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Polymers, Volume 12, Issue 3 (March 2020) – 229 articles

Cover Story (view full-size image): The efficient regeneration of a fully functional tissue assisted by the presence of a polymeric scaffold depends on its design and the manufacturing method used. The incorporation of bioactive compounds during scaffold processing is of particular interest to improve environment–scaffold interactions. Namely, solvent-free manufacturing techniques offer remarkable advantages in terms of incorporation yield and retained activity of the loaded bioactive agents. In this work, solvent-free technologies for the processing of scaffolds are discussed, highlighting meaningful cases reported in the regenerative medicine field. View this paper.
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Article
Emulsifier-Free Acrylate-Based Emulsion Prepared by Reverse Iodine Transfer Polymerization
Polymers 2020, 12(3), 730; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030730 - 24 Mar 2020
Cited by 5 | Viewed by 1250
Abstract
The self-emulsifying acrylate-based emulsions with solid content 45 wt.% were prepared in 3.5 h by reverse iodine transfer polymerization (RITP), and the polymer molecular weight (Mn) could be 30,000 g·mol−1. The influences of methacrylic acid (MAA) amount, soft/hard [...] Read more.
The self-emulsifying acrylate-based emulsions with solid content 45 wt.% were prepared in 3.5 h by reverse iodine transfer polymerization (RITP), and the polymer molecular weight (Mn) could be 30,000 g·mol−1. The influences of methacrylic acid (MAA) amount, soft/hard monomer mass ratio, and iodine amount on polymerization and latex were investigated. A moderate amount of ionized MAA was needed to stabilize the emulsion. Glass transition temperature (Tg) was decreased with the increasing mass ratio of soft/hard monomer. A higher iodine amount resulted in lower Mn. The increased Mn after chain extension of the polymer with water-insoluble monomers in iterative one-pot method proved the living of polymer. Compared with conventional emulsion polymerization, molecular weight (Mn) could be controlled, and Mn of polymer synthesized in RITP emulsion polymerization is higher; emulsion of polyacrylate-containing hydroxyl monomer units prepared by RITP emulsifier-free radical polymerization is more stable. Good properties, such as hardness, water resistance, adhesion, and increased value of maximum tensile of films modified by reaction of polyacrylate with melamine–formaldehyde (MF) resin, indicated potential application in baking coating. Full article
(This article belongs to the Section Polymer Chemistry)
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Article
Properties of Poplar Fiber/PLA Composites: Comparison on the Effect of Maleic Anhydride and KH550 Modification of Poplar Fiber
Polymers 2020, 12(3), 729; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030729 - 24 Mar 2020
Cited by 6 | Viewed by 1254
Abstract
To improve the interfacial adhesion and dispersion of a poplar fiber in a polylactic acid (PLA) matrix, maleic anhydride (MA) and a silane coupling agent (KH550) were used to modify the poplar fiber. The poplar fiber/PLA composites were produced with different modifier contents. [...] Read more.
To improve the interfacial adhesion and dispersion of a poplar fiber in a polylactic acid (PLA) matrix, maleic anhydride (MA) and a silane coupling agent (KH550) were used to modify the poplar fiber. The poplar fiber/PLA composites were produced with different modifier contents. The mechanical, thermal, rheological, and physical properties of composites were investigated. A comparison of different natural fiber modifications on the properties of composites was also analyzed. The results showed that both MA and KH550 could improve the interfacial adhesion between the poplar fiber and PLA, resulting in the enhanced mechanical properties of the composite, with 17% and 23% increases of tensile strength for 0.5% MA and 2% KH550, respectively. The thermal properties of the composites were improved at 6% KH550 (a 9% enhancement of T90%) and decreased at 0.5% MA (a 6% decrement of T90%). The wettability of the composites obtained a 11.3% improvement at 4% KH550 and a 5% reduction at 4% MA. Therefore, factors such as mechanical properties, economic efficiency, and durability should be carefully considered when choosing the modifier to improve the property of the composite. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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Article
Comparative Structure-Property Characterization of Poly(3-Hydroxybutyrate-Co-3-Hydroxyvalerate)s Films under Hydrolytic and Enzymatic Degradation: Finding a Transition Point in 3-Hydroxyvalerate Content
Polymers 2020, 12(3), 728; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030728 - 24 Mar 2020
Cited by 10 | Viewed by 1612
Abstract
The hydrolytic and enzymatic degradation of polymer films of poly(3-hydroxybutyrate) (PHB) of different molecular mass and its copolymers with 3-hydroxyvalerate (PHBV) of different 3-hydroxyvalerate (3-HV) content and molecular mass, 3-hydroxy-4-methylvalerate (PHB4MV), and polyethylene glycol (PHBV-PEG) produced by the Azotobacter chroococcum 7B by controlled [...] Read more.
The hydrolytic and enzymatic degradation of polymer films of poly(3-hydroxybutyrate) (PHB) of different molecular mass and its copolymers with 3-hydroxyvalerate (PHBV) of different 3-hydroxyvalerate (3-HV) content and molecular mass, 3-hydroxy-4-methylvalerate (PHB4MV), and polyethylene glycol (PHBV-PEG) produced by the Azotobacter chroococcum 7B by controlled biosynthesis technique were studied under in vitro model conditions. The changes in the physicochemical properties of the polymers during their in vitro degradation in the pancreatic lipase solution and in phosphate-buffered saline for a long time (183 days) were investigated using different analytical techniques. A mathematical model was used to analyze the kinetics of hydrolytic degradation of poly(3-hydroxyaklannoate)s by not autocatalytic and autocatalytic hydrolysis mechanisms. It was also shown that the degree of crystallinity of some polymers changes differently during degradation in vitro. The total mass of the films decreased slightly up to 8–9% (for the high-molecular weight PHBV with the 3-HV content 17.6% and 9%), in contrast to the copolymer molecular mass, the decrease of which reached 80%. The contact angle for all copolymers after the enzymatic degradation decreased by an average value of 23% compared to 17% after the hydrolytic degradation. Young’s modulus increased up to 2-fold. It was shown that the effect of autocatalysis was observed during enzymatic degradation, while autocatalysis was not available during hydrolytic degradation. During hydrolytic and enzymatic degradation in vitro, it was found that PHBV, containing 5.7–5.9 mol.% 3-HV and having about 50% crystallinity degree, presents critical content, beyond which the structural and mechanical properties of the copolymer have essentially changed. The obtained results could be applicable to biomedical polymer systems and food packaging materials. Full article
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Article
Visualization Analysis of Defibration and Distributive Uniformity of Fibers in Long-fiber-reinforced, Injection-Molded Resins
Polymers 2020, 12(3), 727; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030727 - 24 Mar 2020
Viewed by 885
Abstract
The pursuit of mechanical strength in the injection molding of long-fiber-reinforced resins continues to pose major challenges, namely (1) improvement of fiber defibration and fiber distribution and (2) suppression of fiber breakage during the molding machine’s plastication process. In the present study, a [...] Read more.
