationic polymers with tailored structures can be incorporated into various products via surface grafting, wet-end addition, blending, or reactive extrusion, effectively addressing the dilemma of improving substrate properties and bacterial growth. Moreover, the pre-commercial trial conducted successfully for making antimicrobial paper packaging has also been addressed. Full article

(This article belongs to the Special Issue Antimicrobial Polymers II)

► Show Figures

Graphical abstract

12 pages, 3019 KB

Open AccessEditor’s ChoiceArticle

The Relationships between the Working Fluids, Process Characteristics and Products from the Modified Coaxial Electrospinning of Zein

by Menglong Wang, Tao Hai, Zhangbin Feng, Deng-Guang Yu, Yaoyao Yang and SW Annie Bligh

Polymers 2019, 11(8), 1287; https://doi.org/10.3390/polym11081287 - 1 Aug 2019

Cited by 78 | Viewed by 7099

Abstract

The accurate prediction and manipulation of nanoscale product sizes is a major challenge in material processing. In this investigation, two process characteristics were explored during the modified coaxial electrospinning of zein, with the aim of understanding how this impacts the products formed. The [...] Read more.

The accurate prediction and manipulation of nanoscale product sizes is a major challenge in material processing. In this investigation, two process characteristics were explored during the modified coaxial electrospinning of zein, with the aim of understanding how this impacts the products formed. The characteristics studied were the spreading angle at the unstable region (θ) and the length of the straight fluid jet (L). An electrospinnable zein core solution was prepared and processed with a sheath comprising ethanolic solutions of LiCl. The width of the zein nanoribbons formed (W) was found to be more closely correlated with the spreading angle and straight fluid jet length than with the experimental parameters (the electrolyte concentrations and conductivity of the shell fluids). Linear equations W = 546.44L − 666.04 and W = 2255.3θ − 22.7 could be developed with correlation coefficients of R_wl² = 0.9845 and R_wθ² = 0.9924, respectively. These highly linear relationships reveal that the process characteristics can be very useful tools for both predicting the quality of the electrospun products, and manipulating their sizes for functional applications. This arises because any changes in the experimental parameters would have an influence on both the process characteristics and the solid products’ properties. Full article

(This article belongs to the Special Issue Natural Fibres and their Composites)

► Show Figures

Graphical abstract

22 pages, 1975 KB

Open AccessEditor’s ChoiceReview

A Review on Reverse Osmosis and Nanofiltration Membranes for Water Purification

by Zi Yang, Yi Zhou, Zhiyuan Feng, Xiaobo Rui, Tong Zhang and Zhien Zhang

Polymers 2019, 11(8), 1252; https://doi.org/10.3390/polym11081252 - 29 Jul 2019

Cited by 481 | Viewed by 42279

Abstract

Sustainable and affordable supply of clean, safe, and adequate water is one of the most challenging issues facing the world. Membrane separation technology is one of the most cost-effective and widely applied technologies for water purification. Polymeric membranes such as cellulose-based (CA) membranes [...] Read more.

Sustainable and affordable supply of clean, safe, and adequate water is one of the most challenging issues facing the world. Membrane separation technology is one of the most cost-effective and widely applied technologies for water purification. Polymeric membranes such as cellulose-based (CA) membranes and thin-film composite (TFC) membranes have dominated the industry since 1980. Although further development of polymeric membranes for better performance is laborious, the research findings and sustained progress in inorganic membrane development have grown fast and solve some remaining problems. In addition to conventional ceramic metal oxide membranes, membranes prepared by graphene oxide (GO), carbon nanotubes (CNTs), and mixed matrix materials (MMMs) have attracted enormous attention due to their desirable properties such as tunable pore structure, excellent chemical, mechanical, and thermal tolerance, good salt rejection and/or high water permeability. This review provides insight into synthesis approaches and structural properties of recent reverse osmosis (RO) and nanofiltration (NF) membranes which are used to retain dissolved species such as heavy metals, electrolytes, and inorganic salts in various aqueous solutions. A specific focus has been placed on introducing and comparing water purification performance of different classes of polymeric and ceramic membranes in related water treatment industries. Furthermore, the development challenges and research opportunities of organic and inorganic membranes are discussed and the further perspectives are analyzed. Full article

(This article belongs to the Special Issue Polymeric Materials for Water and Wastewater Management)

► Show Figures

Figure 1

17 pages, 6564 KB

Open AccessEditor’s ChoiceArticle

Assembly of Polyacrylamide-Sodium Alginate-Based Organic-Inorganic Hydrogel with Mechanical and Adsorption Properties

by Yiying Yue, Xianhui Wang, Qinglin Wu, Jingquan Han and Jianchun Jiang

Polymers 2019, 11(8), 1239; https://doi.org/10.3390/polym11081239 - 26 Jul 2019

Cited by 60 | Viewed by 8727

Abstract

Hydrogels have been widely used in water purification. However, there is not much discussion and comparison about the effects of different nanofillers on the reinforcement and adsorption performances of hydrogels, which can be subjected to rapid water flow and possess strong adsorption ability. [...] Read more.

