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ISSN / EISSN : 20734360 / 20734360
Current Publisher: MDPI (10.3390)
Total articles ≅ 4,688
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Yan Wu, Yuqing Bian, Feng Yang, Yang Ding, Kexin Chen
Published: 21 September 2019
by MDPI
Polymers, Volume 11; doi:10.3390/polym11101540

Abstract:Chitosan (CS) and graphene (Gr) were used to modify bamboo fiber fabrics to develop new bamboo fiber fabrics (CGBFs) with antimicrobial properties. The CGBFs were prepared by chemical crosslinking with CS as binder assistant and Gr as functional finishing agent. The method of firmly attaching the CS/Gr to bamboo fiber fabrics was explored. On the basis of the constant amount of CS, the best impregnation modification scheme was determined by changing the amount of Gr and evaluating the properties of the CS/Gr modified bamboo fiber fabrics. The results showed that the antibacterial rate of CGBFs with 0.3 wt% Gr was more than 99%, and compared with the control sample, the maximum tensile strength of CGBF increased by 1% in the longitudinal direction and 7.8% in the weft direction. The elongation at break increased by 2.2% in longitude and 57.3% in latitude. After 20 times of washing with WOB (without optical brightener) detergent solution, the antimicrobial rate can still be more than 70%. Therefore, these newly CS/Gr modified bamboo fiber fabrics hold great promise for antibacterial application in home decoration and clothing textiles.
Yongchang Jiang, Zhao Zhang, Zheng Zhou, Hui Yang, Qilong Zhang
Published: 21 September 2019
by MDPI
Polymers, Volume 11; doi:10.3390/polym11101541

Abstract:Polymer dielectric materials are extensively used in electronic devices. To enhance the dielectric constant, ceramic fillers with high dielectric constant have been widely introduced into polymer matrices. However, to obtain high permittivity, a large added amount (>50 vol%) is usually needed. With the aim of improving dielectric properties with low filler content, satellite–core-structured [email protected] ([email protected]) nanoparticles were fabricated as fillers for a poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix. The interfacial polarization effect is increased by Fe2O3 nanoparticles, and thus, composite permittivity is enhanced. Besides, the satellite–core structure prevents Fe2O3 particles from directly contacting each other, so that the dielectric loss remains relatively low. Typically, with 20 vol% [email protected] nanoparticle fillers, the permittivity of the composite is 31.7 (1 kHz), nearly 1.8 and 3.0 times that of 20 vol% BT composites and pure polymers, respectively. Nanocomposites also achieve high breakdown strength (>150 KV/mm) and low loss tangent (~0.05). Moreover, the composites exhibited excellent flexibility and maintained good dielectric properties after bending. These results demonstrate that composite films possess broad application prospects in flexible electronics.
Yang Zhang, Jincheng Mao, Jinzhou Zhao, Tao Xu, Anqi Du, Zhaoyang Zhang, Wenlong Zhang, Shaoyun Ma
Published: 20 September 2019
by MDPI
Polymers, Volume 11; doi:10.3390/polym11101539

Abstract:The quaternary polymer was synthesized by radical polymerization and characterized by 1H NMR. The tests of critical associating concentration and SEM suggest that there is a multilayered and robust network structure in the polymer solution. An excellent elasticity in the polymer solution by the first normal stress difference, viscoelasticity, and thixotropy was observed. The critical crosslinker concentration of polymer with sodium dodecyl sulfate and its interaction mechanism were investigated. According to the reaction kinetics, the supramolecular structure had the lowest activation energy, stable network structure, and greater thermal stability. Then the polymer was employed in the fracturing fluid due to its excellent elasticity using the intermolecular forces, which showed superior sand suspension capacity by dynamic sand suspension measurement. Meanwhile, a theoretical analysis was proposed as to why polymer solution has excellent suspension and drag reduction properties. Therefore, this polymer could be an alternative in many fields, especially in fracking, which is significant for the development of oil and gas resources in deep wells.
Pang, Zhao, Qin, Shifeng Zhang, Li, Huiwen Pang, Shujun Zhao, Tao Qin, Jianzhang Li
Published: 20 September 2019
by MDPI
Polymers, Volume 11; doi:10.3390/polym11101536

