Iranian Journal of Polymer Science and Technology
Year:2002 | Volume:14 | Issue:5 (ISSUE NO.55)|Papers Count:6

In Sioplas crosslinking of low density polyethylene, the effect of incorporation of ethylene vinyl acetate copolymer (EVA) on gel content, mechanical and thermal properties has been studied. It is found that both tensile strength and elongation at break were increased in crosslinked product. DSC and TGA thermograms show a reduction in the melting point and an uprise in the degradation temperature. Furthermore, the addition of EVA gave rise to higher amount of gel content and lower cure time at the same condition.

This research investigates the application of high-cis polybutadiene produced by Arak petrochemical company in the production of high impact polystyrene (HIPS). By using an industrial setup of polymerization as reference that has been applied for low-cis pulyhutadiene production, it was tried to produce a high-cis polybutadiene by gradual increase of its percentage of high-cis content in six polymerization steps. A constant temperature was selected for all of the reactions. The reactions were accomplished by mass polymerization without using peroxides initiators and 5% ethyl benzene as solvent. In all the trend in the conversion determination of parameters such as: gel content, swelling index and molecular weight. By comparing the results it seems that the direct (not gradual) polymerization instead of the Arak high-cis polybutadiene shows the least changes.

The present work tries to obtain a simple means of simultaneous measurement of steady shear viscosity and normal stress difference in polymer melts and high concentrated solutions. The task is performed by using a rotating rod viscometer. In the experiments the steady shear viscosity is obtained by the measurement of the torque and the normal stress difference obtained by measuring the free surface height developed due to the rod climbing (Weissenberg Effect).A one dimensional unsteady modeling of the nonlinear viscoelastic flow using Leonov model will enable us to obtain the time dependent torque and the free surface height at various shear rates for a given fluid. Hence, the device is calibrated for a known fluid, and by using the calibration curves and reading the torque and free surface height, the steady shear viscosity and the normal stress di1terence could be obtained for any fluid by using the obtained numerical simulation data.

Nitrile rubber, NBR, is one of the important elastomers in rubber industry. It has good mechanical properties and high resistance to nonpolar oils. These advantages and its good flexibility makes this elastomer useful in many areas of applications. The blending of this elastomer with phenolic resin, a low cost and high temperature resistance resin, offers different applications particularly in high temperature environment. They are, therefore, being used as a structural adhesive, ablators and heat shields. In this paper, The effects of phenolic novolack resin and its amount have been investigated on the thermal properties of nitrile elastomers. Results show that the increasing phenolic resin up to 65% shifted the Tg towards higher temperatures. The storage modulus increased and the amount of its variation over broad range of temperature is decreased. Thermal gravimetric analysis also showed the significant increase of thermal stability of these blends. By adding the phenolic resin, the coefficient of thermal conductivity (k) of phenolic-nitrile blends has increased, but the coefficient of thermal expansion (a) and heat capacity (Cp) are independent of the amount of phenolic resin.

Phenolic resin, a low cost and high temperature resistance resin offers different applications particularly for high temperature environment. It is necessary to compound this resin with other material due to its brittleness and high shrinkage. Nitrile rubber NBR, is one of the important polar elastomers in rubber industry. The blending of this elastomer with phenolic resin is one of the important methods of modification of phenolic resin properties. In this paper the effects of acrylonitrile (ACN) content of NBR from 33 to 50% have been investigated on the properties of these blends. DMTA and thermal gravimetric analysis shows that the mechanical and thermal properties of these blends increased significantly at high amount of ACN. It seems that a reactive compatibilization occurs at high amount of ACN. Results also show that by increasing the amount of ACN the thermal conductivity coefficient increases, but the thermal expansion coefficient decreases. This may be due to the increase polarity of these blends that increases along with ACN contents.

In this paper, a newly developed hybrid composites materials called GLALL has been investigated. The effect of aluminium in the GRP laminates under different loading conditions, such as tension, impact, transverse and torsional vibration has been studied. The torsional vibration test was conducted also at different temperatures. All the results were obtained and compared together and the conclusion was obviously shows that the presence of aluminium layer in fibre composite laminates would result in better toughness and ductility and hence better damage tolerance of composits materials besides the high strength and stiffness as well as lower density. Also the natural frequencies of GLALL beams and tubes were higher than GRP composites. Through its unique combination of properties, GLALL can be a strong candidate material for aircraft industries.