THE EFFECT OF CRYSTALLINITY ON THE PROPERTIES OF INJECTION MOLDED POLYPROPYLENE AND POLYACETAL

The effect of the degree of crystallinity on properties has been studied for two injection molded semicrystalline engineering thermoplastic materials, polypropylene and polyacetal. The differences in the degree of crystallinity were obtained initially by altering the mold temperature and hence and the polymer cooling rate. The effects of (1) annealing and (2) small changes in the melt temperature were also studied. The degree of crystallinity was evaluated by X-ray diffraction and differential scanning calorimetry (d.s.c.). Only small changes in the degree of crystallinity were recorded but considerable differences in microstructures were induced for both polypropylene and polacetal. Tensile and tract properties were measured and area discussed in terms of the microstructural changes in the moldings.