Temperature dependency of cavitation in impact copolymer polypropylene during stretching

Abstract Cavitation in the impact copolymer polypropylene (ICP) and its corresponding homo-isotactic polypropylene (homo-iPP) during stretching was investigated using ultra-small angle X-ray scattering technique. Different from the iPP showing a suppressed cavitation around yielding at high deformation temperature (Td), the ICP presented a more intensive cavitation at elevated Td. This unusual Td dependency of cavitation around yielding observed in ICP was suggested to be caused by the changes of the stability of the rubber particles dispersed in iPP matrix. The rubber particles exhibit a multi-phase core-shell structure which contains crystallizable polyethylene segments in the core layer, the amorphous polymer of ethylene-propylene random copolymer in the inner shell layer, and the crystallizable polypropylene segments in the outer shell layer. The softening and melting from the inner shell to the core and the outer shell took place as the Td increased. It can be envisaged that the fraction of unstable regions inside the rubber particles and the debonding between the iPP matrix and the dispersed phase gradually increased providing more nucleation sites for cavities at high Td, a more intensive cavitation was thus observed.