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All issues / Volume 3 (2009) / Issue 9 (September)

Electrical properties of polymer matrix composites: current impact and future trends
G. C. Psarras
Vol. 3., No.9., Pages 533-533, 2009
DOI: 10.3144/expresspolymlett.2009.66
Effect of cure cycle on curing process and hardness for epoxy resin
J. Zhang, Y. C. Xu, P. Huang
Vol. 3., No.9., Pages 534-541, 2009
DOI: 10.3144/expresspolymlett.2009.67
A 3-dimensional finite element model is developed to simulate and analyze the temperature and degree of cure field of epoxy casting part during cure process. The present model based on general finite element software ABAQUS is verified by literature example and experimental data. The numerical results show good agreement with literature example and measured data, and are even more accurate than the simulation of literature. After modeling successfully, the influence of temperature cure cycle ramps have on the temperature and degree of cure gradient is investigated. Moreover, the effect of non-uniform temperature and degree of cure field within epoxy casting part on hardness is demonstrated. The present model provides an accurate and novel method that allows further insight into the process of cure for epoxy resin.
The effect of zinc oxide nanoparticle morphology on activity in crosslinking of carboxylated nitrile elastomer
M. Przybyszewska, M. Zaborski
Vol. 3., No.9., Pages 542-552, 2009
DOI: 10.3144/expresspolymlett.2009.68
The aim of this work was to study the activity of several nanosized zinc oxides in the crosslinking of carboxylated nitrile elastomer (XNBR). In this article, we discuss the effect of zinc oxide nanoparticles with respect to their specific surface area, particle size and morphology (spheres, whiskers, and snowflakes) on the crosslinking density and mechanical properties of vulcanisates. The morphology of nanoparticles considerably influences the activity of zinc oxide towards carboxylated nitrile rubber. As a crosslinking agent, zinc oxide with snowflake particles seems to be the most active. The application of nanosized zinc oxide allows the amount of ZnO to be reduced by almost 40%, as compared to vulcanisates containing microsized particles. Moreover, vulcanisates crosslinked with zinc oxide nanoparticles exhibit thermoplastic properties that enable this material to be recycled, which is very important from an ecological point of view.
Chitosan-g-polyaniline: a creatine amidinohydrolase immobilization matrix for creatine biosensor
A. Tiwari, S. K. Shukla
Vol. 3., No.9., Pages 553-559, 2009
DOI: 10.3144/expresspolymlett.2009.69
A novel matrix composed of chitosan-graft-polyaniline (CHIT-g-PANI) was electrochemically prepared to investigate the immobilization of creatine amidinohydrolase (CAH). CAH enzyme was covalently immobilized with the CHIT-g-PANI matrix using glutaraldehyde as a linker. The resulting CAH/CHIT-g-PANI biomatrix was characterized with Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), contact angle measurement and cyclic voltammetry (CV) taking CHIT-g-PANI as a reference. The influence of various parameters on CAH enzyme activity within the matrix was investigated including pH, temperature, and time. The Michaelis-Menten constant and apparent activities for the CAH enzyme were calculated to be 0.51 mM and 83.59 mg/cm2, respectively; indicating CHIT-g-PANI matrix has a high affinity to immobilize CAH enzyme.
An experimental study on mechanical properties of GFRP braid-pultruded composite rods
M. S. Ahmadi, M. S. Johari, M. Sadighi, M. Esfandeh
Vol. 3., No.9., Pages 560-568, 2009
DOI: 10.3144/expresspolymlett.2009.70
In this work, a conventional textile braiding machine was modified and added to a pultrusion line in order to produce glass fiber reinforced composite rods by braiding-pultrusion technique. Braid-pultruded (BP) rods were produced with three braid roving linear densities and also with three different braid angles. To study the influence of overbraiding on mechanical properties of pultruded rods, unidirectional (UD) rods, without braided fabric, were produced, as well. All rod types were subjected to tensile, bending and torsion tests. The experimental results showed that BP rods have considerably higher shear modulus, but lower tensile modulus and flexural rigidity than those of UD pultruded rods, when fiber volume fraction is kept constant. Moreover, rods produced with higher braid roving linear densities had better torsional, but lower tensile and flexural properties. The highest shear modulus was observed in BP rods with braid angle of 45°.
