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All issues / Volume 13 (2019) / Issue 6 (June)

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T. Czigany
Vol. 13., No.6., Pages 500-500, 2019
DOI: 10.3144/expresspolymlett.2019.41
This is an editorial article. It has no abstract.
Effect of horizontal shift between fabric layers on the meso-scale-void formation in liquid composite molding
B. Yang, C. Y. Zhao, F. Y. Bi, S. B. Wang, C. Ma, S. L. Wang
Vol. 13., No.6., Pages 501-511, 2019
DOI: 10.3144/expresspolymlett.2019.42
Accurate prediction of void content is the foundation of process optimization for Liquid Composite Molding (LCM). During mold filling, void formation is a three-dimensional flow process, while at present the void formation is treated as a result of in-plane air entrapment, the resin and air flows on the thickness direction are totally neglected. In this paper, resin flows in the adjacent layers are considered to analyze the three-dimensional air entrapment and the meso-scalevoid formation. Firstly, the horizontal shift between fabric layers is analyzed, the mesopore coverage modes under different shift states are summarized. Then based on the mathematical models of micro and meso flows, the three-dimensional void entrapment processes under different cladding flow modes are studied in detail, a mathematical model for the prediction of meso-scale-void formation is established. Finally, a series of mold filling and void measurement experiments are carried out to verify the above model.
Composite beads of silica gel, alginate and poly(aspartic acid) for the immobilization of a lipase enzyme
E. Krisch, D. Balogh-Weiser, J. Klimko, B. Gyarmati, K. Laszlo, L. Poppe, A. Szilagyi
Vol. 13., No.6., Pages 512-523, 2019
DOI: 10.3144/expresspolymlett.2019.43
Silica gel/alginate/poly(aspartic acid) composite beads were prepared for immobilization of lipase B enzyme from Candida antarctica (CaLB). CaLB was first adsorbed on functionalized mesoporous silica gel particles, which were then entrapped in the interpenetrating network of thiolated poly(aspartic acid) and alginate, cross-linked by zinc ions. Finally, the beads were chemically stabilized by poly(ethylene glycol) diglycidyl ether, a bisepoxide cross-linker. In this manner, spherical biocatalysts with a diameter of 3–4 mm were prepared and their biocatalytic performance was tested by kinetic resolution of racemic 1-phenylethanol. The activity of CaLB in the beads was comparable to that of CaLB physically adsorbed on silica gel particles. The composite beads were easy to recover after use and no loss of biocatalytic activity was observed even after five test reaction cycles. Furthermore, the CaLB in the composite beads showed sufficient thermal stability up to 90 °C, contrary to CaLB adsorbed only on silica gel particles.
Preparation and properties of a novel quaternary copolymerized thermoplastic polyimide
X. Liu, X. W. Cao, G. J. He, T. C. Xing
Vol. 13., No.6., Pages 524-532, 2019
DOI: 10.3144/expresspolymlett.2019.44
A series of quaternary copolymerized thermoplastic polyimides (PI) films with good thermal resistance has been synthesized via two-step method from bicomponent isomeric dianhydrides, 2,3′,3,4′-biphenyltetracarboxylic dianhydride (α-BPDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA), and bicomponent flexible diamines, 4,4′-oxydianiline (ODA) and 1,3-bis(4′-aminophenoxy)benzene (TPE-R). By adjusting the molar ratio of dianhydrides to diamines, its effects on the thermal stability, thermoplasticity and solubility of PI films were investigated in detail. The results showed that these quaternary copolymerized PI films were in possession of both thermoplasticity and excellent thermal stability. It is derived from the synergetic effect of isomeric dianhydrides and flexible diamines. It has also been found that there is one critical molar ratio between dianhydrides and diamines, that is, α-BPDA:s-BPDA:ODA:TPE-R = 50:50:50:50, at which the overall performance is optimal.
A fully encapsulated piezoelectric–triboelectric hybrid nanogenerator for energy harvesting from biomechanical and environmental sources
C. Y. Chen, C. Y. Tsai, M. H. Xu, C. T. Wu, C. Y. Huang, T. H. Lee, Y. K. Fuh
Vol. 13., No.6., Pages 533-542, 2019
DOI: 10.3144/expresspolymlett.2019.45
In this paper, a hybrid nanogenerator with concurrently harvested piezoelectric and triboelectric mechanisms, called a fully encapsulated piezoelectric–triboelectric hybrid nanogenerator (PTHG), is demonstrated. In the construction of piezoelectric nanogenerator (PENG), an in-situ poling near-field electrospinning (NFES) was utilized to direct-write piezoelectric polymeric nano/micro fibers (NMFs) polyvinylidene fluoride (PVDF) as the functional layer of piezoelectric nanogenerators. On the other hand, the nano-textured functional layer of triboelectric nanogenerators (TENGs) is also concurrently combined with PENG. This hybridized nanogenerator was demonstrated to simultaneously harvest piezoelectric and triboelectric output such that the superimposed peak output voltage /current signals of ~130 V/4 µA at 2 Hz, which can be translated to the area power density of 8.34 mW/m2. Individually measured TENG under a hand-induced strain 0.2 and 2 Hz actuation, the output voltage/current peak is measured about 110 V/2.8 µA, while the PENG counterpart shows the the output voltage/current peak is about 18 V/0.6 µA. In addition, the proposed PTHG can harvest sustainable energy sources such as rain water with the output maximum voltage reaches ~20 V and area power density ~0.981 mW/m2 for dropping rate of 10 ml/s. This research shows the substantial improvement in the synergy of nano-textured triboelectric and piezoelectric functional layers. The practical application of the self-powered system can be ubiquitously implemented in the sustainable energy sources and future industry 4.0 scenarios to provide the stand alone energy sources of IoT sensors.
