Iranian Journal of Polymer Science and Technology
Year:2010 | Volume:23 | Issue:2 (ISSUE NO. 106)|Papers Count:7

Polymeric nanoparticles with biodegradable and biocompatible polymers are good candidates in peptide drugs delivery systems. In this study, we success- fully prepared chitosan nanoparticles including salicylic acid as a model drug by emulsion cross-linking "in oil" method. The various dynamic parameters are considered, including the speed of stirrer, the duration of injecting the aqueous phase into oil phase and the condition of precipitation of particles.It is found that the optimum conditions are achieved at 2000 rpm when the aqueous phase is added within 30 min into the oil phase. According to optimum conditions the nanoparticles of chitosan (the peak of size distribution in 100 nm) were prepared and the drug content and the release behavior were estimated.The results demonstrate, that the drug content of nanoparticles is 35% (w/w).The release behavior of nanoparticles during first 4 hour conform best to Higuchi model and thereafter up to maximum 48 h the amount of drug released is negligible.

The Nafion 117 membrane was doped with SiO2 particles by sol-gel reaction.The reaction conditions to minimize leaching were investigated by using full factorial design of experiment. The results from the full factorial analysis indicated that the lowest amount of leaching takes place at 60oC without addition of acid and swelling of membranes prior to the reaction. The membranes, prepared at optimum reaction conditions, were characterized using differential scanning calorimetry (DSC), and for water uptake, ion exchange capacity, and cell performance.The water uptake of Nafion/SiO2 membrane with 7% of doping level increased up to 44% that is 26% higher than that of the pure Nafion membrane. The same trend was obtained for proton exchange capacity. DSC Measurements for modified samples showed an increase in Tg as compared to unmodified sample. Fuel cell test was carried out at 70oC and 110oC. At 110oC the modified membrane with 7 wt% of SiO2 showed improved fuel cell performance compared to the pure Nafion. For instance, at 200 mA/cm2 the voltage gained by composite membrane was twice higher than that of the pure Nafion.

Afinite element model is developed for simulation of the curing process of a thick axisymmetric rubber article reinforced by metal plates during the molding and cooling stages. The model consists of the heat transfer equa- tion and a newly developed kinetics model for the determination of the state of cure in the rubber. The latter is based on the modification of the well-known Kamal-Sourour model. The thermal contact of the rubber with metallic surfaces (inserts and molds) and the variation of the thermal properties (conductivity and specific heat) with temperature and state-of-cure are taken into consideration. The ABAQUS code is used in conjunction with an in-house developed user subroutine to solve the governing equations. Having compared temperature profile and variation of the state-of-cure with experimentally measured data, the accuracy and applicability of the model is confirmed. It is also shown that this model can be successfully used for the optimization of curing process which gives rise to reduction of the molding time.

The glass transition temperature of several PVAc (1)-b -poly(MA- co -MMA) (2) terpolymers with different fractions of methyl acrylate (MA) and methyl methacrylate (MMA) repeating units in random copolymer (block 2) were calculated with Barton, Kwei and topological equations. The calculation was on the basis of the correlation between the fraction of repeating units in random copolymers and theoretical equations and linear correlation of topological index of VAc, MA and MMA atomic structures in topological equations. The experimental values of the glass transition temperature of block 2 show a positive deviation from linearity in both Barton and Kwei theoretically calculated values. Therefore, agreement between the theoretical and experimental values were reached with summation of the effects of sequence distributions in random copolymer (R, calculated with1H NMR and statistical methods) to the linear theoretical data in Barton equation and the effect of interactions between the copolymer chains in Kwei equation (q=14.9). The glass transition temperature of 308 K was calculated for PVAc block with topological equation and it was near to the experimental value (310 K). Furthermore, the calculated glass transition temperatures of the block 2 with linear method were considerably close to the experimentally obtained data and increased with mole fraction of MMA in random copolymer.

Cross-linked polymeric organogels have attracted much attention in recent years. Most synthesized organogels are based on low molecular weight or denderitic materials. The study focuses on the preparation of an alcohol absorbent organogel based on 2-acrylamido-2-methylpropane sulphonic acid (AMPS) through cross-linking polymerization. Polyethylene glycol diacrylate-400 and ammonium persulphate were used as crosslinker and thermal initiator, respectively.Neutralization of acid groups increases swelling in superabsorbents. In this study, the effect of neutralization degree (N.D) on alcogel swelling was studied. The absorbency in alcohols and water are unexpectedly reduced with increased N.D. Also, the effect of N.D on thermal, mechanical and rheological properties was investigated, and found that increase in N.D leads to increased glass transition temperature, thermal stability and storage modulus.

Atechnical feasibility study has been conducted on production of nano- and micro-fibrils from nylon 6/polypropylene grafted with maleic anhydride/ polypropylene blended films. Fibrils are prepared in four consecutive steps.In the first step the polymers melt blended in an extruder with and without compatibilizers to produce chips; in the second step films are extruded from polymer blends chips, in the third step films are cold drawn with different draw ratios at room temperature and in the forth step fibrils are extracted by Soxhlet extraction with formic acid as solvent for nylon 6. The films and fibrils were examined by scanning electron microscope and FTIR spectroscopy. It is found that the polypropylene dispersed phase deforms and coalesces into elongated fibrils during drawing operation. The fibrils’ diameters in the blends containing compatibilizer are more uniform and are smaller than those from films without compatibilizers. The thinnest polypropylene fibril observed has a diameter around 300 nm with the aspect ratio above 150. The stress-elongation curves show three distinctive regions, elastic, yield and hardening-leading to breakage. The elastic region is short and follows by necking and yield, i.e., elongation without increase in load. The hardening region is accompanied by the increase in the slope. The deformations of the polypropylene particles are noticed during the last regions of the extension; the fibril deformations seem to be more severe during breakage.

MgCl2/C2H5OH adducts with constant relative ratio of 1/3 were prepared and kept at 120oC for different lengths of times of 5, 10, 20, 30, 50, 90, 120 and 220 h. Then the samples were quenched and analyzed by XRD and BET. No meaningful changes were observed in the specific surface area of the samples, while XRD spectra showed 3 peaks at 2q<15o for samples kept at 120oC for 5 h. These 3 peaks were gradually replaced by a single peak for samples kept at 120oC for 120 h and beyond. Dealcoholation of the samples caused a dramatic change in specific surface area from 3.6 m2/g to 284.7 m2/g. Also XRD indicated that the peak at 2q<15o totally vanished and it was replaced by a weak amorphous type of peak. Catalysts produced from these supports were used to polymerize ethylene.It was observed that with increasing the specific surface area of the supports and the time of polymerization, the activity of the catalysts was enhanced dramatically.