DEBONDING AND FRACTURE OF PARTICULATE-FILLED ISOTACTIC POLYPROPYLENE

Experimental data on particulate-filled polypropylene rupture are pres ented, with discussion and explanation of the regularities found. The systems studied are characterized by ductile properties of a semi-crys talline matrix and a low level of interfacial interaction. Polypropyle ne as a host and aluminum hydroxide particles, without or with anti-ad hesive treatment, were used. Two concentration regions of different de bonding micromechanisms were found. At low filler fraction (<15-20 vol . %) particles debond independently and completely at the initial stag es of drawing, and a microhomogeneous flow mechanism takes place. Abov e a critical filler content, debonding proceeds in a correlated way wi th the formation of narrow craze-like deformation zones transverse to the stretching axes. These zones screen new debondings in their neighb orhoods, more or less efficiently, dependent upon filler fraction and, hence, the porosity inside crazes and the level of interfacial intera ction. Whether microhomogeneous or craze-like mechanisms occur essenti ally determines the regularities of further deformation and fracture: localized or macrohomogeneous now, ductile or quasi-brittle fracture, the drop or the rise of ultimate strains with increase of particle dia meters. A theoretical description of the transition between microhomog eneous and craze-like mechanisms is proposed.