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Polymers, Volume 11, Issue 2 (February 2019) – 200 articles

Cover Story (view full-size image): The electrochromic properties of conductive polymers make them suitable for use in energy-efficient reflective displays and labels. This work explores a UV patterning technique combined with vapor phase polymerization to form electrochromic conductive polymer films embedded with greyscale high-resolution images. A novel device architecture enables picture-to-picture displays in which two such overlapping images can be made to appear and disappear one at a time, by reciprocal oxidation and reduction of two patterned conductive polymer films. Finally, the study demonstrates that the patterning technique can also be used to form electrochromic patterns on porous paper substrates. View Paper here.
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13 pages, 3634 KiB  
Article
Synthesis and Physical Properties of Non-Crystalline Nylon 6 Containing Dimer Acid
by Ching-Nan Huang, Chang-Mou Wu, Hao-Wen Lo, Chiu-Chun Lai, Wei-Feng Teng, Lung-Chang Liu and Chien-Ming Chen
Polymers 2019, 11(2), 386; https://doi.org/10.3390/polym11020386 - 25 Feb 2019
Cited by 12 | Viewed by 5832
Abstract
In this study, a long carbon chain dimer acid is introduced into a nylon 6 structure and is copolymerized with different structural amines to produce amorphous nylon 6 by 4,4′-methylenebis(2-methylcyclohexylamine) (MMCA) in different copolymerization ratios. The effect of different structures and copolymerization ratios [...] Read more.
In this study, a long carbon chain dimer acid is introduced into a nylon 6 structure and is copolymerized with different structural amines to produce amorphous nylon 6 by 4,4′-methylenebis(2-methylcyclohexylamine) (MMCA) in different copolymerization ratios. The effect of different structures and copolymerization ratios on the properties of nylon 6 is determined, along with the thermal properties, crystallinity, water absorption, dynamic mechanical properties, and optical properties. It is found that the melting point and the thermal cracking temperature Td10 of nylon 6 are respectively between 176 °C and 213 °C and 378 °C to 405 °C. The effect of introducing a bicyclohexane group containing a methyl side chain is greater than that of a meta-benzene ring, so COMM (synthesized by Caprolactam (C), dimer oleic acid (OA), and 4,4′-Methylenebis(2-methylcyclohexylamine) (MMCA)) has the lowest melting point, enthalpy, and crystallinity. As the copolymerization ratio increases, its thermal properties decrease. 10% is the lowest crystallinity. The amine structure containing a bicycloalkyl group has lower water absorption and a 10% copolymerization ratio gives the lowest water absorption. It contains the bicycloalkyl group, COM (synthesized by Caprolactam (C), dimer oleic acid (OA) and 4,4′-Methylenebis(cyclohexylamine) (MCA)), which has the highest loss modulus. The lowest loss modulus is noted for a copolymerization ratio of 7% and the value of tan δ increases as the copolymerization ratio increases. The introduction of nylon 6 with the bicycloalkyl groups, COMM and COM, significantly increases transparency. As the copolymerization ratio increases, the transparency increases and the haze decreases. The best optical properties are achieved for 10% copolymerization. Full article
(This article belongs to the Special Issue Thermal Properties and Applications of Polymers)
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12 pages, 2547 KiB  
Article
Calculated Terahertz Spectra of Glycine Oligopeptide Solutions Confined in Carbon Nanotubes
by Dongxiong Ling, Mingkun Zhang, Jianxun Song and Dongshan Wei
Polymers 2019, 11(2), 385; https://doi.org/10.3390/polym11020385 - 25 Feb 2019
Cited by 3 | Viewed by 3123
Abstract
To reduce the intense terahertz (THz) wave absorption of water and increase the signal-to-noise ratio, the THz spectroscopy detection of biomolecules usually operates using the nanofluidic channel technologies in practice. The effects of confinement due to the existence of nanofluidic channels on the [...] Read more.
To reduce the intense terahertz (THz) wave absorption of water and increase the signal-to-noise ratio, the THz spectroscopy detection of biomolecules usually operates using the nanofluidic channel technologies in practice. The effects of confinement due to the existence of nanofluidic channels on the conformation and dynamics of biomolecules are well known. However, studies of confinement effects on the THz spectra of biomolecules are still not clear. In this work, extensive all-atom molecular dynamics simulations are performed to investigate the THz spectra of the glycine oligopeptide solutions in free and confined environments. THz spectra of the oligopeptide solutions confined in carbon nanotubes (CNTs) with different radii are calculated and compared. Results indicate that with the increase of the degree of confinement (the reverse of the radius of CNT), the THz absorption coefficient decreases monotonically. By analyzing the diffusion coefficient and dielectric relaxation dynamics, the hydrogen bond life, and the vibration density of the state of the water molecules in free solution and in CNTs, we conclude that the confinement effects on the THz spectra of biomolecule solutions are mainly to slow down the dynamics of water molecules and hence to reduce the THz absorption of the whole solution in confined environments. Full article
(This article belongs to the Special Issue Simulations of Polymers)
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28 pages, 3597 KiB  
Review
Emergence of Flexible White Organic Light-Emitting Diodes
by Dongxiang Luo, Qizan Chen, Baiquan Liu and Ying Qiu
Polymers 2019, 11(2), 384; https://doi.org/10.3390/polym11020384 - 22 Feb 2019
Cited by 43 | Viewed by 8109
Abstract
Flexible white organic light-emitting diodes (FWOLEDs) have considerable potential to meet the rapidly growing requirements of display and lighting commercialization. To achieve high-performance FWOLEDs, (i) the selection of effective flexible substrates, (ii) the use of transparent conducting electrodes, (iii) the introduction of efficient [...] Read more.
Flexible white organic light-emitting diodes (FWOLEDs) have considerable potential to meet the rapidly growing requirements of display and lighting commercialization. To achieve high-performance FWOLEDs, (i) the selection of effective flexible substrates, (ii) the use of transparent conducting electrodes, (iii) the introduction of efficient device architectures, and iv) the exploitation of advanced outcoupling techniques are necessary. In this review, recent state-of-the-art strategies to develop FWOLEDs have been summarized. Firstly, the fundamental concepts of FWOLEDs have been described. Then, the primary approaches to realize FWOLEDs have been introduced. Particularly, the effects of flexible substrates, conducting electrodes, device architectures, and outcoupling techniques in FWOLEDs have been comprehensively highlighted. Finally, issues and ways to further enhance the performance of FWOLEDs have been briefly clarified. Full article
(This article belongs to the Special Issue Polymer-Based Flexible Printed Electronics and Sensors)
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16 pages, 3916 KiB  
Article
Modeling of High-Efficiency Multi-Junction Polymer and Hybrid Solar Cells to Absorb Infrared Light
by Jobeda J. Khanam and Simon Y. Foo
Polymers 2019, 11(2), 383; https://doi.org/10.3390/polym11020383 - 22 Feb 2019
Cited by 27 | Viewed by 6634
Abstract
In this paper, we present our work on high-efficiency multi-junction polymer and hybrid solar cells. The transfer matrix method is used for optical modeling of an organic solar cell, which was inspired by the McGehee Group in Stanford University. The software simulation calculates [...] Read more.
