engleski

Effect of styrene/ethylene/buthylene/styrene block copolymer on dynamic mechanical behaviour and 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 -150 °C to 160 °C. The primary viscoelastic function were obtained. The blends were also investigated in creep fatique regime and relaxations were obtained at temperatures 25, 35, 45, 55 and 65°C. The master curves for the reference temperature 25°C were created by time temperature superposition principle. Processability and dynamic mechanical behaviour of PS-HI, SEBS and PS-HI+SEBS blends depend on the copolymer and blends composition, the phase content time and temperature. 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 copolymer in the blends. The curves of primary viscoelastic functions storage modulus (E’ ), loss modulus (E˝) and loss tangent (tgδ ) vs. temperature changes with the decreament of the hard phase PS content. The tgδ of the soft phase ethylene/buthylene (EB) increases, while the tgδ of the hard phase PS and storage modulus decrease. All samples have a single 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 examined samples. These effects are more pronounced in samples with lower content of the hard phase PS. The time temperature correspondence principle was applied to creat master curves for the reference temperature 25°C for the creep modulus of PS-HI, SEBS and PS-HI+SEBS blends. The microscopic morphology of the examined systems confirmed the main conclusions obtained in the analysis of 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 same micrographs in witnesses of the photopgraphs fast of white crests and in PS- HI+SEBS blends with higher SEBS content as globular structure.

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

Glavni autori: Tamara Holjevac Grgurić, Rek Vesna