The pursuit of mechanical strength in the injection molding of long-fiber-reinforced resins continues to pose major challenges, namely (1) improvement of fiber defibration and fiber distribution and (2) suppression of fiber breakage during the molding machine’s plastication process. In the present study, a new defibration and distribution evaluation mold is developed to quantitatively evaluate the defibration and distribution of long fibers in nozzle-injected resin. A quantitative analysis method using this evaluation mold is proposed for visualizing and observing long-glass-fiber-reinforced resin up to 30 wt % and long carbon fiber-reinforced resin up to 10 wt %. The method, based on the intensity of light transmitted from a backlight source, is also used to evaluate areas of undefibrated fiber pilling and for evaluating the influence of molding conditions on fiber defibration and uniform distribution. The results clarify that fiber distribution non-uniformity can be reduced by improving the concentration adjustment procedure for the dry blending of high-concentration pellets. Additional results show that fiber defibration and distributive uniformity can be improved by applying high back pressure. Full article
(This article belongs to the Special Issue Advances on Injection Molding of Polymers)
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Article
Effect of Chitin Nanocrystals on Crystallization and Properties of Poly(lactic acid)-Based Nanocomposites
Polymers 2020, 12(3), 726; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030726 - 24 Mar 2020
Cited by 4 | Viewed by 2347
Abstract
The crystalline phase of poly(lactic acid) (PLA) has crucial effects on its own properties and nanocomposites. In this study, the isothermal crystallization of PLA, triethyl citrate-plasticized PLA (PLA–TEC), and its nanocomposite with chitin nanocrystals (PLA–TEC–ChNC) at different temperatures and times was investigated, and [...] Read more.
The crystalline phase of poly(lactic acid) (PLA) has crucial effects on its own properties and nanocomposites. In this study, the isothermal crystallization of PLA, triethyl citrate-plasticized PLA (PLA–TEC), and its nanocomposite with chitin nanocrystals (PLA–TEC–ChNC) at different temperatures and times was investigated, and the resulting properties of the materials were characterized. Both PLA and PLA–TEC showed extremely low crystallinity at isothermal temperatures of 135, 130, 125 °C and times of 5 or 15 min. In contrast, the addition of 1 wt % of ChNCs significantly improved the crystallinity of PLA under the same conditions owing to the nucleation effect of the ChNCs. The samples were also crystallized at 110 °C to reach their maximal crystallinity, and PLA–TEC–ChNC achieved 48% crystallinity within 5 min, while PLA and PLA–TEC required 40 min to reach a similar level. Moreover, X-ray diffraction analysis showed that the addition of ChNCs resulted in smaller crystallite sizes, which further influenced the barrier properties and hydrolytic degradation of the PLA. The nanocomposites had considerably lower barrier properties and underwent faster degradation compared to PLA–TEC110. These results confirm that the addition of ChNCs in PLA leads to promising properties for packaging applications. Full article
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Article
Comparison of the Foamability of Linear and Long-Chain Branched Polypropylene—The Legend of Strain-Hardening as a Requirement for Good Foamability
Polymers 2020, 12(3), 725; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030725 - 24 Mar 2020
Cited by 6 | Viewed by 1537
Abstract
Polypropylene (PP) is an outstanding material for polymeric foams due to its favorable mechanical and chemical properties. However, its low melt strength and fast crystallization result in unfavorable foaming properties. Long-chain branching of PP is regarded as a game changer in foaming due [...] Read more.
Polypropylene (PP) is an outstanding material for polymeric foams due to its favorable mechanical and chemical properties. However, its low melt strength and fast crystallization result in unfavorable foaming properties. Long-chain branching of PP is regarded as a game changer in foaming due to the introduction of strain hardening, which stabilizes the foam morphology. In this work, a thorough characterization with respect to rheology and crystallization characteristics of a linear PP, a PP/PE-block co-polymer, and a long-chain branched PP are conducted. Using these results, the processing window in foam-extrusion trials with CO2 and finally the foam properties are explained. Although only LCB-PP exhibits strain hardening, it neither provide the broadest foaming window nor the best foam quality. Therefore, multiwave experiments were conducted to study the gelation due to crystallization and its influence on foaming. Here, linear PP exhibited a gel-like behavior over a broad time frame, whereas the other two froze quickly. Thus, apart from strain hardening, the crystallization behavior/crystallization kinetics is of utmost importance for foaming in terms of a broad processing window, low-density, and good morphology. Therefore, the question arises, whether strain hardening is really essential for low density foams with a good cellular morphology. Full article
(This article belongs to the Special Issue Rheology and Processing of Polymers)
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Article
Melt Rheological Behavior and Morphology of Poly(ethylene oxide)/Natural Rubber-graft-Poly(methyl methacrylate) Blends
Polymers 2020, 12(3), 724; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030724 - 24 Mar 2020
Cited by 1 | Viewed by 1089
Abstract
The influence of morphology on the rheological properties of poly(ethylene oxide) (PEO) and natural rubber-graft-poly(methyl methacrylate) (NR-g-PMMA) blends in the melt was investigated. The blends were prepared at different blend compositions by a solution-casting method. Linear viscoelastic shear oscillations [...] Read more.
The influence of morphology on the rheological properties of poly(ethylene oxide) (PEO) and natural rubber-graft-poly(methyl methacrylate) (NR-g-PMMA) blends in the melt was investigated. The blends were prepared at different blend compositions by a solution-casting method. Linear viscoelastic shear oscillations measurements were performed in order to determine the elastic and viscous properties of the blends in the melt. The rheological results suggested that the blending of the two constituents reduced the elasticity and viscosity of the blends. The addition of an even small amount of NR-g-PMMA to PEO changed the liquid-like behavior of PEO to more solid-like behavior. Morphological investigations were carried out by optical microscopy to establish the relationship between morphology and melt viscosity. Depending on the blend compositions and viscosities, either droplet–matrix or co-continuous morphologies was observed. PEO/NR-g-PMMA blends exhibited a broad co-continuity range, and phase inversion was suggested to occur at the PEO/NR-g-PMMA blend with a mass ratio of 60/40 (m/m), when NR-g-PMMA was added to PEO as a matrix. Full article
(This article belongs to the Special Issue Advanced Polymeric Materials)
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Article
Synthesis, Physical, Mechanical and Antibacterial Properties of Nanocomposites Based on Poly(vinyl alcohol)/Graphene Oxide–Silver Nanoparticles
Polymers 2020, 12(3), 723; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030723 - 24 Mar 2020
Cited by 24 | Viewed by 1799
Abstract
The design of new materials with antimicrobial properties has emerged in response to the need for preventing and controlling the growth of pathogenic microorganisms without the use of antibiotics. In this study, partially reduced graphene oxide decorated with silver nanoparticles (GO–AgNPs) was incorporated [...] Read more.
