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All issues / Volume 12 (2018) / Issue 2 (February)

Need for a unified theory of the electrical properties of composites with fractal structure
Gy. Banhegyi
Vol. 12., No.2., Pages 113-113, 2018
DOI: 10.3144/expresspolymlett.2018.9
This is an editorial article. It has no abstract.
Combined compatibilization and plasticization effect of low molecular weight poly(lactic acid) in poly(lactic acid)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blends
A. Amor, N. Okhay, A. Guinault, G. Miquelard-Garnier, C. Sollogoub, M. Gervais
Vol. 12., No.2., Pages 114-125, 2018
DOI: 10.3144/expresspolymlett.2018.10
Improving overall properties of poly(lactic acid) (PLA) by blending it with another biobased polymer has been a strong field of research over the last years. In this study we demonstrate the synergetic effect of a small amount (between 0.1 and 1 wt%) of oligomer-like PLA (oLA) on the thermal, mechanical and gas barrier properties of the widely studied PLA-poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) blends (90–10 wt%). Films of PLA/PHBV/oLA blends were prepared via single-screw extrusion. oLA being miscible with both PLA and PHBV, its compatibilizing effect was demonstrated by a decrease of the interfacial tension, a slight shift in the Tgs of both polymers, and an increase in the elongation at break. It was also showed that oLA had a plasticizing effect on the PHBV dispersed phase, increasing its crystallinity rate. This resulted in a decrease in the permeability of the films while improving Young’s modulus.
Factors influencing catalytic behavior of titanium complexes bearing bisphenolate ligands toward ring-opening polymerization of L-lactide and ε-caprolactone
M-T. Jiang, S. R. Kosuru, Y. H. Lee, W-Y. Lu, J. K. Vandavasi, Y-C. Lai, M. Y. Chiang, H-Y. Chen
Vol. 12., No.2., Pages 126-135, 2018
DOI: 10.3144/expresspolymlett.2018.11
A series of titanium complexes bearing substituted diphenolate ligands (RCH(phenolate)2, where R = H, CH3, o-OTs-phenyl, o-F-phenyl, o-OMe-phenyl, 2,4-OMe-phenyl) was synthesized and studied as catalysts for the ring opening polymerization of L-lactide and ε-caprolactone. Ligands were designed to probe the role of chelate effect and steric effect in the catalytic performance. From the structure of triphenolate (with one extra coordination site than diphenolate ligand) Ti complex, TriOTiOiPr2, we found no additional chelation to influence the catalytic activity of Ti complexes. It was found that bulky aryl groups in the diphenolate ligands decreased the rate of polymerization most. We conclude that steric effect is the most controlling factor in these polymerization reactions by using Ti complexes bearing diphenolate ligands as catalysts since it is responsible for the exclusion of needed space for incoming monomer by the bulky substituents on the catalyst.
A fully packaged self-powered sensor based on near-field electrospun arrays of poly(vinylidene fluoride) nano/micro fibers
Y.-K. Fuh, S.-Ch. Li, Ch.-Y. Chen, Ch.-Y. Tsai
Vol. 12., No.2., Pages 136-145, 2018
DOI: 10.3144/expresspolymlett.2018.12
Energy harvesting devices based on the triboelectric and piezoelectric principles have been widely developed to scavenge wasteful and tiny mechanical energy into usable electrical energy. In particular, triboelectric energy harvesting generators with relatively simpler structure and piezoelectric fiber-based counterpart with extremely light weight compositions showed a very promising application in the self-powered sensors. In this paper, a novel hybridization of graphenebased piezoelectric generator (GBPG) and graphene-PET triboelectric generator (GPTG) were simultaneously packaged. The integrated structure, graphene-based hybridized self-powered sensor (GHSPS), was demonstrated to be optically transparent and mechanically robust. For the piezoelectrically harvesting device, an in-situ poling and direct-write near-field electrospinning (NFES) Poly(vinylidene fluoride) (PVDF) piezoelectric fibers were fabricated and integrated with a single layer chemical vapor deposition (CVD) grown graphene. On the other hand for GPTG counterpart, two composite layers of a single layer graphene/PET simultaneously served as triboelectrically rubbing layers as well as bottom/top electrode. This GHSPS successfully superimposed both piezoelectric and triboelectric electricity and the synergistically higher output voltage/current/power were measured as ~6 V/280 nA/172 nW in one press-and-release cycle of finger induced motion. The proposed GHSPS showed a promising application in the field of self-powered sensors to be ubiquitously implemented in the future Industry 4.0 scenarios.
