| An analysis is made on the effects of rubber particle size on the mechanical properties and deformation mechanisms of transparent polyvinyl chloride (PVC) blends containing core-shell methyl methacrylate-butadiene-styrene (MBS) impact modifiers. The critical interparticle distance was found not to be the criterion for the brittle-ductile transition in these blends. TEM studies on blends with a bimodal distribution of particle sizes show that in the whitened zone of Izod specimens the larger rubber particles cavitate and expand on yielding, while the smaller particles remain intact. However, Izod test results show that monodisperse small MBS rubber particles can toughen the PVC matrix very effectively, especially at low temperatures and at low rubber concentrations, where they perform better than the larger particles. In Izod tests carried out on PVC blends containing10phr of MBS, the ductile brittle (DB) transition temperature shifts upwards from～10℃to～30℃with increasing particle size. The deformation mechanisms responsible for these effects are discussed.Core-shell structured poly (butadiene-graft-styrene)(PB-g-PS) particles were synthesized by emulsion grafting polymerization. The core-shell particles were designed with similar grafting degree but different internal structure. Then the core-shell particles were blended with polystyrene (PS). From transmission electron microscope (TEM) photographs, it could be found that three different internal structure particles:rarely sub-inclusion, a large number of small sub-inclusions and large scale sub-inclusions were realized. It was also found that PB-g-PS with the large scale sub-inclusions showed the slight aggregation of rubber particles in the matrix. The dynamic mechanical analysis (DMA) showed that core-shell particles with a large number of small sub-inclusions had the lowest glass transition temperature (Tg). It was found that this microstructure increased the effective volume fraction of the rubber phase with a result of improving the toughness of modified polystyrene, and the large scale sub-inclusions in the core contributed to higher impact strength of PS/PB-g-PS blends. |
