EFFECTS OF BIODEGRADABLE POLYPROPYLENE ADDITIVE ON THE IMPACT STRENGTH AND SPHERULITES GROWTH RATE OF ISOTACTIC POLYPROPYLENE

The effect of a biodegradable polypropylene additive on the nucleation intensity, spherulite growth rates, and the impact strength of isotactic polypropylene was studied by means of polarized light microscopy and impact testing. A single screw extruder was used to prepare polypropylene/biodegradable additive composites in which the weight % of the additive was varied between 0.25 and 2. It has been found that the addition of a biodegradable additive to isotactic polypropylene matrix increases the intensity of the spherulites at all covered isothermal crystallization temperature in the range from 125 to 145oC. In comparison with the neat isotactic polypropylene spherulites, much smaller spherulites were obtained at all crystallization temperatures for the isotactic polypropylene/biodegradable additive composite. The obtained results show that the presence of the biodegradable additive enhances spherulite growth rate at low crystallization temperatures (below 135oC) while the effect of this additive is almost negligible at high crystallization temperature (above 135oC). The enhancement in polypropylene's spherulites growth rate was attributed to the reduction in polypropylene's viscosity by the addition of the biodegradable additive. At higher crystallization temperatures, the viscosity of molten polypropylene is already low and the addition of the additive did not decrease it further and hence did not increase the growth rate. In general, the addition of the biodegradable polypropylene additive reduced the impact strength and this reduction approaches 55% when 2 wt% of additive is added to iPP. The high intensity of nucleation and the small size of the final spherulites within the comp