Preparation, Structureand Properties Of SBR/HIPS Thermoplastic Vulcanizates

Thermoplastic vulcanizates (TPVs) based on styrene-butadiene rubber (SBR)/high impact polystyrene (HIPS) blends were prepared by dynamic vulcanization, the influence of composition, preparing technique on the morphology and mechanical properties of SBR/HIPS TPVs were researched, the rheological behavior, dynamic viscoelastic behavior, stress relaxation, the remilling and thermal aging influence on mechanical properties of the prepared SBR/HIPS TPVs were also investigated systematically. The results were as follows:(1) A series of TPVs were prepared by changing the composition and species of raw materials, and processing techniques, the mechanical properties and microstructure were studied. Considering the proper elasticity, strength and low hardness, the weight ratio of SBR/HIPS blend should range from 70/30 to 60/40.(2) The influence of EVA and aromatic oil content on the elasticity, tension set at break, hardness and mechanical properties were researched. The results showed that the addition of EVA in the matrix could improve the operability of dynamic vulcanization process significantly. For the SBR/EVA/HIPS TPV where the aromatic oil was filled in the resin phase, the shore A hardness decreased obviously, however, tensile set at break only decreased slightly. With the increase of aromatic oil content in the resin phase of TPVs, the velocity of stress relaxation increased.(3) The mechanical properties of TPVs were markedly enhanced by filling carbon black (CB) in SBR phase. With the increase of CB content, the velocity of stress relaxation decreased. A rubber process analyzer reveals that the incorporation of EVA in the TPVs led to the decrease of storage modulus and the obvious increase of tanδwith the incerasing frequency. Comparing with TPV without CB filling, the storage modulus and loss modulus of TPVs filled with CB decreased, while the loss factor (tanδ) did not change significantly. Panye effect could be observed for all the TPVs.(4) SBS had a good compatibilization effect on the SBR/EVA/HIPS TPVs. The tensile strength went through a maximum value at a compatibilizer resin content of 6 phr, and the elongation at break and tear strength increased with increasing SBS content. A rubber process analyzer reveals that the storage modulus increased with increasing frequency, however, the incorporation of SBS in the TPVs led to the decrease of storage modulus. The tanδdecreased continuously with increasing frequency.(5) As determined by capillary rheometer, the melt rheological behavior of SBR/HIPS, SBR/EVA/HIPS and SBR/EVA/aromatic oil/HIPS TPVs showed that the apparent viscosity decreased obviously with the increase of shear rate, indicating the obvious pseudoplastic behavior. At low shear rate, the apparent viscosity of these TPVs was considerably higher than that of neat HIPS and decreased with the increase of HIPS concentration. At high shear rate, the apparent viscosity of SBR/HIPS TPVs was very close to that of neat HIPS, indicating the well formability at high shear rate. Filling aromatic oil in the resin phase, the flowability of TPVs melt could be improved significantly.(6) The dynamic viscoelastic behavior of SBR/EVA/HIPS, SBR/EVA/aromatic oil/HIPS and SBR/CB/EVA/HIPS TPVs showed that with the increase of scanning frequency, it was hard for the mobility of chain segments to keep up with the increasing frequency, TPV showed the higher rigidity, the storage modulus and the lower loss modulus and the tanδ. With the addition of EVA and aromatic oil in the resin phase of TPVs, the mobility of chain segments was increased, leading to the decreased friction among macromolecule chains and storage modulus, however, tanδhad almost no change. Loss peak was appeared near the transition temperature (Tg) of HIPS, the presence of aromatic oil enhance the movement of chain segments, leading to the slightly decrease of Tg.(7) The stress relaxation of SBR/EVA/HIPS, SBR/EVA/aromatic oil/HIPS and SBR/CB/EVA/HIPS TPVs showed that the stress relaxation of TPVs in our study was mainly determined by the resin phase, the crosslinked SBR particles dispersed in the HIPS resin had less effect on the stress relaxation. With the addition of EVA and aromatic oil in the resin phase, the friction among macromolecules was decreased, the segmental mobility of HIPS was significantly enhanced, resulting in the decreased velocity of stress relaxation.(8) The influence of remilling times and thermal aging time on the mechanical properties and microstructures of the SBR/EVA/HIPS TPVs were studied. The results showed that remilling times had less influences on TPV's properties, indicating the excellent remilling properties of TPVs. The thermal aging led to the increase of tensile strength and decrease of elongation of TPVs.