Polymers

7 pages, 13804 KB

Open AccessEditor’s ChoiceCommunication

Fabrication and Biocompatibility of Electroconductive Silk Fibroin/PEDOT: PSS Composites for Corneal Epithelial Regeneration

by Promita Bhattacharjee and Mark Ahearne

Polymers 2020, 12(12), 3028; https://doi.org/10.3390/polym12123028 - 17 Dec 2020

Cited by 14 | Viewed by 3919

Abstract

The aim of this study was to develop matrices that can support human corneal epithelial cells and innervation by incorporating a conducting polymer, poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), into silk fibroin (SF). Polyvinyl alcohol (PVA) was used as a crosslinking agent to enhance the [...] Read more.

The aim of this study was to develop matrices that can support human corneal epithelial cells and innervation by incorporating a conducting polymer, poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), into silk fibroin (SF). Polyvinyl alcohol (PVA) was used as a crosslinking agent to enhance the mechanical properties of the matrices. The impact of PEDOT:PSS on the materials’ physical properties and cellular responses was examined. The electrical impedance of matrices decreased with increasing concentration of PEDOT:PSS suggesting improved electroconductivity. However, light transmittance also decreased with increasing PEDOT:PSS. Young’s modulus was unaffected by PEDOT:PSS but was increased by PVA. The viability of corneal epithelial cell on the matrices was unaffected by the incorporation of PEDOT:PSS except at the highest concentration tested 0.3% (w/v), which led to a cytotoxic response. These findings suggest that SF/PEDOT:PSS with a PEDOT:PSS concentration of 0.1–0.2% would be a suitable biomaterial for epithelium regeneration. Full article

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

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16 pages, 3413 KB

Open AccessEditor’s ChoiceArticle

Characterization of Porcine Urinary Bladder Matrix Hydrogels from Sodium Dodecyl Sulfate Decellularization Method

by Chen-Yu Kao, Huynh-Quang-Dieu Nguyen and Yu-Chuan Weng

Polymers 2020, 12(12), 3007; https://doi.org/10.3390/polym12123007 - 16 Dec 2020

Cited by 30 | Viewed by 4810

Abstract

Urinary bladder matrix (UBM) is one of the most studied extracellular matrixes (ECM) in the tissue engineering field. Although almost all of the UBM hydrogels were prepared by using peracetic acid (PAA), recent studies indicated that PAA was not a trustworthy way to [...] Read more.

Urinary bladder matrix (UBM) is one of the most studied extracellular matrixes (ECM) in the tissue engineering field. Although almost all of the UBM hydrogels were prepared by using peracetic acid (PAA), recent studies indicated that PAA was not a trustworthy way to decellularize UBM. A stronger detergent, such as sodium dodecyl sulfate (SDS), may help tackle this issue; however, its effects on the hydrogels’ characteristics remain unknown. Therefore, the objective of this study was to develop a more reliable protocol to decellularize UBM, using SDS, and to compare the characteristics of hydrogels obtained from this method to the widely employed technique, using PAA. The results indicated that SDS was superior to PAA in decellularization efficacy. Different decellularization methods led to dissimilar gelation kinetics; however, the methods did not affect other hydrogel characteristics in terms of biochemical composition, surface morphology and rheological properties. The SDS-treated hydrogels possessed excellent cytocompatibility in vitro. These results showed that the SDS decellularization method could offer a more stable and safer way to obtain acellular UBM, due to reducing immunogenicity. The hydrogels prepared from this technique had comparable characteristics as those from PAA and could be a potential candidate as a scaffold for tissue remodeling. Full article

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

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21 pages, 734 KB

Open AccessEditor’s ChoiceArticle

Direct Joule Heating as a Means to Efficiently and Homogeneously Heat Thermoplastic Prepregs

by Jochen Wellekötter and Christian Bonten

Polymers 2020, 12(12), 2959; https://doi.org/10.3390/polym12122959 - 11 Dec 2020

Cited by 10 | Viewed by 4556

Abstract

Although direct Joule heating is a known technique for heating carbon fiber reinforced plastics, it is a yet unexplored heating method for thermoplastic prepregs before back-injection molding. The knowledge obtained from resistance welding, for example, is not directly transferable because of considerably higher [...] Read more.

Although direct Joule heating is a known technique for heating carbon fiber reinforced plastics, it is a yet unexplored heating method for thermoplastic prepregs before back-injection molding. The knowledge obtained from resistance welding, for example, is not directly transferable because of considerably higher heated volumes and more complex shapes. In this study, the governing parameters and process limits are established for this method. The influences of the contacting, the materials used, and the size of the heated part are investigated with respect to the part temperature and heating efficiency. The findings show that the quality of heating is determined by the shape and size of the electrodes. Larger electrodes lead to a more homogeneous temperature distribution. Parts based on woven fabric can be heated more homogeneously because of the existence of intersections between rovings, generating contact between fibers. An increase in part width results in uneven heating behavior. Full article

(This article belongs to the Special Issue Fiber-Reinforced Polymer-Based Composites: Processing, Characterization and Performance)

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10 pages, 2574 KB

Open AccessEditor’s ChoiceArticle

A Novel Silicon/Phosphorus Co-Flame Retardant Polymer Electrolyte for High-Safety All-Solid-State Lithium Ion Batteries

by Li Zeng, Lu Jia, Xingang Liu and Chuhong Zhang

Polymers 2020, 12(12), 2937; https://doi.org/10.3390/polym12122937 - 9 Dec 2020

Cited by 15 | Viewed by 5401

Abstract

Developing a solid polymer electrolyte with superior flame retardancy and lithium-ion transportation properties is still a challenge. Herein, an intrinsic silicon/phosphorus co-flame retardant polymer solid electrolyte was prepared by using polyethylene glycol (PEG) co-polymerized with silicon and phosphorus-containing monomers. Due to the synergistic [...] Read more.

Developing a solid polymer electrolyte with superior flame retardancy and lithium-ion transportation properties is still a challenge. Herein, an intrinsic silicon/phosphorus co-flame retardant polymer solid electrolyte was prepared by using polyethylene glycol (PEG) co-polymerized with silicon and phosphorus-containing monomers. Due to the synergistic flame-retardant effect of silicon and phosphorus elements, this polymer electrolyte exhibits excellent thermal stability and flame resistance. Moreover, the ionic conductivity of the electrolyte at 25 °C is as high as 2.98 × 10⁻⁵ S/cm when the mass ratio of LiN(SO₂CF₃)₂ (LiTFSI) and the prepared polymer electrolyte is 10:1. What is more, the LiFePO₄/Li all-solid-state battery assembled with this solid electrolyte can work stably at a high temperature of 60 °C and exhibits a specific capacity of 129.2 mAh/g at 0.2 C after 100 cycles, providing a promising application prospect for high-safety lithium-ion batteries. Full article

(This article belongs to the Special Issue Feature Papers of Green and Sustainable Chemistry in Polymer Science)

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18 pages, 2685 KB

Open AccessEditor’s ChoiceReview

Photo-Crosslinked Silk Fibroin for 3D Printing

by Xuan Mu, Jugal Kishore Sahoo, Peggy Cebe and David L. Kaplan

Polymers 2020, 12(12), 2936; https://doi.org/10.3390/polym12122936 - 9 Dec 2020

Cited by 84 | Viewed by 13026

Abstract

Silk fibroin in material formats provides robust mechanical properties, and thus is a promising protein for 3D printing inks for a range of applications, including tissue engineering, bioelectronics, and bio-optics. Among the various crosslinking mechanisms, photo-crosslinking is particularly useful for 3D printing with [...] Read more.

Silk fibroin in material formats provides robust mechanical properties, and thus is a promising protein for 3D printing inks for a range of applications, including tissue engineering, bioelectronics, and bio-optics. Among the various crosslinking mechanisms, photo-crosslinking is particularly useful for 3D printing with silk fibroin inks due to the rapid kinetics, tunable crosslinking dynamics, light-assisted shape control, and the option to use visible light as a biocompatible processing condition. Multiple photo-crosslinking approaches have been applied to native or chemically modified silk fibroin, including photo-oxidation and free radical methacrylate polymerization. The molecular characteristics of silk fibroin, i.e., conformational polymorphism, provide a unique method for crosslinking and microfabrication via light. The molecular design features of silk fibroin inks and the exploitation of photo-crosslinking mechanisms suggest the exciting potential for meeting many biomedical needs in the future. Full article

(This article belongs to the Special Issue 3D/4D Printing with Polymers, Polymer Hydrogels and Adaptive Soft Materials)

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14 pages, 1704 KB

Open AccessEditor’s ChoiceArticle

Drug-Eluting Biodegradable Implants for the Sustained Release of Bisphosphonates

by Cintya Dharmayanti, Todd A. Gillam, Desmond B. Williams and Anton Blencowe

Polymers 2020, 12(12), 2930; https://doi.org/10.3390/polym12122930 - 7 Dec 2020

Cited by 27 | Viewed by 5525

Abstract

Despite being one of the first-line treatments for osteoporosis, the bisphosphonate drug class exhibits an extremely low oral bioavailability (<1%) due to poor absorption from the gastrointestinal tract. To overcome this, and to explore the potential for sustained drug release, bioerodible poly(lactic [...] Read more.

Despite being one of the first-line treatments for osteoporosis, the bisphosphonate drug class exhibits an extremely low oral bioavailability (<1%) due to poor absorption from the gastrointestinal tract. To overcome this, and to explore the potential for sustained drug release, bioerodible poly(lactic acid) (PLA) and poly(D,L-lactide-co-glycolide) (PLGA) implants loaded with the bisphosphonate alendronate sodium (ALN) were prepared via hot-melt extrusion. The rate of drug release in vitro was modulated by tailoring the ratio of lactide to glycolide in the polymer and by altering the ALN-loading of the implants. All investigated implants exhibited sustained ALN release in vitro between 25 to 130 days, where implants of greater glycolide composition and higher ALN-loadings released ALN more rapidly. All PLGA implants demonstrated a sigmoidal release profile, characterised by an initial surface dissolution phase, followed by a period of zero-order drug diffusion, then relaxation or erosion of the polymer chains that caused accelerated release over the subsequent days. Contrastingly, the PLA implants demonstrated a logarithmic release profile, characterised by a gradual decrease in ALN release over time. Full article

(This article belongs to the Collection Polymers for Controlled Drug Release)

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18 pages, 11787 KB

Open AccessEditor’s ChoiceArticle

Micellar Carriers Based on Amphiphilic PEG/PCL Graft Copolymers for Delivery of Active Substances

by Justyna Odrobińska and Dorota Neugebauer

Polymers 2020, 12(12), 2876; https://doi.org/10.3390/polym12122876 - 30 Nov 2020

Cited by 11 | Viewed by 4741

Abstract

Amphiphilic copolymers of alkyne functionalized 2-hydroxyethyl methacrylate (AlHEMA) and poly(ethylene glycol) methyl ether methacrylate (MPEGMA) with graft or V-shaped graft topologies were synthesized. The functionalization of poly(ε-caprolactone) (PCL) with azide group enabled attachment to P(AlHEMA-co-MPEGMA) copolymers via a “click” alkyne-azide reaction. [...] Read more.

