Thermal characterization of thermoplastic elastomeric natural rubber-polypropylene blends

Abstract

Abstract The thermal behaviour of natural rubber-polypropylene (NR/PP) thermoplastic elastomeric blends has been studied by a number of different techniques, e.g. differential scanning calorimetry (DSC), thermogravimetry (TG) and dynamic mechanical analysis (DMA). The melting temperature ( T m) for polypropylene is 165°C. DSC results show a drop in the T m value with increasing rubber content. The effect of 20 parts of an interfacial agent, like ethylene-propylene diene rubber (EPDM) or chlorinated polyethylene (CPE), is similar. Heat of fusion (Δ H) values exhibit a similar trend indicating increasing isolation of the crystallizable component at high rubber content. There is a 79% drop in crystallinity with the incorporation of 70 parts of natural rubber. The glass transition temperature ( T g) of the rubber phase, can be detected by this technique. The T g of the blends is higher than that of pure NR. The elevation of T g coupled with the depression of T m indicate the kinetic restriction on the crystallization process. The TGA shows that the onset of degradation for pure PP is delayed with the addition of rubber. Differential thermogravimetry (DTG) curves for the blends display two peaks. The highest thermal stability is attained with the addition of ethylene-propylene diene rubber to the NR/PP blend. Dynamic mechanical analysis shows the existence of two T g values—one corresponding with the amorphous phase and the other with the polypropylene phase—indicating the incompatibility of the blends. The values of the elastic modulus also display a sharp change in magnitude in the vicinity of the glass transition temperature. The intensity of the damping (tan δ) peak is found to be governed by the overall blend crystallinity. A new method for calculation of crystallinity by DMA is also suggested.