Fillers: their effect on the failure modes of plastics

Abstract

Thermoplastic polymers filled with rigid inorganic particles display higher values of Young’s modulus, better thermal stability, and lower wear under friction than do unfilled polymers. Unfortunately, fillers also lead to dramatic reductions in the fracture strain of the polymer [1] under tensile load and embrittlement. Some polymers, such as polytetra-fluoroethylene (PTFE, trade mark Teflon^®), yield uniformly. However, more usually we get non-uniform yielding with propagation of a neck through the entire length of a specimen as in polyethylene (PE) and polypropylene (PP). If a polymer yields with necking an increase in filler content leads to fracture during neck propagation, to quasibrittle fracture during formation of a neck and, finally, to true brittle fracture as illustrated by Figure 1. With brittle and quasibrittle failure modes fracture strain is roughly 100-fold lower than that of unfilled polymer.