Amphiphilic copolymers of alkyne functionalized 2-hydroxyethyl methacrylate (AlHEMA) and poly(ethylene glycol) methyl ether methacrylate (MPEGMA) with graft or V-shaped graft topologies were synthesized. The functionalization of poly(ε-caprolactone) (PCL) with azide group enabled attachment to P(AlHEMA-co-MPEGMA) copolymers via a “click” alkyne-azide reaction. The introduction of PCL as a second side chain type in addition to PEG resulted in heterografted copolymers with modified properties such as biodegradability. “Click” reactions were carried out with efficiencies between 17–70% or 32–50% (for lower molecular weight PCL, 4000 g/mol, or higher molecular weight PCL, 9000 g/mol, respectively) depending on the PEG grafting density. The graft copolymers were self-assembled into micellar superstructures with the ability to encapsulate active substances, such as vitamin C (VitC), arbutin (ARB) or 4-n-butylresorcinol (4nBRE). Drug loading contents (DLC) were obtained in the range of 5–55% (VitC), 39–91% (ARB) and 42–98% (4nBRE). In vitro studies carried out in a phosphate buffer saline (PBS) solution (at pH 7.4 or 5.5) gave the maximum release levels of active substances after 10–240 min depending on the polymer system. Permeation tests in Franz chambers indicated that the bioactive substances after release by micellar systems penetrated through the artificial skin membrane in small amounts, and a majority of the bioactive substances remained inside the membrane, which is satisfactory for most cosmetic applications. Full article

(This article belongs to the Collection Polymers for Controlled Drug Release)

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14 pages, 7706 KB

Open AccessEditor’s ChoiceArticle

Phase Separation within a Thin Layer of Polymer Solution as Prompt Technique to Predict Membrane Morphology and Transport Properties

by Tatiana Anokhina, Ilya Borisov, Alexey Yushkin, Gleb Vaganov, Andrey Didenko and Alexey Volkov

Polymers 2020, 12(12), 2785; https://doi.org/10.3390/polym12122785 - 25 Nov 2020

Cited by 16 | Viewed by 3527

Abstract

In this work, the precipitation of a thin layer of a polymer solution was proposed to imitate the process of asymmetric membrane formation by a non-solvent induced phase separation (NIPS) technique. The phase inversion within the thin (<500 μm) and bulk (~2 cm) [...] Read more.

In this work, the precipitation of a thin layer of a polymer solution was proposed to imitate the process of asymmetric membrane formation by a non-solvent induced phase separation (NIPS) technique. The phase inversion within the thin (<500 μm) and bulk (~2 cm) layer of polyamic-acid (PAA) in N-methyl-2-pyrrolidone (NMP) by using water as non-solvent was considered. It was shown that polymer films formed within the “limited” layer of polymer solution showed a good agreement with the morphology of corresponded asymmetric flat-sheet membranes even in the case of three-component casting solution (PAA/NMP/EtOH). At the same time, the polymer films formed on the interface of two bulk phases (“infinite” regime) did not fully correspond to the membrane structure. It was shown that up to 50% of NMP solvent in PAA solution can be replaced by ethanol, which can have a renewable origin. By changing the ethanol content in the casting solution, the average size of transport pores can be varied in the range of 12–80 nm, and the liquid permeance from 16.6 up to 207 kg/m²∙h∙bar. To summarize, the precipitation of polymer solution within the thin layer can be considered a prompt technique and a powerful tool for fast screening and optimization of the complex composition of casting solutions using its small quantity. Furthermore, the prediction of membrane morphology can be done without casting the membrane, further post-treatment procedures, and scanning electron microscopy (SEM) analysis. Full article

(This article belongs to the Special Issue Advanced Polymeric Materials for Membrane Technology)

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10 pages, 1533 KB

Open AccessEditor’s ChoiceArticle

Tandem Mass-Remainder Analysis of Industrially Important Polyether Polyols

by Mahir Hashimov, Ákos Kuki, Tibor Nagy, Miklós Zsuga and Sándor Kéki

Polymers 2020, 12(12), 2768; https://doi.org/10.3390/polym12122768 - 24 Nov 2020

Cited by 4 | Viewed by 2872

Abstract

The characteristics of the polyalkylene oxide polyether polyols highly influence the properties of final polyurethane products. As a novel approach, in order to gain structural information, the recently invented data mining procedures, namely the Mass-remainder analysis (MARA) and the Multistep Mass-remainder analysis (M-MARA) [...] Read more.

The characteristics of the polyalkylene oxide polyether polyols highly influence the properties of final polyurethane products. As a novel approach, in order to gain structural information, the recently invented data mining procedures, namely the Mass-remainder analysis (MARA) and the Multistep Mass-remainder analysis (M-MARA) are successfully applied for the processing of tandem mass spectrometry (MS/MS) data of various industrially important polyether polyols. M-MARA yields an ultra-simplified graphical representation of the MS/MS spectra and sorts the product ions based on their double bond equivalent (DBE) values. The maximum DBE values unambiguously differentiate among the various polyether polyols. Accordingly, the characteristic DBE values were 0, 1 for the linear diol polyethers, 0, 1, 2 for the three-arm, and 0, 1 2, 3, 4 for the six-arm polyether polyols. In addition, it was also found that the characteristic collision energy necessary for the optimum fragmentation yield depended linearly on the molecular weight of the polyols. This relationship offers an easy way for instrument tuning to gain structural information. Full article

(This article belongs to the Section Polymer Analysis and Characterization)

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16 pages, 9992 KB

Open AccessEditor’s ChoiceArticle

Reliability of Free Inflation and Dynamic Mechanics Tests on the Prediction of the Behavior of the Polymethylsilsesquioxane–High-Density Polyethylene Nanocomposite for Thermoforming Applications

by Fouad Erchiqui, Khaled Zaafrane, Abdessamad Baatti, Hamid Kaddami and Abdellatif Imad

Polymers 2020, 12(11), 2753; https://doi.org/10.3390/polym12112753 - 21 Nov 2020

Cited by 2 | Viewed by 2639

Abstract

Numerical modeling of the thermoforming process of polymeric sheets requires precise knowledge of the viscoelastic behavior under conjugate effect pressure and temperature. Using two different experiments, bubble inflation and dynamic mechanical testing on a high-density polyethylene (HDPE) nanocomposite reinforced with polymethylsilsesquioxane HDPE (PMSQ–HDPE) [...] Read more.

Numerical modeling of the thermoforming process of polymeric sheets requires precise knowledge of the viscoelastic behavior under conjugate effect pressure and temperature. Using two different experiments, bubble inflation and dynamic mechanical testing on a high-density polyethylene (HDPE) nanocomposite reinforced with polymethylsilsesquioxane HDPE (PMSQ–HDPE) nanoparticles, material constants for Christensen’s model were determined by the least squares optimization. The viscoelastic identification relative to the inflation test seemed to be the most appropriate for the numerical study of thermoforming of a thin PMSQ–HDPE part. For this purpose, the finite element method was considered. Full article

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

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13 pages, 1793 KB

Open AccessEditor’s ChoiceArticle

Kinetic Study of the Thermal and Thermo-Oxidative Degradations of Polystyrene Reinforced with Multiple-Cages POSS

by Ignazio Blanco, Gianluca Cicala, Claudio Tosto and Francesco Agatino Bottino

Polymers 2020, 12(11), 2742; https://doi.org/10.3390/polym12112742 - 19 Nov 2020

Cited by 8 | Viewed by 2750

Abstract

A comprehensive kinetics degradation study is carried out on novel multiple cages polyhedral oligomeric silsesquioxane (POSS)/polystyrene (PS) composites at 5% (w/w) of POSS to assess their thermal behavior with respect to the control PS and other similar POSS/PS systems [...] Read more.

A comprehensive kinetics degradation study is carried out on novel multiple cages polyhedral oligomeric silsesquioxane (POSS)/polystyrene (PS) composites at 5% (w/w) of POSS to assess their thermal behavior with respect to the control PS and other similar POSS/PS systems studied in the past. The composites are synthesized by in situ polymerization of styrene in the presence of POSSs and characterized by ¹H-NMR. The characteristics of thermal parameters are determined using kinetics literature methods, such as those developed by Kissinger and Flynn, Wall, and Ozawa (FWO), and discussed and compared with each other and with those obtained in the past for similar POSS/PS composites. A good improvement in the thermal stability with respect to neat polymer is found, but not with respect to those obtained in the past for polystyrene reinforced with single- or double-POSS cages. This behavior is attributed to the greater steric hindrance of the three-cages POSS compared with those of single- or double-cage POSS molecules. Full article

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

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22 pages, 7012 KB

Open AccessEditor’s ChoiceArticle

Composites Based on Poly(Lactic Acid) (PLA) and SBA-15: Effect of Mesoporous Silica on Thermal Stability and on Isothermal Crystallization from Either Glass or Molten State

by Tamara M. Díez-Rodríguez, Enrique Blázquez-Blázquez, Ernesto Pérez and María L. Cerrada

Polymers 2020, 12(11), 2743; https://doi.org/10.3390/polym12112743 - 19 Nov 2020

Cited by 16 | Viewed by 3714

Abstract

Several composites based on an L-rich poly(lactic acid) (PLA) with different contents of mesoporous Santa Barbara Amorphous (SBA-15) silica were prepared in order to evaluate the effect of the mesoporous silica on the resultant PLA materials by examining morphological aspects, changes in [...] Read more.

Several composites based on an L-rich poly(lactic acid) (PLA) with different contents of mesoporous Santa Barbara Amorphous (SBA-15) silica were prepared in order to evaluate the effect of the mesoporous silica on the resultant PLA materials by examining morphological aspects, changes in PLA phases and their transitions, and, primarily, the influence on some final properties. Melt extrusion was chosen for the obtainment of the composites, followed by quenching from the melt to prepare films. Completely amorphous samples were then attained, as deduced from X-ray diffraction and differential scanning calorimetry (DSC) analyses. Thermogravimetric analysis (TGA) results demonstrated that the presence of SBA-15 particles in the PLA matrix did not exert any significant influence on the thermal decomposition of these composites. An important nucleation effect of the silica was found in PLA, especially under isothermal crystallization either from the melt or from its glassy state. As expected, isothermal crystallization from the glass was considerably faster than from the molten state, and these high differences were also responsible for a more considerable nucleating role of SBA-15 when crystallizing from the melt. It is remarkable that the PLA under analysis showed very close temperatures for cold crystallization and its subsequent melting. Moreover, the type of developed polymorphs did not accomplish the common rules previously described in the literature. Thus, all the isothermal experiments led to exclusive formation of the α modification, and the observation of the α’ crystals required the annealing for long times at temperatures below 80 °C, as ascertained by both DSC and X-ray diffraction experiments. Finally, microhardness (MH) measurements indicated a competition between the PLA physical aging and the silica reinforcement effect in the as-processed amorphous films. Physical aging in the neat PLA was much more important than in the PLA matrix that constituted the composites. Accordingly, the MH trend with SBA-15 content was strongly dependent on aging times. Full article

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

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9 pages, 2006 KB

Open AccessEditor’s ChoiceCommunication

Polymerization-Induced Microphase Separation with Long-Range Order in Melts of Gradient Copolymers

by Alexey A. Gavrilov and Alexander V. Chertovich

Polymers 2020, 12(11), 2637; https://doi.org/10.3390/polym12112637 - 10 Nov 2020

Cited by 7 | Viewed by 3758

Abstract

In this work, we studied the question of whether it is possible to develop a one-step approach for the creation of microphase-separated materials with long-range order with the help of spontaneous gradient copolymers, i.e., formed during controlled copolymerization solely due to the large [...] Read more.

In this work, we studied the question of whether it is possible to develop a one-step approach for the creation of microphase-separated materials with long-range order with the help of spontaneous gradient copolymers, i.e., formed during controlled copolymerization solely due to the large difference in the reactivity ratios. To that end, we studied the polymerization-induced microphase separation in bulk on the example of a monomer pair with realistic parameters based on styrene (S) and vinylpirrolydone (VP) by means of computer simulation. We showed that for experimentally reasonable chain lengths, the structures with long-range order start to appear at the conversion degree as low as 76%; a full phase diagram in coordinates (fraction of VP—conversion degree) was constructed. Rather rich phase behavior was obtained; moreover, at some VP fractions, order–order transitions were observed. Finally, we studied how the conversion degree at which the order–disorder transition occurs changes upon varying the maximum average chain length in the system. Full article

(This article belongs to the Special Issue Phase Transitions in Polymers and Polymer Morphologies)

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19 pages, 10959 KB

Open AccessEditor’s ChoiceArticle

Poly(3-Hydroxybutyrate)-Multiwalled Carbon Nanotubes Electrospun Scaffolds Modified with Curcumin

by Nader Tanideh, Negar Azarpira, Najmeh Sarafraz, Shahrokh Zare, Aida Rowshanghiyas, Nima Farshidfar, Aida Iraji, Moein Zarei and Miroslawa El Fray

Polymers 2020, 12(11), 2588; https://doi.org/10.3390/polym12112588 - 4 Nov 2020

Cited by 29 | Viewed by 4464

Abstract

Appropriate selection of suitable materials and methods is essential for scaffolds fabrication in tissue engineering. The major challenge is to mimic the structure and functions of the extracellular matrix (ECM) of the native tissues. In this study, an optimized 3D structure containing poly(3-hydroxybutyrate) [...] Read more.

