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All issues / Volume 2 (2008) / Issue 8 (August)

Polymers and 'strange' liquids
G. Banhegyi
Vol. 2., No.8., Pages 539-539, 2008
DOI: 10.3144/expresspolymlett.2008.64
Personal view on ionic liquids and supercritical liquids, especially supercritical water in relation to polymer science.
Preparation and characterization of electrospun fibers of Nylon 11
M. Dhanalakshmi, J. P. Jog
Vol. 2., No.8., Pages 540-545, 2008
DOI: 10.3144/expresspolymlett.2008.65
Nylon 11 nanofibers mats were successfully prepared by electrospinning process from formic acid solution. The scanning electron microscopy (SEM) images showed that nanofibers with uniform diameter were produced when the polymer concentration was 10% w/v, whereas ribbons were formed at a higher concentration. The crystalline structure of the nanofibers mats was investigated using X-ray diffraction (XRD) and it was found that the nanofibers mats crystallized in α form. The melt crystallized as well as solution casted films however exhibited γ form. The thermal properties of these samples were studied using differential scanning calorimetry (DSC) and it was observed that electrospun fibers showed higher crystallinity than the melt-crystallized samples. However, the crystallinity of electrospun fibers was lower than the solution-crystallized sample.
Effect of mixing sequence on the curing of amine-hardened epoxy/ alumina nanocomposites as assessed by optical refractometry
M. Philipp, P. C. Gervais, R. Sanctuary, U. Mueller, J. Baller, B. Wetzel, J. K. Krueger
Vol. 2., No.8., Pages 546-552, 2008
DOI: 10.3144/expresspolymlett.2008.66
High performance refractometry has been proven to be a useful tool to elucidate the isothermal curing process of nanocomposites. As a model system an amine-hardening epoxy filled with non-surface-treated alumina nanoparticles was selected. The tremendous resolution of this experimental technique is used to study morphological changes within nanocomposites via the refractive index. It is shown that these morphological changes are not simply due to the curing process but also depend on the sequence of mixing the nanoparticles either first into the resin or first into the hardener. Independent of the resin/hardener composition, the type of the mixing sequence discriminates systematically between two distinct refractive index curves produced by the curing process. The difference between the two refractive index curves increases monotonically with curing time, which underlines the importance of the initial molecular environment of the nanoparticles.
Selective Michael-type addition of a D-glucuronic acid derivative in the synthesis of model substances for uronic acid containing polysaccharides
K. Bergman, J. Hilborn, T. Bowden
Vol. 2., No.8., Pages 553-559, 2008
DOI: 10.3144/expresspolymlett.2008.67
A flexible protocol for the preparation of model substances for uronic acid containing polysaccharides is presented. We have synthesized a D-glucuronic acid derivative which is designed so that it easily can be conjugated with different structures and architectures by selective Michael-type addition. By successful coupling of the glucuronic acid derivative to polyethylene glycol with high degree of conversion, products were obtained that were easily characterized and which resembled polysaccharides in terms of solubility and purification methods that could be employed. The model substance can potentially be used to facilitate optimization of low-degree modification reactions of high molecular weight D-glucuronic acid containing polysaccharides.
Relationship between fiber degradation and residence time distribution in the processing of long fiber reinforced thermoplastics
H. Zhuang, R. Pu, Y. Zong, G. C. Dai
Vol. 2., No.8., Pages 560-568, 2008
DOI: 10.3144/expresspolymlett.2008.68
Long fiber reinforced thermoplastics (LFT) were processed by in-line compounding equipment with a modified single screw extruder. A pulse stimulus response technique using PET spheres as the tracer was adopted to obtain residence time distribution (RTD) of extrusion compounding. RTD curves were fitted by the model based on the supposition that extrusion compounding was the combination of plug flow and mixed flow. Characteristic parameters of RTD model including P the fraction of plug flow reactor (PFR) and d the fraction of dead volume of continuous stirred tank reactor (CSTR) were used to associate with fiber degradation presented by fiber length and dispersion. The effects of screw speed, mixing length and channel depth on RTD curves, and characteristic parameters of RTD models as well as their effects on the fiber degradation were investigated. The influence of shear force with different screw speeds and variable channel depth on fiber degradation was studied and the main impetus of fiber degradation was also presented. The optimal process for obtaining the balance of fiber length and dispersion was presented.
