Fracture behaviour of polypropylene/glass bead elastomer composites by using the essential work-of-fracture method

The plane-stress static fracture response of blends composed of isotactic polypropylene glass beads (GBs) and an elastomer of styrene/ethylene–butylene/styrene type (SEBS) in both the ungrafted state and the grafted state with maleic acid anhydride (SEBS-g-MA) was studied at room temperature and v=1 mm min-1 cross-head speed. The volume fraction of GBs was kept constant (10 vol%) whereas that of the elastomer was set for 5 and 20 vol%, respectively. Deeply double edge-notched specimens of different ligaments were cut from pressed sheets of about 1 mm thickness and subjected to tensile tests at ambient temperature. The development of the plastic and process zone was studied in situ, i.e., during loading of the specimens, by light microscopy and infrared thermography. From the specific work of fracture versus ligament length plots, the essential and non-essential work of fracture components were determined. It was established that the essential work-of-fracture approach works well for these hybrid composites. The specific essential work of fracture, we, increased with increasing amount of the rubbery modifier but depended on its type. Grafting changed the morphology of the composites (SEBS-g-MA covered the GBs, whereas SEBS was present as an additional dispersed phase) and affected both the essential (slightly) and the non-essential or plastic work (considerably) terms. It was established that SEBS-g-MA is a less efficient toughener than SEBS because of the substantial differences in the related failure modes. © 1998 Chapman & Hall