In this paper, we present our work on high-efficiency multi-junction polymer and hybrid solar cells. The transfer matrix method is used for optical modeling of an organic solar cell, which was inspired by the McGehee Group in Stanford University. The software simulation calculates the optimal thicknesses of the active layers to provide the best short circuit current (JSC) value. First, we show three designs of multi-junction polymer solar cells, which can absorb sunlight beyond the 1000 nm wavelengths. Then we present a novel high-efficiency hybrid (organic and inorganic) solar cell, which can absorb the sunlight with a wavelength beyond 2500 nm. Approximately 12% efficiency was obtained for the multi-junction polymer solar cell and 20% efficiency was obtained from every two-, three- and four-junction hybrid solar cell under 1 sun AM1.5 illumination. Full article
(This article belongs to the Special Issue Polymer-Based Solar Cells)
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8 pages, 1820 KiB  
Article
Effect of Hydration in Corona Layer on Structural Change of Thermo-Responsive Polymer Micelles
by Yusuke Akino, Kosuke Morimoto, Kengo Tsuboi, Satoshi Kanazawa and Isamu Akiba
Polymers 2019, 11(2), 382; https://doi.org/10.3390/polym11020382 - 22 Feb 2019
Cited by 3 | Viewed by 3121
Abstract
The effect of hydration in corona layer on temperature responsiveness of polymer micelles consisting of poly(N-vinyl pyrrolidone)-block-poly(n-octadecyl acrylate) (PVP-b-PODA) was investigated. Small-angle X-ray scattering and dynamic light scattering showed two-step shape change of PVP-b [...] Read more.
The effect of hydration in corona layer on temperature responsiveness of polymer micelles consisting of poly(N-vinyl pyrrolidone)-block-poly(n-octadecyl acrylate) (PVP-b-PODA) was investigated. Small-angle X-ray scattering and dynamic light scattering showed two-step shape change of PVP-b-PODA micelles around 45 and 65 °C with elevating temperature, although only one-step shape change was observed at 45 °C in cooling process. In the first step, shape of PVP-b-PODA micelles was changed from disk to ellipsoidal oblate at the melting temperature (Tm) of PODA, although similar micelles consisting of another amphiphilic block copolymers containing PODA simply changed from disk to sphere at the Tm with elevating temperature. PVP-b-PODA micelles changed to spherical shape above 65 °C. Two-dimensional (2D) 1H-NMR showed the PVP chains were perfectly dehydrated above 65 °C. Therefore, it was suggested that the appearance of ellipsoidal shape between Tm of PODA and 65 °C was caused owing to shape memory effect of pseudo network of corona layer due to robust hydration of PVP chains. Full article
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12 pages, 3290 KiB  
Article
Delayed Crosslinking Amphiphilic Polymer Gel System with Adjustable Gelation Time Based on Competitive Inclusion Method
by Bin Xu, Huiming Zhang and He Bian
Polymers 2019, 11(2), 381; https://doi.org/10.3390/polym11020381 - 21 Feb 2019
Cited by 7 | Viewed by 4753
Abstract
Delayed crosslinking polymer gel systems are widely utilized in deep profile control processes for water production control in oilfields. In this paper, a kind of delayed crosslinking amphiphilic polymer gel system with adjustable gelation time based on competitive inclusion was prepared and its [...] Read more.
Delayed crosslinking polymer gel systems are widely utilized in deep profile control processes for water production control in oilfields. In this paper, a kind of delayed crosslinking amphiphilic polymer gel system with adjustable gelation time based on competitive inclusion was prepared and its delayed crosslinking gelling properties were studied. The amphiphilic polymer of P(acrylamide (AM)–sodium acrylate (NaA)–N-dodecylacrylamide (DDAM)) was synthesized and it showed much better salt resistance, temperature resistance, and shear resistance performance compared with hydrolyzed polyacrylamide (HPAM). Phenol can be controlled released from the the cavity of β-cyclodextrin (β-CD) ring in the presence of the hydrophobic group used as the competitive inclusion agent in the amphiphilic polymer backbone. Accordingly, the gelation time of the delayed crosslinking amphiphilic polymer gel system is closely related to release rate of the crosslinker from the the cavity of β-CD ring. This study screened an amphiphilic polymer with good salt resistance and temperature resistance performance, which can be used in high temperature and high salinity reservoirs, and provided a feasible way to control the gelation time of the polymer gel system by the competitive inclusion method. Full article
(This article belongs to the Special Issue Hydrophilic Polymers)
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14 pages, 6330 KiB  
Article
Investigation of the Structure-Property Effect of Phosphorus-Containing Polysulfone on Decomposition and Flame Retardant Epoxy Resin Composites
by Wei Zhao, Yongxiang Li, Qiushi Li, Yiliang Wang and Gong Wang
Polymers 2019, 11(2), 380; https://doi.org/10.3390/polym11020380 - 21 Feb 2019
Cited by 9 | Viewed by 3888
Abstract
The flame retardant modification of epoxy (EP) is of great signification for aerospace, automotive, marine, and energy industries. In this study, a series of EP composites containing different variations of phosphorus-containing polysulfone (with a phosphorus content of approximately 1.25 wt %) were obtained. [...] Read more.
The flame retardant modification of epoxy (EP) is of great signification for aerospace, automotive, marine, and energy industries. In this study, a series of EP composites containing different variations of phosphorus-containing polysulfone (with a phosphorus content of approximately 1.25 wt %) were obtained. The obtained EP/polysulfone composites had a high glass transition temperature (Tg) and high flame retardancy. The influence of phosphorus-containing compounds (ArPN2, ArPO2, ArOPN2 and ArOPO2) on the thermal properties and flame retardancy of EP/polysulfone composites was investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), a UL-94 vertical burning test, and cone calorimeter tests. The phosphorus-containing polysulfone enhanced the thermal stability of EP. The more stable porous char layer, less flammable gases, and a lower apparent activation energy at a high degree of conversion demonstrated the high gas inhibition effect of phosphorus-containing compounds. Moreover, the gas inhibition effect of polysulfone with a P–C bond was more efficient than the polysulfone with a P–O–C bond. The potential for optimizing flame retardancy while maintaining a high Tg is highlighted in this study. The flame-retardant EP/polysulfone composites with high thermal stability broaden the application field of epoxy. Full article
(This article belongs to the Special Issue Flame Retardancy of Polymeric Materials)
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21 pages, 4487 KiB  
Article
Tablet of Ximenia Americana L. Developed from Mucoadhesive Polymers for Future Use in Oral Treatment of Fungal Infections
by Lucas Almeida, João Augusto Oshiro Júnior, Milena Silva, Fernanda Nóbrega, Jéssica Andrade, Widson Santos, Angélica Ribeiro, Marta Conceição, Germano Veras and Ana Cláudia Medeiros
Polymers 2019, 11(2), 379; https://doi.org/10.3390/polym11020379 - 20 Feb 2019
Cited by 13 | Viewed by 4163
Abstract
The use of biocompatible polymers such as Hydroxypropylmethylcellulose (HPMC), Hydroxyethylcellulose (HEC), Carboxymethylcellulose (CMC), and Carbopol in solid formulations results in mucoadhesive systems capable of promoting the prolonged and localized release of Active Pharmaceutical Ingredients (APIs). This strategy represents a technological innovation that can [...] Read more.
