Preparation, Structure And Properties Of HIPS/HVPBR TPV And HIPS/WSBRP TPE

Thermoplastic vulcanizate (TPV) based on high impact polystyrene (HIPS)/high vinyl polybutadiene rubber (HVPBR) composites were prepared by dynamic vulcanization. The mechanical properties, morphology, morphology evolution of the rubber phase and dynamic viscoelastic behavior such as compression set and its reversibility, Payne effect and Mullins effect and its reversibility of TPV were researched systematically. The influences of the ratio of rubber and plastic, compatibilizer and reinforcing agents on the properties of TPV were investigated. The thermoplastic elastomers (TPEs) based on HIPS/waste styrene butadiene rubber powder (WSBRP) and (HDPE)/waste ethylene-propylene-diene monomer vulcanizate powder (WEPDMP) were prepared by melt-compounding. The mechanical properties, morphology, and Mullins effect of HIPS/WSBRP TPE were researched systematically. The influences of the ratio of rubber and plastic, compatibilizer and plasticizer on the properties of the TPE were investigated. Material with positive temperature coefficient (PTC) was obtained by adding carbon nanotubes (CNTs) to HDPE/WEPDMP composite. The PTC and volume expansivity behaviors and the CNTs conductive network of the composite were also investigated. The results were as follows:(1) TPV based on HIPS/HVPBR blends were prepared by dynamic vulcanization, and the influences of blending ratio and heat-treatment temperature on the reversible recovery of compression set, together with the mechanism and model construction of the reversible recovery of the TPV, were investigated systematically. Increasing the HVPBR content in TPV and increasing heat-treatment temperature would lead to the fast recovery of compression set; moreover, the TPV had fully reversible deformation ability when the heat-treatment temperature was close to the Tg of HIPS. The reversible recovery mechanism was discussed based on the characteristics of the reversible recovery curves of compression set. A mathematical model to explain the reversible recovery of compression set was established.(2) Reseach of compatibilization of the HIPS/HVPBR TPV showed that the styrene-butadiene-styrene (SBS) block copolymer had an excellent compatibilization effect on the dynamically vulcanized HIPS/HVPBR TPV. Compared with those of HIPS/HVPBR TPV, the tensile strength, elongation at break and tearing strength of HIPS/HVPBR composite with 12 phr SBS incorporation were improved by about 163%,312% and 67%, respectively. Morphology studies showed that the interface interaction of the TPVs was enhanced and the particle sizes of the dispersed phase were decreased with the incorporation of SBS compatibilizer.(3) The Phase morphology evolution was researched by field emission scanning electron microscope. Experimental results indicated that the rubber phase was fragmented continuously during the dynamic vulcanization and was evolved into spherical particles with the diameters of 3-5 μm at 6 min (t90). Compared with that of HIPS/HVPBR TPV, the diameters of HVPBR particles in HIPS/SBS/HVPBR TPV were much smaller and the surfaces were much rougher. The microstructure images of HIPS/SBS/HVPBR TPV indicated that large amounts of clutter-like lamellar structure were formed in the surface of the rubber particles during the dynamic vulcanization. It would inevitably lead to the remarkably increased interface area and the enhanced interface interaction between the crosslinked HVPBR rubber and HIPS resin.(4) Mullins effect under cyclic loading-unloading tests, in uniaxial tension and uniaxial compression, together with its reversibility of HIPS/SBS/HVPBR TPV were investigated systematically. Experimental results indicated that an obvious stress softening phenomenon could be observed obviously in the uniaxial loading-unloading cycles in tension and compression tests. The maximum stress during loading-unloading cycle could recover partially; moreover, the maximum stress recovery ability could be remarkably enhanced by increasing heat treatment temperature. Increasing the strain, the storage modulus of the TPV deceased greatly and showed the Payne effect. The Payne effect of the TPV would be weakened by the decrease of the scanning frequency and the increase of the scanning temperature.(5) The blends based on HIPS/WSBRP were prepared by melt-compounding. In order to improve the properties, aromatic oil (AO) and SBS were added into the HIPS matrix. The results showed that the incorporation of the SBS and AO the leading to the obviously increasing of elongation at break of the blends. The fracture surface morphology of the HIPS/SBS/AO/WSBRP TPE was smooth, indicating the strong deformation recovery ability. Mullins effect results showed that the HIIS/SBS/AO/WSBRP TPE had relatively lower residual deformation and internal friction loss than those of HIPS/WSBRP composite, indicating the improvement of elastic reversibility.(6) Composites based on HDPE/WEPDMP/CNTs were prepared by melt-compounding. The influence of CNTs dosage on the PTC effect of the composites was researched. The mechanism of the PTC behavior was researched based on the characterization of volume expansivity and the CNTs conductive network in composites. The results showed that the CNTs in matrix were intertwined and formed a conductive network. Increasing temperature to the melting region of HDPE matrix, the rapidly volume expansion of composites led to the occurrence of PTC behavior. The PTC behavior of the conductive composites can be predicted according to the quantitative characterization of volume expansivity.