دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و سوم شماره 2 (پیاپی 106، خرداد و تیر 1389)

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

The Nafion 117 membrane was doped with SiO2 particles by sol-gel reaction.The reaction conditions to minimize leaching were investigated by usingfull factorial design of experiment. The results from the full factorial analysisindicated that the lowest amount of leaching takes place at 60oC without additionof acid and swelling of membranes prior to the reaction. The membranes, preparedat optimum reaction conditions, were characterized using differential scanningcalorimetry (DSC), and for water uptake, ion exchange capacity, and cell performance.The water uptake of Nafion/SiO2 membrane with 7% of doping level increasedup to 44% that is 26% higher than that of the pure Nafion membrane. The same trendwas obtained for proton exchange capacity. DSC Measurements for modified samplesshowed an increase in Tg as compared to unmodified sample. Fuel cell test wascarried out at 70oC and 110oC. At 110oC the modified membrane with 7 wt% of SiO2showed improved fuel cell performance compared to the pure Nafion. For instance,at 200 mA/cm2 the voltage gained by composite membrane was twice higher thanthat of the pure Nafion.

Afinite element model is developed for simulation of the curing process ofa thick axisymmetric rubber article reinforced by metal plates during themolding and cooling stages. The model consists of the heat transfer equationand a newly developed kinetics model for the determination of the state of curein 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 andmolds) and the variation of the thermal properties (conductivity and specific heat)with temperature and state-of-cure are taken into consideration. The ABAQUS codeis used in conjunction with an in-house developed user subroutine to solve the governingequations. Having compared temperature profile and variation of the state-ofcurewith experimentally measured data, the accuracy and applicability of the modelis confirmed. It is also shown that this model can be successfully used for the optimizationof 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 methylmethacrylate (MMA) repeating units in random copolymer (block 2) werecalculated with Barton, Kwei and topological equations. The calculation was on thebasis of the correlation between the fraction of repeating units in random copolymersand theoretical equations and linear correlation of topological index of VAc, MA andMMA atomic structures in topological equations. The experimental values of theglass transition temperature of block 2 show a positive deviation from linearity inboth Barton and Kwei theoretically calculated values. Therefore, agreement betweenthe theoretical and experimental values were reached with summation of the effectsof sequence distributions in random copolymer (R, calculated with 1H NMR and statisticalmethods) to the linear theoretical data in Barton equation and the effect ofinteractions between the copolymer chains in Kwei equation (q = 14.9). The glasstransition temperature of 308 K was calculated for PVAc block with topologicalequation and it was near to the experimental value (310 K). Furthermore, the calculatedglass transition temperatures of the block 2 with linear method were considerablyclose to the experimentally obtained data and increased with mole fraction ofMMA in random copolymer.

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

Atechnical feasibility study has been conducted on production of nano- andmicro-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 compatibilizersto 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 andin the forth step fibrils are extracted by Soxhlet extraction with formic acid as solventfor nylon 6. The films and fibrils were examined by scanning electron microscope andFTIR spectroscopy. It is found that the polypropylene dispersed phase deforms and coalescesinto elongated fibrils during drawing operation. The fibrils’ diameters in theblends containing compatibilizer are more uniform and are smaller than those from filmswithout compatibilizers. The thinnest polypropylene fibril observed has a diameteraround 300 nm with the aspect ratio above 150. The stress-elongation curves show threedistinctive regions, elastic, yield and hardening-leading to breakage. The elastic regionis short and follows by necking and yield, i.e., elongation without increase in load. Thehardening region is accompanied by the increase in the slope. The deformations of thepolypropylene particles are noticed during the last regions of the extension; the fibrildeformations seem to be more severe during breakage.

MgCl2/C2H5OH adducts with constant relative ratio of 1/3 were preparedand 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 byXRD and BET. No meaningful changes were observed in the specific surface area ofthe samples, while XRD spectra showed 3 peaks at 2θ<15o for samples kept at 120oCfor 5 h. These 3 peaks were gradually replaced by a single peak for samples kept at120oC for 120 h and beyond. Dealcoholation of the samples caused a dramaticchange in specific surface area from 3.6 m2/g to 284.7 m2/g. Also XRD indicatedthat the peak at 2θ<15o totally vanished and it was replaced by a weak amorphoustype of peak. Catalysts produced from these supports were used to polymerize ethylene.It was observed that with increasing the specific surface area of the supportsand the time of polymerization, the activity of the catalysts was enhanced dramatically.