Appropriate selection of suitable materials and methods is essential for scaffolds fabrication in tissue engineering. The major challenge is to mimic the structure and functions of the extracellular matrix (ECM) of the native tissues. In this study, an optimized 3D structure containing poly(3-hydroxybutyrate) (P3HB), multiwalled carbon nanotubes (MCNTs) and curcumin (CUR) was created by electrospinning a novel biomimetic scaffold. CUR, a natural anti-inflammatory compound, has been selected as a bioactive component to increase the biocompatibility and reduce the potential inflammatory reaction of electrospun scaffolds. The presence of CUR in electrospun scaffolds was confirmed by ¹H NMR and Fourier-transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) revealed highly interconnected porosity of the obtained 3D structures. Addition of up to 20 wt% CUR has enhanced mechanical properties of the scaffolds. CUR has also promoted in vitro bioactivity and hydrolytic degradation of the electrospun nanofibers. The developed P3HB-MCNT composite scaffolds containing 20 wt% of CUR revealed excellent in vitro cytocompatibility using mesenchymal stem cells and in vivo biocompatibility in rat animal model study. Importantly, the reduced inflammatory reaction in the rat model after 8 weeks of implantation has also been observed for scaffolds modified with CUR. Overall, newly developed P3HB-MCNTs-CUR electrospun scaffolds have demonstrated their high potential for tissue engineering applications. Full article

(This article belongs to the Special Issue Polymeric Materials for Regenerative Medicine and Advanced Structures)

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10 pages, 798 KB

Open AccessEditor’s ChoiceArticle

Hyperbranched Polyglycerols as Robust Up-Conversion Nanoparticle Coating Layer for Feasible Cell Imaging

by Mingcong Hao, Tongtong Wu, Qunzhi Chen, Xueyan Lian, Haigang Wu and Bingyang Shi

Polymers 2020, 12(11), 2592; https://doi.org/10.3390/polym12112592 - 4 Nov 2020

Cited by 6 | Viewed by 2665

Abstract

Owing to the wide spectrum of excitation wavelengths of up-conversion nanoparticles (UCNPs) by precisely regulating the percentage of doping elements, UCNPs have been emerging as bioimaging agents. The key drawback of UCNPs is their poor dispersibility in aqueous solution and it is hard [...] Read more.

Owing to the wide spectrum of excitation wavelengths of up-conversion nanoparticles (UCNPs) by precisely regulating the percentage of doping elements, UCNPs have been emerging as bioimaging agents. The key drawback of UCNPs is their poor dispersibility in aqueous solution and it is hard to introduce the chemical versatility of function groups. In our study, we present a robust and feasible UCNP modification approach by introducing hyperbranched polyglycerols (hbPGs) as a coating layer. When grafted by hbPGs, the solubility and biocompatibility of UCNPs are significantly improved. Moreover, we also systematically investigated and optimized the chemical modification approach of amino acids or green fluorescence protein (GFP), respectively, grafting onto hbPGs and hbPGs-g-UCNP by oxidizing the vicinal diol to be an aldehyde group, which reacts more feasibly with amino-containing functional molecules. Then, we investigated the drug-encapsulating properties of hbPGs-Arg with DOX and cell imaging of GFP-grafted hbPGs-g-UCNP, respectively. The excellent cell imaging in tumor cells indicated that hbPG-modification of UCNPs displayed potential for applications in drug delivery and disease diagnosis. Full article

(This article belongs to the Special Issue Polymers for Diagnostics and Therapy)

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21 pages, 65081 KB

Open AccessEditor’s ChoiceArticle

Polymer Conformations, Entanglements and Dynamics in Ionic Nanocomposites: A Molecular Dynamics Study

by Ahmad Moghimikheirabadi, Clément Mugemana, Martin Kröger and Argyrios V. Karatrantos

Polymers 2020, 12(11), 2591; https://doi.org/10.3390/polym12112591 - 4 Nov 2020

Cited by 14 | Viewed by 5646

Abstract

We investigate nanoparticle (NP) dispersion, polymer conformations, entanglements and dynamics in ionic nanocomposites. To this end, we study nanocomposite systems with various spherical NP loadings, three different molecular weights, two different Bjerrum lengths, and two types of charge-sequenced polymers by means of molecular [...] Read more.

We investigate nanoparticle (NP) dispersion, polymer conformations, entanglements and dynamics in ionic nanocomposites. To this end, we study nanocomposite systems with various spherical NP loadings, three different molecular weights, two different Bjerrum lengths, and two types of charge-sequenced polymers by means of molecular dynamics simulations. NP dispersion can be achieved in either oligomeric or entangled polymeric matrices due to the presence of electrostatic interactions. We show that the overall conformations of ionic oligomer chains, as characterized by their radii of gyration, are affected by the presence and the amount of charged NPs, while the dimensions of charged entangled polymers remain unperturbed. Both the dynamical behavior of polymers and NPs, and the lifetime and amount of temporary crosslinks, are found to depend on the ratio between the Bjerrum length and characteristic distance between charged monomers. Polymer–polymer entanglements start to decrease beyond a certain NP loading. The dynamics of ionic NPs and polymers is very different compared with their non-ionic counterparts. Specifically, ionic NP dynamics is getting enhanced in entangled matrices and also accelerates with the increase of NP loading. Full article

(This article belongs to the Special Issue Theory of Polymers at Interfaces)

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19 pages, 1764 KB

Open AccessEditor’s ChoiceArticle

Topological Disentanglement of Linear Polymers under Tension

by Michele Caraglio, Boris Marcone, Fulvio Baldovin, Enzo Orlandini and Attilio L. Stella

Polymers 2020, 12(11), 2580; https://doi.org/10.3390/polym12112580 - 3 Nov 2020

Cited by 7 | Viewed by 3140

Abstract

We develop a theoretical description of the topological disentanglement occurring when torus knots reach the ends of a semiflexible polymer under tension. These include decays into simpler knots and total unknotting. The minimal number of crossings and the minimal knot contour length are [...] Read more.

We develop a theoretical description of the topological disentanglement occurring when torus knots reach the ends of a semiflexible polymer under tension. These include decays into simpler knots and total unknotting. The minimal number of crossings and the minimal knot contour length are the topological invariants playing a key role in the model. The crossings behave as particles diffusing along the chain and the application of appropriate boundary conditions at the ends of the chain accounts for the knot disentanglement. Starting from the number of particles and their positions, suitable rules allow reconstructing the type and location of the knot moving on the chain Our theory is extensively benchmarked with corresponding molecular dynamics simulations and the results show a remarkable agreement between the simulations and the theoretical predictions of the model. Full article

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

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14 pages, 5629 KB

Open AccessEditor’s ChoiceArticle

In-Situ Observations of Microscale Ductility in a Quasi-Brittle Bulk Scale Epoxy

by Olivier Verschatse, Lode Daelemans, Wim Van Paepegem and Karen De Clerck

Polymers 2020, 12(11), 2581; https://doi.org/10.3390/polym12112581 - 3 Nov 2020

Cited by 14 | Viewed by 3488

Abstract

Fiber reinforced composite materials are typically comprised of two phases, i.e., the reinforcing fibers and a surrounding matrix. At a high volume fraction of reinforcing fibers, the matrix is confined to a microscale region in between the fibers (1–200 µm). Although these regions [...] Read more.

Fiber reinforced composite materials are typically comprised of two phases, i.e., the reinforcing fibers and a surrounding matrix. At a high volume fraction of reinforcing fibers, the matrix is confined to a microscale region in between the fibers (1–200 µm). Although these regions are interconnected, their behavior is likely dominated by their micro-scale. Nevertheless, the characterization of the matrix material (without reinforcing fibers) is usually performed on macroscopic bulk specimens and little is known about the micro-mechanical behavior of polymer matrix materials. Here, we show that the microscale behavior of an epoxy resin typically used in composite production is clearly different from its macroscale behavior. Microscale polymer specimens were produced by drawing microfibers from vitrifying epoxy resin. After curing, tensile tests were performed on a large set of pure epoxy microfiber specimens with diameters ranging from 30 to 400 µm. An extreme ductility was observed for microscale epoxy specimens, while bulk scale epoxy specimens showed brittle behavior. The microsized epoxy specimens had a plastic deformation behavior resulting in a substantially higher ultimate tensile strength (up to 380 MPa) and strain at break (up to 130 %) compared to their bulk counterpart (68 MPa and 8%). Polarized light microscopy confirmed a rearrangement of the internal epoxy network structure during loading, resulting in the plastic deformation of the microscale epoxy. This was further accompanied by in-situ electron microscopy to further determine the deformation behavior of the micro-specimens during tensile loading and make accurate strain measurements using video-extensometry. This work thus provides novel insights on the epoxy material behavior at the confined microscale as present in fiber reinforced composite materials. Full article

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

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11 pages, 4507 KB

Open AccessEditor’s ChoiceArticle

Effects of SiO₂ Filler in the Shell and Wood Fiber in the Core on the Thermal Expansion of Core–Shell Wood/Polyethylene Composites

by Lichao Sun, Haiyang Zhou, Guanggong Zong, Rongxian Ou, Qi Fan, Junjie Xu, Xiaolong Hao and Qiong Guo

Polymers 2020, 12(11), 2570; https://doi.org/10.3390/polym12112570 - 2 Nov 2020

Cited by 13 | Viewed by 3554

Abstract

The influence of nano-silica (nSiO₂) and micro-silica (mSiO₂) in the shell and wood fiber filler in the core on the thermal expansion behavior of co-extruded wood/polyethylene composites (Co-WPCs) was investigated to optimize the thermal expansion resistance. The cut Co-WPCs [...] Read more.

The influence of nano-silica (nSiO₂) and micro-silica (mSiO₂) in the shell and wood fiber filler in the core on the thermal expansion behavior of co-extruded wood/polyethylene composites (Co-WPCs) was investigated to optimize the thermal expansion resistance. The cut Co-WPCs samples showed anisotropic thermal expansion, and the thermal expansion strain and linear coefficient of thermal expansion (LCTE) decreased by filling the shell layer with rigid silica, especially nSiO₂. Finite element analysis indicated that the polymer-filled shell was mainly responsible for the thermal expansion. The entire Co-WPCs samples exhibited a lower thermal expansion strain than the cut Co-WPCs samples due to protection by the shell. Increasing the wood fiber content in the core significantly decreased the thermal expansion strain and LCTE of the Co-WPCs. The Co-WPCs whose core layer was filled with 70% wood fiber exhibited the greatest anisotropic thermal expansion. Full article

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

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10 pages, 2862 KB

Open AccessEditor’s ChoiceCommunication

Characteristics of Thermosetting Polymer Nanocomposites: Siloxane-Imide-Containing Benzoxazine with Silsesquioxane Epoxy Resins

by Chih-Hao Lin, Wen-Bin Chen, Wha-Tzong Whang and Chun-Hua Chen

Polymers 2020, 12(11), 2510; https://doi.org/10.3390/polym12112510 - 28 Oct 2020

Cited by 16 | Viewed by 3454

Abstract

A series of innovative thermosetting polymer nanocomposites comprising of polysiloxane-imide-containing benzoxazine (PSiBZ) as the matrix and double-decker silsesquioxane (DDSQ) epoxy or polyhedral oligomeric silsesquioxane (POSS) epoxy were prepared for improving thermosetting performance. Thermomechanical and dynamic mechanical characterizations indicated that both DDSQ and POSS [...] Read more.