Abstract:It remains a great challenge to fabricate bio-based soy protein isolate (SPI) composite film with both favorable water resistance and excellent mechanical performance. In this study, waterborne epoxy emulsions (WEU), which are low-cost epoxy crosslinkers, together with mussel-inspired dopamine-decorated silk fiber (PSF), were used to synergistically improve the water resistance and mechanical properties of SPI-based film. A stable crosslinking network was generated in SPI-based films via multiple physical and chemical combinations of WEU, PSF, and soy protein matrixes, and was confirmed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray diffraction (XRD), and solid state 13C nuclear magnetic resonance (13C NMR). As expected, remarkable improvement in both water resistance and Young’s modulus (up to 370%) was simultaneously achieved in SPI-based film. The fabricated SPI-based film also exhibited favorable thermostability. This study could provide a simple and environmentally friendly approach to fabricate high-performance SPI-based film composites in food packaging, food preservation, and additive carrier fields.
Siavash Bayani, Hamid R. Taghiyari, Antonios N. Papadopoulos
Published: 20 September 2019
by MDPI
Polymers, Volume 11; doi:10.3390/polym11101538

Abstract:The aim of this study was to investigate the physical and mechanical properties of thermally modified beech wood impregnated with silver nano-suspension and to examine their relationship with the crystallinity of cellulose. Specimens were impregnated with a 400 ppm nanosilver suspension (NS); at least, 90% of silver nano-particles ranged between 20 and 100 nano-meters. Heat treatment took place in a laboratory oven at three temperatures, namely 145, 165, and 185 °C. Physical properties and mechanical properties of treated wood demonstrated statistically insignificant fluctuations at low temperatures compared to control specimens. On the other hand, an increase of temperature to 185 °C had a significant effect on all properties. Physical properties (volumetric swelling and water absorption) and mechanical properties (MOR and MOE) of treated wood demonstrated statistically insignificant fluctuations at low temperatures compared to control specimens. This degradation ultimately resulted in significant decrease in MOR, impact strength, and physical properties. However, thermal modification at 185 °C did not seem to cause significant fluctuations in MOE and compression strength parallel to grain. As a consequence of the thermal modification, part of amorphous cellulose was changed to crystalline cellulose. At low temperatures an increased crystallinity caused some of the properties to be improved. Crystallinity also demonstrated a decrease in NS-HT185 in comparison to HT185 treatment. TCr indices in specimens thermally treated at 145 °C revealed a significant increase as a result of impregnation with nanosilver suspension. This improvement in TCr index resulted in a noticeable increase in MOR and MOE values. Other properties did not show significant fluctuations, suggesting that the effect of the increased crystallinity and cross-linking in lignin was more than the negative effect of the low cell-wall polymer degradation caused by thermal modification. Change of amorphous cellulose to crystalline cellulose, as well as cross-linking in lignin, partially ameliorated the negative effects of thermal degradation at higher temperatures and therefore, compression parallel to grain and modulus of elasticity did not decrease significantly. Overall, it can be concluded that increased crystallinity and cross-linking in lignin can compensate for some decreased properties caused by thermal modification, but it would be significantly dependent on the temperature under which modification is carried out. Impregnating specimens with silver nano-suspension prior to thermal modification enhanced the effects of thermal modification as a result of improved thermal conductivity.
Lukas Sommerauer, Jakub Grzybek, Michael S. Elsaesser, Artur Benisek, Thomas Sepperer, Edgar Dachs, Nicola Hüsing, Alexander Petutschnigg, Gianluca Tondi
Published: 20 September 2019
by MDPI
Polymers, Volume 11; doi:10.3390/polym11101533

Abstract:Furfuryl alcohol (FA) and lactic acid (LA) are two of the most interesting biomolecules, easily obtainable from sugars and hence extremely attractive for green chemistry solutions. These substances undergo homopolymerization and they have been rarely considered for copolymerization. Typically, FA homopolymerizes exothermically in an acid environment producing inhomogeneous porous materials, but recent studies have shown that this reaction can be controlled and therefore we have implemented this process to trigger the copolymerization with LA. The mechanical tests have shown that the blend containing small amount of FA were rigid and the fracture showed patterns more similar to the one of neat polyfurfuryl alcohol (PFA). This LA-rich blend exhibited higher chloroform and water resistances, while thermal analyses (TG and DSC) also indicated a higher furanic character than expected. These observations suggested an intimate interconnection between precursors which was highlighted by the presence of a small band in the ester region of the solid state 13C–NMR, even if the FT-IR did not evidence any new signal. These studies show that these bioplastics are basically constituted of PLA and PFA homopolymers with some small portion of covalent bonds between the two moieties.
Mamduh J. Aljaafreh, Saradh Prasad, Mohamad S. AlSalhi, Zeyad A. AlAhmed, Muneerah M. Al-Mogren
Published: 20 September 2019
by MDPI
Polymers, Volume 11; doi:10.3390/polym11101534

