مجله ایرانی پلیمر
سال:1384 | دوره: | شماره: |تعداد مقالات:9

The kinetic of the thermal degradation of rigid polyvinyl chloride (PVC) under nitrogen atmosphere was studied by bromometry titration at various temperatures (160-190oC) in the presence of ethylene diamine tetra acetic acid (EDTA), 1,2 propane diol, benzoic acid, and phenol as thermal stabilizers. The rate of dehydrochlorination at 1% degradation (RDH) and the time required for dehydrochlorination to attain 1% conversion (tDH) were used to assess the effect of the additives on the thermal susceptibility of PVC. It was found that the values of the RDH were relatively lower and the tDH were considerably higher than the value obtained in the absence of the additives. The degradation rate coefficients were determined from the rate of dehydrochlorinating. The following rate expressions R=k[PVC]0.77[benzoic acid]-0.40, R=k[PVC]0.71[1,2 propane diol]-1.78, R=K[PVC]0.67[EDTA]-2.18, and R=k[PVC]0.88[phenol]-0.28 were obtained. The activation energies determined from the temperature dependence of the rate coefficients of the polymers degradation. The activation energies of the PVC degradation in the presence of EDTA, 1,2 propane diol, benzoic acid, phenol, and also in the absence of stabilizer were obtained 28, 27.5, 26.8, 26, and 24.5 kcalmol-1, respectively. The results show that the order of increasing stabilizing effect was EDTA >1,2 propane diol>benzoic acid> phenol. The results also, reveal greater stabilizing efficiencies of the investigated materials compared to non stabilizer.

The effects of some factors, i.e., long chain branches on EPDM and PP backbone and short side chain branches of HDPE on melt extensibility and melt elasticity were studied and compared with those of ternary blends of linear PPs. Long chain branched EPDM, long chain branched PP, and linear PE with small side chains were used to increase the molecular entanglements and melt drawability and to improve melt elasticity. Using three linear PP in the blends, showed a synergistic effect on melt elasticity in a certain percentage of composition. The experimental results have been indicated that both ternary blends of linear PPs and ternary blends containing a branched PP increased molecular entanglements and affected on melt elasticity. HDPE as a polyolefin with short side chains showed better effect on melt elasticity and melt drawability than ternary linear PP blends. Long chain branches of EPDM considerably improved its damping factor (tan d) and steady state creep compliance (Je0). The effect of long chain branched EPDM and high molecular weight linear PE with small branches, on melt tension force and damping factor of blends were measured and compared with those of blends containing a long chain branched PP. Long chain branched PP(LCB-PP) showed a distinct effect on melt extensibility of blends. The most significant effect is observed by using the PE and long chain branched PP, both.

The effects of paper sludge (PS) and kaolin on properties of PP/EPDM composites were examined. The mechanical properties, morphology, water absorption and thermal properties were investigated. At a similar filler loading, PP/EPDM/kaolin composites show higher mechanical properties (such as tensile strength and elongation-at-break, except Youngs modulus), lower water absorption, and better thermal stability compared to PP/EPDM/PS composites. However PP/EPDM/PS composites exhibit better Youngs modulus and percentage of crystallinity than PP/EPDM/kaolin composites. SEM of tensile fracture surfaces of composites show that the PP/EPDM/kaolin composites have better filler dispersion and filler-matrix interaction than PP/EPDM/PS composites.

One of the most important post-reactor modifications of polyethylene is cross-linking. It improves some properties of polyethylene such as: environmental stress cracking resistance, chemical and abrasion resistance, and service temperature. In this study, the effect of peroxide cross-linking on the rheological behaviour of low density polyethylene was investigated by using a combination of creep test and differential scanning calorimeter (DSC) in isotherm condition. The used peroxide was di-cumyl peroxide and its concentration was 2 wt%. The experiments were carried out at 150, 160, and 170oC and the change of bulk viscosity due to network developing was determined. For delivering of local derivatives, smoothing techniques were applied on creep data. The rate of increment of viscosity increased with increasing the temperature and the major of this increment took place in the first stages of reaction.