The design of new materials with antimicrobial properties has emerged in response to the need for preventing and controlling the growth of pathogenic microorganisms without the use of antibiotics. In this study, partially reduced graphene oxide decorated with silver nanoparticles (GO–AgNPs) was incorporated as a reinforcing filler with antibacterial properties to poly(vinyl alcohol) (PVA) for preparation of poly(vinyl alcohol)/graphene oxide-silver nanoparticles nanocomposites (PVA/GO–AgNPs). AgNPs, spherical in shape and with an average size of 3.1 nm, were uniformly anchored on the partially reduced GO surface. PVA/GO–AgNPs nanocomposites showed exfoliated structures with improved thermal stability, tensile properties and water resistance compared to neat PVA. The glass transition and crystallization temperatures of the polymer matrix increased with the incorporation of the hybrid. The nanocomposites displayed antibacterial activity against Staphylococcus aureus and Escherichia coli in a filler content- and time-dependent manner. S. aureus showed higher susceptibility to PVA/GO–AgNPs films than E. coli. Inhibitory activity was higher when bacterial cells were in contact with nanocomposite films than when in contact with leachates coming out of the films. GO–AgNPs based PVA nanocomposites could find application as wound dressings for wound healing and infection prevention. Full article
(This article belongs to the Special Issue Metal- and Metal Hybrid-Filled Polymer Nanocomposites)
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Article
Theoretical Insights into the Structures and Capacitive Performances of Confined Ionic Liquids
Polymers 2020, 12(3), 722; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030722 - 24 Mar 2020
Cited by 1 | Viewed by 1159
Abstract
Room-temperature ionic liquids (RTILs) together with nano-porous electrodes are the most promising materials for supercapacitors and batteries. Many theoretical works have addressed the structures and performances of RTILs inside nanopores. However, only limited attention has been given to how the dispersion forces of [...] Read more.
Room-temperature ionic liquids (RTILs) together with nano-porous electrodes are the most promising materials for supercapacitors and batteries. Many theoretical works have addressed the structures and performances of RTILs inside nanopores. However, only limited attention has been given to how the dispersion forces of RTILs influence the behavior of ions inside the slit pores. Toward this aim, we investigate the effects of various dispersion forces between ions on the macroscopic structures in nanoconfinement and the capacitance performance of supercapacitors by the classical density functional theory (CDFT). The results show that the dispersion force can significantly change the mechanism of the charging process and even the shape of differential capacitance curves. In addition, the voltage-dependent structures of RTILs with appropriate dispersion force appears in a given silt pore, which leads to extremely high capacitance and enhances the energy storage density. We hope that this work could further offer guidance for the optimizing of electrolytes for electrical double layer capacitors, like tuning the dispersion force between ions by adding/removing certain chemical groups on the cations and anions of RTILs. Full article
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Article
Material Properties Influencing the Charge Decay of Electret Filters and their Impact on Filtration Performance
Polymers 2020, 12(3), 721; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030721 - 24 Mar 2020
Cited by 26 | Viewed by 2021
Abstract
Electret filters as opposed to mechanical filters display the enhanced ability to capture airborne particles with the electrostatic attraction. However, the environmental aging during shelf-life or use may cancel its benefit by dissipating the charges. This work investigates the polymeric attributes influencing the [...] Read more.
Electret filters as opposed to mechanical filters display the enhanced ability to capture airborne particles with the electrostatic attraction. However, the environmental aging during shelf-life or use may cancel its benefit by dissipating the charges. This work investigates the polymeric attributes influencing the charge decay and the electrostatic filtration of electret filters, employing polymers with different dielectric constants (εr) and wettability. As accelerated aging, high temperature (120 °C) or high humidity (25 °C, 90% RH) was applied to the electret filters for 48 h. For the humidity aging, wetting property of material was a critical factor affecting the charge decay and the filtration performance, as the absorbed water increases the electrical conductivity. For the thermal aging, the material with the highest εr deteriorated the electric potential and the filtration performance by the largest extent, due to the lower band gap energy for charge transfer. The results of this study implicate that εr and wettability are important material parameters influencing the electric conductivity and chain mobility, and they can be used as convenient predictors for charge retention capacity affecting the robust electrostatic filtration performance. Full article
(This article belongs to the Special Issue Polymeric Materials for Filtration and Purification)
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Article
Synthesis and Evaluation of Scalable D-A-D π-Extended Oligomers as p-Type Organic Materials for Bulk-Heterojunction Solar Cells
Polymers 2020, 12(3), 720; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030720 - 24 Mar 2020
Cited by 8 | Viewed by 1765
Abstract
The synthesis and characterization of four novel donor-acceptor-donor π-extended oligomers, incorporating naphtha(1–b)thiophene-4-carboxylate or benzo(b)thieno(3,2-g) benzothiophene-4-carboxylate 2-octyldodecyl esters as end-capping moieties, and two different conjugated core fragments, is reported. The end-capping moieties are obtained via a cascade sequence of sustainable organic reactions, and then [...] Read more.
The synthesis and characterization of four novel donor-acceptor-donor π-extended oligomers, incorporating naphtha(1–b)thiophene-4-carboxylate or benzo(b)thieno(3,2-g) benzothiophene-4-carboxylate 2-octyldodecyl esters as end-capping moieties, and two different conjugated core fragments, is reported. The end-capping moieties are obtained via a cascade sequence of sustainable organic reactions, and then coupled to benzo(c)(1,2,5)thiadiazole and its difluoro derivative as the electron-poor π-conjugated cores. The optoelectronic properties of the oligomers are reported. The novel compounds revealed good film forming properties, and when tested in bulk-heterojunction organic photovoltaic cell devices in combination with PC61BM, revealed good fill factors, but low efficiencies, due to their poor absorption profiles. Full article
(This article belongs to the Special Issue Synthesis, Characterization and Simulation of Soft Matter with EUSMI)
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Article
Ferrocene-Based Conjugated Microporous Polymers Derived from Yamamoto Coupling for Gas Storage and Dye Removal
Polymers 2020, 12(3), 719; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030719 - 24 Mar 2020
Cited by 10 | Viewed by 1537
Abstract
Conjugated microporous polymers (CMPs) have conjugated skeleton and permanent porosity, and exhibit huge potential in developing novel functional materials for resolving the challenging energy and environment issues. Metal-containing CMPs often exhibited unique properties. In the present manuscript, ferrocene-based conjugated microporous polymers (FcCMPs) were [...] Read more.
