engleski

Effect of Styrene/Ethylene/Buthylene/Styrene Block Copolymer on Dynamic Mechanical Behaviourand Processability of High Impact Polystyrene

Blends of high impact polystyrene (PS-HI) and styrene/ethylene/buthylene/styrene block copolymer (SEBS) are investigated to determine the effects of the rubber on the polymer properties. The processing behaviour of the PS-HI + SEBS blends are analyzed and the dynamic mechanical behaviour of the processed blends are examined. Rheological behaviour of prepared blends during processing was followed by measuring the torque, output and melt pressure in the twin extruder Haake Record 90. Dynamical mechanical analysis was performed in temperature range – 1500C to 1600C. The blends were also investigated in creep fatigue regime and relaxations were determined at temperatures 25, 35, 45, 55 and 650C. Master curves for the reference temperature 250C were created using time-temperature superposition principle. With increasing SEBS content there is not significant increase of the torque value for the blends below rubber content of 70 % weight with respect to neat PS-HI. The influence of SEBS content on the increase of the apparent viscosity is observed above 40 % weight of SEBS. The curves of storage modulus E’ , loss modulus E’ ’ and loss tangent tan vs. temperature are affected by lowering of the hard phase PS content, tan of the soft phase ethylene/buthylene (EB) increases, while the tan for the PS hard phase and storage modulus decrease. All samples have a single glass transition temperature Tg of the hard phase. At the constant load the creep values of PS-HI, SEBS and PS-HI + SEBS blends increase and those of the creep modulus decrease over a period of time for all samples examined. These effects are more pronounced in samples with lower content of the hard phase PS. The energy-time-temperature correspondence principle was applied to create master curves for the reference temperature 250C for the creep modulus of PS-HI, SEBS and PS-HI + SEBS blends. Microscopic morphology results confirm the main conclusions obtained from the processing and DMA behaviour of the blends. A phase separated microstructure is more pronounced in the PS-HI + SEBS blends. The rise in fracture energy with SEBS introduction appears in the SEM microphotographies in whiteness of the photographs, first as white crests and in PS-HI+SEBS blend with higher SEBS content as globular structures.

High impact polystyrene (PSHI) . Styrene/ethylene/buthylene/styrene (SEBS) .

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