A series of innovative thermosetting polymer nanocomposites comprising of polysiloxane-imide-containing benzoxazine (PSiBZ) as the matrix and double-decker silsesquioxane (DDSQ) epoxy or polyhedral oligomeric silsesquioxane (POSS) epoxy were prepared for improving thermosetting performance. Thermomechanical and dynamic mechanical characterizations indicated that both DDSQ and POSS could effectively lower the coefficient of thermal expansion by up to approximately 34% and considerably increase the storage modulus (up to 183%). Therefore, DDSQ and POSS are promising materials for low-stress encapsulation for electronic packaging applications. Full article

(This article belongs to the Section Polymer Applications)

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10 pages, 1902 KB

Open AccessEditor’s ChoiceArticle

Re-Processing of Multilayer Plastic Materials as a Part of the Recycling Process: The Features of Processed Multilayer Materials

by Ville Lahtela, Shekhar Silwal and Timo Kärki

Polymers 2020, 12(11), 2517; https://doi.org/10.3390/polym12112517 - 28 Oct 2020

Cited by 31 | Viewed by 8040

Abstract

The weight of packaging materials will be increased with advanced innovations, such as multilayer plastic. The consequence of the advanced innovations is challenges in the following reuse activities. This study aimed to investigate the properties of multilayer plastic materials after recycling processes and [...] Read more.

The weight of packaging materials will be increased with advanced innovations, such as multilayer plastic. The consequence of the advanced innovations is challenges in the following reuse activities. This study aimed to investigate the properties of multilayer plastic materials after recycling processes and will increase the awareness of plastic packaging material for reuse options. In this research, the materials were produced from food packages by crushing them and treating them with injection molding equipment. The implementation of materials in the processing was tested, and the structural and mechanical characteristics of the produced plastic materials was evaluated and discussed. Based on the completed tests, plastic materials used in food packages have the clearest differences in the material features, for instance, the melt flow rate and elongation rate in the tensile test that varied between 2.96–48.4 g/10min and 2–289%, respectively. The variation in the characterizations ranged widely between the material structures. The results indicate that solid plastic packaging materials have better mechanical features compared to foil materials. The structural analysis of materials showed that multilayer plastic includes a wide spectrum of different elements within materials, creating a challenge for future recycling. Full article

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14 pages, 5975 KB

Open AccessEditor’s ChoiceArticle

Topology Optimization of Metal and Carbon Fiber Reinforced Plastic (CFRP) Laminated Battery-Hanging Structure

by Jiaju Chen, Yanan Xu and Yunkai Gao

Polymers 2020, 12(11), 2495; https://doi.org/10.3390/polym12112495 - 27 Oct 2020

Cited by 7 | Viewed by 3838

Abstract

This study addressed the topology optimization of a carbon fiber reinforced plastic (CFRP) laminated battery-hanging structure of an electric vehicle. To accommodate parameterization for thickness and orientation of CFRP materials, the discrete material and thickness optimization (DMTO) technique was adopted. To include metal [...] Read more.

This study addressed the topology optimization of a carbon fiber reinforced plastic (CFRP) laminated battery-hanging structure of an electric vehicle. To accommodate parameterization for thickness and orientation of CFRP materials, the discrete material and thickness optimization (DMTO) technique was adopted. To include metal material as a reinforcement structure into the optimization simultaneously, the DMTO technique was extended here to achieve concurrent optimization of CFRP thickness topology, CFRP orientation selection and the topology of the metal reinforcement plate. Manufacturing constraints were applied, including suppressing intermediate void across the thickness direction of the laminate, contiguity constraint and the symmetrical layers. Sensitivities of the objective function were derived with respect to design variables. To calculate analytical sensitivities, finite element analysis was conducted and strain vectors were exported from a commercial software (ABAQUS) into a mathematical analysis tool (MATLAB). The design objective was to minimize the local displacement subject to the constraints of manufacturing and mass fraction. The mechanical performance of the optimized CFRP structure was compared with the original steel structure. To validate the optimization results, a prototype of the CFRP battery-hanging structure was fabricated and experimental testing was conducted. The results show that the total mass of the CFRP battery-hanging structure was reduced by 34.3% when compared with the steel one, while the mechanical property was improved by 25.3%. Full article

(This article belongs to the Special Issue Carbon Based on Fibers, Polymers and Composites)

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16 pages, 5605 KB

Open AccessEditor’s ChoiceArticle

Morphological Changes in Astrocytes by Self-Oxidation of Dopamine to Polydopamine and Quantification of Dopamine through Multivariate Regression Analysis of Polydopamine Images

by Anik Karan, Elnaz Khezerlou, Farnaz Rezaei, Leon Iasemidis and Mark A. DeCoster

Polymers 2020, 12(11), 2483; https://doi.org/10.3390/polym12112483 - 26 Oct 2020

Cited by 11 | Viewed by 3488

Abstract

Astrocytes, also known as astroglia, are important cells for the structural support of neurons as well as for biochemical balance in the central nervous system (CNS). In this study, the polymerization of dopamine (DA) to polydopamine (PDA) and its effect on astrocytes was [...] Read more.

Astrocytes, also known as astroglia, are important cells for the structural support of neurons as well as for biochemical balance in the central nervous system (CNS). In this study, the polymerization of dopamine (DA) to polydopamine (PDA) and its effect on astrocytes was investigated. The polymerization of DA, being directly proportional to the DA concentration, raises the prospect of detecting DA concentration from PDA optically using image-processing techniques. It was found here that DA, a naturally occurring neurotransmitter, significantly altered astrocyte cell number, morphology, and metabolism, compared to astrocytes in the absence of DA. Along with these effects on astrocytes, the polymerization of DA to PDA was tracked optically in the same cell culture wells. This polymerization process led to a unique methodology based on multivariate regression analysis that quantified the concentration of DA from optical images of astrocyte cell culture media. Therefore, this developed methodology, combined with conventional imaging equipment, could be used in place of high-end and expensive analytical chemistry instruments, such as spectrophotometry, mass spectrometry, and fluorescence techniques, for quantification of the concentration of DA after polymerization to PDA under in vitro and potentially in vivo conditions. Full article

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

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21 pages, 1956 KB

Open AccessEditor’s ChoiceArticle

Cellulose Nanofibers from a Dutch Elm Disease-Resistant Ulmus minor Clone

by Laura Jiménez-López, María E. Eugenio, David Ibarra, Margarita Darder, Juan A. Martín and Raquel Martín-Sampedro

Polymers 2020, 12(11), 2450; https://doi.org/10.3390/polym12112450 - 23 Oct 2020

Cited by 24 | Viewed by 3739

Abstract

The potential use of elm wood in lignocellulosic industries has been hindered by the Dutch elm disease (DED) pandemics, which have ravaged European and North American elm groves in the last century. However, the selection of DED-resistant cultivars paves the way for their [...] Read more.

The potential use of elm wood in lignocellulosic industries has been hindered by the Dutch elm disease (DED) pandemics, which have ravaged European and North American elm groves in the last century. However, the selection of DED-resistant cultivars paves the way for their use as feedstock in lignocellulosic biorefineries. Here, the production of cellulose nanofibers from the resistant Ulmus minor clone Ademuz was evaluated for the first time. Both mechanical (PFI refining) and chemical (TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation) pretreatments were assessed prior to microfluidization, observing not only easier fibrillation but also better optical and barrier properties for elm nanopapers compared to eucalyptus ones (used as reference). Furthermore, mechanically pretreated samples showed higher strength for elm nanopapers. Although lower nanofibrillation yields were obtained by mechanical pretreatment, nanofibers showed higher thermal, mechanical and barrier properties, compared to TEMPO-oxidized nanofibers. Furthermore, lignin-containing elm nanofibers presented the most promising characteristics, with slightly lower transparencies. Full article

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

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18 pages, 4177 KB

Open AccessEditor’s ChoiceArticle

Phase Equilibrium and Interdiffusion in Poly(Vinyl Methyl Ether)-Water System

by Uliana V. Nikulova and Anatoly E. Chalykh

Polymers 2020, 12(11), 2445; https://doi.org/10.3390/polym12112445 - 22 Oct 2020

Cited by 12 | Viewed by 2913

Abstract

The phase state diagram of the poly(vinyl methyl ether)-water system in a wide concentration range was obtained by the optical interferometry method. It was shown that this system was characterized by a complicated phase equilibrium with two lower critical solution temperatures, one of [...] Read more.

The phase state diagram of the poly(vinyl methyl ether)-water system in a wide concentration range was obtained by the optical interferometry method. It was shown that this system was characterized by a complicated phase equilibrium with two lower critical solution temperatures, one of which was located in the concentrated region at 21 °C, and the other one in the region of a dilute solution at 31 °C. In the framework of the Flory–Huggins theory, pair interaction parameters were calculated for different parts of the binodal curves, and an attempt was made to reverse simulate the diagram in different conditions. It was suggested that the unusual character of the diagram was associated with the formation of a complicated complex between PVME and water in the middle region of the compositions. Concentration profiles for different temperatures were constructed. For the first time for this system, the numerical values of the diffusion coefficients of poly(vinyl methyl ether) (PVME) into water and water in PVME were obtained. Concentration and temperature dependences of diffusion coefficients were constructed and analyzed. The kinetics of water sorption in PVME was plotted, the clustering integral was calculated, and the approximate number of molecules in a water cluster was estimated. It was shown that in the dilute solution region upon passing through the binodal curve, the interphase disappeared immediately, and the remaining fluctuation of the concentration decreased in size with time. The kinetics of this process was estimated from the change in the size of such a particle. Full article

(This article belongs to the Section Polymer Physics and Theory)

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11 pages, 2163 KB

Open AccessEditor’s ChoiceArticle

Axial Orientation of Co-Crystalline Phases of Poly(2,6-Dimethyl-1,4-Phenylene)Oxide Films

by Manohar Golla, Baku Nagendra, Christophe Daniel, Paola Rizzo and Gaetano Guerra

Polymers 2020, 12(10), 2394; https://doi.org/10.3390/polym12102394 - 17 Oct 2020

Cited by 9 | Viewed by 2961

Abstract

Films exhibiting co-crystalline (CC) phases between a polymer host and low-molecular-mass guest molecules are relevant for many applications. As is usual for semi-crystalline polymers, axially oriented films can give relevant information on the crystalline structure, both by Wide Angle X-ray diffraction fiber patterns [...] Read more.

Films exhibiting co-crystalline (CC) phases between a polymer host and low-molecular-mass guest molecules are relevant for many applications. As is usual for semi-crystalline polymers, axially oriented films can give relevant information on the crystalline structure, both by Wide Angle X-ray diffraction fiber patterns and by polarized Fourier-transform infrared spectroscopy. Axially oriented CC phases of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) with 1,3,5-trimethylbenzene (mesitylene) can be simply obtained by the stretching of CC PPO films. In fact, due to the plasticization effect of this highly boiling guest, PPO orientation can occur in a stretching temperature range (170–175 °C) nearly 50 °C lower than that generally needed for PPO films (220–230 °C). This low stretching temperature range allows avoidance of polymer oxidation, as well as formation of the mesomorphic dense γ PPO phase. Axially oriented CC phases of PPO with toluene, i.e., with a more volatile guest, can be instead obtained by the stretching (in the same low temperature range: 170–175 °C) of CC PPO blend films with polystyrene. Full article

(This article belongs to the Section Polymer Physics and Theory)

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10 pages, 4516 KB

Open AccessEditor’s ChoiceCommunication

Urethane-Acrylate/Aramid Nanocomposites Based on Graphenic Materials. A Comparative Study of Their Mechanical Properties

by Israel Gago, Manuel del Río, Gerardo León and Beatriz Miguel

Polymers 2020, 12(10), 2388; https://doi.org/10.3390/polym12102388 - 16 Oct 2020

Cited by 4 | Viewed by 2626

Abstract

Urethane-acrylate thermoset resins (UATR) are a new type of polymeric matrix that have recently made a strong breakthrough in the composites sector. This is because of their properties, which make them an advantageous alternative to epoxy resins, especially if they are reinforced with [...] Read more.