Conjugated microporous polymers (CMPs) have conjugated skeleton and permanent porosity, and exhibit huge potential in developing novel functional materials for resolving the challenging energy and environment issues. Metal-containing CMPs often exhibited unique properties. In the present manuscript, ferrocene-based conjugated microporous polymers (FcCMPs) were designed and synthesized with 1,1′-dibromoferrocene and 5,10,15,20-Tetrakis(4- bromophenyl) porphyrin (FcCMP-1) or Tetra (p-bromophenyl) methane (FcCMP-2) as building units via Yamamoto coupling. FcCMPs were amorphous, and exhibited excellent thermal and physicochemical stability. The BET surface area of FcCMP-1 and FcCMP-2 was 638 m2/g and 422 m2/g, respectively. In comparison with FcCMP-2, FcCMP-1 displayed better gas storage capacity due to higher porosity. FcCMPs were also used as an adsorbent for removal of methyl violet from aqueous solution, and exhibited excellent adsorption properties due to the interaction between electron-rich conjugated structure of the polymers and methyl violet with cationic groups. Moreover, FcCMPs could be extracted and regenerated by an eluent and then re-used for high efficient removal of methyl violet. Full article
(This article belongs to the Special Issue Porous Polymer Micro- and Nano-Structures)
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Article
Novel Solid-State Emissive Polymers and Polymeric Blends from a T-Shaped Benzodifuran Scaffold: A Comparative Study
Polymers 2020, 12(3), 718; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030718 - 24 Mar 2020
Cited by 1 | Viewed by 883
Abstract
Two novel polyimines were synthesized from a benzodifuran based diamino monomer and two dialdehydes bearing bulky groups and a flexible spacer. The polymers display tuned luminescence performance according to the presence of half-salen groups. The effect of the intramolecular bond on the emission [...] Read more.
Two novel polyimines were synthesized from a benzodifuran based diamino monomer and two dialdehydes bearing bulky groups and a flexible spacer. The polymers display tuned luminescence performance according to the presence of half-salen groups. The effect of the intramolecular bond on the emission properties were examined. Two model compounds, replicating the same emissive Schiff base cores, were synthetized. From the models, dye-doped blends in the fluorophore/matrix ratio, resembling the polymers, were produced. Amorphous thin films of the covalent polymers and the polymeric blends were obtained by spin-coating technique. The Photoluminescent (PL) response of the different macromolecular systems were qualitatively and quantitatively examined and compared. Full article
(This article belongs to the Special Issue Fluorescent Polymeric Probes)
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Article
Long-Term Evaluation of Dip-Coated PCL-Blend-PEG Coatings in Simulated Conditions
Polymers 2020, 12(3), 717; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030717 - 24 Mar 2020
Cited by 9 | Viewed by 1423
Abstract
Our study focused on the long-term degradation under simulated conditions of coatings based on different compositions of polycaprolactone-polyethylene glycol blends (PCL-blend-PEG), fabricated for titanium implants by a dip-coating technique. The degradation behavior of polymeric coatings was evaluated by polymer mass loss measurements of [...] Read more.
Our study focused on the long-term degradation under simulated conditions of coatings based on different compositions of polycaprolactone-polyethylene glycol blends (PCL-blend-PEG), fabricated for titanium implants by a dip-coating technique. The degradation behavior of polymeric coatings was evaluated by polymer mass loss measurements of the PCL-blend-PEG during immersion in SBF up to 16 weeks and correlated with those yielded from electrochemical experiments. The results are thoroughly supported by extensive compositional and surface analyses (FTIR, GIXRD, SEM, and wettability investigations). We found that the degradation behavior of PCL-blend-PEG coatings is governed by the properties of the main polymer constituents: the PEG solubilizes fast, immediately after the immersion, while the PCL degrades slowly over the whole period of time. Furthermore, the results evidence that the alteration of blend coatings is strongly enhanced by the increase in PEG content. The biological assessment unveiled the beneficial influence of PCL-blend-PEG coatings for the adhesion and spreading of both human-derived mesenchymal stem cells and endothelial cells. Full article
(This article belongs to the Special Issue Biopolymers for Biomedical Applications)
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Article
Dynamic Mechanical Behavior Analysis of Flax/Jute Fiber-Reinforced Composites under Salt-Fog Spray Environment
Polymers 2020, 12(3), 716; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030716 - 24 Mar 2020
Cited by 13 | Viewed by 1258
Abstract
Over the last decades, natural fiber-reinforced polymer composites (NFRPs) gained great attention in several engineering fields thanks to the reduction of the environmental impact and the end-of-life cost disposal. Unfortunately, the use of NFRPs is limited, mainly due to their weak resistance against [...] Read more.
Over the last decades, natural fiber-reinforced polymer composites (NFRPs) gained great attention in several engineering fields thanks to the reduction of the environmental impact and the end-of-life cost disposal. Unfortunately, the use of NFRPs is limited, mainly due to their weak resistance against humid environments. Since limited literature is available about the evolution of the dynamic mechanical response of NFRPs under aggressive environments, this paper aims to investigate the damping properties of flax, jute and flax/jute epoxy composites exposed to salt-fog up to 60 days. Furthermore, sodium bicarbonate fiber treatment was performed to improve the composites’ durability. The effectiveness of treatment was evidenced for full flax-reinforced composites, whereas no beneficial effect was found for jute composites. Moreover, treated hybrid laminates having outer laminae reinforced with flax showed better damping behavior than their hybrid counterparts during the whole aging campaign. Full article
(This article belongs to the Special Issue Advances in Braided Polymer Composites)
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Article
Robust Polymer Planar Bragg Grating Sensors Embedded in Commercial-Grade Composites
Polymers 2020, 12(3), 715; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030715 - 23 Mar 2020
Cited by 4 | Viewed by 1019
Abstract
This contribution demonstrates the functionality of polymer planar Bragg grating (PPBG) sensors integrated into commercial-grade carbon fiber reinforced polymer (CFRP) components. Multiple CFRP specimens are generated by curing a stack of pre-impregnated fibers inside of a heated mechanical press, exposing the polymer sensor [...] Read more.
