دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و دوم شماره 5 (پیاپی 103، آذر و دی 1388)

Improvements in the properties of ordinary sidewall compound (NR/BR) with the addition of EPDM by reactive processing method were evaluated. The results show that ozone resistance of these sidewalls was improved with increased addition of EPDM. Also the tensile strength and elongation-at-break were increased in comparison with NRBREPDM compounds that were made by non-reactive processing. SEM Photographs show that the reactive processing method helps to improve the compatibility of these three elastomers compared with NRBREPDM system made by non-reactive processing. The results of fatigue-to-failure and tear resistance show that compounds prepared by reactive processing have a better property in comparison with non-reactive samples. Tensile and elongation-at-break of the reactive samples were superior to the non-reactive samples after aging.

Poly(vinyl acetate) is synthesized via solution polymerization, and then it is converted to poly(vinyl alcohol) by alkaline alcoholysis. The aim of the work study was to investigate statistically the influence of reaction variables in vinyl acetate polymerization, the conversion of this monomer to polymer, degree of branching of acetyl group in poly(vinyl acetate), as well as the molecular weight of poly(vinyl alcohol), using Taguchi experimental design approach. The reaction variables were polymerization time, molar ratio of initiator to monomer, and volume ratio of monomer to solvent. The statistical analysis of variance of the results revealed that all factors have significantly influenced the conversion and degree of branching. Volume ratio of monomer to solvent is the only factor affecting the molecular weight of poly(vinyl alcohol), and has the greatest influence on all responses. By increasing this ratio, the conversion, degree of branching of acetyl group in poly(vinyl acetate), and molecular weight of poly(vinyl alcohol) were increased.

Full factorial experimental design (23) for the evaluation of slurry ethylene polymerization in the presence of an industrial TiCl4/MgCl2 Ziegler-Natta catalyst was employed. The following parameters were used as independent variables: Al/Ti molar ratio, reaction temperature and hydrogen partial pressure. The total polymerization pressure was 9 bar. Catalyst activity, MFI (melt flow index) and melting temperature were statistically analyzed through response surface method. Hydrogen partial pressure had the most and temperature had the least effect on catalyst activity. Catalyst activity was affected by binary interactions of Al/Ti molar ratio-hydrogen partial pressure and temperature-hydrogen partial pressure. No interaction of temperature-Al/Ti molar ratio was found. Hydrogen partial pressure, temperature and their interaction had the strongest influence on MFI. Cubic models were employed for describing the surface responses of catalyst activity and melt flow index as a function of operating variables. The effects of Al/Ti molar ratio, reaction temperature, hydrogen partial pressure and their interactions were not significant from statistical point of view. Therefore no cubic model was employed.

The creep/recovery behavior of wood flour-polypropylene was compared with medium density fiberboard (MDF) and particleboard. For this purpose, wood flour-polypropylene composites (with and without compatibilizer) were manufactured by using a laboratory twin-screw extruder. The MDF and particleboard panels were obtained from local producers. Short term flexural creep tests at 30% of ultimate bending load were performed by using flexural creep equipment. The total time to complete every test was 120 min (60 min creep and 60 min recovery). Also Findley creep model was used for the prediction of creep behavior of the materials under study. The results showed that fractional deflection and relative creep in wood flour-polypropylene composites are higher than MDF and particleboard whereas MDF and particleboard exhibited higher percent recovery rather than wood flour-polypropylene composite. Creep modulus at the first phase of creep in wood flour-polypropylene composite was higher than MDF and particleboard but more decreases were observed for creep modulus of wood-plastic composite at the end of creep phase. Coupling agent (MAPP) improved creep/recovery behavior of wood flour-polypropylene composite. Also Findley creep model predicted the creep behavior of studied materials very well.

The nylon and nylon/lycra yarns were coated with electrically conductive polymers such as polyaniline and polypyrrole, via chemical polymerization process. Electrical conductivity of the coated yarns was measured at various strain levels using two-point probe technique and their strain sensitivities were studied. The results showed that, electrical conductivity of the coated yarns decreased with an increase in strain level. A sharp decrease in the electrical conductivity of the nylon/lycra coated yarn with the strain level was recorded whereas, a small drop in the electrical conductivity of the nylon coated yarn was observed. Linear relationships were found between the electrical conductivity and length for the nylon and nylon/lycra coated yarns. The polyaniline coated yarns showed higher strain sensitivity compared to polypyrrole coated yarns. Repeatability of the strain sensitivity of the coated yarns was examined and the coated nylon/lycra yarn showed better repeatability compared to that of coated nylon yarn. The coated yarns were proposed as a flexible strain sensor in the field of intelligent materials.

Studies on Nano Barium Strontium Titanate/Cellulose Derivatives Composites چکیده [English] Studies were carried out on the preparation and properties of the composites made from cellulose acetate butyrate and cellulose acetate propionate with various amounts of barium strontium titanate nano-particle. The nano-particles of barium strontium titanate (BST) with formulation of Ba0. 77Sr0. 23TiO3 were made by sol-gel method and their purity and particle size were analyzed by X-ray diffraction (XRD). The composites were prepared with BST nano-particle loading of 10 to 50 vol%, and their distribution in the composites studied using SEM imaging. The dielectric constant of the composites was measured at 1 kHz and 100 kHz at room temperature. It was found that the adopted procedure produced dense and uniform composites. The dielectric constant of the composites increased with the solid content of BST and followed the modified Lichtenecker equation. The increasing rate of dielectric constant with increased BST content was more pronounced for the BST/CAP composite. The dielectric constant of the composites decreased with increasing the frequency which was more obvious at higher loading of BST nano-particle.

Microstructural investigation of low molecular weight 1,4-polybutadiene (1,4-PBD) was studied by 1H and 13C nuclear magnetic resonance spectroscopy (NMR). The isomer contents of 1,4-cis, 1,4-trans and 1,2- vinyl in polybutadiene microstructure were determined. The number average molecular weight for low molecular weight polybutadiene was measured by NMR techniques and comparison was made with gel permeation chromatography (GPC) results. Due to the presence of methyl end group and considering the repeating units in 1,4-PBD microstructure, the number average molecular weight was calculated by NMR techniques. This study was accomplished by obtaining cis-trans isomerization in non-pyrolytic anaerobic conditions at 200 to 250oC. The results showed that increase in heat treatment time increased the trans isomer and decreased the cis isomer contents respectively. The presence of 1,2-vinyl isomers increased the average molecular weights by heat treatment time at 250oC and did not lead to any chain scission in 1,4-PBD.

To describe the rheological behavior of polymer blends using emulsionbased (Palierne theory) as well as micromechanical models (Coranapproach), two immiscible polymeric blend systems of poly(trimethylene terephthalate) (PTT)/polyamide-12 (PA12) and PTT/polyethylene (PE) having different levels of molecular interactions were investigated as model systems. The role of interfacial interactions, viscosity ratio, composition, and shear rate were also explored with respect to the aforementioned theories. For both systems no reasonable agreement was noticed between the experimental data and Palierne model predictions, which was related to high viscosity ratio and high dispersed phase content. Nevertheless, the PTT/PE blend, having almost a zero interfacial thickness due to the absence of intermolecular interaction, exhibited a seemingly better correlation with experimental data compared to PTT/PA12 system. Moreover a better agreement between experimental and theoretical data was obtained in the blend where the viscosity of dispersed phase was higher than that of matrix. Also, in both model systems, the values predicted from Palierne were closer to empirical data at higher frequencies most likely due to breakdown in physical network structure. Coran analysis due to its micromechanical origin could give outputs in good agreement with the experimental results in both model systems.