Urethane-acrylate thermoset resins (UATR) are a new type of polymeric matrix that have recently made a strong breakthrough in the composites sector. This is because of their properties, which make them an advantageous alternative to epoxy resins, especially if they are reinforced with high-performance fibers such as aramids. Graphene-based nanocomposites are one of the most dynamic research fields in nanotechnology, because graphenic materials greatly improve the properties of traditional composites. This work represents a comparative study of the effect of adding three types of graphenic materials on the mechanical properties of UATR/aramid composites. Several UATR polymeric matrices were doped at 2% w/w with graphene nanoplatelets (GNPs), reduced graphene oxide (rGO) and pristine few-layer graphene (FLG), and reinforced with Twaron CT709 para-aramid fibers. The obtained laminates showed low density (1.38 g·cm⁻³), a high volumetric fiber–resin ratio (80:20), homogeneous dispersion of the nanoreinforcement, high reproducibility, and easy scalability. The tensile, flexural and impact strength properties of the undoped composite and the graphene-doped nanocomposites were determined. FLG-doped nanocomposites showed the highest increase in all the mentioned mechanical properties and attained a very significant relative improvement over the undoped laminate (up to 134.4% in a_CU). Full article

(This article belongs to the Special Issue Mechanical Reinforcement and Multifunctionality of Polymer Nanocomposites)

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16 pages, 6769 KB

Open AccessEditor’s ChoiceArticle

Core-Shell Nanofibers of Polyvinylidene Fluoride-based Nanocomposites as Piezoelectric Nanogenerators

by Deepalekshmi Ponnamma, Mariem Mohammed Chamakh, Abdulrhman Mohmmed Alahzm, Nisa Salim, Nishar Hameed and Mariam Al Ali AlMaadeed

Polymers 2020, 12(10), 2344; https://doi.org/10.3390/polym12102344 - 13 Oct 2020

Cited by 46 | Viewed by 5647

Abstract

Flexible piezoelectric nanogenerators (PENG) are widely applied to harvest sustainable energy from multiple energy sources. The rational and simple design of PENG have great potential in soft electronics. Here we design a highly flexible PENG using the polyvinylidene fluoride (PVDF) and its copolymer, [...] Read more.

Flexible piezoelectric nanogenerators (PENG) are widely applied to harvest sustainable energy from multiple energy sources. The rational and simple design of PENG have great potential in soft electronics. Here we design a highly flexible PENG using the polyvinylidene fluoride (PVDF) and its copolymer, polyvinylidene hexafluoropropylene (PVDF-HFP) with two nanoarchitectures of semiconducting metal oxides, TiO₂ and ZnO. The nanotubes of TiO₂ and nanoflowers of ZnO are embedded in these different polymeric media by solvent mixing, and new fiber mats are generated by coaxial electrospinning technique. This process aligns the dipoles of polymers and nanomaterials, which is normally a pre-requisite for higher piezo potential. With excellent mechanical strength and flexibility, the tailored lightweight fiber mats are capable of producing good output voltage (a maximum of 14 V) during different mechanical vibrations at various frequencies and in response to human motions. The hybrid nanocomposite PENG is durable and inexpensive and has possible applications in wearable electronics. Full article

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

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20 pages, 7258 KB

Open AccessEditor’s ChoiceArticle

The Effect of Dye and Pigment Concentrations on the Diameter of Melt-Electrospun Polylactic Acid Fibers

by N.K. Balakrishnan, K. Koenig and G. Seide

Polymers 2020, 12(10), 2321; https://doi.org/10.3390/polym12102321 - 11 Oct 2020

Cited by 26 | Viewed by 4935

Abstract

Sub-microfibers and nanofibers produce more breathable fabrics than coarse fibers and are therefore widely used in the textiles industry. They are prepared by electrospinning using a polymer solution or melt. Solution electrospinning produces finer fibers but requires toxic solvents. Melt electrospinning is more [...] Read more.

Sub-microfibers and nanofibers produce more breathable fabrics than coarse fibers and are therefore widely used in the textiles industry. They are prepared by electrospinning using a polymer solution or melt. Solution electrospinning produces finer fibers but requires toxic solvents. Melt electrospinning is more environmentally friendly, but is also technically challenging due to the low electrical conductivity and high viscosity of the polymer melt. Here we describe the use of colorants as additives to improve the electrical conductivity of polylactic acid (PLA). The addition of colorants increased the viscosity of the melt by >100%, but reduced the electrical resistance by >80% compared to pure PLA (5 GΩ). The lowest electrical resistance of 50 MΩ was achieved using a composite containing 3% (w/w) indigo. However, the thinnest fibers (52.5 µm, 53% thinner than pure PLA fibers) were obtained by adding 1% (w/w) alizarin. Scanning electron microscopy revealed that fibers containing indigo featured polymer aggregates that inhibited electrical conductivity, and thus increased the fiber diameter. With further improvements to avoid aggregation, the proposed melt electrospinning process could complement or even replace industrial solution electrospinning and dyeing. Full article

(This article belongs to the Special Issue Conductive Polymer Composites)

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10 pages, 2567 KB

Open AccessEditor’s ChoiceArticle

The Role of Interfacial Interactions on the Functional Properties of Ethylene–Propylene Copolymer Containing SiO₂ Nanoparticles

by Iman Taraghi, Sandra Paszkiewicz, Izabela Irska, Krzysztof Pypeć and Elżbieta Piesowicz

Polymers 2020, 12(10), 2308; https://doi.org/10.3390/polym12102308 - 9 Oct 2020

Cited by 3 | Viewed by 2258

Abstract

In this paper, the mechanical properties, thermal stability, and transparency of ethylene–propylene copolymer (EPC) elastomer modified with various weight percentages (1, 3, and 5 wt.%) of SiO₂ nanofillers have been studied. The nanocomposites were prepared via a simple melt mixing method. The [...] Read more.

In this paper, the mechanical properties, thermal stability, and transparency of ethylene–propylene copolymer (EPC) elastomer modified with various weight percentages (1, 3, and 5 wt.%) of SiO₂ nanofillers have been studied. The nanocomposites were prepared via a simple melt mixing method. The morphological results revealed that the nanofillers were uniformly dispersed in the elastomer, where a low concentration of SiO₂ (1 wt.%) had been added into the elastomer. The FTIR showed that there are interfacial interactions between EPC matrix and silanol groups of SiO₂ nanoparticles. Moreover, by the addition of 1 wt.% of SiO₂ in the EPC, the tensile strength and elongation at break of EPC increased by about 38% and 27%, respectively. Finally, all samples were optically transparent, and the transparency of the nanocomposites reduced by increasing the content of SiO₂ nanoparticles. Full article

(This article belongs to the Special Issue Mechanical Reinforcement and Multifunctionality of Polymer Nanocomposites)

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12 pages, 2189 KB

Open AccessEditor’s ChoiceArticle

Electrodeposited Polyaniline Nanofibers and MoO₃ Nanobelts for High-Performance Asymmetric Supercapacitor with Redox Active Electrolyte

by Wei Meng, Yanlin Xia, Chuanguo Ma and Xusheng Du

Polymers 2020, 12(10), 2303; https://doi.org/10.3390/polym12102303 - 8 Oct 2020

Cited by 25 | Viewed by 4856

Abstract

Transition molybdenum oxides (MoO₃) and conductive polymer (polyaniline, PANI) nanomaterials were fabricated and asymmetric supercapacitor (ASC) was assembled with MoO₃ nanobelts as negative electrode and PANI nanofibers as a positive electrode. Branched PANI nanofibers with a diameter of 100 nm [...] Read more.

Transition molybdenum oxides (MoO₃) and conductive polymer (polyaniline, PANI) nanomaterials were fabricated and asymmetric supercapacitor (ASC) was assembled with MoO₃ nanobelts as negative electrode and PANI nanofibers as a positive electrode. Branched PANI nanofibers with a diameter of 100 nm were electrodeposited on Ti mesh substrate and MoO₃ nanobelts with width of 30–700 nm were obtained by the hydrothermal reaction method in an autoclave. Redox active electrolyte containing 0.1 M Fe^2+/3+ redox couple was adopted in order to enhance the electrochemical performance of the electrode nano-materials. As a result, the PANI electrode shows a great capacitance of 3330 F g⁻¹ at 1 A g⁻¹ in 0.1 M Fe^2+/3+/0.5 M H₂SO₄ electrolyte. The as-assembled ASC achieved a great energy density of 54 Wh kg⁻¹ at power density of 900 W kg⁻¹. In addition, it displayed significant cycle stability and its capacitance even increased to 109% of the original value after 1000 charge–discharge cycles. The superior performance of the capacitors indicates their promising application as energy storage devices. Full article

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

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23 pages, 2549 KB

Open AccessEditor’s ChoiceArticle

Effect of Clay Nanofillers on the Mechanical and Water Vapor Permeability Properties of Xylan–Alginate Films

by Darrel S. Naidu and Maya J. John

Polymers 2020, 12(10), 2279; https://doi.org/10.3390/polym12102279 - 4 Oct 2020

Cited by 58 | Viewed by 5288

Abstract

In this study, xylan–alginate-based films were reinforced with nanoclays (bentonite or halloysite) by the solvent casting technique. The effect of the nanoclay loadings (1–5 wt %) on various properties—mechanical, optical, thermal, solubility, water sorption, and water vapor permeability (WVP)—of the xylan–alginate films were [...] Read more.

In this study, xylan–alginate-based films were reinforced with nanoclays (bentonite or halloysite) by the solvent casting technique. The effect of the nanoclay loadings (1–5 wt %) on various properties—mechanical, optical, thermal, solubility, water sorption, and water vapor permeability (WVP)—of the xylan–alginate films were examined for their application as food packaging materials. A 5 wt % loading of either bentonite or halloysite resulted in a 49% decrease of the WVP due to the impermeable nature of the silicate layers that make up both bentonite and halloysite. Thermal stability and solubility of the nanocomposite films were not significantly influenced by the presence of the nanoclays, whereas the optical properties were significantly improved when compared to neat xylan–alginate blend. In general, films reinforced with bentonite exhibited superior mechanical and optical properties when compared to both halloysite-based nanocomposite and neat films. Full article

(This article belongs to the Special Issue Multifunctional Ecocomposites)

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36 pages, 7444 KB

Open AccessEditor’s ChoiceReview

Polysaccharide-Based In Situ Self-Healing Hydrogels for Tissue Engineering Applications

by Sheila Maiz-Fernández, Leyre Pérez-Álvarez, Leire Ruiz-Rubio, Jose Luis Vilas-Vilela and Senentxu Lanceros-Mendez

Polymers 2020, 12(10), 2261; https://doi.org/10.3390/polym12102261 - 1 Oct 2020

Cited by 47 | Viewed by 7693

Abstract

In situ hydrogels have attracted increasing interest in recent years due to the need to develop effective and practical implantable platforms. Traditional hydrogels require surgical interventions to be implanted and are far from providing personalized medicine applications. However, in situ hydrogels offer a [...] Read more.

