مجله ایرانی پلیمر
سال:1381 | دوره: | شماره: |تعداد مقالات:7

Glycolysis of recycled polyethylene terephthalate (PET) from post-consumer soft-drink bottles was carried out with ethylene glycol (EG) at different weight ratios of PET to EG using zinc acetate as catalyst at the boiling point of EG under nitrogen atmosphere for a constant time of 8 h. The results showed that in excess of EG (at mole ratio of PET/EG = 0.12) the glycolyzed products contained predominantly bis(hydroxyethyl) terephthalate (BHET). Kinetics of polyesterification of glycolyzed product, BHET, made from a mole ratio of 0.12 of PET/EG with maleic anhydride was also studied without using acid catalyst. The polyesterification was carried out at different temperatures (135, 160, 200 and 210 °C) comparable to the industrial process scheme. It was observed that the acid value of the reaction mixture decreased and the extent of reaction increased sharply with increasing temperature or time of the reaction. At 135 °C the kinetic plots, using third-order kinetics, were non-linear at initial times.

Melt processability and thermal stability of blends of low density polyethylene and ethylene vinyl acetate copolymer modified with different dosages of phosphorylated cashew nut shell liquid (PCNSL) prepolymer have been studied using Brabender Plasticorder and thermogravimetric analysis, respectively. In all the blends having varying proportion of blend components, there was a progressive reduction in melt viscosity index with increase in dosage of PCNSL. The reduction in bandwidth of the Brabender torque profiles with increase in dosage of PCNSL from 0 to 10% indicated a decrease in melt elasticity of the blends. The reduction in indices of melt viscosity and melt elasticity of the blends in presence of PCNSL show the plasticizing effect of the additive and the consequent improvement in processability. The improvement in processability of the blends in presence of PCNSL was further evidenced by the decrease in power consumption during mixing, Modification of the blends with PCNSL resulted in significant improvement in thermal stability of the blends as evidenced by the progressive and significant increase in thermal stability index (T50) and shift in the thermograms to the high temperature region during thermogravimetric analysis.

The ablation of polyvinyl alcohol (PVA) with a multi-line 2.6-3.0 mum HF laser showed a strong interaction due to its relatively high absorption coefficient 7x104 cm-1, particularly hydrogen bands at 3597 cm-1. By using the expression for heat diffusion limit, surface temperature (Ts) of 340 K and 449 K were calculated for fluences of 0.3 and 1 Jcm-2, respectively. The Ts values are well consistent with the PVA melting point of 531 K and SEM photographs. With the average activation energy of 188 KJ mol-1 and rate constant of 6x107 s-1, a value of approximate to6x10-6 s-1 for Tapproximate to(146-230) K is obtained. The thermal degradation effect in short pulse duration was evident by Newtonian rings which basically is an interference pattern created by light, reflects off the boiling ablated material and the underneath solid material.

Enzymatic hydrolysis of cotton fabrics with different weft yarns has been studied. The weft yarns used were commercial cotton yarns produced by the carded, combed, open-end, air-jet and core-spun systems. The effects of cellulases hydrolysis on different fabrics were investigated by measuring the weight loss, the amount of glucose released and the breaking load of weft yarns. The results showed that the weight loss and concentration of glucose in hydrolysis vary with the increase of yarn hairiness. Loss of breaking load in shorter treatment times was related to hairiness of weft yarns but in longer enzymatic hydrolysis times, strength loss was affected by the amount of glucose released.

The relaxation spectrum is an important tool for investigating the behaviour of viscoelastic polymer melts. The most popular procedure for determining the relaxation spectrum is the use of a small-amplitude oscillatory shear experiment to determine the parameters in a multi-mode Maxwell model. However, this is an ill-posed problem and its numerical solution is along with difficulties. The determination of the discrete relaxation spectrum by a linear regression approach is widespread in practice and in the literature. In this work, a non-linear regression technique, based on Marquardt-Levenberg procedure, is applied in which the minimization is performed with respect to both the discrete relaxation times and the elastic moduli. Using this non-linear optimization, the spectrum parameters of a multi-mode Maxwell model were obtained for polybutadiene and polystyrene. It has been shown that in comparison with the other methods, the present approach is more efficient and it was found to give a very good fit with the fewest possible parameters.

In this paper it has been demonstrated that it is possible to generate in situ fibre composite from blends of a thermotropic liquid crystalline polymer (TLCP) and polypropylene by using combination of a modular multi-fed twin-screw extruder with an extensional flow mixer (EFM) as a novel process. Experimental results revealed that almost all TLCP droplets passing through the converging-diverging regions of the EFM are deformed into fibrils oriented to flow direction, indicating that this process does not suffer the limitation imposed by viscosity ratio of the blend components and TLCP concentration. The results obtained from the flow analysis performed on the converging regions of the EFM showed that L/D distribution of the TLCP fibrils can be predicted in terms of the lineal stretch parameter calculated on the basis of kinematical approach.

Cross-linked poly (vinyl alcohol) (PVA) is a prolonged-release micromatrix, a hydrophilic polymer and a potentially interesting hydrogel, which is useful for drug delivery applications. As a part of drug development procedure the aim of this study was to investigate the effect of structural changes on drug release (theophylline) from this polymeric network. The studied parameters included: cross-linking agent (glutaraldehyde) concentration, PVA content of the films, theophylline percentage and their overall effect on swelling of the hydrogels, drug loading efficiency, diffusion and release characteristics of theophylline from PVA films. Changes in glutaraldehyde percentage (or cross-linking density) affected the swelling of the films. However, increasing PVA percentage caused more swelling, Drug loading efficiency was higher in gels with higher glutaraldehyde, PVA and theophylline percentages. Increasing contents of PVA and theophylline promoted the diffusion coefficient and drug release rate but glutaraldehyde had a reverse effect. The pH did not affect the swelling and diffusion coefficient. Water transport and drug release mechanism predominantly followed a Fickian model. It may be concluded that by changing the PVA structural parameters, a rate-controlled drug release is obtained.