The use of biocompatible polymers such as Hydroxypropylmethylcellulose (HPMC), Hydroxyethylcellulose (HEC), Carboxymethylcellulose (CMC), and Carbopol in solid formulations results in mucoadhesive systems capable of promoting the prolonged and localized release of Active Pharmaceutical Ingredients (APIs). This strategy represents a technological innovation that can be applied to improving the treatment of oral infections, such as oral candidiasis. Therefore, the aim of this study was to develop a tablet of Ximenia americana L. from mucoadhesive polymers for use in the treatment of oral candidiasis. An X. americana extract (MIC of 125 μg·mL−1) was obtained by turbolysis at 50% of ethanol, a level that demonstrated activity against Candida albicans. Differential Thermal Analysis and Fourier Transform Infrared Spectroscopy techniques allowed the choice of HPMC as a mucoadhesive agent, besides polyvinylpyrrolidone, magnesium stearate, and mannitol to integrate the formulation of X. americana. These excipients were granulated with an ethanolic solution 70% v/v at PVP 5%, and a mucoadhesive tablet was obtained by compression. Finally, mucoadhesive strength was evaluated, and the results demonstrated good mucoadhesive forces in mucin disk and pig buccal mucosa. Therefore, the study allowed a new alternative to be developed for the treatment of buccal candidiasis, one which overcomes the inconveniences of common treatments, costs little, and facilitates patients’ adhesion. Full article
(This article belongs to the Special Issue Biomedical Polymer Materials)
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21 pages, 11262 KiB  
Article
Femtosecond Laser Fabrication of Engineered Functional Surfaces Based on Biodegradable Polymer and Biopolymer/Ceramic Composite Thin Films
by Albena Daskalova, Irina Bliznakova, Liliya Angelova, Anton Trifonov, Heidi Declercq and Ivan Buchvarov
Polymers 2019, 11(2), 378; https://doi.org/10.3390/polym11020378 - 20 Feb 2019
Cited by 21 | Viewed by 4556
Abstract
Surface functionalization introduced by precisely-defined surface structures depended on the surface texture and quality. Laser treatment is an advanced, non-contact technique for improving the biomaterials surface characteristics. In this study, femtosecond laser modification was applied to fabricate diverse structures on biodegradable polymer thin [...] Read more.
Surface functionalization introduced by precisely-defined surface structures depended on the surface texture and quality. Laser treatment is an advanced, non-contact technique for improving the biomaterials surface characteristics. In this study, femtosecond laser modification was applied to fabricate diverse structures on biodegradable polymer thin films and their ceramic blends. The influences of key laser processing parameters like laser energy and a number of applied laser pulses (N) over laser-treated surfaces were investigated. The modification of surface roughness was determined by atomic force microscopy (AFM). The surface roughness (Rrms) increased from approximately 0.5 to nearly 3 µm. The roughness changed with increasing laser energy and a number of applied laser pulses (N). The induced morphologies with different laser parameters were compared via Scanning electron microscopy (SEM) and confocal microscopy analysis. The chemical composition of exposed surfaces was examined by FTIR, X-ray photoelectron spectroscopy (XPS), and XRD analysis. This work illustrates the capacity of the laser microstructuring method for surface functionalization with possible applications in improvement of cellular attachment and orientation. Cells exhibited an extended shape along laser-modified surface zones compared to non-structured areas and demonstrated parallel alignment to the created structures. We examined laser-material interaction, microstructural outgrowth, and surface-treatment effect. By comparing the experimental results, it can be summarized that considerable processing quality can be obtained with femtosecond laser structuring. Full article
(This article belongs to the Special Issue Functional Polymers for Biomedicine)
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13 pages, 2716 KiB  
Article
Formation of Polyaniline and Polypyrrole Nanocomposites with Embedded Glucose Oxidase and Gold Nanoparticles
by Natalija German, Almira Ramanaviciene and Arunas Ramanavicius
Polymers 2019, 11(2), 377; https://doi.org/10.3390/polym11020377 - 20 Feb 2019
Cited by 59 | Viewed by 5097
Abstract
Several types of polyaniline (PANI) and polypyrrole (Ppy) nanocomposites with embedded glucose oxidase (GOx) and gold nanoparticles (AuNPs) were formed by enzymatic polymerization of corresponding monomers (aniline and pyrrole) in the presence of 6 and 13 nm diameter colloidal gold nanoparticles (AuNPs(6nm) [...] Read more.
Several types of polyaniline (PANI) and polypyrrole (Ppy) nanocomposites with embedded glucose oxidase (GOx) and gold nanoparticles (AuNPs) were formed by enzymatic polymerization of corresponding monomers (aniline and pyrrole) in the presence of 6 and 13 nm diameter colloidal gold nanoparticles (AuNPs(6nm) or AuNPs(13nm), respectively) or chloroaurate ions (AuCl4). Glucose oxidase in the presence of glucose generated H2O2, which acted as initiator of polymerization reaction. The influence of polymerization bulk composition and pH on the formation of PANI- and Ppy-based nanocomposites was investigated spectrophotometrically. The highest formation rate of PANI- and Ppy-based nanocomposites with embedded glucose oxidase and gold nanoparticles (PANI/AuNPs-GOx and Ppy/AuNPs-GOx, respectively) was observed in the solution of sodium acetate buffer, pH 6.0. It was determined that the presence of AuNPs or AuCl4 ions facilitate enzymatic polymerization of aniline and pyrrole. Full article
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19 pages, 3338 KiB  
Article
Assessment of the Tumbling-Snake Model against Linear and Nonlinear Rheological Data of Bidisperse Polymer Blends
by Pavlos S. Stephanou and Martin Kröger
Polymers 2019, 11(2), 376; https://doi.org/10.3390/polym11020376 - 20 Feb 2019
Cited by 6 | Viewed by 3728
Abstract
We have recently solved the tumbling-snake model for concentrated polymer solutions and entangled melts in the academic case of a monodisperse sample. Here, we extend these studies and provide the stationary solutions of the tumbling-snake model both analytically, for small shear rates, and [...] Read more.
We have recently solved the tumbling-snake model for concentrated polymer solutions and entangled melts in the academic case of a monodisperse sample. Here, we extend these studies and provide the stationary solutions of the tumbling-snake model both analytically, for small shear rates, and via Brownian dynamics simulations, for a bidisperse sample over a wide range of shear rates and model parameters. We further show that the tumbling-snake model bears the necessary capacity to compare well with available linear and non-linear rheological data for bidisperse systems. This capacity is added to the already documented ability of the model to accurately predict the shear rheology of monodisperse systems. Full article
(This article belongs to the Special Issue Theory and Simulations of Entangled Polymers)
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16 pages, 10529 KiB  
Article
Facile Synthesis of Methylsilsesquioxane Aerogels with Uniform Mesopores by Microwave Drying
by Xingzhong Guo, Jiaqi Shan, Wei Lei, Ronghua Ding, Yun Zhang and Hui Yang
Polymers 2019, 11(2), 375; https://doi.org/10.3390/polym11020375 - 20 Feb 2019
Cited by 17 | Viewed by 3580
Abstract
Methylsilsesquioxane (MSQ) aerogels with uniform mesopores were facilely prepared via a sol–gel process followed by microwave drying with methyltrimethoxysilane (MTMS) as a precursor, hydrochloric acid (HCl) as a catalyst, water and methanol as solvents, hexadecyltrimethylammonium chloride (CTAC) as a surfactant and template, and [...] Read more.
