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All issues / Volume 10 (2016) / Issue 2 (February)

Can the standard impact tests become a true materials evaluation tool?
P. M. Frontini
Vol. 10., No.2., Pages 83-83, 2016
DOI: 10.3144/expresspolymlett.2016.9
This is an editorial article. It has no abstract.
Synthesis, kinetics of photo-dimerization/photo-cleavage and physical properties of coumarin-containing branched polyurethanes based on polycaprolactones
R. Seoane Rivero, P. Bilbao Solaguren, K. Gondra Zubieta, L. Peponi, A. Marcos-Fernandez
Vol. 10., No.2., Pages 84-95, 2016
DOI: 10.3144/expresspolymlett.2016.10
A series of coumarin-containing branched polyurethanes based on polycaprolactones, hexamethylene diisocyanate and a monohydroxylated coumarin monomer with 5 and 10% content by weight of coumarin units were successfully prepared. Chain architecture was controlled by combination of polycaprolactone (PCL) triol or tetrol with PCL diol. Terminal coumarin units segregated from the polyurethane matrix as measured by differential scanning calorimetry (DSC). Photo-dimerization with 313 nm lamps presented an anomalous behavior in two steps with high irreversibility at high conversions. Photo-dimerization/photo-cleavage reactions showed an increase in irreversibility with the increase in cycles. It was demonstrated that conversion measured by Raman spectroscopy gave the same results than conversion measured by ultraviolet (UV) spectroscopy. Photo-dimerization produced an elastomeric material with much better mechanical properties than non-irradiated material as a consequence of the crosslinking produced. Photo-cleavage decreased the mechanical properties and repeated photo-dimerization increased mechanical properties again.
Electrochemical impedance and spectroscopy study of the EDC/NHS activation of the carboxyl groups on poly(ε-caprolactone)/poly(m-anthranilic acid) nanofibers
Z. Guler, A. S. Sarac
Vol. 10., No.2., Pages 96-110, 2016
DOI: 10.3144/expresspolymlett.2016.11
Electrochemical impedance spectroscopy (EIS) and spectroscopy was applied to investigate the surface activation of carboxyl group (–COOH) containing nanofibers by the reaction of 1-ethyl-3-(dimethyl-aminopropyl) carbodiimide hydrochloride (EDC)/N-hydroxyl succinimide (NHS) in different concentrations. Poly(!-caprolactone)/poly(m-anthranilic acid) (PCL/P3ANA) nanofibers were fabricated by electrospinning and were activated with 5/0.5, 0.5/5, 5/5 and 50/50 mM of EDC/NHS. The surface activation was investigated by Attenuated Total Reflectance Fourier transform infrared spectroscopy (FTIR-ATR) and activation yield was estimated. Albumin was immobilized after surface activation and the amount of covalently immobilized protein was determined by bicinchoninic acid (BCA) assay. Morphology and composition of albumin immobilized nanofibers were characterized by Scanning Electron Microscopy/Energy-Dispersive X-ray Spectroscopy (SEM/EDX) and Atomic force microscope (AFM). EIS measurements indicated that nanofibers become resistant after albumin immobilization. The obtained data revealed that the highest amount of albumin bound to nanofibers activated with 50/50 mM of EDC/NHS which was found to be the optimum concentration for the activation of PCL/P3ANA nanofibers.
Poly(butylene cyclohexanedicarboxylate/diglycolate) random copolymers reinforced with SWCNTs for multifunctional conductive biopolymer composites
E. Fortunati, M. Gigli, F. Luzi, N. Lotti, A. Munari, M. Gazzano, I. Armentano, J. M. Kenny
Vol. 10., No.2., Pages 111-124, 2016
DOI: 10.3144/expresspolymlett.2016.12
The objective of this work was to develop a versatile strategy for preparing multifunctional composite films with tunable properties. Novel conductive composites based on the combination of single walled carbon nanotubes (SWCNTs) and biodegradable poly(butylene cyclohexanedicarboxylate/diglycolate) random copolymers (P(BCEmBDGn)) are here presented. In particular, synthesized PBCE homopolymer and two copolymers containing different amounts of ether–oxygen containing co-units, P(BCE90BDG10) and P(BCE70BDG30), have been considered as matrices of SWCNTs based composites. The effect of incorporation of different amounts of SWCNTs (0.1–0.5–0.75–1 wt%) on morphological, thermal, mechanical and electrical properties was deeply investigated. The morphology of the fracture surfaces is affected by the SWCNT presence, while the increase in the SWCNT content does not provide significant microstructure modifications. The thermal properties underlined that nanotubes can act as nucleating agents, favouring the polymer crystallization process. The mechanical behavior demonstrated that the introduction of carbon nanotubes both in the case of PBCE homopolymer and in random copolymers based formulations exerted a reinforcing effect. All composites exhibit high electrical conductivity in comparison to the neat polymers. This work demonstrates that this combinatorial approach can be used to develop materials with tunable and advanced functional properties.
