CREEP AND PHYSICAL AGING OF INJECTION-MOLDED, FIBER-REINFORCED POLYPROPYLENE

Tensile creep data have been obtained at 23 degrees C as a function of physical age from test pieces of glass fiber reinforced polypropylene cut from injection molded square plaques in directions parallel and t ransverse to the flow direction, Smaller compliances were measured for loading parallel to the flow than for loading in the perpendicular di rection, reflecting the preferential alignment of the fibers with the flow. Two creep functions have been used to model the creep behavior o ver both a limited timescale where the age of the test piece remains e ffectively constant and a wider timescale where significant further ag ing of the material occurs. The results of these analyses reveal signi ficant differences between modeling injection molded polypropylene and compression molded material.