Methylsilsesquioxane (MSQ) aerogels with uniform mesopores were facilely prepared via a sol–gel process followed by microwave drying with methyltrimethoxysilane (MTMS) as a precursor, hydrochloric acid (HCl) as a catalyst, water and methanol as solvents, hexadecyltrimethylammonium chloride (CTAC) as a surfactant and template, and propylene oxide (PO) as a gelation agent. The microstructure, chemical composition, and pore structures of the resultant MSQ aerogels were investigated in detail to achieve controllable preparation of MSQ aerogels, and the thermal stability of MSQ aerogels was also analyzed. The gelation agent, catalyst, solvent, and microwave power have important roles related to the pore structures of MSQ aerogels. Meanwhile, the microwave drying method was found to not only have a remarkable effect on improving production efficiency, but also to be conducive to avoiding the collapse of pore structure (especially micropores) during drying. The resulting MSQ aerogel microwave-dried at 500 W possessed a specific surface area up to 821 m2/g and a mesopore size of 20 nm, and displayed good thermal stability. Full article
(This article belongs to the Special Issue Polymer and Composite Aerogels)
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16 pages, 4439 KiB  
Article
A Novel Method for Deposition of Multi-Walled Carbon Nanotubes onto Poly(p-Phenylene Terephthalamide) Fibers to Enhance Interfacial Adhesion with Rubber Matrix
by Xuan Yang, Qunzhang Tu, Xinmin Shen, Pengxiao Zhu, Yi Li and Shuai Zhang
Polymers 2019, 11(2), 374; https://doi.org/10.3390/polym11020374 - 20 Feb 2019
Cited by 23 | Viewed by 3745
Abstract
In order to enhance the interfacial adhesion of poly(p-phenylene terephthalamide) (PPTA) fibers to the rubber composites, a novel method to deposit multi-walled carbon nanotubes (MWCNTs) onto the surface of PPTA fibers has been proposed in this study. This chemical modification was performed through [...] Read more.
In order to enhance the interfacial adhesion of poly(p-phenylene terephthalamide) (PPTA) fibers to the rubber composites, a novel method to deposit multi-walled carbon nanotubes (MWCNTs) onto the surface of PPTA fibers has been proposed in this study. This chemical modification was performed through the introduction of epoxy groups by Friedel–Crafts alkylation on the PPTA fibers, the carboxylation of MWCNTs, and the ring-opening reaction between the epoxy groups and the carboxyl groups. The morphologies, chemical structures, and compositions of the surface of PPTA fibers were characterized by scanning electron microscope, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results showed that MWCNTs were uniformly deposited onto the surface of PPTA fibers with the covalent bonds. The measurement of contact angles of the fibers with polar solvent and non-polar solvent indicated that the surface energy of deposited fibers significantly increased by 41.9% compared with the untreated fibers. An electronic tensile tester of single-filament and a universal testing machine were utilized to measure the strength change of the fibers after modification and the interfacial adhesion between the fibers and the rubber matrix, respectively. The results showed that the tensile strength had not been obviously reduced, and the pull-out force and peeling strength of the fibers to the rubber increased by 46.3% and 56.5%, respectively. Full article
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14 pages, 2074 KiB  
Article
Mechanically Robust Hybrid POSS Thermoplastic Polyurethanes with Enhanced Surface Hydrophobicity
by Xiuhuan Song, Xiaoxiao Zhang, Tianduo Li, Zibiao Li and Hong Chi
Polymers 2019, 11(2), 373; https://doi.org/10.3390/polym11020373 - 20 Feb 2019
Cited by 26 | Viewed by 4689
Abstract
A series of hybrid thermoplastic polyurethanes (PUs) were synthesized from bi-functional polyhedral oligomeric silsesquioxane (B-POSS) and polycaprolactone (PCL) using 1,6-hexamethylene diisocyanate (HDI) as a coupling agent for the first time. The newly synthesized hybrid materials were fully characterized in terms of structure, morphology, [...] Read more.
A series of hybrid thermoplastic polyurethanes (PUs) were synthesized from bi-functional polyhedral oligomeric silsesquioxane (B-POSS) and polycaprolactone (PCL) using 1,6-hexamethylene diisocyanate (HDI) as a coupling agent for the first time. The newly synthesized hybrid materials were fully characterized in terms of structure, morphology, thermal and mechanical performance, as well as their toughening effect toward polyesters. Thermal gravimeter analysis (TGA) and differential scanning calorimetry (DSC) showed enhanced thermal stability by 76 °C higher in decomposition temperature (Td) of the POSS PUs, and 22 °C higher glass transition temperature (Tg) when compared with control PU without POSS. Static contact angle results showed a significant increment of 49.8° and 53.4° for the respective surface hydrophobicity and lipophilicity measurements. More importantly, both storage modulus (G’) and loss modulus (G’’) are improved in the hybrid POSS PUs and these parameters can be further adjusted by varying POSS content in the copolymer. As a biodegradable hybrid filler, the as-synthesized POSS PUs also demonstrated a remarkable effect in toughening commercial polyesters, indicating a simple yet useful strategy in developing high-performance polyester for advanced biomedical applications. Full article
(This article belongs to the Special Issue POSS-Based Polymers)
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12 pages, 5499 KiB  
Article
Enhancement by Metallic Tube Filling of the Mechanical Properties of Electromagnetic Wave Absorbent Polymethacrylimide Foam
by Leilei Yan, Wei Jiang, Chun Zhang, Yunwei Zhang, Zhiheng He, Keyu Zhu, Niu Chen, Wanbo Zhang, Bin Han and Xitao Zheng
Polymers 2019, 11(2), 372; https://doi.org/10.3390/polym11020372 - 20 Feb 2019
Cited by 21 | Viewed by 4132
Abstract
By the addition of a carbon-based electromagnetic absorbing agent during the foaming process, a novel electromagnetic absorbent polymethacrylimide (PMI) foam was obtained. The proposed foam exhibits excellent electromagnetic wave-absorbing properties, with absorptivity exceeding 85% at a large frequency range of 4.9–18 GHz. However, [...] Read more.