In situ hydrogels have attracted increasing interest in recent years due to the need to develop effective and practical implantable platforms. Traditional hydrogels require surgical interventions to be implanted and are far from providing personalized medicine applications. However, in situ hydrogels offer a wide variety of advantages, such as a non-invasive nature due to their localized action or the ability to perfectly adapt to the place to be replaced regardless the size, shape or irregularities. In recent years, research has particularly focused on in situ hydrogels based on natural polysaccharides due to their promising properties such as biocompatibility, biodegradability and their ability to self-repair. This last property inspired in nature gives them the possibility of maintaining their integrity even after damage, owing to specific physical interactions or dynamic covalent bonds that provide reversible linkages. In this review, the different self-healing mechanisms, as well as the latest research on in situ self-healing hydrogels, is presented, together with the potential applications of these materials in tissue regeneration. Full article

(This article belongs to the Special Issue In-Situ Forming and Self-Healing Hydrogels)

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9 pages, 1660 KB

Open AccessEditor’s ChoiceArticle

Using Thermally Crosslinkable Hole Transporting Layer to Improve Interface Characteristics for Perovskite CsPbBr₃ Quantum-Dot Light-Emitting Diodes

by Chun-Cheng Lin, Shao-Yang Yeh, Wei-Lun Huang, You-Xun Xu, Yan-Siang Huang, Tzu-Hung Yeh, Ching-Ho Tien, Lung-Chien Chen and Zong-Liang Tseng

Polymers 2020, 12(10), 2243; https://doi.org/10.3390/polym12102243 - 29 Sep 2020

Cited by 23 | Viewed by 4615

Abstract

In this paper, a thermally crosslinkable 9,9-Bis[4-[(4-ethenylphenyl)methoxy]phenyl]-N2,N7-di-1-naphthalenyl-N2,N7-diphenyl-9H-fluorene-2,7-diamine (VB-FNPD) film served as the hole transporting layer (HTL) of perovskite CsPbBr₃ quantum-dot light-emitting diodes (QD-LEDs) was investigated and reported. The VB-FNPD film crosslinked at various temperatures in the range of 100~230 °C followed by [...] Read more.

In this paper, a thermally crosslinkable 9,9-Bis[4-[(4-ethenylphenyl)methoxy]phenyl]-N2,N7-di-1-naphthalenyl-N2,N7-diphenyl-9H-fluorene-2,7-diamine (VB-FNPD) film served as the hole transporting layer (HTL) of perovskite CsPbBr₃ quantum-dot light-emitting diodes (QD-LEDs) was investigated and reported. The VB-FNPD film crosslinked at various temperatures in the range of 100~230 °C followed by a spin-coating process to improve their chemical bonds in an attempt to resist the erosion from the organic solvent in the remaining fabrication process. It is shown that the device with VB-FNPD HTL crosslinking at 170 °C has the highest luminance of 7702 cd/m², the maximum current density (J) of 41.98 mA/cm², the maximum current efficiency (CE) of 5.45 Cd/A, and the maximum external quantum efficiency (EQE) of 1.64%. Our results confirm that the proposed thermally crosslinkable VB-FNPD is a candidate for the HTL of QD-LEDs. Full article

(This article belongs to the Section Polymer Applications)

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12 pages, 5173 KB

Open AccessEditor’s ChoiceArticle

A Collagen-Based Scaffold for Promoting Neural Plasticity in a Rat Model of Spinal Cord Injury

by Jue-Zong Yeh, Ding-Han Wang, Juin-Hong Cherng, Yi-Wen Wang, Gang-Yi Fan, Nien-Hsien Liou, Jiang-Chuan Liu and Chung-Hsing Chou

Polymers 2020, 12(10), 2245; https://doi.org/10.3390/polym12102245 - 29 Sep 2020

Cited by 18 | Viewed by 4819

Abstract

In spinal cord injury (SCI) therapy, glial scarring formed by activated astrocytes is a primary problem that needs to be solved to enhance axonal regeneration. In this study, we developed and used a collagen scaffold for glial scar replacement to create an appropriate [...] Read more.

In spinal cord injury (SCI) therapy, glial scarring formed by activated astrocytes is a primary problem that needs to be solved to enhance axonal regeneration. In this study, we developed and used a collagen scaffold for glial scar replacement to create an appropriate environment in an SCI rat model and determined whether neural plasticity can be manipulated using this approach. We used four experimental groups, as follows: SCI-collagen scaffold, SCI control, normal spinal cord-collagen scaffold, and normal control. The collagen scaffold showed excellent in vitro and in vivo biocompatibility. Immunofluorescence staining revealed increased expression of neurofilament and fibronectin and reduced expression of glial fibrillary acidic protein and anti-chondroitin sulfate in the collagen scaffold-treated SCI rats at 1 and 4 weeks post-implantation compared with that in untreated SCI control. This indicates that the collagen scaffold implantation promoted neuronal survival and axonal growth within the injured site and prevented glial scar formation by controlling astrocyte production for their normal functioning. Our study highlights the feasibility of using the collagen scaffold in SCI repair. The collagen scaffold was found to exert beneficial effects on neuronal activity and may help in manipulating synaptic plasticity, implying its great potential for clinical application in SCI. Full article

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

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36 pages, 4245 KB

Open AccessEditor’s ChoiceReview

Fish Collagen: Extraction, Characterization, and Applications for Biomaterials Engineering

by Hafez Jafari, Alberto Lista, Manuela Mafosso Siekapen, Pejman Ghaffari-Bohlouli, Lei Nie, Houman Alimoradi and Amin Shavandi

Polymers 2020, 12(10), 2230; https://doi.org/10.3390/polym12102230 - 28 Sep 2020

Cited by 369 | Viewed by 53500

Abstract

The utilization of marine-based collagen is growing fast due to its unique properties in comparison with mammalian-based collagen such as no risk of transmitting diseases, a lack of religious constraints, a cost-effective process, low molecular weight, biocompatibility, and its easy absorption by the [...] Read more.

The utilization of marine-based collagen is growing fast due to its unique properties in comparison with mammalian-based collagen such as no risk of transmitting diseases, a lack of religious constraints, a cost-effective process, low molecular weight, biocompatibility, and its easy absorption by the human body. This article presents an overview of the recent studies from 2014 to 2020 conducted on collagen extraction from marine-based materials, in particular fish by-products. The fish collagen structure, extraction methods, characterization, and biomedical applications are presented. More specifically, acetic acid and deep eutectic solvent (DES) extraction methods for marine collagen isolation are described and compared. In addition, the effect of the extraction parameters (temperature, acid concentration, extraction time, solid-to-liquid ratio) on the yield of collagen is investigated. Moreover, biomaterials engineering and therapeutic applications of marine collagen have been summarized. Full article

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

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11 pages, 4045 KB

Open AccessEditor’s ChoiceArticle

Influence of Repetitive Square Voltage Duty Cycle on the Electrical Tree Characteristics of Epoxy Resin

by Peng Wang, Suxin Hui, Shakeel Akram, Kai Zhou, Muhammad Tariq Nazir, Yiwen Chen, Han Dong, Muhammad Sufyan Javed and Inzamam Ul Haq

Polymers 2020, 12(10), 2215; https://doi.org/10.3390/polym12102215 - 27 Sep 2020

Cited by 23 | Viewed by 3495

Abstract

The application of wide band-gap power electronic devices brings more challenges to insulating packaging technology. Knowing the influence of applied voltage parameters on insulation performance is helpful to evaluate the insulation condition of electric power equipment. In this paper, the effect of repetitive [...] Read more.

The application of wide band-gap power electronic devices brings more challenges to insulating packaging technology. Knowing the influence of applied voltage parameters on insulation performance is helpful to evaluate the insulation condition of electric power equipment. In this paper, the effect of repetitive square wave voltage duty cycle on the growth characteristics of electrical trees in epoxy resin was studied. The experimental results show that the square wave voltage duty cycle has a significant influence on treeing features. The electrical tree proportion initiation has shown a decreasing trend, and the shape of the electrical tree changes from pine-like to branch-like by increasing the duty cycles. The length and damaged area of electrical tree increased with the increase in the duty cycle up to 10% and then decrease by increasing the duty cycle higher than 30%. It indicates that a low duty cycle will enhance the electron injection and accumulate space charges and thus accelerate electrical tree development. Under short duty cycles, the electric field due to the shielding effect near the needle tip suppresses the electrical tree growth, which results in treeing growth stagnation. The obtained results are helpful to keep these parameters in mind during the design of epoxy-based insulation such high-voltage rotating machines and power electronic device packaging. Full article

(This article belongs to the Special Issue Multi-Functional Smart Dielectric Materials for High Voltage Insulation)

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13 pages, 26517 KB

Open AccessEditor’s ChoiceArticle

Barrier Film of Etherified Hemicellulose from Single-Step Synthesis

by Hui Shao, Yuelong Zhao, Hui Sun, Biao Yang, Baomin Fan, Huijuan Zhang and Yunxuan Weng

Polymers 2020, 12(10), 2199; https://doi.org/10.3390/polym12102199 - 25 Sep 2020

Cited by 12 | Viewed by 3749

Abstract

Hemicellulose with good biodegradability and low oxygen permeability shows great potential in food packaging. However, its strong hydrophilicity leads to its poor moisture resistance, which hinders its wider application. In this paper, a near-hydrophobic hemicellulose was obtained by using single-step synthesis from poplar [...] Read more.

Hemicellulose with good biodegradability and low oxygen permeability shows great potential in food packaging. However, its strong hydrophilicity leads to its poor moisture resistance, which hinders its wider application. In this paper, a near-hydrophobic hemicellulose was obtained by using single-step synthesis from poplar powder via etherification modification with epoxy chloropropane. This proposed approach has the advantage of avoiding the destruction of hemicellulose structure by secondary alkali-hydrolysis, which was what usually occurred in traditional etherification procedures. The feasibility of using epoxy chloropropane as an alkylation reagent to etherify hemicellulose was confirmed, and the reaction mechanism was elucidated. Contact angle test, thermogravimetric analysis, oxygen transmittance test, and infrared spectrum analysis showed that the barrier property and thermal stability of etherified hemicellulose films have been significantly improved. At an epoxy chloropropane/wood powder ratio (volume/weight) of 2/3 (mL/g), the epoxy hemicellulose films contained the most epoxy groups and displayed the best performance, i.e., tensile strength of 14.6 MPa, surface contact angle of 71.7° and oxygen transmission coefficient of 1.9 (cm³·µm)/(m²·d·kPa), showing great promise as barrier film in food-packaging. Full article

(This article belongs to the Special Issue Advanced Polymeric Materials for Membrane Technology)

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10 pages, 2220 KB

Open AccessEditor’s ChoiceCommunication

Fine-Structure Analysis of Perhydropolysilazane-Derived Nano Layers in Deep-Buried Condition Using Polarized Neutron Reflectometry

by Kazuhiro Akutsu-Suyama, Hiroshi Kira, Noboru Miyata, Takayasu Hanashima, Tsukasa Miyazaki, Satoshi Kasai, Dai Yamazaki, Kazuhiko Soyama and Hiroyuki Aoki

Polymers 2020, 12(10), 2180; https://doi.org/10.3390/polym12102180 - 24 Sep 2020

Cited by 6 | Viewed by 4047

Abstract

A large background scattering originating from the sample matrix is a major obstacle for fine-structure analysis of a nanometric layer buried in a bulk material. As polarization analysis can decrease undesired scattering in a neutron reflectivity (NR) profile, we performed NR experiments with [...] Read more.