Characterization of extrusion flow using particle image velocimetry
J. E. Fournier, M. F. Lacrampe, P. Krawczak
Vol. 3., No.9., Pages 569-578, 2009
DOI: 10.3144/expresspolymlett.2009.71
The aim of this study was the characterization of polymer flows within an extrusion die using particle image velocimetry (PIV) in very constraining conditions (high temperature, pressure and velocity). Measurements were realized on semi-industrial equipments in order to have test conditions close to the industrial ones. Simple flows as well as disrupted ones were studied in order to determine the capabilities and the limits of the method. The analysis of the velocity profiles pointed out significant wall slip, which was confirmed by rheological measurements based on Mooney's method. Numerical simulations were used to connect the two sets of measurements and to simulate complex velocity profiles for comparison to the experimental ones. A good agreement was found between simulations and experiments providing wall slip is taken into account in the simulation.
Actin dynamics and the elasticity of cytoskeletal networks
G. A. Buxton, N. Clarke, P. J. Hussey
Vol. 3., No.9., Pages 579-587, 2009
DOI: 10.3144/expresspolymlett.2009.72
The structural integrity of a cell depends on its cytoskeleton, which includes an actin network. This network is transient and depends upon the continual polymerization and depolymerization of actin. The degradation of an actin network, and a corresponding reduction in cell stiffness, can indicate the presence of disease. Numerical simulations will be invaluable for understanding the physics of these systems and the correlation between actin dynamics and elasticity. Here we develop a model that is capable of generating actin network structures. In particular, we develop a model of actin dynamics which considers the polymerization, depolymerization, nucleation, severing, and capping of actin filaments. The structures obtained are then fed directly into a mechanical model. This allows us to qualitatively assess the effects of changing various parameters associated with actin dynamics on the elasticity of the material.
How carbon nanotubes affect the cure kinetics and glass transition temperature of their epoxy composites? – A review
A. Allaoui, N. El Bounia
Vol. 3., No.9., Pages 588-594, 2009
DOI: 10.3144/expresspolymlett.2009.73
Motivated by the widespread and contradictory results regarding the glass transition temperature of carbon nanotube (CNT)/epoxy composites, we reviewed and analyzed the literature results dealing with the effect of unmodified multiwall carbon nanotubes (MWNT) on the cure behaviour of an epoxy resin (as a possible source of this discrepancy). The aim of this work was to clarify the effective role of unmodified multiwall carbon nanotubes on the cure kinetics and glass transition temperature (Tg) of their epoxy composites. It was found that various authors reported an acceleration effect of CNT. The cure reaction was promoted in its early stage which may be due to the catalyst particles present in the CNT raw material. While SWNT may lead to a decrease of Tg due to their bundling tendency, results reported for MWNT suggested an increased or unchanged Tg of the composites. The present status of the literature does not allow to isolate the effect of MWNT on the Tg due to the lack of a study providing essential information such as CNT purity, glass transition temperature along with the corresponding cure degree.
A new route to prepare nanocomposites based on polyvinyl chloride and MgAl layered double hydroxide intercalated with laurylether phosphate
N. H. Huang, J. Q. Wang
Vol. 3., No.9., Pages 595-604, 2009
DOI: 10.3144/expresspolymlett.2009.74
The MgAl layered double hydroxide (LDH) with laurylether phosphate was prepared using reconstruction method. Delamilation of the LDH with laurylether phosphate (LDH-PK) in tetrahydrofuran was characterized by AFM (atomic force microscopy), indicating that a large part of the LDH was delaminated into single, double and multi layers. The delaminated LDH-PK suspension was then used with polyvinyl chloride (PVC) to prepare a series of high-LDH-loading nanocomposites. Both the XRD (X-ray diffraction) patterns and TEM (transmission electron microscopy) photographs of the as-prepared PVC/LDH nanocomposites indicated that the LDH nanolayers dispersed uniformly in the PVC matrix. With differential scanning calorimetry (DSC) the glass transition temperatures of PVC phases in the PVC/LDH nanocomposites were measured and a slightly lower value than that of pristine PVC has been observed. Thermogravimetric analysis results show that the presence of LDH enhanced the dehydrochlorination temperature (Tmax1), reduced the maximum degradation rate (Rmax1) and the 5% weight loss temperature, and promoted the char formation of PVC. However, the thermal degradation temperature (Tmax2) and thermal degradation rate (Rmax2) of the dehydrochlorinated PVC were slightly affected by the presence of LDH. The apparent activation energies were calculated by the method of Flynn-Wall-Ozawa in nitrogen at four different heating rates, showing that the nanofiller increased the apparent activation energies by 10–26 kJ/mol when compared with pristine PVC, probably implying that the LDH nanolayers improve the stability of chlorine atom on the PVC chains.
Published by:

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