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All issues / Volume 3 (2009) / Issue 11 (November)

Thermoset polymers containing bio-based renewable resources
J. Karger-Kocsis
Vol. 3., No.11., Pages 676-676, 2009
DOI: 10.3144/expresspolymlett.2009.84
Editorial corner
PP-EPDM thermoplastic vulcanisates (TPVs) by electron induced reactive processing
K. Naskar, U. Gohs, U. Wagenknecht, G. Heinrich
Vol. 3., No.11., Pages 677-683, 2009
DOI: 10.3144/expresspolymlett.2009.85
Reactive processing combines melt mixing process and chemical reaction simultaneously. TPVs are produced by such reactive processing. Polymer modification with high energy electrons is based on generation of excited atoms or molecules and ions for subsequent molecular changes via radical induced chemical reactions. In the present study, electron induced reactive processing is used for the development of TPVs. A 1.5 MeV electron accelerator was directly coupled to an internal mixer in order to induce chemical reactions by energy input via high energy electrons under dynamic conditions of melt mixing of polypropylene (PP) and ethylene propylene diene monomer rubber (EPDM). The influence of absorbed dose (25 to 100 kGy) as well as electron energy (1.5 and 0.6 MeV) and electron treatment time (15 to 60 s) have been studied. Increased values of both tensile strength and elongation at break of the TPVs indicate in-situ compatibilisation of PP and EPDM as well as cross-linking in the EPDM phase upon electron induced reactive processing. Dynamic mechanical analyses showed a decrease in value of glass transition temperature peak of EPDM in tangent delta curve with increasing dose. This also indicates higher degree of cross-linking in EPDM phase, which is further supported by a gel content that is higher than the EPDM content itself in the blend.
Theoretical investigations on the geometric and electronic structures of polyacetylene molecule under the influence of external electric field
Y. W. Li, J. H. Yao, X. D. Zhu, C. J. Liu, J. Q. Jiang, X. S. Deng
Vol. 3., No.11., Pages 684-691, 2009
DOI: 10.3144/expresspolymlett.2009.86
The geometric and electronic structures of all-trans polyacetylene (PA) molecule in neutral, cationic, and anionic states have been studied theoretically by density functional theory method at the B3LYP/6-31+G* level. The results show that both the geometric and electronic structures of the PA molecule are sensitive to the external electric field (EF). For neutral PA molecule, with the increase of EF, the carbon-carbon single bonds are shortened while the carbon-carbon double bonds are elongated. The energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (LUMO-HOMO gap) decreases with the EF increasing. For cationic PA molecule, the carbon-carbon single bonds and carbon-carbon double bonds on the high potential side are elongated and shortened, respectively. While, the carboncarbon single bonds and carbon-carbon double bonds on the low potential side are shortened and elongated, respectively. Contrary to the neutral PA case, the LUMO-HOMO gap increases with the EF increasing. Contrast to the case of cationic PA, the evolution of carbon-carbon bond lengths for the anionic PA molecule under the external EF reverses. The LUMO-HOMO gap of the anionic PA molecule decreases with the increase of external EF. In addition, the spatial distributions of the HOMO and LUMO under the influence of external EF are also discussed for the PA molecule in neutral, cationic, and anionic states.
Kinetics of structure formation in PP/layered silicate nanocomposites
J. Hari, Z. Dominkovics, E. Fekete, B. Pukanszky
Vol. 3., No.11., Pages 692-702, 2009
DOI: 10.3144/expresspolymlett.2009.87
Polypropylene (PP)/organophilized montmorillonite (OMMT) and polypropylene/organophilized montmorillonite/maleic anhydride grafted polypropylene (MAPP) composites were prepared in an internal mixer under a wide range of processing conditions to study the kinetics of structure formation. Structure and properties were characterized by a variety of techniques. The gallery structure of the organophilic silicate changed in spite of the fact that no compatibilizer was added to PP/OMMT composites. Silicate reflection shifted towards smaller 2θangles, broadened and its intensity decreased indicating intercalation. Transmission electron microscopy (TEM) micrographs even showed individual platelets at long mixing times. However, the extent and direction of changes in the gallery structure of the silicate did not justify those observed in properties. The analysis of the results and additional experiments proved that the degradation of the polymer also takes place during processing leading to the formation of carbonyl and/or carboxyl groups, as well as to the decrease of molecular weight. The modification of the chain structure of the polymer influences interfacial interactions and the intercalation process. Some properties are directly determined by molecular weight (rheological properties, elongation). Both the clay and the MAPP seem to accelerate degradation. Thermooxidative degradation must have disadvantageous effect during the application of PP nanocomposites and needs further study.
Highly organosoluble and transparent polyamides containing cyclohexane and trifluoromethyl moieties: Synthesis and characterization
P. H. Li, C. Y. Wang, G. Li, J. M. Jiang
Vol. 3., No.11., Pages 703-712, 2009
DOI: 10.3144/expresspolymlett.2009.88
New aromatic diamine with cyclohexane moiety substituted with trifluoromethyl group in the side chain, 4,4’-(cyclohexane-1,4-diylbis(oxy))bis(3-(trifluoromethyl)aniline) (2), was successfully synthesized through the Williamson reaction of 1,4-cyclohexanediol and 2-chloro-5-nitrobenzotrifluoride, to yield the intermediate dinitro compound 1, followed by catalytic reduction with hydrazine and Pd/C to afford the diamine 2. This diamine monomer leads to a series of organic-soluble polyamides (4a–d) when reacted with different commercially available aromatic diacids (a–d) via a direct polycondensation with triphenyl phosphite and pyridine. The resulting polymers had inherent viscosities ranging from 0.89 to 1.29 dl/g. All the polymers showed outstanding solubility and could be easily dissolved in amide-type polar aprotic solvents and even dissolved in less polar solvents. All the polymers formed transparent, strong, and flexible films with tensile strengths of 54–68 MPa, Young’s moduli of 1.6–1.9 GPa, and elongations at break of 13.3–15.5%. These polyamide films have low dielectric constants of 2.15–2.88 at 1 MHz and low water absorptions of 1.96–2.84%. Wide-angle X-ray diffraction measurements revealed that these polyamides were amorphous in nature.
