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All issues / Volume 4 (2010) / Issue 10 (October)

New frontiers of shape memory polymers
B. K. Kim
Vol. 4., No.10., Pages 589-589, 2010
DOI: 10.3144/expresspolymlett.2010.73
This is an editorial article. It has no abstract.
Enhancement of interfacial properties of basalt fiber reinforced nylon 6 matrix composites with silane coupling agents
T. Deak, T. Czigany, P. Tamas, Cs. Nemeth
Vol. 4., No.10., Pages 590-598, 2010
DOI: 10.3144/expresspolymlett.2010.74
In this work solution surface treatment was applied for producing basalt fiber reinforced PA6 matrix composites. Beyond scanning electron microscopy, static and dynamic mechanical tests, dynamic mechanical analysis of composites was used for qualifying the interfacial adhesion in a wide temperature range. The loss factor peak height of loss factor is particularly important, because it is in close relationship with the mobility of polymer molecular chain segments and side groups, hence it correlates with the number and strength of primary or secondary bondings established between the matrix and the basalt fibers. It was proven, that the interfacial adhesion between basalt fibers and polyamide can be largely improved by the application of silane coupling agents in the entire usage temperature range of composites. The presence of coupling agents on the surface of basalt fibers was proven by Fourier transform infrared spectroscopy. The best results were obtained by 3-glycidoxypropyltrimethoxysilane coupling agent.
Synthesis and self-assembly behavior of amphiphilic diblock copolymer dextran-block-poly(ε-caprolactone) (DEX-b-PCL) in aqueous media
Y. L. Zhang, X. W. Dou, T. Jin
Vol. 4., No.10., Pages 599-610, 2010
DOI: 10.3144/expresspolymlett.2010.75
An amphiphilic diblock copolymer, dextran-block-poly(ε-caprolactone) (DEX-b-PCL), with a series of welldefined chain lengths of each block was prepared by conjugating a dextran chain with a PCL block via aza-Michael addition reaction under mild conditions. For the dextran block, samples with relatively uniform molecular weight, 3.5 and 6.0 kDa, were used, and the PCL blocks were prepared via ring-opening polymerization at defined ratios of ε-caprolactone to initiator in order to give copolymers with mass fraction of dextran (fDEX) ranging from 0.16 to 0.45. When these copolymers were allowed to self-assemble in aqueous solution, the morphology of assembled aggregates varied as a function of fDEX when characterized by transmission electron microscope (TEM), fluorescence microscope (FM) and dynamic laser scattering (DLS). As fDEX decreases gradually from 0.45 to 0.16, the morphology of the copolymer assembly changes from spherical micelles to worm-like micelles and eventually to polymersomes, together with an increase in particle sizes.
Polypropylene/calcium carbonate nanocomposites – effects of processing techniques and maleated polypropylene compatibiliser
M. Y. A. Fuad, H. Hanim, R. Zarina, Z. A. Mohd. Ishak, Azman Hassan
Vol. 4., No.10., Pages 611-620, 2010
DOI: 10.3144/expresspolymlett.2010.76
The mechanical properties and crystalline characteristics of polypropylene (PP) and nano precipitated calcium carbonate (NPCC) nanocomposites prepared via melt mixing in an internal mixer and melt extrusion in a twin screw extruder, were compared. The effect of maleic anhydride grafted PP (PP-g-MAH) as a compatibiliser was also studied using the internal mixer. At low filler concentration of 5 wt%, impact strength was better for the nanocomposites produced using the internal mixer. At higher filler loading of more than 10 wt%, the extrusion technique was more effective to disperse the nanofillers resulting in better impact properties. The impact results are consistent with the observations made from Scanning Electron Microscope (SEM) morphology study. As expected, the flexural modulus of the nanocomposites increased with filler concentration regardless of the techniques utilised. At a same filler loading, there was also no significant difference in the moduli for the two techniques. The tensile strength of the mixed nanocomposites were found to be inferior to the extruded nanocomposites. Introduction of PP-g-MAH improved the impact strength, tensile strength and modulus of the mixed nanocomposites. The improvements may be attributed to better interfacial adhesion, as evident from the SEM micrographs which displayed better dispersion of the NPCC in the presence of the compatibiliser. Though NPCC particles have weak nucleating effect on the crystallization of the PP, addition of PP-g-MAH into the mixed nanocomposites has induced significant crystallization of the PP.
