Mechanical properties and impact toughness of talc-filled β-crystalline phase polypropylene composites

Injection molded beta-crystalline phase polypropylene (PP) composites containing 5, 10, 20, 30 and 40% (by weight) of talc filler were studied by X-ray diffraction, scanning electron microscopy, static tensile and falling drop weight impact tests. The X-ray diffraction analysis showed that the talc filler suppresses the formation of beta-form PP dramatically. As a result, the beta-PP composites containing talc content greater than or equal to 20 wt% consisted mainly of the alpha-form PP phase. The tensile test showed that the addition of talc filler up to 40 wt% leads to an increase in Young's modulus whereas little effect is observed on the yield strength of composites with the addition of talc up to 30%. This behavior can be attributed to the load bearing effect of talc particles with a platelike structure and to good interfacial bonding exists between the matrix and filler. The impact tests revealed that the critical stain energy release rate (G(c)) of the beta-PP polymers appears to increase initially with the addition of 5 wt% talc; thereafter it decreases significantly with increasing talc content.