DUCTILITY OF FILLED POLYMERS

The ductility of a calcium carbonate-filled amorphous copolyester PETG in a uniaxial tensile test was examined as a function of the filler v olume fraction. A ductile-to-quasi-brittle transition occurred as the volume fraction of filler increased. This transition was from propagat ion of a stable neck through the entire gauge length of the specimen t o fracture in the neck without propagation. The draw stress (lower yie ld stress) did not depend on the filler content and was equal to the d raw stress of the unfilled polymer. It was therefore possible to use a simple model to predict the dependence of the fracture strain on the filler volume fraction. It was proposed that when the fracture strain decreases to the draw strain of the polymer the fracture mechanism cha nges and the fracture strain drops sharply. The critical filler conten t at which the fracture mode changes is determined primarily by the de gree of strain-hardening of the polymer. (C) 1994 John Wiley & Sons, I nc.