Effect of gas saturation conditions on the expansion ratio of microcellular poly(lactic acid)/wood-flour composites
L. M. Matuana, O. Faruk
Vol. 4., No.10., Pages 621-631, 2010
DOI: 10.3144/expresspolymlett.2010.77
Poly(lactic acid) or PLA and PLA/wood-flour composites were microcellular foamed with CO2 through a batch foaming process. Specifically, the gas saturation pressure and time varied during processing to produce PLA foams with a high expansion ratio. A ten fold expansion ratio resulted in microcellular foamed PLA over unfoamed counterpart. The foaming conditions associated with such a high expansion ratio involved a lower gas saturation pressure up to 2.76 MPa, which corresponds to a critical gas concentration of approximately 9.4%. Beyond this critical value, foam expansion decreased significantly. Investigations also studied the effect of incorporating wood flour on the foamability of the resulting PLA/wood-flour composites. The addition of wood flour into the PLA matrix significantly affected the expansion ratio of PLA/wood-flour composite foams.
Dielectric properties of poly(vinylidene fluoride)/CaCu3Ti4O12 nanocrystal composite thick films
P. Thomas, S. Satapathy, K. Dwarakanath, K. B. R. Varma
Vol. 4., No.10., Pages 632-643, 2010
DOI: 10.3144/expresspolymlett.2010.78
The poly(vinylidene fluoride)/CaCu3Ti4O12 (CCTO) nanocrystal composite films (thickness ≈85 µm) with relatively high dielectric permittivity (90 at 100 Hz) were prepared by the solution casting followed by spin coating technique. The structural, the microstructural and the dielectric properties of the composites were studied using X-ray diffraction, Scanning Electron Microscope, and Impedance analyzer respectively. The effective dielectric permittivity (εeff) of the composite increased with increase in the volume fraction of CCTO at all the frequencies (100 Hz to 1 MHz) under investigation. The room temperature dielectric permittivity which is around 90 at 100 Hz, has increased to about 290 at 125°C (100 Hz). These results may be exploited in the development of high energy density capacitors.
Healing of fatigue crack in epoxy materials with epoxy/mercaptan system via manual infiltration
Y. C. Yuan, M. Z. Rong, M. Q. Zhang, G. C. Yang, J. Q. Zhao
Vol. 4., No.10., Pages 644-658, 2010
DOI: 10.3144/expresspolymlett.2010.79
The present work verified the capability of epoxy/mercaptan/tertiary amine system for retarding and/or arresting fatigue cracks in epoxy materials subjected to cyclic loading at room temperature. By using static and dynamic manual infiltration methods, the effects of hydrodynamic pressure crack tip shielding, polymeric wedge and adhesive bonding of the healing agent were revealed. Depending on the applied stress intensity range and the competition between polymerization kinetics of the healing agent and crack growth rate, the above mechanisms exerted different influences on crack retardation under different circumstances. On the whole, the epoxy/mercaptan/tertiary amine system proved to be very effective in obstructing fatigue crack propagation. It formed a promising base for developing self-healing epoxy materials that enable in-situ autonomic rehabilitation of fatigue crack.
Crystalline structure of annealed polylactic acid and its relation to processing
T. Tabi, I. E. Sajo, F. Szabo, A. S. Luyt, J. G. Kovacs
Vol. 4., No.10., Pages 659-668, 2010
DOI: 10.3144/expresspolymlett.2010.80
This paper focuses on the crystalline structure of injection moulding grade poly(lactic acid) (PLA) and the effect of crystalline structure on the processing. The research is induced by the significant differences in crystallinity of the pure PLA resin, and the injection moulded product, and thus the reprocessing of PLA products. 2 mm thick PLA sheets were injection moulded and re-crystallized in a conventional oven at 60–140°C, for 10–60 minutes to achieve various crystalline contents. The properties of these sheets were investigated by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD). In a processing plant the rejected parts are recycled and reused as raw material for further cycles, accordingly the various crystalline content PLA products were reprocessed as a resin, to investigate the processing itself. When PLA products are reprocessed, due to the adherent feature of amorphous PLA processing difficulties may occur. This adherent effect of the amorphous PLA was investigated and characterized.
Published by:

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