By the addition of a carbon-based electromagnetic absorbing agent during the foaming process, a novel electromagnetic absorbent polymethacrylimide (PMI) foam was obtained. The proposed foam exhibits excellent electromagnetic wave-absorbing properties, with absorptivity exceeding 85% at a large frequency range of 4.9–18 GHz. However, its poor mechanical properties would limit its application in load-carrying structures. In the present study, a novel enhancement approach is proposed by inserting metallic tubes into pre-perforated holes of PMI foam blocks. The mechanical properties of the tube-enhanced PMI foams were studied experimentally under compressive loading conditions. The elastic modulus, compressive strength, energy absorption per unit volume, and energy absorption per unit mass were increased by 127.9%, 133.8%, 54.2%, and 46.4%, respectively, by the metallic tube filling, and the density increased only by 5.3%. The failure mechanism of the foams was also explored. We found that the weaker interfaces between the foam and the electromagnetic absorbing agent induced crack initiation and subsequent collapses, which destroyed the structural integrity. The excellent mechanical and electromagnetic absorbing properties make the novel structure much more competitive in electromagnetic wave stealth applications, while acting simultaneously as load-carrying structures. Full article
(This article belongs to the Special Issue Polymeric Foams)
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11 pages, 1977 KiB  
Article
Synthesis, Characterization, and Antifungal Activity of Schiff Bases of Inulin Bearing Pyridine ring
by Lijie Wei, Wenqiang Tan, Jingjing Zhang, Yingqi Mi, Fang Dong, Qing Li and Zhanyong Guo
Polymers 2019, 11(2), 371; https://doi.org/10.3390/polym11020371 - 20 Feb 2019
Cited by 28 | Viewed by 3684
Abstract
As a renewable, biocompatible, and biodegradable polysaccharide, inulin has a good solubility in water and some physiological functions. Chemical modification is one of the important methods to improve the bioactivity of inulin. In this paper, based on 6-amino-6-deoxy-3,4-acetyl inulin (3), three [...] Read more.
As a renewable, biocompatible, and biodegradable polysaccharide, inulin has a good solubility in water and some physiological functions. Chemical modification is one of the important methods to improve the bioactivity of inulin. In this paper, based on 6-amino-6-deoxy-3,4-acetyl inulin (3), three kinds of Schiff bases of inulin bearing pyridine rings were successfully designed and synthesized. Detailed structural characterization was carried out using FTIR, 13C NMR, and 1H NMR spectroscopy, and elemental analysis. Moreover, the antifungal activity of Schiff bases of inulin against three plant pathogenic fungi, including Botrytis cinerea, Fusarium oxysporum f.sp.niveum, and Phomopsis asparagi, were evaluated using in vitro hypha measurements. Inulin, as a natural polysaccharide, did not possess any antifungal activity at the tested concentration against the targeted fungi. Compared with inulin and the intermediate product 6-amino-6-deoxy-3,4-acetyl inulin (3), all the synthesized Schiff bases of inulin derivatives with >54.0% inhibitory index at 2.0 mg/mL exhibited enhanced antifungal activity. 3NS, with an inhibitory index of 77.0% exhibited good antifungal activity against Botrytis cinerea at 2.0 mg/mL. The synthesized Schiff bases of inulin bearing pyridine rings can be prepared for novel antifungal agents to expand the application of inulin. Full article
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9 pages, 1540 KiB  
Article
Contraction of Entangled Polymers After Large Step Shear Deformations in Slip-Link Simulations
by Yuichi Masubuchi
Polymers 2019, 11(2), 370; https://doi.org/10.3390/polym11020370 - 20 Feb 2019
Cited by 7 | Viewed by 3401
Abstract
Although the tube framework has achieved remarkable success to describe entangled polymer dynamics, the chain motion assumed in tube theories is still a matter of discussion. Recently, Xu et al. [ACS Macro Lett. 2018, 7, 190–195] performed a molecular dynamics simulation for entangled [...] Read more.
Although the tube framework has achieved remarkable success to describe entangled polymer dynamics, the chain motion assumed in tube theories is still a matter of discussion. Recently, Xu et al. [ACS Macro Lett. 2018, 7, 190–195] performed a molecular dynamics simulation for entangled bead-spring chains under a step uniaxial deformation and reported that the relaxation of gyration radii cannot be reproduced by the elaborated single-chain tube model called GLaMM. On the basis of this result, they criticized the tube framework, in which it is assumed that the chain contraction occurs after the deformation before the orientational relaxation. In the present study, as a test of their argument, two different slip-link simulations developed by Doi and Takimoto and by Masubuchi et al. were performed and compared to the results of Xu et al. In spite of the modeling being based on the tube framework, the slip-link simulations excellently reproduced the bead-spring simulation result. Besides, the chain contraction was observed in the simulations as with the tube picture. The obtained results imply that the bead-spring results are within the scope of the tube framework whereas the failure of the GLaMM model is possibly due to the homogeneous assumption along the chain for the fluctuations induced by convective constraint release. Full article
(This article belongs to the Special Issue Theory and Simulations of Entangled Polymers)
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13 pages, 2300 KiB  
Article
Spray-Formed Layered Polymer Microneedles for Controlled Biphasic Drug Delivery
by Seok Chan Park, Min Jung Kim, Seung-Ki Baek, Jung-Hwan Park and Seong-O Choi
Polymers 2019, 11(2), 369; https://doi.org/10.3390/polym11020369 - 20 Feb 2019
Cited by 40 | Viewed by 8065
Abstract
In this study we present polymeric microneedles composed of multiple layers to control drug release kinetics. Layered microneedles were fabricated by spraying poly(lactic-co-glycolic acid) (PLGA) and polyvinylpyrrolidone (PVP) in sequence, and were characterized by mechanical testing and ex vivo skin insertion [...] Read more.
In this study we present polymeric microneedles composed of multiple layers to control drug release kinetics. Layered microneedles were fabricated by spraying poly(lactic-co-glycolic acid) (PLGA) and polyvinylpyrrolidone (PVP) in sequence, and were characterized by mechanical testing and ex vivo skin insertion tests. The compression test demonstrated that no noticeable layer separation occurred, indicating good adhesion between PLGA and PVP layers. Histological examination confirmed that the microneedles were successfully inserted into the skin and indicated biphasic release of dyes incorporated within microneedle matrices. Structural changes of a model protein drug, bovine serum albumin (BSA), in PLGA and PVP matrices were examined by circular dichroism (CD) and fluorescence spectroscopy. The results showed that the tertiary structure of BSA was well maintained in both PLGA and PVP layers while the secondary structures were slightly changed during microneedle fabrication. In vitro release studies showed that over 60% of BSA in the PLGA layer was released within 1 h, followed by continuous slow release over the course of the experiments (7 days), while BSA in the PVP layer was completely released within 0.5 h. The initial burst of BSA from PLGA was further controlled by depositing a blank PLGA layer prior to forming the PLGA layer containing BSA. The blank PLGA layer acted as a diffusion barrier, resulting in a reduced initial burst. The formation of the PLGA diffusion barrier was visualized using confocal microscopy. Our results suggest that the spray-formed multilayer microneedles could be an attractive transdermal drug delivery system that is capable of modulating a drug release profile. Full article
(This article belongs to the Special Issue Materials and Methods for New Technologies in Polymer Processing)
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15 pages, 3641 KiB  
Article
Effect of Sodium Trimetaphosphate on Chitosan-Methylcellulose Composite Films: Physicochemical Properties and Food Packaging Application
by Hongxia Wang, Yu Liao, Ailiang Wu, Bing Li, Jun Qian and Fuyuan Ding
Polymers 2019, 11(2), 368; https://doi.org/10.3390/polym11020368 - 20 Feb 2019
Cited by 29 | Viewed by 5463
Abstract
Environmentally friendly food packaging currently attracts much interest. Sodium trimetaphosphate (STMP) finds specialized applications in food, but it is rarely used as a crosslinking agent. In this study, STMP was used as a crosslinking agent to prepare chitosan/methylcellulose composite films. Both antibacterial and [...] Read more.