A new strategy for the synthesis of modified novolac resin and its polymer/clay nanocomposite
R. Mohammad-Rezaei, B. Massoumi, M. Eskandani, M. Abbasian, M. Jaymand
Vol. 13., No.6., Pages 543-552, 2019
DOI: 10.3144/expresspolymlett.2019.46
A novel epoxy nanocomposite composed of epoxidized novolac (ENR), epoxidized polystyrene (EPSt), and nanoclay was fabricated and characterized successfully. For this purpose, the novolac was epoxylated using a substitution nucleophilic reaction between hydroxyl group of novolac and chlorine group of epichlorohydrin. The EPSt was synthesized through the oxidizing of an allylated PSt (All-PSt). A mixture of ENR (70 wt%), EPSt (20 wt%) and Cloisite®R 20A (5 wt%) was cured using ethylenediamine (EDA; 5 wt%) to afford a C-ENR-EPSt/clay nanocomposite. The transition electron microscopy (TEM) as well as powder X-ray diffraction (XRD) analysis revealed that the fabricated nanocomposite has an exfoliated structure. As the thermal property studies results, the addition of EPSt as well as Cloisite® 20A has synergistic effect on the thermal stability of the ENR resin.
Non-woven flax fibre reinforced acrylic based polyester composites: The effect of sodium silicate on mechanical, flammability and acoustic properties
M. F. Ahmad Rasyid, M. S. Salim, H. M. Akil, J. Karger-Kocsis, Z. A. Mohd. Ishak
Vol. 13., No.6., Pages 553-564, 2019
DOI: 10.3144/expresspolymlett.2019.47
Non-woven flax fibre reinforced acrylic-based polyester (NFA) composites were prepared using an impregnation process. A mixture of acrylic-based polyester (Acrodur®) with varying sodium silicate (SS) loadings was applied to impregnate the non-woven flax fibre mat. Flexural tests were performed to evaluate the mechanical properties of the composites. Flammability properties were assessed via UL94 test and limiting oxygen index (LOI). The mechanical properties of NFA composites decreased substantially with increment in SS loading. The addition of SS resulted in significant improvement of flame retardancy, whereby UL94 rating enhanced from V-1 to V-0, while the LOI values increased from 24 to 40. Sound absorption coefficients of the NFA composites were measured via two-microphone transfer function technique in impedance tube. The sound absorption properties of NFA composites also improved with the incorporation of SS, whereby the sound absorption coefficient increased up to 0.87 at 2000 Hz frequency. Based on the overall evaluation, 20 wt% of SS effectively increased flame retardancy and sound absorption properties, along with moderate deterioration in flexural properties. The scanning electron microscopic (SEM) analysis of the composites surfaces displayed formation of voids and irregular structures at higher SS loading, which reduced the mechanical properties of NFA composites. The SEM images offered supportive evidences on the role of hollow lumen structures in natural fibres to ensure better sound absorption performance in NFA composites.
Microwave treatment in waste rubber recycling – recent advances and limitations
K. Formela, A. Hejna, L. Zedler, X. Colom, J. Canavate
Vol. 13., No.6., Pages 565-588, 2019
DOI: 10.3144/expresspolymlett.2019.48
Environmentally-friendly microwave heating is increasingly used in polymer chemistry and technology. The selectivity and highly efficiency in the heat transfer present a huge advantage in systems based on recycling, improving their productivity and economic competitiveness. In case of the industrial recycling of waste rubbers, especially end-of-life tires, microwave-induced devulcanization and pyrolysis are nowadays considered as promising approaches. This work aims to report the recent progress in microwave treatments of vulcanized rubbers with different compositions. Special attention is focused on the correlation between microwave processing parameters and devulcanization/pyrolysis efficiency, which have a significant impact on the structure-property relationships of the obtained products. Moreover, the main challenges affecting the future of the industrial application of the microwave technology in rubber recycling are also discussed.
Published by:

Budapest University of Technology and Economics,
Faculty of Mechanical Engineering, Department of Polymer Engineering