This contribution demonstrates the functionality of polymer planar Bragg grating (PPBG) sensors integrated into commercial-grade carbon fiber reinforced polymer (CFRP) components. Multiple CFRP specimens are generated by curing a stack of pre-impregnated fibers inside of a heated mechanical press, exposing the polymer sensor to a pressure of 7 bar and a temperature of 120 °C for 2 h. After integration, the sensor still exhibits a strong and evaluable signal. Subsequent flexural experiments reveal a linear response of the integrated sensor’s Bragg wavelength to the CFRP specimen’s maximum deflection. Additional findings demonstrate that the embedded PPBG can be used to detect plastic deformations of a CFRP workpiece, whereas a linear correlation of plastic deformation to the resulting Bragg signal offset is determined. A plausibility check of the obtained results is delivered by a comparison of three-point flexural experiments on bulk CFRP workpieces, without integrated sensors and additional specimens featuring external optical sensors affixed to their surface. It is found that PPBGs based on cyclic olefin copolymers are able to overcome the temperature-related limitations of traditional polymer-based optical sensors and can thus be directly integrated into commercial-grade composites during production. Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications II)
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Article
Macroscopic Poly Schiff Base-Coated Bacteria Cellulose with High Adsorption Performance
Polymers 2020, 12(3), 714; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030714 - 23 Mar 2020
Cited by 5 | Viewed by 1210
Abstract
Here, a nanofiber-exfoliated bacteria cellulose aerogel with improved water affinity and high mass transfer was synthesized. Consequently, poly Schiff base can be uniformly coated within the body of bacteria cellulose aerogel without the traditional dispersion treatment. The composite aerogel has adequate mechanical and [...] Read more.
Here, a nanofiber-exfoliated bacteria cellulose aerogel with improved water affinity and high mass transfer was synthesized. Consequently, poly Schiff base can be uniformly coated within the body of bacteria cellulose aerogel without the traditional dispersion treatment. The composite aerogel has adequate mechanical and thermal stability and high mass transfer efficiency. Such an aerogel can serve as a superior adsorbent for flow through adsorption of pollution. Typically, the adsorption capacity towards Cr(VI), Cu(II), Re(VII), Conga red, and Orange G reaches as high as 321.5, 256.4, 153.8, 333.3, and 370.3 mg g−1, respectively. Moreover, the adsorption by this composite aerogel is very fast, such that, for example, at just 2 s, the adsorption is almost finished with Cr(VI) adsorption. Moreover, the composite aerogel exhibits a good adsorption-desorption capability. This research will hopefully shed light on the preparation of bacteria cellulose-derived macroscopic materials powerful in not only environmental areas, but also other related applications. Full article
(This article belongs to the Special Issue Biobased Polymers for Environmental Applications)
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Article
The Piezoresistive Highly Elastic Sensor Based on Carbon Nanotubes for the Detection of Breath
Polymers 2020, 12(3), 713; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030713 - 23 Mar 2020
Cited by 12 | Viewed by 1196
Abstract
Wearable electronic sensor was prepared on a light and flexible substrate. The breathing sensor has a broad assumption and great potential for portable devices in wearable technology. In the present work, the application of a flexible thermoplastic polyurethane/multiwalled carbon nanotubes (TPU/MWCNTs) strain sensor [...] Read more.
Wearable electronic sensor was prepared on a light and flexible substrate. The breathing sensor has a broad assumption and great potential for portable devices in wearable technology. In the present work, the application of a flexible thermoplastic polyurethane/multiwalled carbon nanotubes (TPU/MWCNTs) strain sensor was demonstrated. This composite was prepared by a novel technique using a thermoplastic filtering membrane based on electrospinning technology. Aqueous dispersion of MWCNTs was filtered through membrane, dried and then welded directly on a T-shirt and encapsulated by a thin silicone layer. The sensing layer was also equipped by electrodes. A polymer composite sensor is capable of detecting a deformation by changing its electrical resistance. A T-shirt was capable of analyzing a type, frequency and intensity of human breathing. The sensitivity to the applied strain of the sensor was improved by the oxidation of MWCNTs by potassium permanganate (KMnO4) and also by subsequent application of the prestrain. Full article
(This article belongs to the Special Issue Polymer Processing and Surfaces)
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Communication
Mussel-Inspired Co-Deposition of Polydopamine/Silica Nanoparticles onto Carbon Fiber for Improved Interfacial Strength and Hydrothermal Aging Resistance of Composites
Polymers 2020, 12(3), 712; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030712 - 23 Mar 2020
Cited by 7 | Viewed by 1163
Abstract
A novel and effective strategy was first proposed for the codeposition of a mussel-inspired nanohybrid coating with excellent wettability onto the surface of carbon fibers (CFs) by simultaneous polymerization of bioinspired dopamine (DA) and hydrolysis of commercial tetraethoxysilane (TEOS) in an eco-friendly one-pot [...] Read more.
A novel and effective strategy was first proposed for the codeposition of a mussel-inspired nanohybrid coating with excellent wettability onto the surface of carbon fibers (CFs) by simultaneous polymerization of bioinspired dopamine (DA) and hydrolysis of commercial tetraethoxysilane (TEOS) in an eco-friendly one-pot process. Mussel-inspired nanohybrids could be adhered onto the surface of CFs firmly. The novel modification could afford sufficient polar groups and significantly improve fiber surface roughness and energy without decreasing fiber intrinsic strength, which were advantageous to promote interfacial compatibility and wettability between CFs and matrix resin. As a result, the interfacial shear strength of composites increased to 48.21 ± 1.45 MPa compared to that of untreated composites 29.47 ± 0.88 MPa. Meanwhile, the nanohybrid coating increased significantly composites’ hydrothermal aging resistance. The efficient strategy shows a promising and green platform of surface functionalization of CFs for preparing advanced polymer composites arising from broadly mechanical-demanding and energy-saving usages. Full article
(This article belongs to the Collection Assessment of the Ageing and Durability of Polymers)
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Article
Crystal Structure and Mechanical Properties of Uniaxially Stretched PA612/SiO2 Films
Polymers 2020, 12(3), 711; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030711 - 23 Mar 2020
Cited by 3 | Viewed by 1009
Abstract
Stretching has a significant effect on the microstructure and ultimate performance of semi-crystalline polymers. To investigate the effect of stretching on structure and mechanical properties of uniaxial stretched PA612/SiO2, PA612 and PA612/SiO2 films were prepared at four temperatures close to the [...] Read more.