Environmentally friendly food packaging currently attracts much interest. Sodium trimetaphosphate (STMP) finds specialized applications in food, but it is rarely used as a crosslinking agent. In this study, STMP was used as a crosslinking agent to prepare chitosan/methylcellulose composite films. Both antibacterial and physicochemical properties of the composite film were improved by crosslinking with STMP. The crosslinked films, with good antibacterial activity (~99%), had increased tensile strength, a higher elongation at break, a lower swelling ratio and solubility, and a lower enzymatic degradation than the non-crosslinked films. Furthermore, the crosslinked films showed an excellent preservative effect on fresh-cut wax gourd after three days at room temperature. The obtained films crosslinked by STMP can be potentially applied to the food industry, such as food functional packaging, providing a novel alternative to traditional plastic packages. Full article
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13 pages, 2124 KiB  
Article
Enhancing X-ray Attenuation of 3D Printed Gelatin Methacrylate (GelMA) Hydrogels Utilizing Gold Nanoparticles for Bone Tissue Engineering Applications
by Nehar Celikkin, Simone Mastrogiacomo, X. Frank Walboomers and Wojciech Swieszkowski
Polymers 2019, 11(2), 367; https://doi.org/10.3390/polym11020367 - 20 Feb 2019
Cited by 45 | Viewed by 6086
Abstract
Bone tissue engineering is a rapidly growing field which is currently progressing toward clinical applications. Effective imaging methods for longitudinal studies are critical to evaluating the new bone formation and the fate of the scaffolds. Computed tomography (CT) is a prevailing technique employed [...] Read more.
Bone tissue engineering is a rapidly growing field which is currently progressing toward clinical applications. Effective imaging methods for longitudinal studies are critical to evaluating the new bone formation and the fate of the scaffolds. Computed tomography (CT) is a prevailing technique employed to investigate hard tissue scaffolds; however, the CT signal becomes weak in mainly-water containing materials, which hinders the use of CT for hydrogels-based materials. Nevertheless, hydrogels such as gelatin methacrylate (GelMA) are widely used for tissue regeneration due to their optimal biological properties and their ability to induce extracellular matrix formation. To date, gold nanoparticles (AuNPs) have been suggested as promising contrast agents, due to their high X-ray attenuation, biocompatibility, and low toxicity. In this study, the effects of different sizes and concentrations of AuNPs on the mechanical properties and the cytocompatibility of the bulk GelMA-AuNPs scaffolds were evaluated. Furthermore, the enhancement of CT contrast with the cytocompatible size and concentration of AuNPs were investigated. 3D printed GelMA and GelMA-AuNPs scaffolds were obtained and assessed for the osteogenic differentiation of mesenchymal stem cells (MSC). Lastly, 3D printed GelMA and GelMA-AuNPs scaffolds were scanned in a bone defect utilizing µCT as the proof of concept that the GelMA-AuNPs are good candidates for bone tissue engineering with enhanced visibility for µCT imaging. Full article
(This article belongs to the Special Issue Functional Polymers for Biomedicine)
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18 pages, 3253 KiB  
Article
New Alginate/PNIPAAm Matrices for Drug Delivery
by Catalina N. Cheaburu-Yilmaz, Catalina Elena Lupuşoru and Cornelia Vasile
Polymers 2019, 11(2), 366; https://doi.org/10.3390/polym11020366 - 20 Feb 2019
Cited by 12 | Viewed by 3302
Abstract
This paper deals with a comparative study on the interpolymeric complexes of alginate poly(N-isopropyl acryl amide (PNIPAAm) and corresponding graft copolymers with various compositions in respect to their toxicity, biocompatibility and in vitro and in vivo release of theophylline (THP). Loading [...] Read more.
This paper deals with a comparative study on the interpolymeric complexes of alginate poly(N-isopropyl acryl amide (PNIPAAm) and corresponding graft copolymers with various compositions in respect to their toxicity, biocompatibility and in vitro and in vivo release of theophylline (THP). Loading of the various matrices with theophylline and characterization of loaded matrices was studied by near infrared spectroscopy–chemical imaging (NIR–CI) analysis, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). It was appreciated that THP loading is higher than 40% and the drug is relatively homogeneous distributed within all matrices because of some specific interactions between components of the system. All samples have been found to be non-toxic and biocompatible. It was established that graft copolymers having a good stability show a better drug carrier ability, a higher THP loading, a prolonged release (longer release duration for graft copolymers of 235.4–302.3 min than that for IPC 72/28 of 77.6 min, which means approximately four times slower release from the graft copolymer-based matrices than from the interpolymeric complex) and a good bioavailability. The highest values for THP loading (45%), prolonged release (302.3 min) and bioavailability (175%) were obtained for graft copolymer AgA-g-PNIPAAm 68. The drug release mechanism varies with composition and architecture of the matrix. Full article
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12 pages, 4094 KiB  
Article
Study on Soy-Based Adhesives Enhanced by Phenol Formaldehyde Cross-Linker
by Zhigang Wu, Xuedong Xi, Hong Lei, Jiankun Liang, Jingjing Liao and Guanben Du
Polymers 2019, 11(2), 365; https://doi.org/10.3390/polym11020365 - 19 Feb 2019
Cited by 38 | Viewed by 3338
Abstract
To find the effects of cross-linker phenol-formaldehyde (PF) resin on the performance of soy-based adhesives, the reaction between model compounds hydroxymethyl phenol (HPF) and glutamic acid were studied in this paper. HPF prepared in laboratory conditions showed higher content of hydroxymethyl groups than [...] Read more.
To find the effects of cross-linker phenol-formaldehyde (PF) resin on the performance of soy-based adhesives, the reaction between model compounds hydroxymethyl phenol (HPF) and glutamic acid were studied in this paper. HPF prepared in laboratory conditions showed higher content of hydroxymethyl groups than normal PF resin, which was proved by the results of Electrospray Ionization Mass Spectrometry (ESI-MS) and 13C Nuclear Magnetic Resonance (13C-NMR). The results of ESI-MS, Fourier transform infrared spectroscopy (FT-IR), and 13C-NMR based on resultant products obtained from model compounds showed better water resistance of the soy protein-based adhesive modified by PF-based resin, which indicated the reaction between PF resin and soy protein. However, it seemed that the soy-based adhesive cross-linked by HPF with the maximum content of hydroxymethyl groups did not show the best water resistance. Full article
(This article belongs to the Special Issue Renewable Phenolics for Innovative Composites)
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15 pages, 4333 KiB  
Article
Solution Blown Nylon 6 Nanofibrous Membrane as Scaffold for Nanofiltration
by Ya Liu, Gaokai Zhang, Xupin Zhuang, Sisi Li, Lei Shi, Weimin Kang, Bowen Cheng and Xianlin Xu
Polymers 2019, 11(2), 364; https://doi.org/10.3390/polym11020364 - 19 Feb 2019
Cited by 9 | Viewed by 4354
Abstract
In this work, a nylon 6 nanofibrous membrane was prepared via solution blowing technology and followed hot-press as scaffold for nanofiltration. The structure and properties of the hot-pressed nylon 6 nanofibrous membrane (HNM) were studied the effect of hot-pressing parameters and areal densities. [...] Read more.