Effects of polymerization degree on recovery behavior of PVA/PVP hydrogels as potential articular cartilage prosthesis after fatigue test
Y. Shi, D. S. Xiong, Y. Peng, N. Wang
Vol. 10., No.2., Pages 125-138, 2016
DOI: 10.3144/expresspolymlett.2016.13
Poly (vinyl alcohol)/poly (vinyl pyrrolidone) (PVA/PVP) hydrogels with various polymerization degrees of PVA were synthesized by a repeated freezing-thawing method. The influence of polymerization degree on microstructure, water content, friction coefficient, compressive fatigue and recovery properties of PVA/PVP hydrogels were investigated. The results showed that higher polymerization degree resulted in larger compressive modulus and lower friction coefficient. The fatigue behaviors of PVA/PVP hydrogels were evaluated under sinusoidal compressive loading from 200 to 800 N at 5 Hz for up to 50 000 cycles. The unconfined uniaxial compressive tests of PVA/PVP hydrogels were performed before and after fatigue test. During the fatigue test, the height of the hydrogel rapidly decreased at first and gradually became stable with loading cycles. The compressive tangent modulus measured 0 h after fatigue was significantly larger than the values obtained before test, and then the modulus recovered to its original level for 48 h after test. However, the geometry of hydrogels could not return to the original level due to the creep effects. PVA/PVP hydrogels prepared with lower polymerization degree showed better recovery capability than that prepared with high polymerization degree.
High performances unsaturated polyester based nanocomposites: Effect of vinyl modified nanosilica on mechanical properties
J. D. Rusmirovic, K. T. Trifkovic, B. Bugarski, V. B. Pavlovic, J. Dzunuzovic, M. Tomic, A. D. Marinkovic
Vol. 10., No.2., Pages 139-159, 2016
DOI: 10.3144/expresspolymlett.2016.14
Influences of the vinyl modified nanosilica Aerosil® 380, <Í>i.e./i>, vinyl and methacryloyl silane coupling agent and linseed oil fatty acids (BD) reactive residues, on the mechanical properties of the unsaturated polyester resins (UPes) based nanocomposites, was studied. The polycondensation of maleic anhydride and products of poly(ethylene terephthalate) (PET) depolymerization with propylene glycol, with and without separation of ethylene glycol, yields UPe1 and UPe2 resin, respectively. The hydroxyl terminated PET depolymerization products (glycolyzates) and UPes were characterized by acid and hydroxyl values, Fourier Transform Infrared (FTIR) and nuclear magneti resonance (NMR) spectroscopies. Transmission electron microscopy (TEM) confirmed that silica nanoparticles formed domains of aggregates in the polymer matrix. An increase from 195 to 247% of stress at break (σb), and from 109 to 131% of impact strength (σi) of UPes based nanocomposites was obtained for 1 wt% addition of vinyl modified silica. Flexural strength (σf) increase from 106 to 156% for both UPes based nanocomposites with 1 wt% addition of BD modified silica. Cross-linking density (ν), storage modulus (G'), tanδ and Tg of the nanocomposite were determined from the dynamic mechanical testing and discussed in relation to the structure of silica modification.
Reactive microencapsulation of carbon allotropes in polyamide shell-core structures and their transformation in hybrid composites with tailored electrical properties
F. Oliveira, N. Dencheva, P. Martins, S. Lanceros-Mendez, Z. Denchev
Vol. 10., No.2., Pages 160-175, 2016
DOI: 10.3144/expresspolymlett.2016.15
Polyamide 6 microcapsules (PAMC) loaded with 2–10 wt% of different carbon allotropes: carbon black, multiwalled carbon nanotubes, carbon nanofibers and graphite were synthesized via activated anionic polymerization (AAROP) of ε-caprolactam in solution performed in the presence of the respective micro- or nanosized loads. The forming high-molecular weight microporous PAMC showed typical diameters of 15–35 µm, the filler particles being entrapped in the core as proven by microscopy methods. The melt processing of the loaded microcapsules produced PA6/C-filler hybrid thermoplastic composites with homogeneous distribution of one or two C-fillers even at loads of up to 10% without any functionalization. The crystalline structure of all PAMC and molded composites was studied by thermal and X-ray diffraction methods focusing on possible structure modification during the transition from PAMC to molded plates. Mechanical tests in tension and electrical conductivity measurements showed that transforming loaded PAMC into composites by melt processing could be a facile and rapid method to fabricate polyamide composites with improved mechanical performance and tailored electrical and dielectric properties.
Biocomposites based on poly(lactic acid)/willow-fiber and their injection moulded microcellular foams
M. T. Zafar, N. Zarrinbakhsh, A. K. Mohanty, M. Misra, S. N. Maiti, A. K. Ghosh
Vol. 10., No.2., Pages 176-186, 2016
DOI: 10.3144/expresspolymlett.2016.16
Natural fiber reinforced biocomposites have recently attracted many researchers because of their biodegradability, cost effectiveness and ecofriendliness. The present study investigates the properties of willow-fiber reinforced poly(lactic acid) based composites and their foam processability. Microcellular foams of the composites were prepared by foam injection moulding using nitrogen gas as the blowing agent. The effects of willow-fiber addition on the morphology, mechanical properties, thermal stability, crystallization, and heat deflection temperature (HDT) were studied. At 30 weight percent [wt%] willow-fiber content, unfoamed composites showed good improvement in specific tensile and flexural moduli. Addition of willow-fiber increased crystallinity and the rate of crystallization and yielded narrow crystallite size distribution as observed by differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) results of the foamed composites revealed that increase in willow-fiber content caused smaller average cell size and higher cell density. Specific notch impact strength of foamed composites at both 20 and 30 wt% willow-fiber content showed increasing trend compared to that of their unfoamed counterparts.
Published by:

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