Stretching has a significant effect on the microstructure and ultimate performance of semi-crystalline polymers. To investigate the effect of stretching on structure and mechanical properties of uniaxial stretched PA612/SiO2, PA612 and PA612/SiO2 films were prepared at four temperatures close to the glass transition temperature at various strain. The samples were characterized by a transmission electron microscope (TEM), wide-angle X-ray diffractometer (WAXD), Two-dimensional wide-angle X-ray Scattering (2D-WAXS), differential scanning calorimeter (DSC), dynamic mechanical analyzer (DMA), and stretching tests. The results showed that the α phase was the dominant phase in PA612 casting film, no obvious γ phase was observed, while both stretching and the presence of SiO2 can induce the generation of α phase and improve the crystallinity of PA612. Crystals were oriented along the stretching direction and the b axis was parallel to the equatorial direction after stretching. The interplanar spacing of (010/110) decreased with the increasing stretching temperature and expanded with the increasing strain, while stretching temperature and strain present negligible effect on the interplanar spacing of (100). The grain size increased with the stretching temperature while decreased with strain. The presence of SiO2 led to reduce the yield stress and the stress drop beyond yielding of the composite. Uniaxial stretching gave rise to a significant improvement in the fracture stress and the glass transition temperature. Full article
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Article
Multi-Material 3D Printed Shape Memory Polymer with Tunable Melting and Glass Transition Temperature Activated by Heat or Light
Polymers 2020, 12(3), 710; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030710 - 23 Mar 2020
Cited by 10 | Viewed by 1733
Abstract
Shape memory polymers are attractive smart materials that have many practical applications and academic interest. Three-dimensional (3D) printable shape memory polymers are of great importance for the fabrication of soft robotic devices due to their ability to build complex 3D structures with desired [...] Read more.
Shape memory polymers are attractive smart materials that have many practical applications and academic interest. Three-dimensional (3D) printable shape memory polymers are of great importance for the fabrication of soft robotic devices due to their ability to build complex 3D structures with desired shapes. We present a 3D printable shape memory polymer, with controlled melting and transition temperature, composed of methacrylated polycaprolactone monomers and N-Vinylcaprolactam reactive diluent. Tuning the ratio between the monomers and the diluents resulted in changes in melting and transition temperatures by 20, and 6 °C, respectively. The effect of the diluent addition on the shape memory behavior and mechanical properties was studied, showing above 85% recovery ratio, and above 90% fixity, when the concentration of the diluent was up to 40 wt %. Finally, we demonstrated multi-material printing of a 3D structure that can be activated locally, at two different temperatures, by two different stimuli; direct heating and light irradiation. The remote light activation was enabled by utilizing a coating of Carbon Nano Tubes (CNTs) as an absorbing material, onto sections of the printed objects. Full article
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Review
Conducting Polymer Grafting: Recent and Key Developments
Polymers 2020, 12(3), 709; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030709 - 23 Mar 2020
Cited by 15 | Viewed by 1832
Abstract
Since the discovery of conductive polyacetylene, conductive electroactive polymers are at the focal point of technology generation and biocommunication materials. The reasons why this research never stops growing, are twofold: first, the demands from the advanced technology towards more sophistication, precision, durability, processability [...] Read more.
Since the discovery of conductive polyacetylene, conductive electroactive polymers are at the focal point of technology generation and biocommunication materials. The reasons why this research never stops growing, are twofold: first, the demands from the advanced technology towards more sophistication, precision, durability, processability and cost-effectiveness; and second, the shaping of conducting polymer research in accordance with the above demand. One of the major challenges in conducting polymer research is addressing the processability issue without sacrificing the electroactive properties. Therefore, new synthetic designs and use of post-modification techniques become crucial than ever. This quest is not only advancing the field but also giving birth of new hybrid materials integrating merits of multiple functional motifs. The present review article is an attempt to discuss the recent progress in conducting polymer grafting, which is not entirely new, but relatively lesser developed area for this class of polymers to fine-tune their physicochemical properties. Apart from conventional covalent grafting techniques, non-covalent approach, which is relatively new but has worth creation potential, will also be discussed. The aim is to bring together novel molecular designs and strategies to stimulate the existing conducting polymer synthesis methodologies in order to enrich its fascinating chemistry dedicated toward real-life applications. Full article
(This article belongs to the Special Issue Conducting Polymers: Synthesis, Post-modification and Applications)
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Article
The Inhibition Property and Mechanism of a Novel Low Molecular Weight Zwitterionic Copolymer for Improving Wellbore Stability
Polymers 2020, 12(3), 708; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030708 - 23 Mar 2020
Cited by 47 | Viewed by 1690
Abstract
In this work, a novel low molecular weight zwitterionic copolymer for improving wellbore stability, which is expected to be an alternative to the current shale inhibitors, was obtained by copolymerization of tris hydroxyethyl allyl ammonium bromide (THAAB), 2-acrylamido-2- methyl propane sulfonic acid (AMPS) [...] Read more.
In this work, a novel low molecular weight zwitterionic copolymer for improving wellbore stability, which is expected to be an alternative to the current shale inhibitors, was obtained by copolymerization of tris hydroxyethyl allyl ammonium bromide (THAAB), 2-acrylamido-2- methyl propane sulfonic acid (AMPS) and acrylamide (AM), initiated by a redox initiation system in an aqueous solution. The copolymer, denoted as SX-1, was characterized by FT-IR, TGA-DSC, and GPC. Results demonstrated that the molecular weight of SX-1 was approximately 13,683 g/mol and it displayed temperature resistance up to 225 °C. Regarding the inhibition performance, evaluation experiments showed the hot rolling recovery of a Longmaxi shale sample in 2.0 wt % SX-1 solutions was up to 90.31% after hot rolling for 16 h at 120 °C. The Linear swelling height of Na-MMT artificial core in 2.0 wt % SX-1 solution was just 4.74 mm after 16 h. Methods including particle size analysis, FTIR, XRD, and SEM were utilized to study the inhibition mechanism of SX-1; results demonstrated that SX-1 had entered into the inner layer of sodium montmorillonite (Na-MMT) and adsorbed on the inner surface, and the micro-structure of Na-MMT was successfully changed by SX-1. The particle size of Na-MMT in distilled water was 8.05 μm, and it was observed that its size had increased to 603 μm after the addition of 2.0 wt % of SX-1. Its superior properties make this novel low molecular weight copolymer promising for ensuring wellbore stability, particularly for high temperature wells. Full article
(This article belongs to the Special Issue Colloid and Interface)
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Article
Reliability Analysis of FRP-Confined Concrete at Ultimate using Conjugate Search Direction Method
Polymers 2020, 12(3), 707; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030707 - 23 Mar 2020
Cited by 8 | Viewed by 1130
Abstract
In this paper compressive strength and ultimate strain results in the current database of fiber-reinforced polymer (FRP)-confined concrete are used to determine the reliability of their design space. The Lognormal, Normal, Frechet, Gumbel, and Weibull distributions are selected to evaluate the probabilistic characteristics [...] Read more.