In this work, a nylon 6 nanofibrous membrane was prepared via solution blowing technology and followed hot-press as scaffold for nanofiltration. The structure and properties of the hot-pressed nylon 6 nanofibrous membrane (HNM) were studied the effect of hot-pressing parameters and areal densities. Then an ultra-thin polyamide (PA) active layer was prepared by interfacial polymerization on HNM. The effects of nanofibrous scaffolds on the surface properties of ultra-thin nanofiltration membranes and their filtration performance were studied. Results showed that the nylon 6 nanofibers prepared at a concentration of 15 wt % had a good morphology and diameter distribution and the nanofibers were stacked more tightly and significantly reduced in diameter after hot pressing at 180 °C under the pressure of 15 MPa for 10 s. When the porous scaffold was prepared, HNM with an areal density of 9.4 and 14.1 g/m2 has a better apparent structure, a smaller pore size, a higher porosity and a greater strength. At the same time, different areal densities of HNM have an important influence on the preparation and properties of nanofiltration membranes. With the increase of areal density, the uniformity of HNM increased while their surface roughness and pore size decreased, which is beneficial to the establishment of PA barrier layer. With areal density of 9.4 and 14.1 g/m2, the as-prepared nanofiltration membrane has a smoother surface and more outstanding filtration performance. The pure water flux is 13.1 L m−2 h−1 and the filtration efficiencies for NaCl and Na2SO4 are 81.3% and 85.1%, respectively. Full article
(This article belongs to the Special Issue Polymer for Separation)
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16 pages, 2325 KiB  
Article
Prediction of Thermal Exposure and Mechanical Behavior of Epoxy Resin Using Artificial Neural Networks and Fourier Transform Infrared Spectroscopy
by Audrius Doblies, Benjamin Boll and Bodo Fiedler
Polymers 2019, 11(2), 363; https://doi.org/10.3390/polym11020363 - 19 Feb 2019
Cited by 54 | Viewed by 7944
Abstract
Thermal degradation detection of cured epoxy resins and composites is currently limited to severe thermal damage in practice. Evaluating the change in mechanical properties after a short-time thermal exposure, as well as estimating the history of thermally degraded polymers, has remained a challenge [...] Read more.
Thermal degradation detection of cured epoxy resins and composites is currently limited to severe thermal damage in practice. Evaluating the change in mechanical properties after a short-time thermal exposure, as well as estimating the history of thermally degraded polymers, has remained a challenge until now. An approach to accurately predict the mechanical properties, as well as the thermal exposure time and temperature of epoxy resin, using Fourier-transform infrared spectroscopy (FTIR)-spectroscopy, data processing, and artificial neural networks, is presented here. Therefore, an epoxy resin has been fully cured and exposed to elevated temperatures for different time periods. A FTIR-spectrometer was used to measure molecular changes, using mid-IR (MIR)-FTIR for film samples and near-IR (NIR)-FTIR for bulk samples. A quantitative analysis of the thermally degraded film samples shows oxidation, chain-scission, and dehydration in the FTIR spectra in the MIR-range. Using NIR spectroscopy for the bulk samples, only minor changes in the FTIR spectra could be detected. However, using data processing, molecular information was extracted from the NIR range and a degradation model, using an artificial neural network, has been trained. Even though the changes due to thermal exposure were small, the presented model is capable of accurately predicting the time, temperature, and residual strength of the polymer. Full article
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12 pages, 5892 KiB  
Article
Exploring the Critical Factors Limiting Polyaniline Biocompatibility
by Věra Kašpárková, Petr Humpolíček, Jaroslav Stejskal, Zdenka Capáková, Patrycja Bober, Kateřina Skopalová and Marián Lehocký
Polymers 2019, 11(2), 362; https://doi.org/10.3390/polym11020362 - 19 Feb 2019
Cited by 33 | Viewed by 3658
Abstract
Today, the application of polyaniline in biomedicine is widely discussed. However, information about impurities released from polyaniline and about the cytotoxicity of its precursors aniline, aniline hydrochloride, and ammonium persulfate are scarce. Therefore, cytotoxicity thresholds for the individual precursors and their combinations were [...] Read more.
Today, the application of polyaniline in biomedicine is widely discussed. However, information about impurities released from polyaniline and about the cytotoxicity of its precursors aniline, aniline hydrochloride, and ammonium persulfate are scarce. Therefore, cytotoxicity thresholds for the individual precursors and their combinations were determined (MTT assay) and the type of cell death caused by exposition to the precursors was identified using flow-cytometry. Tests on fibroblasts revealed higher cytotoxicity of ammonium persulfate than aniline hydrochloride. Thanks to the synergic effect, both monomers in combination enhanced their cytotoxicities compared with individual substances. Thereafter, cytotoxicity of polyaniline doped with different acids (sulfuric, nitric, phosphoric, hydrochloric, and methanesulfonic) was determined and correlated with impurities present in respective sample (HPLC). The lowest cytotoxicity showed polyaniline doped with phosphoric acid (followed by sulfuric, methanesulfonic, and nitric acid). Cytotoxicity of polyaniline was mainly attributed to the presence of residual ammonium persulfate and low-molecular-weight polar substances. This is crucial information with respect to the purification of polyaniline and production of its cytocompatible form. Full article
(This article belongs to the Special Issue Conducting Polymers)
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18 pages, 6667 KiB  
Article
Synthesis and Gas-Permeation Characterization of a Novel High-Surface Area Polyamide Derived from 1,3,6,8-Tetramethyl-2,7-diaminotriptycene: Towards Polyamides of Intrinsic Microporosity (PIM-PAs)
by Giuseppe Genduso, Bader S. Ghanem, Yingge Wang and Ingo Pinnau
Polymers 2019, 11(2), 361; https://doi.org/10.3390/polym11020361 - 19 Feb 2019
Cited by 21 | Viewed by 5511
Abstract
A triptycene-based diamine, 1,3,6,8-tetramethyl-2,7-diamino-triptycene (TMDAT), was used for the synthesis of a novel solution-processable polyamide obtained via polycondensation reaction with 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) (6FBBA). Molecular simulations confirmed that the tetrasubstitution with ortho-methyl groups in the triptycene building block reduced rotations around the C–N [...] Read more.
A triptycene-based diamine, 1,3,6,8-tetramethyl-2,7-diamino-triptycene (TMDAT), was used for the synthesis of a novel solution-processable polyamide obtained via polycondensation reaction with 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) (6FBBA). Molecular simulations confirmed that the tetrasubstitution with ortho-methyl groups in the triptycene building block reduced rotations around the C–N bond of the amide group leading to enhanced fractional free volume. Based on N2 sorption at 77 K, 6FBBA-TMDAT revealed microporosity with a Brunauer–Emmett–Teller (BET) surface area of 396 m2 g−1; to date, this is the highest value reported for a linear polyamide. The aged 6FBBA-TMDAT sample showed moderate pure-gas permeabilities (e.g., 198 barrer for H2, ~109 for CO2, and ~25 for O2) and permselectivities (e.g., αH2/CH4 of ~50) that position this polyamide close to the 2008 H2/CH4 and H2/N2 upper bounds. CO2–CH4 mixed-gas permeability experiments at 35 °C demonstrated poor plasticization resistance; mixed-gas permselectivity negatively deviated from the pure-gas values likely, due to the enhancement of CH4 diffusion induced by mixing effects. Full article
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12 pages, 6505 KiB  
Article
Warpage Reduction of Glass Fiber Reinforced Plastic Using Microcellular Foaming Process Applied Injection Molding
by Hyun Keun Kim, Joo Seong Sohn, Youngjae Ryu, Shin Won Kim and Sung Woon Cha
Polymers 2019, 11(2), 360; https://doi.org/10.3390/polym11020360 - 19 Feb 2019
Cited by 27 | Viewed by 5222
Abstract
This study analyzes the fundamental principles and characteristics of the microcellular foaming process (MCP) to minimize warpage in glass fiber reinforced polymer (GFRP), which is typically worse than that of a solid polymer. In order to confirm the tendency for warpage and the [...] Read more.
