Adhesion between individual components and mechanical properties of natural rubber-polypropylene thermoplastic elastomeric blends

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Abstract
Adhesion between individual components and the mechanical properties of natural rubber (NR)-polypropylene (PP) thermoplastic elastomeric blends with reference to adhesion have been studied. The adhesion strength between the component phases was varied by incorporating a third component, namely ethylene propylene diene rubber (EPDM) or chlorinated polyethylene (CPE), and their effects on the mechanical properties were also studied. It was observed that the level of adhesion between NR and PP is improved by incorporating 20 parts of EPDM or CPE in NR. The mechanical properties of the blends are also improved for a particular composition. The enhancement in the strength properties and modulus of an NR:X:PP (where X is the third component) (70:10:30 or 70:20:30) blend is apparent when a correction due to the hard-phase contribution of the blend is made by taking the ratio of the strength of the composite to the strength of the hard phase or modulus of the blends. When the three-component blends were compared with a 90:30 blend of NR-PP, the role of adhesion played by EPDM or CPE in improving the strength and modulus could be demonstrated. In fact, there is a direct qualitative relationship between the adhesion and the mechanical properties in such composites. The stronger the adhesion, the greater the tensile strength and modulus. The higher adhesion strength is further reflected from the morphology of various blends. Separation of the phases during swelling and subsequent drying is restricted in the systems exhibiting higher adhesion strength between the components.