In this paper compressive strength and ultimate strain results in the current database of fiber-reinforced polymer (FRP)-confined concrete are used to determine the reliability of their design space. The Lognormal, Normal, Frechet, Gumbel, and Weibull distributions are selected to evaluate the probabilistic characteristics of six FRP material categories. Following this, safety levels of the database are determined based on a probabilistic model. An iterative reliability method is developed with conjugate search direction for evaluating the reliability. The results show that Lognormal and Gumbel distributions provide best probability distribution for model errors of strength and strain enhancement ratios. The developed conjugate reliability method provides improved robustness over the existing reliability methods owing to its faster convergence to stable results. The results reveal that the part of the database containing normal strength concrete (NSC) heavily confined (i.e., actual confinement ratio (flu,a/f’co) > 0.5) by low and normal modulus carbon fibers (i.e., fiber elastic modulus (Ef) ≤ 260 GPa) and moderately confined (i.e., 0.3 ≤ flu,a/f’co ≤ 0.5) by aramid fibers exhibits a very high safety level. The segments of the database with a low and moderate safety level have been identified as i) NSC moderately and heavily confined by higher modulus glass fibers (i.e., Ef > 60 GPa), ii) high strength concrete (HSC) moderately and heavily confined (i.e., flu,a/f’co > 0.3) by glass fibers, iii) HSC lightly confined (i.e., flu,a/f’co ≤ 0.2) by carbon fibers, and iv) HSC lightly confined by aramid fibers. Additional experimental studies are required on these segments of the database before they can be used reliably for design and modeling purposes. Full article
(This article belongs to the Special Issue Fiber Reinforced Polymers)
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Article
Investigation on the Continuous Wave Mode and the ms Pulse Mode Fiber Laser Drilling Mechanisms of the Carbon Fiber Reinforced Composite
Polymers 2020, 12(3), 706; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030706 - 23 Mar 2020
Cited by 2 | Viewed by 963
Abstract
The near infrared (NIR) laser drilling of a carbon fiber reinforced polymer (CFRP) composite in the continuous wave (CW) mode and the ms pulse mode was investigated by an experiment and a numerical simulation. The relationships between the laser penetrating time, entrance hole [...] Read more.
The near infrared (NIR) laser drilling of a carbon fiber reinforced polymer (CFRP) composite in the continuous wave (CW) mode and the ms pulse mode was investigated by an experiment and a numerical simulation. The relationships between the laser penetrating time, entrance hole diameter, surface heat affected zone (HAZ) width, and material ablation rate and the laser irradiation time and laser peak power densities were obtained from the experiment. For the same average power density of the laser output, 3.5 kW/cm2, it was found that the ms pulse laser mode, which had a higher peak power density, had a higher drilling efficiency. When drilling the same holes, the pulse laser mode, which had the highest peak power density of 49.8 kW/cm2, had the lowest drilling time of 0.23 s and had the smallest surface HAZ width of 0.54 mm. In addition, it was found that the laser penetrating time decreased sharply when the peak power density was higher than 23.4 kW/cm2. After analyzing the internal gas pressure by the numerical simulation, it was considered that a large internal gas pressure appeared, which resulted from polymer pyrolysis, causing a large amount of the mechanical erosion of the composite material to improve the drilling efficiency. Therefore, the ms pulse laser showed its potential and advantage in laser drilling the CFRP composite. Full article
(This article belongs to the Special Issue Laser Processing of Polymer Materials)
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Article
Catalytic Fast Pyrolysis of Poly (Ethylene Terephthalate) (PET) with Zeolite and Nickel Chloride
Polymers 2020, 12(3), 705; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030705 - 23 Mar 2020
Cited by 8 | Viewed by 1287
Abstract
The pyrolysis of poly (ethylene terephthalate) (PET) in the presence of ZSM-5 zeolite and NiCl2 as a catalyst was studied at different temperatures under N2 atmosphere. Quantitative 13C nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FT-IR) were applied [...] Read more.
The pyrolysis of poly (ethylene terephthalate) (PET) in the presence of ZSM-5 zeolite and NiCl2 as a catalyst was studied at different temperatures under N2 atmosphere. Quantitative 13C nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FT-IR) were applied to characterize the waxy and solid residue. The carboxyl and aliphatic hydroxyl groups in the waxy residue have been greatly depleted after the use of zeolite during pyrolysis on the basis of the results of 13C NMR and FT-IR analysis. The proportion of aromatic hydroxyl groups increased by 21.82% when the mass ratio of zeolite to PET was set to 2.0/1.0. The results indicate that ZSM-5 is able to facilitate the decomposition of carboxyl, aliphatic groups, and ether bonds in the primary products produced from the pyrolysis of PET. In addition, the deoxygenation effects on the waxy products have been significantly enhanced with the addition of zeolite based on the results of NMR. Full article
(This article belongs to the Special Issue Thermal Analysis of Polymer Materials)
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Article
Biodegradation Pattern of Glycopolymer Based on D-Mannose Oligomer and Hydroxypropyl Acrylate
Polymers 2020, 12(3), 704; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030704 - 22 Mar 2020
Cited by 3 | Viewed by 995
Abstract
Glycopolymers are polymers with sugar moieties which display biodegradable and/or biocompatible character. They have emerged as an environmentally-friendly solution to classical synthetic polymers and have attracted significant research interest in the past years. Herein, we present the synthesis of a D-mannose based glycopolymer [...] Read more.
