Toughness of neat, rubber modified and filled β-nucleated polypropylene:: From fundamentals to applications

This review highlights several aspects of the toughness of beta-nucleated polypropylene (PP). The focus is on dynamic fracture properties, a topic which is largely documented in the literature. The role of intrinsic parameters like molecular weight, polydispersity and matrix randomization has been discussed, that of extrinsic factors like stress-state, processing conditions, test speed and temperature illustrated. Under defined conditions, the toughness is also defined by the content and spatial distribution of the beta-nucleating agent. The increase in fracture resistance is more pronounced in PP homopolymers than in random or rubber-modified copolymers. In the case of sequential copolymers, the molecular architecture inhibits a maximization of the amount of beta-phase; in that of heterophasic systems, the rubber phase mainly controls the fracture behavior. The performance of beta-nucleated PP has been explained in terms of smaller spherulitic size, lower packing density and favorable lamellar arrangement of the beta-modification which induce a higher mobility of both crystalline and amorphous phases. The damage process is accompanied by numerous microvoids, the development of which has been utilized for breathable films. Other interesting application segments are fibers, glass-fiber reinforced PP, thermoformable grades and piping systems.