Iranian Journal of Polymer Science and Technology
Year:2003 | Volume:16 | Issue:4 (ISSUE NO. 66)|Papers Count:7

In production of nylon 6 filament yarns several parameters of the drawing operation were changed and the properties of yarns were measured. Drawing parameters were those of time dependent and temperature dependent. The time dependent parameters include the number of wraps of yarn around the godet rolls, the length o drawing zone, the length of winding zone and the duration of the time that the yarn left on the packages. The temperature dependent parameters include the temperature of the drawing zone and the winding zone. Tensile strength, breaking elongation, initial modulus, the work of rapture and the yarn shrinkage were measured. Analysis of the results shows that the yarn properties were more sensitive to the temperature dependent parameters than the time dependent parameters. It was found that the yarn shrinkage can be reduced by increasing the temperature of the drawing and the winding zone and the increase in the duration of the time that yarn left on the packages. Using regression analysis, the relation between yarn shrinkage at 130°C and the temperature of the drawing and the winding zone were found to be linear, but the relation between shrinkage and the duration of the time that the yarn left on the packages were logarithmic. The results were explained by the current theories of the effect of time and temperature dependent parameters on the nylon 6 yam properties.

Retreaded tires have been introduced as one of the recycled rubber products, and the used carcass has been re-entered into the consuming cycle after being retreaded in a special manner. The separation of the tread from the used carcass depends on several working factors. In retreated tires, the role of cushion gum passes very effectively on adhesion of tread to carcass. In this study, the effect of carbon black and synthetic rubber blend on the properties of cushion gum and the adhesion of cured compound on a segment of tire carcass has been investigated. The results showed that the smaller particle size of carbon black and optimization usage of the BR in cushion gum, can improve the adhesion of tread to carcass.

Emulsion copolymerization of vinyl acetate-ethylene is carried out in a pressure reactor. Control of parameters such as pressure, temperature, monomer concentration, etc., is essential because they affect final properties of the copolymers. In emulsion polymerization of vinyl acetate-ethylene the aim is to obtain a polymer having substantial ethylene content (15-20 wt%) with high vinyl acetate conversion, Increasing emulsifier concentration based on a mix emulsifier with protective colloid increases the viscosity of emulsion medium which in turn reduces the diffusion of monomers. Consequently, vinyl acetate conversion and ethylene content were both decreased. Addition of buffer to the emulsion system maintained pH at a constant value which facilitated a constant rate of initiator decompositon during polymerization. As a result, monomer conversion and ethylene content of the copolymers were decreased. Glass transition temperature of the copolymers have been also investigated.

Poly (L-lactide) is a chiral crystalline and biodegradable polymer. High molecular weight poly (L-lactide) is preferred in the production of surgical implant for internal fixation. These polymers are usually synthesized from L-lactide (cyclic di-ester of L-lactic acid). For the production of poly (L-lactide), bulk polymerization is the preferred procedure, but high temperature of the reaction may cause the thermal degradation of polymer. Therefore, optimizing the temperature and the duration time of the reaction for synthesis of high molecular weight polymer are very important. It is found that polymerization time and maximum molecular weight increase with decreasing reaction temperature, but when the reaction temperature is above the melting point of polymers, degradation is more extensive and faster, therefore, when the reaction temperature is set under the melting point of polymer the maximum molecular weight and the polymerization time are slightly changed. Glass transition temperature (Tg) and melting point (Tm) increased with increasing molecular weight. Tg and Tm of obtained polymers are 65-69°C and 160-180°C, respectively.

In this work the dynamic rheological behavior of high-density polyethylene (HDPE) filled with carbon black (CB) has been studied in the melt state. Dynamic rheological properties in terms of storage modulus (G'), loss modulus (G") and loss factor (tan δ) have been studied for HDPE/CB composites. The frequency and temperature dependence of dynamic rheological properties of HDPE containing various concentrations and two grades of CB with different structures have been characterized. The effect of CB content (2.5-40 wt %) on the rheological properties has been investigated. These results show that when the CB concentration increases the storage and loss modulus increase and the loss factor decreases. The effect of temperature on the rheological properties has been studied and the results show that the storage and loss modulus decrease with increasing temperature, but the loss factor, in the region of low frequencies decreases with increasing temperature, while an inverse behavior is observed at high frequency region. This is an interesting point which is not reported up to the present time. The effects of CB structure on the rheological behavior of composites have been studied as well. These results show that the structure of carbon black has a significant effect on the rheological behavior of filled polymeric systems.

PVC in the form of emulsion resin is used in plastisol technology. Among its disadvantages: resin degradation during melt processing, high melt and gel temperature, resin's high viscosity in gel and melt temperature and low solubility can be mentioned. Copolymerization of vinyl chloride wih other monomers is a suitable route to modify such properties. Vinyl acetate comonomer improves many of the PVC problems. In this study copolymerization of vinyl chloride with 15.2 percent vinyl acetate was performed in a batch emulsion copolymerization system. Vinyl chloride content in both gas and liquid phase in the reactor, pressure variation and the effect of initiation on the reaction kinetics were investigated. Chemical structure and copolymer composition were characterized by FTIR and NMR spectroscopy. K-Value of the copolymers which is related to molecular weight was determined by solution viscometry.