Deformation and fracture behavior of pp/ash composites under different loading conditions

M. PAGNUSSAT, M. MONTOYA, M.J. ABAD, L. BARRAL LOSADA, C. BERNAL

Buenos Aires, Argentina

Conferencia; COMAT 2005; 2005

In this work, deformation and fracture behavior of polypropylene filled with organic ash under different loading conditions was investigated. The morphology of PP reinforced with ash was found to be composed of ash particles dispersed in the PP matrix. In tensile tests, all PP samples displayed ductile behavior characterized by a decrease of load after yield (strain softening) followed by a plateau. PP/ash composites displayed less ductility than pure PP as a result of the poor interfacial adhesion between both phases and the subsequent particle debonding. An increasing trend of Young´s modulus with filler content was observed whereas yield strength, yield strain and failure strain were found to decrease probably due to the debonding between PP and ash. In quasi-static fracture tests, neat polypropylene exhibited non linear load-displacement behavior. On the contrary, the composite with 10 wt.% of ash displayed completely stable crack growth. The quasi-static resistance to crack initiation was characterized by the critical stress intensity factor, Kc. The composite displayed a lower value of resistance to crack initiation than pure polypropylene, probably due to the presence of critical-size flaws derived from debonding of second-phase particles that induced premature failure. However, the incorporation of ash into PP led to a significant improvement in the crack propagation resistance as more energy was absorbed by the composite specimens to fracture. On the other hand, under impact fracture both neat PP and the composite assayed exhibited completely brittle behavior. Therefore, the critical energy release rate was adopted to characterize fracture behavior in this condition. The impact fracture initiation parameter was also higher for neat PP than for the 10 wt.% ash composite. As a result of the poor interfacial adhesion between PP and ash, subsequent particle debonding occurred and critical-size flaws were created inducing premature failure. In addition, matrix stretching could not develop under impact loads.