STRUCTURES AND PROPERTIES OF INJECTION MOLDINGS OF GLASS FIBER-FILLED POLYPROPYLENES

Two polypropylene (PP)-glass fiber (GF) compounds were injection -molded. One was a polypropylene filled with 0, 10, 20 and 30 wt.-% of an untreated glass fiber. A second was a compound filled with 20 wt.-% of a silane-treated GF plus 5wt.-% of a maleic anhydride-grafted PP. Flexural test specimens were injection-molded from the filled PPs at cylinder temperatures of 200 to 320-degrees-C. Properties such as flexural modulus, flexural strength, heat distortion temperature, Izod impact strength, and mold shrinkage as well as higher-order structures such as mean fiber length, crystallinity, beta-crystal content, thickness of skin layer, a*-axis-oriented component fraction, and crystalline orientation fraction were measured and structure-property relationships were studied. A simulation of molecular orientation was carried out from the viewpoint of growth of a melt orientation at the gate and its relaxation in the mold cavity.