Mechanical behavior of CaCO3 particulate-filled beta-crystalline phase polypropylene composites

beta-crystalline phase polypropylene (PP) composites containing 5, 10, 20, 30, and 40% (by weight) of CaCO3 filler were prepared by injection molding. The beta-form PP was produced by adding a bicomponent beta-nucleator consisting of equal amounts of pimelic acid and calcium stearate. The morphology, static tensile, and impact properties of these composites were investigated in this study. Scanning electron microscopy (SEM) observations revealed that the beta-spherulites of the polymer matrix of the composites exhibit curved lamellae and sheaf-like structures. The fillers were observed to disperse within the inter-lamellar spacings of the beta-PP composite containing 10% calcium carbonate addition. However, the filler particles tend to link together to form larger aggregates when the filler content reaches 20%. Static tensile measurements showed that the elastic modulus of the composites increases with increasing filler content but the yield strength decreases with increasing filler addition. The falling weight Charpy impact test indicated that the beta-PP polymer exhibits the highest critical strain energy release rate (G(c)) value. However, there was a drastic drop in G(c) of the beta-PP composites with increasing filler content. The results are discussed and explained in terms of materials morphology.