Structure-Property Relations in Visbroken(Peroxide Treated)Impact Polypropylene Copolymers

摘要

Impact polypropylene(PP)copolymer(reactor blend)or a post-reactor blend of PP and ethylene-propylene rubber(EPR),is an immisible two-phase system consisting of PP as a matrix and EPR as a dispersed phase.When the amount and the molecular weight of EPR in such a blend exceed certain limits,then visbreaking of such a blend leads to an unusual melt Theological behavior-namely,a viscosity up-turn at low frequencies as seen in the dynamic measurements of the molten polymer.We attribute this unusual behavior to the formation of an "interacting network structure" between the two immisible phases via grafted molecules created during the visbreaking process.This melt network structure is carried over into the solid state as evidenced from the optical micrographs of the isothermally crystallized samples.The control of this network structure is important because it affects such properties as stiffness,impact strength and bruise resistance.This paper describes the relation between the extent of viscosity up-turn with the impact resistance and flex modulus of the injection molded samples.