A large background scattering originating from the sample matrix is a major obstacle for fine-structure analysis of a nanometric layer buried in a bulk material. As polarization analysis can decrease undesired scattering in a neutron reflectivity (NR) profile, we performed NR experiments with polarization analysis on a polypropylene (PP)/perhydropolysilazane-derived SiO₂ (PDS)/Si substrate sample, having a deep-buried layer of SiO₂ to elucidate the fine structure of the nano-PDS layer. This method offers unique possibilities for increasing the amplitude of the Kiessig fringes in the higher scattering vector (Q_z) region of the NR profiles in the sample by decreasing the undesired background scattering. Fitting and Fourier transform analysis results of the NR data indicated that the synthesized PDS layer remained between the PP plate and Si substrate with a thickness of approximately 109 Å. Furthermore, the scattering length density of the PDS layer, obtained from the background subtracted data appeared to be more accurate than that obtained from the raw data. Although the density of the PDS layer was lower than that of natural SiO₂, the PDS thin layer had adequate mechanical strength to maintain a uniform PDS layer in the depth-direction under the deep-buried condition. Full article

(This article belongs to the Special Issue Advances in Multifunctional Smart Coatings)

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44 pages, 9288 KB

Open AccessEditor’s ChoiceReview

Recent Advances in the Synthesis and Application of Polymer Compartments for Catalysis

by Tai-Lam Nghiem, Deniz Coban, Stefanie Tjaberings and André H. Gröschel

Polymers 2020, 12(10), 2190; https://doi.org/10.3390/polym12102190 - 24 Sep 2020

Cited by 40 | Viewed by 12008

Abstract

Catalysis is one of the most important processes in nature, science, and technology, that enables the energy efficient synthesis of essential organic compounds, pharmaceutically active substances, and molecular energy sources. In nature, catalytic reactions typically occur in aqueous environments involving multiple catalytic sites. [...] Read more.

Catalysis is one of the most important processes in nature, science, and technology, that enables the energy efficient synthesis of essential organic compounds, pharmaceutically active substances, and molecular energy sources. In nature, catalytic reactions typically occur in aqueous environments involving multiple catalytic sites. To prevent the deactivation of catalysts in water or avoid unwanted cross-reactions, catalysts are often site-isolated in nanopockets or separately stored in compartments. These concepts have inspired the design of a range of synthetic nanoreactors that allow otherwise unfeasible catalytic reactions in aqueous environments. Since the field of nanoreactors is evolving rapidly, we here summarize—from a personal perspective—prominent and recent examples for polymer nanoreactors with emphasis on their synthesis and their ability to catalyze reactions in dispersion. Examples comprise the incorporation of catalytic sites into hydrophobic nanodomains of single chain polymer nanoparticles, molecular polymer nanoparticles, and block copolymer micelles and vesicles. We focus on catalytic reactions mediated by transition metal and organocatalysts, and the separate storage of multiple catalysts for one-pot cascade reactions. Efforts devoted to the field of nanoreactors are relevant for catalytic chemistry and nanotechnology, as well as the synthesis of pharmaceutical and natural compounds. Optimized nanoreactors will aid in the development of more potent catalytic systems for green and fast reaction sequences contributing to sustainable chemistry by reducing waste of solvents, reagents, and energy. Full article

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

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14 pages, 2453 KB

Open AccessEditor’s ChoiceArticle

Grafting with RAFT—gRAFT Strategies to Prepare Hybrid Nanocarriers with Core-shell Architecture

by José L. M. Gonçalves, Edgar J. Castanheira, Sérgio P. C. Alves, Carlos Baleizão and José Paulo Farinha

Polymers 2020, 12(10), 2175; https://doi.org/10.3390/polym12102175 - 23 Sep 2020

Cited by 12 | Viewed by 4776

Abstract

Stimuli-responsive polymer materials are used in smart nanocarriers to provide the stimuli-actuated mechanical and chemical changes that modulate cargo delivery. To take full advantage of the potential of stimuli-responsive polymers for controlled delivery applications, these have been grafted to the surface of mesoporous [...] Read more.

Stimuli-responsive polymer materials are used in smart nanocarriers to provide the stimuli-actuated mechanical and chemical changes that modulate cargo delivery. To take full advantage of the potential of stimuli-responsive polymers for controlled delivery applications, these have been grafted to the surface of mesoporous silica particles (MSNs), which are mechanically robust, have very large surface areas and available pore volumes, uniform and tunable pore sizes and a large diversity of surface functionalization options. Here, we explore the impact of different RAFT-based grafting strategies on the amount of a pH-responsive polymer incorporated in the shell of MSNs. Using a “grafting to” (gRAFT-to) approach we studied the effect of polymer chain size on the amount of polymer in the shell. This was compared with the results obtained with a “grafting from” (gRAFT-from) approach, which yield slightly better polymer incorporation values. These two traditional grafting methods yield relatively limited amounts of polymer incorporation, due to steric hindrance between free chains in “grafting to” and to termination reactions between growing chains in “grafting from.” To increase the amount of polymer in the nanocarrier shell, we developed two strategies to improve the “grafting from” process. In the first, we added a cross-linking agent (gRAFT-cross) to limit the mobility of the growing polymer and thus decrease termination reactions at the MSN surface. On the second, we tested a hybrid grafting process (gRAFT-hybrid) where we added MSNs functionalized with chain transfer agent to the reaction media containing monomer and growing free polymer chains. Our results show that both modifications yield a significative increase in the amount of grafted polymer. Full article

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

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25 pages, 2124 KB

Open AccessEditor’s ChoiceReview

The Potential for Bio-Sustainable Organobromine-Containing Flame Retardant Formulations for Textile Applications—A Review

by A Richard Horrocks

Polymers 2020, 12(9), 2160; https://doi.org/10.3390/polym12092160 - 22 Sep 2020

Cited by 46 | Viewed by 6713

Abstract

This review considers the challenge of developing sustainable organobromine flame retardants (BrFRs) and alternative synergists to the predominantly used antimony III oxide. Current BrFR efficiencies are reviewed for textile coatings and back-coatings with a focus on furnishing and similar fabrics covering underlying flammable [...] Read more.

This review considers the challenge of developing sustainable organobromine flame retardants (BrFRs) and alternative synergists to the predominantly used antimony III oxide. Current BrFR efficiencies are reviewed for textile coatings and back-coatings with a focus on furnishing and similar fabrics covering underlying flammable fillings, such as flexible polyurethane foam. The difficulty of replacing them with non-halogen-containing systems is also reviewed with major disadvantages including their extreme specificity with regard to a given textile type and poor durability.The possibility of replacing currently used BrFRs for textiles structures that mimic naturally occurring organobromine-containing species is discussed, noting that of the nearly 2000 such species identified in both marine and terrestrial environments, a significant number are functionalised polybrominated diphenyl ethers, which form part of a series of little understood biosynthetic biodegradation cycles.The continued use of antimony III oxide as synergist and possible replacement by alternatives, such as the commercially available zinc stannates and the recently identified zinc tungstate, are discussed. Both are effective as synergists and smoke suppressants, but unlike Sb₂0₃, they have efficiencies dependent on BrFR chemistry and polymer matrix or textile structure. Furthermore, their effectiveness in textile coatings has yet to be more fully assessed.In conclusion, it is proposed that the future of sustainable BrFRs should be based on naturally occurring polybrominated structures developed in conjunction with non-toxic, smoke-suppressing synergists such as the zinc stannates or zinc tungstate, which have been carefully tailored for given polymeric and textile substrates. Full article

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

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15 pages, 41306 KB

Open AccessEditor’s ChoiceArticle

Characterization of Bone Marrow and Wharton’s Jelly Mesenchymal Stromal Cells Response on Multilayer Braided Silk and Silk/PLCL Scaffolds for Ligament Tissue Engineering

by Xing Liu, Adrien Baldit, Emilie de Brosses, Frédéric Velard, Ghislaine Cauchois, Yun Chen, Xiong Wang, Natalia de Isla and Cédric Laurent

Polymers 2020, 12(9), 2163; https://doi.org/10.3390/polym12092163 - 22 Sep 2020

Cited by 9 | Viewed by 3734

Abstract

(1) Background: A suitable scaffold with adapted mechanical and biological properties for ligament tissue engineering is still missing. (2) Methods: Different scaffold configurations were characterized in terms of morphology and a mechanical response, and their interactions with two types of stem cells (Wharton’s [...] Read more.

(1) Background: A suitable scaffold with adapted mechanical and biological properties for ligament tissue engineering is still missing. (2) Methods: Different scaffold configurations were characterized in terms of morphology and a mechanical response, and their interactions with two types of stem cells (Wharton’s jelly mesenchymal stromal cells (WJ-MSCs) and bone marrow mesenchymal stromal cells (BM-MSCs)) were assessed. The scaffold configurations consisted of multilayer braids with various number of silk layers (n = 1, 2, 3), and a novel composite scaffold made of a layer of copoly(lactic acid-co-(e-caprolactone)) (PLCL) embedded between two layers of silk. (3) Results: The insertion of a PLCL layer resulted in a higher porosity and better mechanical behavior compared with pure silk scaffold. The metabolic activities of both WJ-MSCs and BM-MSCs increased from day 1 to day 7 except for the three-layer silk scaffold (S3), probably due to its lower porosity. Collagen I (Col I), collagen III (Col III) and tenascin-c (TNC) were expressed by both MSCs on all scaffolds, and expression of Col I was higher than Col III and TNC. (4) Conclusions: the silk/PLCL composite scaffolds constituted the most suitable tested configuration to support MSCs migration, proliferation and tissue synthesis towards ligament tissue engineering. Full article

(This article belongs to the Special Issue Polymers for Cell Engineering)

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13 pages, 6130 KB

Open AccessEditor’s ChoiceArticle

Fatigue Behavior of 3D Braided Composites Containing an Open-Hole

by Shuangqiang Liang, Qihong Zhou, Haiyang Mei, Ge Chen and Frank Ko

Polymers 2020, 12(9), 2147; https://doi.org/10.3390/polym12092147 - 21 Sep 2020

Cited by 6 | Viewed by 3959

Abstract

The static and dynamic mechanical performances of notched and un-notched 3D braided composites were studied. The effect of longitudinal laid-in yarn was investigated in comparison with low braiding angle composites. The specimens were fatigue tested for up to millions of cycles, and the [...] Read more.

The static and dynamic mechanical performances of notched and un-notched 3D braided composites were studied. The effect of longitudinal laid-in yarn was investigated in comparison with low braiding angle composites. The specimens were fatigue tested for up to millions of cycles, and the residual strength of the samples that survived millions of cycles was tested. The cross-section of the 3D braided specimens was observed after fatigue loading. It was found that the static and fatigue properties of low angle 3D braided behaved better than longitudinally reinforced 3D braided composites. For failure behavior, pure braids contain damage better and show less damage area than the braids with longitudinal yarns under fatigue loading. More cracks occurred in the 3D braided specimen with axial yarn cross-section along the longitudinal and transverse direction. Full article

(This article belongs to the Special Issue Reinforced Polymer Composites II)

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15 pages, 3463 KB

Open AccessEditor’s ChoiceArticle

Highly Thermal Stable Phenolic Resin Based on Double-Decker-Shaped POSS Nanocomposites for Supercapacitors

by Wei-Cheng Chen, Yuan-Tzu Liu and Shiao-Wei Kuo

Polymers 2020, 12(9), 2151; https://doi.org/10.3390/polym12092151 - 21 Sep 2020

Cited by 23 | Viewed by 4073

Abstract

In this study we incorporated various amounts of a double-decker silsesquioxane (DDSQ) into phenolic/DDSQ hybrids, which we prepared from a bifunctionalized phenolic DDSQ derivative (DDSQ-4OH), phenol, and CH₂O under basic conditions (with DDSQ-4OH itself prepared through hydrosilylation of nadic anhydride with [...] Read more.