Hydrogels have been widely used in water purification. However, there is not much discussion and comparison about the effects of different nanofillers on the reinforcement and adsorption performances of hydrogels, which can be subjected to rapid water flow and possess strong adsorption ability. In this work, polyacrylamide (PAAM)-sodium alginate (SA) interpenetrating polymer network-structured hydrogels were prepared by in situ polymerization. PAAM formed the first flexible network and SA constructed the second rigid network. Three kinds of inorganic nanoparticles including carbon nanotubes (CNTs), nanoclays (NCs), and nanosilicas (NSs) were incorporated into a PAAM-SA matrix via hydrogen bond. The obtained hydrogels exhibited a macroporous structure with low density (≈1.4 g/cm³) and high water content (≈83%). Compared with neat PAAM-SA, the hydrogels with inorganic nanoparticles possessed excellent mechanical strengths and elasticities, and the compression strength of PAAM-SA-NS reached up to 1.3 MPa at ε = 60% by adding only 0.036 g NS in a 30 g polymer matrix. However, CNT was the best filler to improve the adsorption capacity owing to its multi-walled hollow nanostructure, and the adsorption capacity of PAAM-SA-CNT was 1.28 times higher than that of PAAM-SA. The prepared hydrogels can be potential candidates for use as absorbents to treat wastewater. Full article

(This article belongs to the Special Issue Natural Compounds for Natural Polymers)

► Show Figures

Graphical abstract

19 pages, 5585 KB

Open AccessEditor’s ChoiceArticle

Thermal Stability, Fire and Smoke Behaviour of Epoxy Composites Modified with Plant Waste Fillers

by Kamila Salasinska, Mateusz Barczewski, Monika Borucka, Rafał L. Górny, Paweł Kozikowski, Maciej Celiński and Agnieszka Gajek

Polymers 2019, 11(8), 1234; https://doi.org/10.3390/polym11081234 - 25 Jul 2019

Cited by 58 | Viewed by 4710

Abstract

The influence of plant fillers on the flammability and smoke emission of natural composites was investigated. Epoxy composites with 15, 25, and 35 wt % of walnut and hazelnut shell, as well as sunflower husk, were prepared and examined. The ground organic components [...] Read more.

The influence of plant fillers on the flammability and smoke emission of natural composites was investigated. Epoxy composites with 15, 25, and 35 wt % of walnut and hazelnut shell, as well as sunflower husk, were prepared and examined. The ground organic components were characterized by grain size distribution, thermogravimetric analysis (TGA) and microstructure observations (SEM). The composite materials were subjected to dynamic mechanical analysis (DMA) and structural evaluation with scanning electron microscopy. Cone calorimeter tests and TGA determined the influence of plant waste filler addition on thermal stability and flammability. Moreover, the semi-volatile and volatile compounds that evolved during the thermal decomposition of selected samples were identified using a steady state tube furnace and a gas chromatograph with a mass spectrometer. The intensity of the degradation reduced as a function of increasing filler content, while the yield of residue corresponded to the amount of lignin that is contained in the tested plants. Moreover, the incorporation of agricultural waste materials resulted in the formation of a char layer, which inhibits the burning process. The yield of char depended on the amount and type of the filler. The composites containing ground hazelnut shell formed swollen char that was shaped in multicellular layers, similar to intumescent fire retardants. Full article

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

► Show Figures

Figure 1

19 pages, 5973 KB

Open AccessEditor’s ChoiceArticle

Water Resistant Self-Extinguishing Low Frequency Soundproofing Polyvinylpyrrolidone Based Electrospun Blankets

by Jessica Passaro, Paolo Russo, Aurelio Bifulco, Maria Teresa De Martino, Veronica Granata, Bonaventura Vitolo, Gino Iannace, Antonio Vecchione, Francesco Marulo and Francesco Branda

Polymers 2019, 11(7), 1205; https://doi.org/10.3390/polym11071205 - 19 Jul 2019

Cited by 26 | Viewed by 6339

Abstract

This paper shows that an eco-friendly electrospinning process allows us to produce water resistant sound absorbers with reduced thickness and excellent sound-absorption properties in the low and medium frequency range (250–1600 Hz) for which which human sensitivity is high and traditional materials struggle [...] Read more.