Results of long time tests are given for migration of dioctyl phthalate (DOP) from solid PVC discs into well-stirred colza oil. The following factors were examined: time, plasticization level (from 20 to 50 wt%), and temperature (30 and 50°C). The use of labeled DOP and radioactivity measurements in conjunction with weight loss give quantitative information on the mass exchanged (plasticizer migration and colza oil penetration) and lead to DOP concentration profiles that are developed through the bulk of polymer during the process. Mathematical model investigated in this study takes into account the following conditions: (1) the concentration of colza oil in the polymer matrix was neglected; (2) the diffusion in transient conditions through the PVC mass with DOP concentration-dependent diffusivity was considered. Statistical analysis shows that this self-consistent model is able to reproduce, to a good approximation for the DOP, the concentration profiles in the polymer, and the kinetics of transfer into the oil.

The protein immobilization ability of cross-linked polyacrylamide (CLP) was studied in one-phase binary-solvent systems. Four miscible solvents in water; 2 protic (methanol, 2-propanol) and 2 aprotic (THF, acetonitrile), and bovine serum albumin (BSA) as target protein were chosen. According to the results of a study on the sieve structure of CLP, the polymer which was made from 1.69 M acrylamide and 2.03 ×10-2 M bis-acryl amide was selected for the research. Results showed that CLP immobilization efficiency increased as the co-solvent share in the binary-solvents increased. However, it was not necessary to omit water. The immobilization efficiency of CLP was satisfying in the binary systems containing about 50% 2-propanol or acetonitrile, or 70% Methanol or THF. The CLP immobilization performance was very high when the organic solvent share was increased above 90% in all the studied binary media. The outcome suggests that the tolerable level of water and the role of co-solvent in the applied system are mainly affected by the amphiphilic nature of CLP. Assumingly, the amphiphilic structure helps CLP to be applied in one-phase binary systems containing co-solvent from various groups of protic or aprotic with different log P.

Owing to the significant changes in tyre geometry especially for truck tyres with complex patterns and high thickness at tread area, the effect of heat transfer in circumferential direction on temperature field development during tyre curing should be taken into account. This work is basedon the development of a three dimensional nonlinear finite element model for simulation of tyre curing process of in mould. The heat conduction equation was solved by the use of a standard Galerkin technique in a Cartesian coordinate system. Transient temperature field was modelled using the implicit-  q method. The Kamal and Sourour empirical cure reaction kinetic equation was also used to calculate the state and rate of cure as a function of time. Based on the developed model, an interactive computer program was written in Visual Basic. This program was used to simulate the curing process of a 12-24 truck tyre in mould. Results of our simulations showed that distributions of both temperature and state of cure in circumferential direction cannot be ignored. The applicability of the model was also verified by comparison between the temperature profiles at two points inside the tyre with experimental data. It has been shown that there is a very good agreement between the model predictions and actual data.

Generation of heat via viscous dissipation of nucured filled rubber compounds can lead to significant temperature increment, which its estimation is very important. In this work, viscous heating and stress relaxation on uncured carbon black and silica filled SBR compounds and heat build up of the cured one were investigated by rubber process analyzer (RPA2000) instrument. These compounds were prepared in Haake internal mixer at 60oC, 10 min mixing time and a rotor speed of 40 rpm. The mixing was followed by using a two-roll mill with adding curing agents. A part of these compounds was used to prepare the cured samples for Goodrich flexometer, to determine the heat build up of cured compounds. There was a similar trend in the data of both measurings. The results of this study showed that with increasing the particle size, i.e., decreaseing the structure of carbon black, the amount of generated heat has reduced. Fillers which cause higher viscous heating in the uncured compounds also impart higher heat build up in the cured compounds. Results also demonstrated that compounds which containg larger particle size, i.e., lower structure carbon black have shorter relaxation time. In silica filled SBR, viscous heating, heat build up, and stress relaxation have been increased, also.

Aliphatic polyesters are the source of the attractive polymeric matrices that are currently investigated for making controlled drug delivery devices. In spite of the large number of investigations dealing with LA/GA polymers which have been reported in the literature, only little is known about the degradation mechanism of these polyesters in solid state. In this study poly (L,D-lactide-co-glycolide) 50:50 (PLGA) was hydrolyzed at 37oC for periods up to 56 days. PLGA discs were prepared in 60oC and the results of their in vitro biodegradation behaviour are reported. We observed that hydrolysis of PLGA proceeds in 7 stages: surface hydrolysis ,outer layers hydrolysis, outer layers water soluble oligomers formation, exiting water soluble oligomers, bulk hydrolysis and exiting degradation products, bulk catalyzed hydrolysis, and at the last step fragile porous structure formation. The remained porous structure is crystallized and shows more resistance to further degradation.