In this study we incorporated various amounts of a double-decker silsesquioxane (DDSQ) into phenolic/DDSQ hybrids, which we prepared from a bifunctionalized phenolic DDSQ derivative (DDSQ-4OH), phenol, and CH₂O under basic conditions (with DDSQ-4OH itself prepared through hydrosilylation of nadic anhydride with DDSQ and subsequent reaction with 4-aminophenol). We characterized these phenolic/DDSQ hybrids using Fourier transform infrared spectroscopy; ¹H, ¹³C, and ²⁹Si nuclear magnetic resonance spectroscopy; X-ray photoelectron spectroscopy (XPS); and thermogravimetric analysis. The thermal decomposition temperature and char yield both increased significantly upon increasing the DDSQ content, with the DDSQ units providing an inorganic protection layer on the phenolic surface, as confirmed through XPS analyses. We obtained carbon/DDSQ hybrids from the phenolic/DDSQ hybrids after thermal curing and calcination at 900 °C; these carbon/DDSQ hybrids displayed electrochemical properties superior to those of previously reported counterparts. Full article

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

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19 pages, 2907 KB

Open AccessEditor’s ChoiceArticle

Strong Plasmon–Exciton Coupling in Ag Nanoparticle—Conjugated Polymer Core-Shell Hybrid Nanostructures

by Christopher E. Petoukhoff, Keshav M. Dani and Deirdre M. O’Carroll

Polymers 2020, 12(9), 2141; https://doi.org/10.3390/polym12092141 - 19 Sep 2020

Cited by 9 | Viewed by 5178

Abstract

Strong plasmon–exciton coupling between tightly-bound excitons in organic molecular semiconductors and surface plasmons in metal nanostructures has been studied extensively for a number of technical applications, including low-threshold lasing and room-temperature Bose-Einstein condensates. Typically, excitons with narrow resonances, such as J-aggregates, are [...] Read more.

Strong plasmon–exciton coupling between tightly-bound excitons in organic molecular semiconductors and surface plasmons in metal nanostructures has been studied extensively for a number of technical applications, including low-threshold lasing and room-temperature Bose-Einstein condensates. Typically, excitons with narrow resonances, such as J-aggregates, are employed to achieve strong plasmon–exciton coupling. However, J-aggregates have limited applications for optoelectronic devices compared with organic conjugated polymers. Here, using numerical and analytical calculations, we demonstrate that strong plasmon–exciton coupling can be achieved for Ag-conjugated polymer core-shell nanostructures, despite the broad spectral linewidth of conjugated polymers. We show that strong plasmon–exciton coupling can be achieved through the use of thick shells, large oscillator strengths, and multiple vibronic resonances characteristic of typical conjugated polymers, and that Rabi splitting energies of over 1000 meV can be obtained using realistic material dispersive relative permittivity parameters. The results presented herein give insight into the mechanisms of plasmon–exciton coupling when broadband excitonic materials featuring strong vibrational–electronic coupling are employed and are relevant to organic optoelectronic devices and hybrid metal–organic photonic nanostructures. Full article

(This article belongs to the Special Issue Polymeric Materials for Optical Applications II)

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11 pages, 4430 KB

Open AccessEditor’s ChoiceArticle

Semiconducting Properties of the Hybrid Film of Elastic Poly(styrene-b-butadiene-b-styrene) Block Copolymer and Semiconducting Poly(3-hexylthiophene) Nanofibers

by Takanori Goto, Jun Morita, Yuya Maekawa, Shinji Kanehashi and Takeshi Shimomura

Polymers 2020, 12(9), 2118; https://doi.org/10.3390/polym12092118 - 17 Sep 2020

Cited by 2 | Viewed by 3071

Abstract

We investigated the electrical properties of a composite film loaded with semi-conductive poly(3-hexylthiophene) (P3HT) nanofibers dispersed in poly(styrene-b-butadiene-b-styrene) (SBS). This structure can be regarded as the hybrid of SBS matrix with elastic mechanical properties and P3HT nanofibers with semiconducting [...] Read more.

We investigated the electrical properties of a composite film loaded with semi-conductive poly(3-hexylthiophene) (P3HT) nanofibers dispersed in poly(styrene-b-butadiene-b-styrene) (SBS). This structure can be regarded as the hybrid of SBS matrix with elastic mechanical properties and P3HT nanofibers with semiconducting properties. The P3HT nanofibers were embedded in the fingerprint pattern of microphase-separated SBS, as observed by scanning force microscopy. Furthermore, the electrical conductivity and field-effect mobility of the composite films were evaluated. The field-effect mobility was estimated to be 6.96 × 10⁻³ cm² V⁻¹ s⁻¹, which is consistent with the results of previous studies on P3HT nanofibers dispersed in an amorphous polymer matrix including poly(methyl methacrylate) and polystyrene, and we found that the P3HT nanofiber network was connected in the SBS bulk matrix. The film was stretchable; however, at elongation by two times, the nanofiber network could not follow the elongation of the SBS matrix, and the conductivity decreased drastically. The field-effect transistor of this film was operated by bending deformation with a radius of curvature of 1.75 cm, though we could not obtain an off-state and the device operated in a normally-on state. Full article

(This article belongs to the Special Issue Conducting Polymer-Based Hybrid Nanomaterials)

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12 pages, 3915 KB

Open AccessEditor’s ChoiceArticle

Novel Conjugated Polymers Containing 3-(2-Octyldodecyl)thieno[3,2-b]thiophene as a π-Bridge for Organic Photovoltaic Applications

by Jong-Woon Ha, Jong Baek Park, Hea Jung Park and Do-Hoon Hwang

Polymers 2020, 12(9), 2121; https://doi.org/10.3390/polym12092121 - 17 Sep 2020

Cited by 8 | Viewed by 3812

Abstract

3-(2-Octyldodecyl)thieno[3,2-b]thiophen was successfully synthesized as a new π-bridge with a long branched side alkyl chain. Two donor-π-bridge-acceptor type copolymers were designed and synthesized by combining this π-bridge structure, a fluorinated benzothiadiazole acceptor unit, and a thiophene or thienothiophene donor unit, ( [...] Read more.

3-(2-Octyldodecyl)thieno[3,2-b]thiophen was successfully synthesized as a new π-bridge with a long branched side alkyl chain. Two donor-π-bridge-acceptor type copolymers were designed and synthesized by combining this π-bridge structure, a fluorinated benzothiadiazole acceptor unit, and a thiophene or thienothiophene donor unit, (PT-ODTTBT or PTT-ODTTBT respectively) through Stille polymerization. Inverted OPV devices with a structure of ITO/ZnO/polymer:PC₇₁BM/MoO₃/Ag were fabricated by spin-coating in ambient atmosphere or N₂ within a glovebox to evaluate the photovoltaic performance of the synthesized polymers (effective active area: 0.09 cm²). The PTT-ODTTBT:PC₇₁BM-based structure exhibited the highest organic photovoltaic (OPV) device performance, with a maximum power conversion efficiency (PCE) of 7.05 (6.88 ± 0.12)%, a high short-circuit current (J_sc) of 13.96 mA/cm², and a fill factor (FF) of 66.94 (66.47 ± 0.63)%; whereas the PT-ODTTBT:PC₇₁BM-based device achieved overall lower device performance. According to GIWAXS analysis, both neat and blend films of PTT-ODTTBT exhibited well-organized lamellar stacking, leading to a higher charge carrier mobility than that of PT-ODTTBT. Compared to PT-ODTTBT containing a thiophene donor unit, PTT-ODTTBT containing a thienothiophene donor unit exhibited higher crystallinity, preferential face-on orientation, and a bicontinuous interpenetrating network in the film, which are responsible for the improved OPV performance in terms of high J_sc, FF, and PCE. Full article

(This article belongs to the Special Issue High-Functional Polymeric Materials)

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13 pages, 2286 KB

Open AccessEditor’s ChoiceArticle

Effects of Poly(ethylene-co-glycidyl methacrylate) on the Microstructure, Thermal, Rheological, and Mechanical Properties of Thermotropic Liquid Crystalline Polyester Blends

by Sang Hoon Lee, Ha-Bin Jeon, Gyu-Hyun Hwang, Young Seung Kwon, Ji-Su Lee, Gyu-Tae Park, Soo-Yeon Kim, Ha-Eun Kang, Eun-Ji Choi, Sun-Hwa Jang, Youn Eung Lee and Young Gyu Jeong

Polymers 2020, 12(9), 2124; https://doi.org/10.3390/polym12092124 - 17 Sep 2020

Cited by 18 | Viewed by 5426

Abstract

In this study, a series of thermotropic liquid crystalline polyester (TLCP)-based blends containing 1–30 wt% poly(ethylene-co-glycidyl methacrylate) (PEGMA) were fabricated by masterbatch-assisted melt-compounding. The scanning electron microscopy (SEM) images showed a uniformly dispersed microfibrillar structure for the TLCP component in cryogenically-fractured [...] Read more.

In this study, a series of thermotropic liquid crystalline polyester (TLCP)-based blends containing 1–30 wt% poly(ethylene-co-glycidyl methacrylate) (PEGMA) were fabricated by masterbatch-assisted melt-compounding. The scanning electron microscopy (SEM) images showed a uniformly dispersed microfibrillar structure for the TLCP component in cryogenically-fractured blends, without any phase-separated domains. The FT-IR spectra showed that the carbonyl stretching bands of TLCP/PEGMA blends shifted to higher wavenumbers, suggesting the presence of specific interactions and/or grafting reactions between carboxyl/hydroxyl groups of TLCP and glycidyl methacrylate groups of PEGMA. Accordingly, the melting and crystallization temperatures of the PEGMA component in the blends were greatly lowered compared to the TLCP component. The thermal decomposition peak temperatures of the PEGMA and TLCP components in the blends were characterized as higher than those of neat PEGMA and neat TLCP, respectively. From the rheological data collected at 300 °C, the shear moduli and complex viscosities for the blend with 30 wt% PEGMA were found to be much higher than those of neat PEGMA, which supports the existence of PEGMA-g-TLCP formed during the melt-compounding. The dynamic mechanical thermal analysis (DMA) analyses demonstrated that the storage moduli of the blends decreased slightly with the PEGMA content up to 3 wt%, increased at the PEGMA content of 5 wt%, and decreased again at PEGMA contents above 7 wt%. The maximum storage moduli for the blend with 5 wt% PEGMA are interpreted to be due to the reinforcing effect of PEGMA-g-TLCP copolymers. Full article

(This article belongs to the Special Issue High-Functional Polymeric Materials)

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17 pages, 3907 KB

Open AccessEditor’s ChoiceArticle

Tunable Wettability of Biodegradable Multilayer Sandwich-Structured Electrospun Nanofibrous Membranes

by A. K. M. Mashud Alam, Elena Ewaldz, Chunhui Xiang, Wangda Qu and Xianglan Bai

Polymers 2020, 12(9), 2092; https://doi.org/10.3390/polym12092092 - 15 Sep 2020

Cited by 22 | Viewed by 5214

Abstract

This research aims to develop multilayer sandwich-structured electrospun nanofiber (ENF) membranes using biodegradable polymers. Hydrophilic regenerated cellulose (RC) and hydrophobic poly (lactic acid) (PLA)-based novel multilayer sandwich-structures were created by electrospinning on various copper collectors, including copper foil and 30-mesh copper gauzes, to [...] Read more.

This research aims to develop multilayer sandwich-structured electrospun nanofiber (ENF) membranes using biodegradable polymers. Hydrophilic regenerated cellulose (RC) and hydrophobic poly (lactic acid) (PLA)-based novel multilayer sandwich-structures were created by electrospinning on various copper collectors, including copper foil and 30-mesh copper gauzes, to modify the surface roughness for tunable wettability. Different collectors yielded various sizes and morphologies of the fabricated ENFs with different levels of surface roughness. Bead-free thicker fibers were collected on foil collectors. The surface roughness of the fine fibers collected on mesh collectors contributed to an increase in hydrophobicity. An RC-based triple-layered structure showed a contact angle of 48.2°, which is comparable to the contact angle of the single-layer cellulosic fabrics (47.0°). The polar shift of RC membranes on the wetting envelope is indicative of the possibility of tuning the wetting behavior by creating multilayer structures. Wettability can be tuned by creating multilayer sandwich structures consisting of RC and PLA. This study provides an important insight into the manipulation of the wetting behavior of polymeric ENFs in multilayer structures for applications including chemical protective clothing. Full article

(This article belongs to the Special Issue Polymeric Materials for Filtration and Purification)

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