Study on the combustion behavior of high impact polystyrene nanocomposites produced by different extrusion processes
G. Sanchez-Olivares, A. Sanchez-Solis, G. Camino, O. Manero
Vol. 2., No.8., Pages 569-578, 2008
DOI: 10.3144/expresspolymlett.2008.69
The combustion behavior of a blend made of high impact polystyrene (HIPS) with sodium montmorillonite (MMT-Na+) and triphenyl phosphite (TPP), as a halogen-free flame retardant, is analyzed in detail in this work. The blend is processed through various extrusion methods aimed to improve clay dispersion. The UL94 method in vertical position, oxygen index and cone calorimetric measurements assess HIPS blend behavior in combustion. TGA, FTIR, SEM and X-ray measurements, together with mechanical and rheological tests evaluate the thermal degradation, morphology, intercalation and degree of dispersion of particles. The use of a static-mixing die placed at the extreme of a single screw extruder improves clay platelets distribution and reduces the peak heat release rate better than employing a twin screw extrusion process. In addition, mechanical and rheological properties are affected substantially by changing the extrusion process. A correlation between clay dispersion and HIPS fire retardant properties is found, as the peak heat release rate decreases with good clay dispersion in cone calorimetric tests.
Synthesis of tri-block copolymers through reverse atom transfer radical polymerization of methyl methacrylate using polyurethane macroiniferter
H. Verma, T. Kannan
Vol. 2., No.8., Pages 579-588, 2008
DOI: 10.3144/expresspolymlett.2008.70
Reverse atom transfer radical polymerization was successfully used for the first time to synthesis tri-block copolymers. Poly (methyl methacrylate)-block-polyurethane-block-poly (methyl methacrylate) tri-block copolymers were synthesized using tetraphenylethane-based polyurethane as a macroiniferter, copper(II) halide as a catalyst and N, N, N′, N″, N″-pentamethyldiethylenetriamine as a ligand. Controlled nature of the polymerization was confirmed by the linear increase of number average molecular weight with increasing conversion. Mole contents of poly (methyl methacrylate) present in the tri-block copolymers were calculated using proton nuclear magnetic resonance spectroscopy and the results were comparable with the gel permeation chromatography results. Differential scanning calorimetric results confirmed the presence of two different types of blocks in the tri-block copolymers.
Azo polymers with electronical push and pull structures prepared via RAFT polymerization and its photoinduced birefringence behavior
H. Z. Cao, W. Zhang, J. Zhu, X. R. Chen, Z. P. Cheng, J. H. Wu, X. L. Zhu
Vol. 2., No.8., Pages 589-601, 2008
DOI: 10.3144/expresspolymlett.2008.71
Two methacrylate monomers containing azo and electronical push and pull structure, e.g. 2-Methyl-acrylic-acid-2-{[4-(4-cyano-phenylazo)-3-methyl-phenyl]-ethyl-amino-ethyl ester (MACP) with cyano substituted and 2-Methylacrylic-acid-2-{ethyl-[4-(4-methoxy-phenylazo)-3-methyl-phenyl]-amino}-ethyl ester (MAMP) with methoxy substituted, were synthesized and polymerized using 2-cyanoprop-2-yl dithiobenzoate (CPDB) as chain transfer agent and 2,2'-azobisisobutyronitrile (AIBN) as initiator. The results showed that the polymerization displayed characteristics of ‘living’/controlled free radical polymerization. Thus, the obtained polymers, polyMACP (pMACP) and polyMAMP (pMAMP), had controlled molecular weights and narrow molecular weights distribution. The chain extension experiments of pMACP and pMAMP using styrene as the second monomer were successfully carried out. The photo-induced trans-cis-trans isomerization kinetic of pMACP and pMAMP in chloroform solution were described. Marked differences in rate for the trans-cis and cis-trans isomerization of pMACP and pMAMP were observed in chloroform solution due to the different electronic effects in these two polymers. Photoinduced birefringence and surface relief grating (SRG) of the pMACP and pMAMP were investigated in thin film state.
A novel thermoplastic elastomer based on dynamically vulcanized polypropylene/acrylic rubber blends
B. G. Soares, D. M. Santos, A. S. Sirqueira
Vol. 2., No.8., Pages 602-613, 2008
DOI: 10.3144/expresspolymlett.2008.72
Thermoplastic elastomer based on polypropylene (PP) and acrylic rubber (ACM) was investigated, with special attention on the compatibilization and dynamic vulcanization. ACM component contains chlorine and carboxyl groups along the backbone, which act as center for the curing and reactive compatibilization. The last event was carried out by adding a combination of maleic anhydride-modified PP (PP-g-MA) and triethylene tetramine (TETA), which act as interfacial agents between PP and ACM phases. The effectiveness of the compatibilization was suggested from mixing torque and viscosity, determined from rheological measurements. Outstanding mechanical performance, especially elongation at break, and better tensile set (lower values) were obtained with the compatibilization. The dynamic vulcanization also resulted in good mechanical properties for compatibilized blends, but the performance was inferior to that observed for non vulcanized blends. The effect of the compatibilization and/or dynamic vulcanization on the dynamic mechanical, thermal, morphological and stress relaxation properties was investigated.
Published by:

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