This study analyzes the fundamental principles and characteristics of the microcellular foaming process (MCP) to minimize warpage in glass fiber reinforced polymer (GFRP), which is typically worse than that of a solid polymer. In order to confirm the tendency for warpage and the improvement of this phenomenon according to the glass fiber content (GFC), two factors associated with the reduction of the shrinkage difference and the non-directionalized fiber orientation were set as variables. The shrinkage was measured in the flow direction and transverse direction, and it was confirmed that the shrinkage difference between these two directions is the cause of warpage of GFRP specimens. In addition, by applying the MCP to injection molding, it was confirmed that warpage was improved by reducing the shrinkage difference. To further confirm these results, the effects of cell formation on shrinkage and fiber orientation were investigated using scanning electron microscopy, micro-CT observation, and cell morphology analysis. The micro-CT observations revealed that the fiber orientation was non-directional for the MCP. Moreover, it was determined that the mechanical and thermal properties were improved, based on measurements of the impact strength, tensile strength, flexural strength, and deflection temperature for the MCP. Full article
(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)
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16 pages, 6338 KiB  
Article
Characterization of Polyurethane Foam Waste for Reuse in Eco-Efficient Building Materials
by Raúl Gómez-Rojo, Lourdes Alameda, Ángel Rodríguez, Verónica Calderón and Sara Gutiérrez-González
Polymers 2019, 11(2), 359; https://doi.org/10.3390/polym11020359 - 19 Feb 2019
Cited by 48 | Viewed by 8538
Abstract
In the European Union, the demand for polyurethane is continually growing. In 2017, the estimated value of polyurethane production was 700,400 Tn, of which 27.3% is taken to landfill, which causes an environmental problem. In this paper, the behaviour of various polyurethane foams [...] Read more.
In the European Union, the demand for polyurethane is continually growing. In 2017, the estimated value of polyurethane production was 700,400 Tn, of which 27.3% is taken to landfill, which causes an environmental problem. In this paper, the behaviour of various polyurethane foams from the waste of different types of industries will be analyzed with the aim of assessing their potential use in construction materials. To achieve this, the wastes were chemically tested by means of CHNS, TGA, and leaching tests. They were tested microstructurally by means of SEM. The processing parameters of the waste was calculated after identifying its granulometry and its physical properties i.e., density and water absorption capacity. In addition, the possibility of incorporating these wastes in plaster matrices was studied by determining their rendering in an operational context, finding out their mechanical resistance to flexion and compression at seven days, their reaction to fire as well as their weight per unit of area, and their thermal behaviour. The results show that in all cases, the waste is inert and does not undergo leaching. The generation process of the waste determines the foam’s microstructure in addition to its physical-chemical properties, which directly affect building materials in which they are included, thus offering different ways in which they can be applied. Full article
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15 pages, 8571 KiB  
Article
Comparative Study on Kinetics of Ethylene and Propylene Polymerizations with Supported Ziegler–Natta Catalyst: Catalyst Fragmentation Promoted by Polymer Crystalline Lamellae
by Zhen Zhang, Baiyu Jiang, Feng He, Zhisheng Fu, Junting Xu and Zhiqiang Fan
Polymers 2019, 11(2), 358; https://doi.org/10.3390/polym11020358 - 19 Feb 2019
Cited by 21 | Viewed by 6176
Abstract
The kinetic behaviors of ethylene and propylene polymerizations with the same MgCl2-supported Ziegler–Natta (Z–N) catalyst containing an internal electron donor were compared. Changes of polymerization activity and active center concentration ([C*]) with time in the first 10 min were determined. Activity [...] Read more.
The kinetic behaviors of ethylene and propylene polymerizations with the same MgCl2-supported Ziegler–Natta (Z–N) catalyst containing an internal electron donor were compared. Changes of polymerization activity and active center concentration ([C*]) with time in the first 10 min were determined. Activity of ethylene polymerization was only 25% of that of propylene, and the polymerization rate (Rp) quickly decayed with time (tp) in the former system, in contrast to stable Rp in the latter. The ethylene system showed a very low [C*]/[Ti] ratio (<0.6%), in contrast to a much higher [C*]/[Ti] ratio (1.5%–4.9%) in propylene polymerization. The two systems showed noticeably different morphologies of the nascent polymer/catalyst particles, with the PP/catalyst particles being more compact and homogeneous than the PE/catalyst particles. The different kinetic behaviors of the two systems were explained by faster and more sufficient catalyst fragmentation in propylene polymerization than the ethylene system. The smaller lamellar thickness (<20 nm) in nascent polypropylene compared with the size of nanopores (15–25 nm) in the catalyst was considered the key factor for efficient catalyst fragmentation in propylene polymerization, as the PP lamellae may grow inside the nanopores and break up the catalyst particles. Full article
(This article belongs to the Special Issue Catalytic Polymerization)
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10 pages, 2345 KiB  
Article
Characterization of the Fluidity of the Ultrasonic Plasticized Polymer Melt by Spiral Flow Testing under Micro-Scale
by Bingyan Jiang, Yang Zou, Tao Liu and Wangqing Wu
Polymers 2019, 11(2), 357; https://doi.org/10.3390/polym11020357 - 18 Feb 2019
Cited by 17 | Viewed by 5293
Abstract
The fluidity of a molten polymer plasticized by ultrasonic vibration was characterized by spiral flow testing based on an Archimedes spiral mold with microchannels. Mold inserts with various channel depths from 250 to 750 µm were designed and fabricated to represent the size [...] Read more.
The fluidity of a molten polymer plasticized by ultrasonic vibration was characterized by spiral flow testing based on an Archimedes spiral mold with microchannels. Mold inserts with various channel depths from 250 to 750 µm were designed and fabricated to represent the size effect under micro-scale. The effect of ultrasonic plasticizing parameters and the mold temperature on the flow length was studied to determine the rheological nature of polymers and control parameters. The results showed that the flow length decreased with reduced channel depth due to the size effect. By increasing ultrasonic amplitude, ultrasonic action time, plasticizing pressure, and mold temperature, the flow length could be significantly increased for both the amorphous polymer polymethyl methacrylate (PMMA) and the semi-crystalline polymers polypropylene (PP) and polyamide 66 (PA66). The enhanced fluidity of the ultrasonic plasticized polymer melt could be attributed to the significantly reduced shear viscosity. Full article
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