Abstract:We demonstrated the time-resolved dynamics of laser action from the conductive oligomer (CO) 1,4-Bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF). Absorption and fluorescence spectra were studied for BECV-DHF in different solvents under a wide range of concentrations. The Fourier-transform infrared spectroscopy (FTIR) spectrum was measured using simulation and experiments. The Ultraviolet-Visible (UV-VIS) spectra of the BECV-DHF were simulated in two different solutions. This CO formed a dimer and had two vibration bands in nonpolar solvents, partially dissolved in polar protic solvents, and created an H-type aggregate in polar aprotic solvents. BECV-DHF produced amplified spontaneous emission (ASE) at 464 nm in many solvents. The high efficiency of ASE is due to the waveguiding and self-assembly nature of the oligomer, which is very rare for optically pumped systems. However, BECV-DHF did not produce ASE in polar protic solvents. BECV-DHF produced ASE in both longitudinal and transverse pumping, and the full-width half maximum (FWHM) was 4 nm and 8 nm respectively for different solvents, such as toluene and acetone. The CO had a very low threshold pump energy (~0.5 mJ). The ASE efficiency was approximately 20%. The time-resolved spectroscopy (TRS) studies showed a temporal Gaussian-shaped ASE output from this CO. BECV-DHF shows remarkably high stability compare to the conjugated polymer (CP) PFO-co-pX.
Li, Tsai, Fang, Wang, Lin, Keng-Yuan Li, Cheng-Chia Tsai, Chih-Hsiang Fang, Yin-Lin Wang, Feng-Huei Lin, et al.
Published: 20 September 2019
by MDPI
Polymers, Volume 11; doi:10.3390/polym11101535

Abstract:Molar pits and fissures tend to be affected by caries due to cleaning difficulties. As such, the filling of pits and cracks with sealants is common to deter the onset of caries. However, current clinical practices rely on sealants that lack the ability to release and recharge fluoride ions. Thus, we herein report the development of a fluoride—montmorillonite nanocomposite resin that has the potential to provide sustained release of fluoride due to the strong adsorption of fluoride by montmorillonite. X-ray diffractometry, thermogravimetric analysis, and Fourier-transform infrared spectroscopy were employed to confirm the successful insertion of the polymer into the interlayer structure. The mechanical properties (viscosity, hardening depth, hardness, diametral tensile strength, flexural strength, and wear resistance) of the developed composite resin were then examined, and simulation of the oral environment demonstrated a good fluoride ion release and recharge ability for the effective prevention of dental caries. Finally, we demonstrated the non-cytotoxic nature of this material using the water-soluble tetrazolium salt (WST-1) test. We expect that the described fluoride-containing composite resin may become a new clinical option in the near future.
Dalila Rocco, Alessandro Prescimone, Y. Maximilian Klein, Dariusz J. Gawryluk, Edwin C. Constable, Catherine E. Housecroft
Published: 20 September 2019
by MDPI
Polymers, Volume 11; doi:10.3390/polym11101537

Abstract:We wish to make the following corrections to our published paper [1]
Yan, Florian J. Stadler, Pierre Guillet, Clément Mugemana, Charles-André Fustin, Gohy, Christian Bailly, Zhi-Chao Yan, Jean-François Gohy
Published: 20 September 2019
by MDPI
Polymers, Volume 11; doi:10.3390/polym11101532

Abstract:The linear and nonlinear rheology of associative colloidal polymer assemblies with metallo-supramolecular interactions is herein studied. Polystyrene-b-poly(tert-butylacrylate) with a terpyridine ligand at the end of the acrylate block is self-assembled into micelles in ethanol, a selective solvent for the latter block, and supramolecularly connected by complexation to divalent metal ions. The dependence of the system elasticity on polymer concentration can be semi-quantitatively understood by a geometrical packing model. For strongly associated (Ni2+, Fe2+) and sufficiently concentrated systems (15 w/v%), any given ligand end-group has a virtually 100% probability of being located in an overlapping hairy region between two micelles. By assuming a 50% probability of intermicellar crosslinks being formed, an excellent prediction of the plateau modulus was achieved and compared with the experimental results. For strongly associated but somewhat more dilute systems (12 w/v%) that still have significant overlap between hairy regions, the experimental modulus was lower than the predicted value, as the effective number of crosslinkers was further reduced along with possible density heterogeneities. The reversible destruction of the network by shear forces can be observed from the strain dependence of the storage and loss moduli. The storage moduli of the Ni2+ and Zn2+ systems at a lower concentration (12 w/v%) showed a rarely observed feature (i.e., a peak at the transition from linear to nonlinear regime). This peak disappeared at a higher concentration (15 w/v%). This behavior can be rationalized based on concentration-dependent network stretchability.