Glycopolymers are polymers with sugar moieties which display biodegradable and/or biocompatible character. They have emerged as an environmentally-friendly solution to classical synthetic polymers and have attracted significant research interest in the past years. Herein, we present the synthesis of a D-mannose based glycopolymer with biodegradable features. The glycopolymer was synthesized by radical copolymerization between a D-mannose oligomer bearing polymerizable double bonds and 2-hydroxypropyl acrylate, in a weight ratio of 1:2. The copolymerization kinetics was investigated by differential scanning calorimetry (DSC) and the activation energy of the process was comparatively assessed by Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa methods. The obtained glycopolymer displayed good thermal behavior, fact proven by thermogravimetrical (TG) analysis and it was submitted to biodegradation inside a bioreactor fed with water from the Bega River as the source of microbial inoculum. The glycopolymer sample degraded by approximately 60% in just 23 days. The biodegradation pattern of the glycopolymer was successfully fitted against a modified sigmoidal exponential function. The kinetic model coefficients and its accuracy were calculated using Matlab and the correlation coefficient is more than promising. The changes inside glycopolymer structure after biodegradation were studied using TG and FTIR analyses, which revealed that the sugar moiety is firstly attacked by the microbial consortia as nutrient source for proliferation. Full article
(This article belongs to the Special Issue Glycopolymers and Polysaccharide-Based Copolymers)
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Article
The Effect of Dielectric Polarization Rate Difference of Filler and Matrix on the Electrorheological Responses of Poly(ionic liquid)/Polyaniline Composite Particles
Polymers 2020, 12(3), 703; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030703 - 22 Mar 2020
Cited by 7 | Viewed by 1082
Abstract
By using different conductivity of polyaniline as filler, a kind of poly(ionic liquid)/polyaniline composite particles was synthesized to investigate the influence of dielectric polarization rate difference between filler and matrix on the electrorheological response and flow stability of composite-based electrorheological fluids under simultaneous [...] Read more.
By using different conductivity of polyaniline as filler, a kind of poly(ionic liquid)/polyaniline composite particles was synthesized to investigate the influence of dielectric polarization rate difference between filler and matrix on the electrorheological response and flow stability of composite-based electrorheological fluids under simultaneous effect of shear and electric fields. The composite particles were prepared by a post ion-exchange procedure and then treated by ammonia or hydrazine to obtain different conductivity of polyaniline. Their electrorheological response was measured by dispersing these composite particles in insulating carrier liquid under electric fields. It showed that the composite particles treated by ammonia had the strongest electrorheological response and most stable flow behavior in a broad shear rate region from 0.5 s−1 to 1000 s−1. By using dielectric spectroscopy, it found that the enhanced electrorheological response with stable flow depended on the matching degree of the dielectric polarization rates between poly(ionic liquid) matrix and polyaniline filler. The closer their polarization rates are, the more stable the flow curves are. These results are helpful to design optimal composite-based electrorheological materials with enhanced and stable ER performance. Full article
(This article belongs to the Special Issue Stimuli Responsive Polymers II)
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Article
Bio-Nanocomposite Hydrogel Based on Zinc Alginate/Graphene Oxide: Morphology, Structural Conformation, Thermal Behavior/Degradation, and Dielectric Properties
Polymers 2020, 12(3), 702; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030702 - 22 Mar 2020
Cited by 12 | Viewed by 1746
Abstract
Bio-nanocomposite hydrogels based on sodium alginate (SA) as polymer matrix and graphene oxide (GO) nanosheets with zinc as crosslinking agent were synthesized with the aim of incorporating the intrinsic properties of their constituents (bioactivity and antimicrobial activity). Thus, stable and highly interconnected networks [...] Read more.
Bio-nanocomposite hydrogels based on sodium alginate (SA) as polymer matrix and graphene oxide (GO) nanosheets with zinc as crosslinking agent were synthesized with the aim of incorporating the intrinsic properties of their constituents (bioactivity and antimicrobial activity). Thus, stable and highly interconnected networks were obtained from GO nanosheets dispersed in SA matrices through interactions with low amounts of zinc. The GO nanosheets were successfully incorporated into the alginate matrix in the form of a complex nano-network involving different interactions: Bonds between alginate chains induced by Zn ions (egg box structure), interactions between GO nanosheets through Zn ions and hydrogen bonds between alginate chains, and GO nanosheets. The molecular interactions and morphology were confirmed by Fourier-transform infrared spectroscopy and transmission electron microscopy. The composite’s structural organization showed enhanced thermal stability. The glass transition temperature shifted to a higher temperature due to the reduced mobility induced by additional crosslinking bonds after incorporating the GO nanosheets and Zn into the polymer matrix. Finally, the dielectric behavior revealed that charge carrier mobility was hampered by the compact structure of the nanonetwork, which reduced conductivity. The combined properties of these nanocomposite hydrogels make them attractive biomaterials in the field of regenerative medicine and wound care since both surface bioactivity and antibacterial behavior are two critical factors involved in the success of a biomaterial. Full article
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Article
Influence of Heat Sink on the Mold Temperature of Gypsum Mold Used in Injection Molding
Polymers 2020, 12(3), 701; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12030701 - 21 Mar 2020
Cited by 3 | Viewed by 1180
Abstract
Gypsum molds have been developed as an alternative for the Rapid tooling (RT) method used in injection molding. However, the poor capability of the heat delivery forces the gypsum mold to operate under a high-risk condition, and distortion of the molded part becomes [...] Read more.
Gypsum molds have been developed as an alternative for the Rapid tooling (RT) method used in injection molding. However, the poor capability of the heat delivery forces the gypsum mold to operate under a high-risk condition, and distortion of the molded part becomes apparent. The goal is to investigate the effect of a heat sink on the reduction of the gypsum mold temperature and to establish a methodology for the heat sink design. The methodology used the advantage of the electrical circuit concept to analyze the mold temperature. The heat transfer of a mold was modeled using an equivalent thermal circuit. After all the components on the circuit were determined, the heat transfer rate could then be calculated. Once the heat transfer rate was known, the mold temperature could be easily analyzed. A modified thermal circuit considering transverse heat conduction was also proposed, which estimated the mold temperature more accurately. The mold temperature was reduced by 16.8 °C when a gypsum mold was installed with a 40 mm thick heat sink in a parallel configuration. Moreover, the reduction of the mold temperature improved the deflection of the molded part from 0.78 mm to 0.54 mm. This work provides a quick approach to analyze the mold temperature based on the thermal circuit concept. As the cooling system of the mold was modularized analytically, important properties of the cooling system in the heat transfer process were revealed by analyzing the thermal circuit of the mold, for example, the heat transfer rate or the mold temperature. Full article
(This article belongs to the Special Issue Advances on Injection Molding of Polymers)
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