This paper shows that an eco-friendly electrospinning process allows us to produce water resistant sound absorbers with reduced thickness and excellent sound-absorption properties in the low and medium frequency range (250–1600 Hz) for which which human sensitivity is high and traditional materials struggle to match, that also pass the fire tests which are mandatory in many engineering areas. The structure and composition were studied through Scanning Electron Microscopy (SEM), Fourier Transform InfraRed (FTIR) Spectroscopy and ThermoGravimetric Analysis (TGA). The density, porosity and flow resistivity were measured. Preliminary investigation of the thermal conductivity through Differential Scanning Calorimetry (DSC) shows that they have perspectives also for thermal insulation. The experimental results indicate that the achievements are to be ascribed to the chemical nature of Polyvinylpyrrolidone (PVP). PVP is, in fact, a polymeric lactam with a side polar group that may be easily released by a thermooxidative process. The side polar groups allow for using ethanol for electrospinning than relying on a good dispersion of silica gel particles. The silica particles dimensionally stabilize the mats upon thermal treatments and confer water resistance while strongly contributing to the self-extinguishing property of the materials. Full article

► Show Figures

Graphical abstract

16 pages, 6770 KB

Open AccessEditor’s ChoiceArticle

Chitosan/Glycosaminoglycan Scaffolds: The Role of Silver Nanoparticles to Control Microbial Infections in Wound Healing

by Giuseppina Sandri, Dalila Miele, Angela Faccendini, Maria Cristina Bonferoni, Silvia Rossi, Pietro Grisoli, Angelo Taglietti, Marco Ruggeri, Giovanna Bruni, Barbara Vigani and Franca Ferrari

Polymers 2019, 11(7), 1207; https://doi.org/10.3390/polym11071207 - 19 Jul 2019

Cited by 66 | Viewed by 5715

Abstract

Cutaneous wounds represent a major issue in medical care, with approximately 300 million chronic and 100 million traumatic wound patients worldwide, and microbial infections slow the healing process. The aim of this work was to develop electrospun scaffolds loaded with silver nanoparticles (AgNPs) [...] Read more.

Cutaneous wounds represent a major issue in medical care, with approximately 300 million chronic and 100 million traumatic wound patients worldwide, and microbial infections slow the healing process. The aim of this work was to develop electrospun scaffolds loaded with silver nanoparticles (AgNPs) to enhance cutaneous healing, preventing wound infections. AgNPs were directly added to polymeric blends based on chitosan (CH) and pullulan (PUL) with hyaluronic acid (HA) or chondroitin sulfate (CS) to be electrospun obtaining nanofibrous scaffolds. Moreover, a scaffold based on CH and PUL and loaded with AgNPs was prepared as a comparison. The scaffolds were characterized by chemico–physical properties, enzymatic degradation, biocompatibility, and antimicrobial properties. All the scaffolds were based on nanofibers (diameters about 500 nm) and the presence of AgNPs was evidenced by TEM and did not modify their morphology. The scaffold degradation was proven by means of lysozyme. Moreover, the AgNPs loaded scaffolds were characterized by a good propensity to promote fibroblast proliferation, avoiding the toxic effect of silver. Furthermore, scaffolds preserved AgNP antimicrobial properties, although silver was entrapped into nanofibers. Chitosan/chondroitin sulfate scaffold loaded with AgNPs demonstrated promotion of fibroblast proliferation and to possess antimicrobial properties, thus representing an interesting tool for the treatment of chronic wounds. Full article

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

► Show Figures

Graphical abstract

7 pages, 1727 KB

Open AccessEditor’s ChoiceArticle

Determination of Surface Accessibility of the Cellulose Substrate According to Enzyme Sorption

by Ekaterina M. Podgorbunskikh, Aleksey L. Bychkov and Oleg I. Lomovsky

Polymers 2019, 11(7), 1201; https://doi.org/10.3390/polym11071201 - 18 Jul 2019

Cited by 26 | Viewed by 4258

Abstract

As a heterogeneous process, enzymatic hydrolysis depends on the contact area between enzymes and the cellulose substrate. The surface area of a substrate is typically evaluated through the sorption of gases (nitrogen, argon, or water vapor) or sorption of high-molecular-weight pigments or proteins. [...] Read more.