In-vitro cytotoxic activities of poly(2-ethyl-2-oxazoline)-based amphiphilic block copolymers prepared by CuAAC click chemistry
S. Gulyuz, U. U. Ozkose, P. Kocak, D. Telci, O. Yilmaz, M. A. Tasdelen
Vol. 12., No.2., Pages 146-158, 2018
DOI: 10.3144/expresspolymlett.2018.13
Synthesis and characterization of well-defined amphiphilic block copolymers containing poly(2-ethyl-2-oxazoline) as hydrophilic block and poly(ε-caprolactone) or poly(L-lactide) as hydrophobic block is achieved by copper-catalyzed azide-alkyne cycloaddition (CuAAC) click chemistry. The clickable precursors, α-alkyne-functionalized poly(ε-caprolactone) and poly(L-lactide) and ω-azido-functionalized poly(2-ethyl-2-oxazoline) are simply prepared and joined using copper sulfate/ascorbic acid catalyst system at room temperature. The structures of precursors and amphiphilic block copolymers are characterized by spectroscopic, chromatographic and thermal analyses. The cytotoxic activities of resulting amphiphilic block copolymers and their precursors are investigated in the prostate epithelial and cancer cells under in-vitro conditions. The treatment of the healthy prostate epithelial cell line PNT1A reveals that no significant cytotoxicity, whereas some significant toxic effects on the prostate cancer cell lines are observed.
Soluble collagen dissolution and assembling in pressurized carbon dioxide water solutions
L. Zubal, W. Bonani, D. Maniglio, R. Ceccato, D. Renciuk, A. Hampl, C. Migliaresi, J. Jancar, L. Vojtova
Vol. 12., No.2., Pages 159-170, 2018
DOI: 10.3144/expresspolymlett.2018.14
Dissolution and gelation procedures have a great influence on gelation time, microstructure and mechanical properties of reconstituted collagen products. We have investigated the dissolution of atelocollagen in CO2/water solutions at low temperature (4 °C) at different CO2 pressures (0.3–0.9 MPa), as well as gelation kinetics and physico-chemical properties of the hydrogel obtained after CO2 removal. Compared to conventional methods, the CO2-assisted technique resulted in faster soluble collagen dissolution and faster gelation into transparent gels characterized by thin 10 nm fibrils. Electrophoresis and CD spectroscopy demonstrated that the process did not denature the soluble collagen. The possibility to obtain collagen dissolution and gelation without the use of chemical agent other than water and CO2 makes this process particularly appealing for biomedical applications.
Dissolution behavior of Mg/Si-doped vaterite particles in biodegradable polymer composites
P. Zhou, T. Kasuga
Vol. 12., No.2., Pages 171-179, 2018
DOI: 10.3144/expresspolymlett.2018.15
Tuning the ion release ability of bioactive materials is one of the key factors for bone repair and regeneration. Calcium (Ca2+), magnesium (Mg2+), and silicate ions were reported to enhance the activity of bone-forming cells. In this work, the dissolution behavior of magnesium- and silicate-doped calcium carbonate (vaterite), denoted as MgSiV, embedded in three kinds of biodegradable polymers in Tris buffer solutions (TBS) were examined to find an effective ion releasing system. Poly(L-lactic acid) (PLLA) and poly(D,L-lactide-co-glycolide) (PDLLG, lactide:glycolide = 75:25 or 50:50; denoted as PDLLG75 and PDLLG50, respectively) were chosen as the matrix polymers. The Mg2+ and silicate ions were released rapidly within 3 d of soaking. Continuous release of Ca2+ ions from the composites induced the formation of aragonite on the film surfaces in the presence of Mg2+ ions. The amount of ions released from the MgSiV-PLLA composite was lesser than those released from the PDLLG-based composites. The fast degradation of PDLLG50 induced a decrease in the pH of TBS. The MgSiV-PDLLG75 composite exhibited a rapid release of Mg2+ ions, a continuous release of Ca2+ ions, and a controlled release of silicate ions with no reduction in the pH of TBS. Such release phenomena are caused by the formation of pathways for ion release, originating from the water uptake ability of PDLLG75.
Preparation and stress-strain behavior of in-situ epoxidized natural rubber/SiO2 hybrid through a sol-gel method
S. M. Li, T. W. Xu, Z. X. Jia, B. C. Zhong, Y. F. Luo, D. M. Jia, Z. Peng
Vol. 12., No.2., Pages 180-185, 2018
DOI: 10.3144/expresspolymlett.2018.16
In this paper, epoxidized natural rubber was reinforced by silica generated in-situ though the sol-gel method using tetraethoxysilane(TEOS) as precursor. The results showed that the ring opening reaction of epoxy group appeared in the in-situ reaction progress, where the hydrogen bond between Si–OH and C–OH was mainly formed to enhance the stress-strain behavior of ESH simultaneously. During the hot pressing progress, the compound was crosslinked via the chemical reaction of Si–OH and C–OH. The chemical bond between Si–OH and C–OH reinforced rubber-filler interaction, resulting further improved the stress-strain behavior. Besides, comparing with precipitated SiO2 filled ENR, the dispersion of SiO2 in ENR matrix was distinctly more uniform though the sol-gel method, along with the enhancement of mechanical properties. Herein, our findings open up a new way to prepare an environmentally friendly rubber composite with excellent dispersion and strong rubber-filler interaction without curing agent effectively.
Published by:

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