Theoretical prediction of hysteretic rubber friction in ball on plate configuration by finite element method
L. Palfi, T. Goda, K. Varadi
Vol. 3., No.11., Pages 713-723, 2009
DOI: 10.3144/expresspolymlett.2009.89
This paper has investigated theoretically the influence of sliding speed and temperature on the hysteretic friction in case of a smooth, reciprocating steel ball sliding on smooth rubber plate by finite element method (FEM). Generalized Maxwell-models combined with Mooney-Rivlin model have been used to describe the material behaviour of the ethylenepropylene-diene-monomer (EPDM) rubber studied. Additionally, the effect of the technique applied at the parameter identification of the material model and the number of Maxwell elements on the coefficient of friction (COF) was also investigated. Finally, the open parameter of the Greenwood-Tabor analytical model has been determined from a fit to the FE results. By fitting, as usual, the Maxwell-model to the storage modulus master curve the predicted COF, in a broad frequency range, will be underestimated even in case of 40-term Maxwell-model. To obtain more accurate numerical prediction or to provide an upper limit for the hysteretic friction, in the interesting frequency range, the Maxwell parameters should be determined, as proposed, from a fit to the measured loss factor master curve. This conclusion can be generalized for all the FE simulations where the hysteresis plays an important role.
Effects of bromination on the viscoelastic response of vinyl ester nanocomposites
A. M. Almagableh, P. R. Mantena, A. Alostaz, W. Liu, L. T. Drzal
Vol. 3., No.11., Pages 724-732, 2009
DOI: 10.3144/expresspolymlett.2009.90
Fire, smoke and toxicity are of significant concern for composite materials used in marine applications. Bromination of vinyl ester resin imparts fire retardancy as manifested by a reduction in the amount of smoke, carbon monoxide, and corrosive combustion products. In this research, the viscoelastic properties, modulus (stiffness) and damping (energy dissipation), of 1.25 and 2.5 wt. percent nanoclay and exfoliated graphite nanoplatelet (xGnP) reinforced non-brominated and brominated vinyl ester have been studied over a range of temperature and frequency. Effects of frequency on the viscoelastic behavior were investigated using a Dynamic Mechanical Analyzer (DMA) by sweeping the frequency over three decades: 0.01, 0.1, 1 and 10 Hz, and temperature range from 30–150°C at a step rate of 4°C per minute. Master curves were generated by time-temperature superposing the experimental data at a reference temperature. The nano reinforced composites showed a drop in initial storage modulus with bromination. Nanocomposites with 1.25 and 2.5 wt. percent graphite had the highest storage modulus among brominated specimens. Bromination was also found to significantly increase the glass transition temperature (Tg) and damping for all nanocomposites. Among the brominated specimens, 1.25 wt. Percent graphite platelet reinforced vinyl ester exhibited the best viscoelastic response with high damping and glass transition temperature, along with superior storage modulus over a longer time period.
Sulfated cellulose thin films with antithrombin affinity
R. Grombe, M. F. Gouzy, U. Freudenberg, T. Pompe, S. Zschoche, F. Simon, K.-J. Eichhorn, A. Janke, B. Voit, C. Werner
Vol. 3., No.11., Pages 733-742, 2009
DOI: 10.3144/expresspolymlett.2009.91
Cellulose thin films were chemically modified by in situ sulfation to produce surfaces with anticoagulant characteristics. Two celluloses differing in their degree of polymerization (DP): CEL I (DP 215–240) and CEL II (DP 1300–1400) were tethered to maleic anhydride copolymer (MA) layers and subsequently exposed to SO3•NMe3 solutions at elevated temperature. The impact of the resulting sulfation on the physicochemical properties of the cellulose films was investigated with respect to film thickness, atomic composition, wettability and roughness. The sulfation was optimized to gain a maximal surface concentration of sulfate groups. The scavenging of antithrombin (AT) by the surfaces was determined to conclude on their potential anticoagulant properties.
Aluminium trihydroxide in combination with ammonium polyphosphate as flame retardants for unsaturated polyester resin
T. D. Hapuarachchi, T. Peijs
Vol. 3., No.11., Pages 743-751, 2009
DOI: 10.3144/expresspolymlett.2009.92
The thermal and reaction to fire characteristics of a flame retardant unsaturated polyester (UP) ternary system are presented here. Thermal gravimetric analysis showed an improved thermal stability between 200–600°C with the addition of ammonium polyphosphate (APP) and aluminium trihydroxide (ATH) formulation. Cone calorimetry tests indicated that ATH is more efficient than calcium carbonate at delaying the ignition time, lowering the carbon monoxide yield and lowering the peak heat release (PHRR). However the addition of APP and ATH to the formulation failed to demonstrate any significant synergistic effect at reducing the PHRR.
Published by:

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