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Rheological properties and morphology of high impact polystyrene and styrene/ethylene/buthylene/styrene blends

The multiphases polymer systems, thermoplastic materials modified with thermoplastic elastomers are intensively studied to developed the new engineering materials with new or improved properties. Blends of high impact polystyrene (PS-HI) and styrene /ethylene/buthylene/styrene block copolymer (SEBS) are investigated to determine the effect of rubber on the polymer properties. In this paper the processing behaviour of PS-HI +SEBS blends are analysed and primary as well as secondary, viscoelastic functions of the processed blends are obtained. Rheologycal behaviour of the blends during processing was followed by measuring the torque, out put and melt pressure in twin extruder Haake Record 90.The viscoelastic functions, storage modulus (E') loss modulus (E'') and loss tangent (tg d) were obtained by Dynamic Mechanical Analyser 983, TA Instruments. The creep relaxation measurements were obtained in creep fatigue regime at temperatures 25, 35, 45, 55 and 65 oC. Processing and viscoelastic behaviour was correlated with the morphology of the blends studied by scanning electron microscopy. The results show that rheologycal behaviour in blends processability as well as their viscoelastic functions and their morphology depend on the copolymers and blends compositions, number of phases and phase content. The influence of SEBS content on the increase of the apparent viscosity is observed above 40 % weight of SEBS copolymer in the blends. The torque value of the blends is not significant increase with SEBS content below 70 % weight with respect to neat PS-HI. All samples have a single Tg of the hard phase. The storage modulus (E'), and the tg d of the hard phase decreased with increase of the soft phase. At the constant load the creep values of all examined samples increase and those of the creep modulus decrease over a period of time. The master curves were created for the reference temperature 25 oC. A phase separated microstructure is more pronounced in the PS-HI + SEBS blends. The rise in fracture energy with SEBS introduction occurs.

high impact polystyrene (PS-HI); styrene/ethylene/buthylene/styrene block copolymer (SEBS); PS-HI+SEBS blends rheological properties; processing; dynamic mechanical analysis; master curves; morphology.

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