دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و یکم شماره 3 (پیاپی 95، امرداد و شهریور 1387)

The variations in plastic injection molding process may lead to the inconsistency of molded part's dimensions. Furthermore, due to the speed of production as well as post-shrinkage of molded parts make the control of process difficult and give inaccurate molded parts. The objective of this research is to predict the dimensions of injection molded parts on the basis of cavity pressure during the molding process. At the first stage of experimentations, the variations of molding process were determined under a base setting condition by using cavity pressure measurement approach. At the second stage, the effects of molding parameters on the cavity pressure profile as well as part's dimensions were studied. Following, an artificial neural-network model was implemented capable of predicting the molded part's dimensions based on the cavity pressure. To increase the efficiency of proposed model, three features of the cavity pressure trace encompassing maximum cavity pressure, cavity pressure-time integral value, as well as time to reach the maximum pressure were selected as neural-network inputs.

With respect to the physical and mechanical limited qualities of bitumen, it benefits from certain specificability in application and its life service. Polymers as the most important modifiers of bitumen are applied to it in order to improve its functional efficiency. Among various polymers, styrene-butadiene- styrene (SBS) is the best modifier of the bitumen. In this work, SBS polymer as one of the modifiers of elastomeric thermoplastics with different weight percentages (2% to 5%) have been mixed with bitumen (60/70) of Isfahan Refinary and its effect on different properties of the bitumen for example penetration index, softening point, Frass breaking point and reduction in weight perecentage has been studied. Furthermore, in this paper, the modified bitumen property on performance grade is the preferred category. Classification of modified bitumen based on performance grade makes it possible to provide perfect bitumen pattern in different climates.

Modification of the mechanical properties of silicone rubber were considered for drug delivery systems by using high-energy electron beam (E-beam). In this research work, two different medical grades of silicone rubbers were used to prepare matrices containing 10wt% progesterone with 2 mm thickness and irradiated with E-beam at dose range of 25 up to 200 kGy. Then, the mechanical properties as well as in vitro drug release from matrices were investigated. It was observed that the mechanical properties of matrices increased initially as a function of irradiation dose due to increasing crosslink density and reduction of the molecular weight between the crosslinks and eventually they were leveled off. Also, there was no significant difference in the progesterone release by increasing the irradiation dose. Progesterone crystal modification was not observed during E-beam crosslinking process.

Since reusing waste tire as a cheap filler is considerably high, in this study, recycled rubber to replace NR/BR is used up to 15 phr and the positive and negative aspects of the rubber powder and reclaimed rubber in the physical, dynamical and processing properties are evaluated. The results showed that in the presence of recycled rubber, the cure rate, crack growth resistance, tear strength and processability of compound are improved and the tensile strength and resilience are slightly decreased. Moreover, the presence of recycled rubber up to 10 phr has no notable effect on crosslink content and modulus. The use of recycled rubber (specially reclaimed rubber), makes noticeable improvement on cure rate which because of the necessity to lower expenes there is no need to use cure ingredients such as acceleratorsor ZnO.

In this research work with the aid of Tagouchi experimental design and rawing of interaction curves with Minitab software, the best rotor speed and dump temperature of mixing for physico-mechanical and rheological properties of the rubber compound with three mixing steps was obtained. Moreover by plotting the mean curves in Excel worksheet, the dependency of properties on rotor speed, dump temperature and mixing energy were analyzed. The Results showed that dispersion was improved with increasing rotor speed and dump temperature at the lower total time. The best dispersion occurred at the highest dump temperature and the rotor speed in the second stage. We attributed better dispersion to lower filler-filler interaction, because of the mixing process performed at higher temperatures when we used higher rotor speeds at higher dump temperatures. Effect of rotor speed and dump temperature on tension properties were negligible. However, the higher dump temperature had negative effect on tear resistance, whereas, the high rotor speed had positive effect. The same results were observed for die swell while the governed mechanism on these properties was studied as well.

The polymeric and non-polymeric petrochemical wastes are environmentally unfavorable materials. We have to found a way to reuse these wastes in a safe manner. In styrene-butadiene rubber (SBR) production plant two major wastes are produced one is a fine rubber powder and the other is recycled N-methyl pyrrolidone (NMP). In high-density polyethylene (HDPE) production plant also a low molecular weight polymer waste is produced which does not degrade in environment easily. On the other hand, bitumen is usually blended with thermoplastics, rubbers and an oil to produce polymermodified bitumens. Effect of SBR, PE and NMP wastes on vacuum bottom residue of crude oil distillation was investigated. The results of penetration, softening point and Frass tests revealed the advantages of SBR and PE wastes at high temperatures and suggest NMP waste as a good bitumen extender. The results of the Marshal test on the prepared polymer-modified hot-mix asphalt of the optimum formulation highlight the superiority of its strength and its lower flow as compared with those of standard 60/70 penetration grade bitumen.

MCM-41 is one of the groups of mesoporous materials that have wide applications as adsorbents, ion exchangers and catalyst supports. In this work spherical and rod-like MCM-41s were synthesized in homogeneous and heterogeneous reaction media, respectively. For synthesis of these materials the cationic surfactant cetyltrimethylammonium bromide (CTMABr) was used as template and tetraethylorthosilicate (TEOS) was used as the silica source. The polymerization process of the silica source was performed in basic and acidic media using ammonia or HCl as catalysts. BET (Brunauer-Emmett-Teller), FTIR, X-Ray diffraction and scanning electron microscopy analysis confirmed the structures of these synthesized materials. Finally a mechanism was proposed for the formation of these structures.

Lactide was synthesized by reverse polymerization of low molecular weight poly(lactic acid) with two different molecular weights:1500 and 2500. Two different lactide purification processes such as: recrystallization in ethyl acetate and washing the crude lactide with ether before recrystallization in ethyl acetate were evaluated. It has been demonstrated that increasing the molecular weight of poly(lactic acid) does not influence the production yield, melting point and optical rotation of lactide. The washing of crude lactide with ether and recrystallization in ethyl acetate can be carried out in a short period of time (within 1 day) at a high yield (35%) using less solvent. In contrast, the first purification method gives lower (11%) production yield by using higher amount of solvent at longer time. It is also found that the purification methods do not have any specific effect on the properties of lactide.

Natural rubber/fiber composites were prepared in a laboratory mixer using new and waste short nylon fiber by a one-step mixing process. Fiber loading and bonding agent effects on the microstructure and mechanical properties of the composites were studied. The cure characteristics of composites were investigated by using rheometer. Cure and scorching times of the composites decreased while maximum torques increased with increasing fiber loading. The mechanical properties of the composites improved with increasing the short fibers. The adhesion between the fiber and the rubber was enhanced by the addition of a dry bonding system consisting of resorcinol, hexamethylene tetramine and hydrated silica (HRH).