Effect of calcium stearate and pimelic acid addition on mechanical properties of heterophasic isotactic polypropylene/ethylene-propylene rubber blend

The effects of various heterogeneous nucleating agents (i.e. sodium benzoate, talcum, dimethyl dibenzylsorbitol, and a combination of calcium stearate and pimelic acid) on the mechanical properties of heterophasic copolymer of isotactic polypropylene and ethylene-propylene rubber (iPP/EPR blend) were investigated for a fixed filler loading of 0.1 wt%. Only the sample filled with a combination of calcium stearate and pimelic acid (Ca-Pim) exhibited a greater notched Izod impact strength value than that of the unfilled sample. The effect of Ca-Pim addition at various loadings was further investigated and the results revealed that iPP/EPR blend loaded with 0.001 wt% Ca-Pim showed the greatest improvement in the notched Izod impact strength (an increase of ca. 3.5-fold over that of the unfilled sample) at the expense of both the tensile strength at yield and flexural modulus. It was concluded, based on wide-angle X-ray diffraction, differential scanning calorimetry and scanning electron microscopy results, that the presence of the beta-crystals (with the K-beta value being 0.75) was responsible for the great improvement in the notched Izod impact strength observed. (C) 2003 Elsevier Ltd. All rights reserved.