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All issues / Volume 14 (2020) / Issue 1 (January)

Disposable or single-use plastics? Neither! Recyclable or reusable plastics!
T. Czigany
Vol. 14., No.1., Pages 1-1, 2020
DOI: 10.3144/expresspolymlett.2020.1
This is an editorial article. It has no abstract.
Achieving thermally conductive low loss PVDF-based dielectric composites via surface functionalization and orientation of SiC nanowires
B. Wang, X. H. Yin, D. Peng, R. H. Lv, B. Na, H. S. Liu, X. B. Gu, W. Wu, J. L. Zhou, Y. Zhang
Vol. 14., No.1., Pages 2-11, 2020
DOI: 10.3144/expresspolymlett.2020.2
Semi-conductive silicon carbide (SiC) nanowires were amino-functionalized to achieve better dispersion in poly(vinylidene fluoride) (PVDF) matrix. It was found that PVDF based composites with amino-functionalized SiC (f-SiC) nanowires exhibited lower loss tangent than their counterparts with bare SiC nanowires, especially at a filler loading of 13.8 vol%. The loss tangent at 1 kHz of PVDF/f-SiC nanowires (86.2/13.8, v/v) composite is only 0.048, which is nearly one quarter of that of its counterpart with bare SiC nanowires. The nearly one order of magnitude lower AC conductivity at 1 kHz is responsible for the remarkable decrease of the loss tangent, since the interlacing of f-SiC nanowires was avoided via their parallel orientation, facilitated by the enhanced interfacial interaction. In addition to the low loss, the PVDF/f-SiC nanowires (86.2/13.8, v/v) composite exhibited about twofold increase of the dielectric permittivity at 1 kHz, compared to neat PVDF. Moreover, the thermal conductivity of PVDF/f-SiC nanowires (86.2/13.8, v/v) composite was increased to twice that of neat PVDF. The thermally conductive, high dielectric permittivity, and low loss PVDF/f-SiC nanowires composites may find potential applications in capacitors for microelectronics.
Artificial reactor containing polymeric bilayer architectures for the formation of self-controlled tandem catalytic-ability
Z. Xia, W. Wei, M. Zhu, S. Wu, X. Shen, S. Li
Vol. 14., No.1., Pages 12-25, 2020
DOI: 10.3144/expresspolymlett.2020.3
For addressing the present challenges in tandem catalysts, an artificial reactor capable of self-controlled tandem catalytic-ability was reported in this study. Inspired from the polymeric properties and divisional isolation for tandem processes in natural biological systems, this reactor was fabricated with polymeric bilayer architectures. The first layer was made of a reactive shape memory polymer that contained thermosensitive polymeric networks, acting as a molecular switch for the occurrence of the precedent hydrolysis of bis(4-nitrophenyl)carbonate. The second layer consisted of a molecularly-imprinted polymer and encapsulated Ag nanoparticles, allowing access to the succeeding reduction of the intermediate 4-nitrophenol. In a cooperative way, the polymeric bilayer architectures planted in this artificial reactor led to the formation of self-controlled tandem catalytic-ability. The suggested design for this artificial reactor shares a promising prospect with the struggling tandem catalysts, which leads to opportunities to develop controllable tandem processes.
Poly(butylene terephthalate)/polylactic acid based copolyesters and blends: miscibility-structure-property relationship
I. Irska, S. Paszkiewicz, K. Goracy, A. Linares, T. A. Ezquerra, R. Jedrzejewski, Z. Roslaniec, E. Piesowicz
Vol. 14., No.1., Pages 26-47, 2020
DOI: 10.3144/expresspolymlett.2020.4
A series of aliphatic-aromatic copolyesters based on poly(butylene terephthalate) (PBT) and poly(lactic acid) (PLA) have been synthesized by means of a novel reactive blending procedure coupled with polycondensation in melt. The obtained copolymers were further compared with PBT and PLA homopolymers and PBT/PLA non-compatibilized physical blends in order to investigate the effect of transesterification reactions on the structural, morphological, thermal and mechanical performance. Properties of the obtained materials have been found strictly dependent on the preparation process and blend/copolymer composition. The PBT/PLA physical blends appeared as highly crystalline, phase separated systems that exhibit brittle behavior. On the other hand, the applied method of reactive blending enhanced interfacial adhesion and promoted the arrangement of PBT and PLA in blocks of different lengths. Although the PBT-b-PLA copolyesters were found to be miscible in amorphous phase, the phase separation that has arisen from PBT crystalline domains occurs. Along with an increase in PLA weight fraction in copolymers, the length of aromatic sequences decreased which in turn resulted in shifting the values of melting temperatures (Tm) toward lower ones and decreased the degree of crystallinity (xc). Moreover, PBT-b-PLA copolymer with 30 wt% of PLA units has been demonstrated as a promising thermoplastic shape memory polymer (SMP) with a switching temperature of 35 °C.