As a heterogeneous process, enzymatic hydrolysis depends on the contact area between enzymes and the cellulose substrate. The surface area of a substrate is typically evaluated through the sorption of gases (nitrogen, argon, or water vapor) or sorption of high-molecular-weight pigments or proteins. However, lignocellulosic biomass uninvolved in the reaction because of inefficient binding or even the complete inhibition of the enzymes on the surface consisting of lignin or inorganic compounds is erroneously taken into account under these conditions. The initial rate of enzymatic hydrolysis will directly depend on the number of enzymes efficiently sorbed onto cellulose. In this study, the sorption of cellulolytic enzymes was used to evaluate the surface accessibility of the cellulose substrate and its changes during mechanical pretreatment. It was demonstrated that for pure cellulose, mechanical activation did not alter the chemical composition of the surface and the initial rate of hydrolysis increased, which was inconsistent with the data on the thermal desorption of nitrogen. New active cellulose sorption sites were shown to be formed upon. the mechanical activation of plant biomass (wheat straw), and the ultimate initial rate of hydrolysis corresponding to saturation of the accessible surface area with enzyme molecules was determined. Full article

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

► Show Figures

Graphical abstract

21 pages, 2638 KB

Open AccessEditor’s ChoiceReview

Lignin-Based Polyurethanes: Opportunities for Bio-Based Foams, Elastomers, Coatings and Adhesives

by Mona Alinejad, Christián Henry, Saeid Nikafshar, Akash Gondaliya, Sajad Bagheri, Nusheng Chen, Sandip K. Singh, David B. Hodge and Mojgan Nejad

Polymers 2019, 11(7), 1202; https://doi.org/10.3390/polym11071202 - 18 Jul 2019

Cited by 217 | Viewed by 23665

Abstract

Polyurethane chemistry can yield diverse sets of polymeric materials exhibiting a wide range of properties for various applications and market segments. Utilizing lignin as a polyol presents an opportunity to incorporate a currently underutilized renewable aromatic polymer into these products. In this work, [...] Read more.

Polyurethane chemistry can yield diverse sets of polymeric materials exhibiting a wide range of properties for various applications and market segments. Utilizing lignin as a polyol presents an opportunity to incorporate a currently underutilized renewable aromatic polymer into these products. In this work, we will review the current state of technology for utilizing lignin as a polyol replacement in different polyurethane products. This will include a discussion of lignin structure, diversity, and modification during chemical pulping and cellulosic biofuels processes, approaches for lignin extraction, recovery, fractionation, and modification/functionalization. We will discuss the potential of incorporation of lignins into polyurethane products that include rigid and flexible foams, adhesives, coatings, and elastomers. Finally, we will discuss challenges in incorporating lignin in polyurethane formulations, potential solutions and approaches that have been taken to resolve those issues. Full article

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

► Show Figures

Graphical abstract

21 pages, 5369 KB

Open AccessEditor’s ChoiceReview

Polylactide (PLA) and Its Blends with Poly(butylene succinate) (PBS): A Brief Review

by Shen Su, Rodion Kopitzky, Sengül Tolga and Stephan Kabasci

Polymers 2019, 11(7), 1193; https://doi.org/10.3390/polym11071193 - 17 Jul 2019

Cited by 295 | Viewed by 28070

Abstract

Polylactide (PLA), poly(butylene succinate) (PBS) and blends thereof have been researched in the last two decades due to their commercial availability and the upcoming requirements for using bio-based chemical building blocks. Blends consisting of PLA and PBS offer specific material properties. However, their [...] Read more.

Polylactide (PLA), poly(butylene succinate) (PBS) and blends thereof have been researched in the last two decades due to their commercial availability and the upcoming requirements for using bio-based chemical building blocks. Blends consisting of PLA and PBS offer specific material properties. However, their thermodynamically favored biphasic composition often restricts their applications. Many approaches have been taken to achieve better compatibility for tailored and improved material properties. This review focuses on the modification of PLA/PBS blends in the timeframe from 2007 to early 2019. Firstly, neat polymers of PLA and PBS are introduced in respect of their origin, their chemical structure, thermal and mechanical properties. Secondly, recent studies for improving blend properties are reviewed mainly under the focus of the toughness modification using methods including simple blending, plasticization, reactive compatibilization, and copolymerization. Thirdly, we follow up by reviewing the effect of PBS addition, stereocomplexation, nucleation, and processing parameters on the crystallization of PLA. Next, the biodegradation and disintegration of PLA/PBS blends are summarized regarding the European and International Standards, influencing factors, and degradation mechanisms. Furthermore, the recycling and application potential of the blends are outlined. Full article

(This article belongs to the Special Issue Environmentally Sustainable Polymers)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Editor’s Choice Articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI