Effect of Starch on the Mechanical and Rheological Properties of Polypropylene

Blends of starch (tapioca) and polypropylene were prepared in various wt/wt concentrations ranging from 100% polypropylene resins to 5:95, 10:90, 20:80, 30:70, 40:60, and 50:50 wt% starch to wt% polypropylene blends. Then the rheological and mechanical properties of the resulting blends were determined using Plastometer and Universal Testing Machine respectively. Tensile strength, percentage elongation, flexural modulus, Izod impact, vicat softening temperature and melt flow index tests were carried out according to American standard for testing and materials procedure. The melt flow index was found to decrease linearly with increasing starch concentrations up to 30 wt% starch to wt% plastic, beyond which no flow was observed. The presence of starch in polypropylene was found to have positive effect on some of the mechanical properties like flexural modulus and Izod impact strength, whereas a negative impact was obtained on the tensile strength and percentage elongation. It was observed that higher starch loadings above 30% reduced the mechanical properties while lower starch loadings below 30% improved some mechanical properties. In addition, higher starch loadings above 30% does not favor the melt flow index and the Izod impact strength since there was no flow due to lower vicat softening temperature. Thus, with the aid of controlled incorporation of the starch additive, several properties of the modified polypropylene specimen could be enhanced.