Highlight of primary and secondary relaxations in amorphous stereocomplex polylactides
N. Varol, X. Monnier, L. Delbreilh, A. Saiter, K. Fatyeyeva, E. Dargent
Vol. 14., No.1., Pages 48-62, 2020
DOI: 10.3144/expresspolymlett.2020.5
A racemic mixture of two stereoregular polylactides (PLAs) (i.e. PLLA and PDLA) allows obtaining wholly amorphous stereocomplex PLA films by solvent casting method. The amorphous phase behavior of stereocomplex PLA is compared with that of PLLA and PDLA by advanced thermal analysis, such as Fast Scanning Calorimetry (FSC) and Dielectric Relaxation Spectroscopy (DRS). FSC allows us to quench at very high cooling rate (up to 4000 K・s–1) the studied polymers and to obtain glassy amorphous phases with high excess of enthalpy. It is shown that stereocomplexation has no influence on the glass transition temperature, the physical aging and on the cooperativity. The α and β processes were examined to study the dielectric properties, such as relaxation time, dielectric strength, and fragility. The results of FSC and DRS are correlated to determine the values of cooperativity length which are found to be similar in a wide temperature range. It is found that the studied polymers have the similar dielectric properties independently on their tacticity.
Poly(N-isopropylacrylamide-co-N-vinylpyrrolidone) thermoresponsive microspheres: The low drug loading ensures the pulsatile release mechanism
G. Fundueanu, M. Constantin, S. Bucatariu, P. Ascenzi
Vol. 14., No.1., Pages 63-76, 2020
DOI: 10.3144/expresspolymlett.2020.6
Poly(N-isopropylacrylamide-co-N-vinylpyrrolidone) (poly(NIPAAm-co-NVP)) with a co-monomer molar ratio in copolymer of 91.5/8.5 (NIPAAm/NVP) was synthesized as an interesting thermosensitive material possessing a sharp phase transition at 36 °C under simulated physiological conditions. The effect of the co-monomer molar ratio as well as of the ionic strength and nature of ions on the lower critical solution temperature (LCST) was investigated. Cross-linked poly(NIPAAm-co-NVP) thermoresponsive microspheres were synthesized by the suspension polymerization technique respecting the same NIPAAm/NVP molar ratio as for linear polymer. The microspheres were loaded with the model drug diclofenac (DF) by the solvent evaporation method; differential scanning calorimetry (DSC) demonstrates a dispersion of drug crystals within the polymeric matrix. The DF release rate is deeply influenced by the drug loading degree. Only microspheres with low DF loading are able to release the bioactive compound through a pulsatile mechanism.
Modeling meso-scale-void formation during through-thickness flow in liquid composite molding
B. Yang, F. Y. Bi, S. L. Wang, C. Ma, S. B. Wang, S. Li
Vol. 14., No.1., Pages 77-89, 2020
DOI: 10.3144/expresspolymlett.2020.7
Void formation during in-plane flow has been widely researched, while the void prediction method for throughthickness flow has not been reported, which restricts the effective quality control for through-thickness permeating type liquid composite molding (LCM). In this paper, the structural morphology and connectivity of mesopores in multi-layer woven fabrics have been studied, the difference between intra-yarn and inter-yarn flow paths during through-thickness permeating has been analyzed, and the air entrapment processes in different types of mesopores have been revealed. Based on the modeling of micro and meso through-thickness flow, a mathematical model to predict the formation and size of mesoscale-void has been established, the variation of intra-yarn flow path under different compaction conditions has been analyzed to guarantee the precision of the model. Experimental method has been designed to measure the size of meso-scale-void formed during through-thickness LCM, comparisons between prediction and experimental results have demonstrated the correctness of the above model.
Highly efficient encapsulation of curcumin into and pH-controlled drug release from poly(ε-caprolactone) nanoparticles stabilized with a novel amphiphilic hyperbranched polyglycerol
N. Zs. Nagy, Z. Varga, J. Mihaly, Gy. Kasza, B. Ivan, E. Kiss
Vol. 14., No.1., Pages 90-101, 2020
DOI: 10.3144/expresspolymlett.2020.8
The hardly water-soluble curcumin with low bioavailability was successfully encapsulated into biodegradable polymeric particles by nanoprecipitation. By using the more hydrophobic poly(ε-caprolactone) (PCL) instead of poly(lactic-co-glycolic acid) 50:50 (PLGA) significantly increased drug load was achieved. The stronger interaction between curcumin and PCL than PLGA was supported by Fourier-transform infrared spectroscopy (FTIR) measurements. As efficient colloid stabilizer, a novel amphiphilic polymer, hyperbranched polyglycerol with one long alkyl chain (C18-HbPG) was used which has better membrane affinity than the widely used Pluronics, and it enables further functionalization of the drug carrier as well. A Box-Behnken experimental design was applied to prepare and optimize the properties of curcumin loaded PCL nanoparticles (NPs) varying the initial drug load, composition of the organic phase and volume ratio of aqueous and organic phases. The volume of the organic phase was found to be the most relevant parameter for encapsulation, and it can be used to control the size and drug content of the NPs. The curcumin load of 10 w/w% of the NPs with diameter below 120 nm was observed in the optimal system. Cumulative controlled release of curcumin with strong pH-dependence into simulated gastric fluids with up to ~80% is found after 8–12 hours.
Published by:

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