Study of poly (ethylene vinyl acetate)-carboxylated nitrile rubber (XNBR) blends with reference to their shrinkability

Heat shrinkability, a collective property, of the polymer is being utilised in various applications - mainly in the field of encapsulation. The elastic memory is introduced into the system in the form of an elastomeric phase. Here, the blends of ethylene vinyl acetate (EVA) and carboxylated nitrile rubber (XNBR) were studied with reference to their shrinkability. It was found that with increasing cure time shrinkability was decreased. On the other hand, with increasing elastomer content, the shrinkage was increased up to a certain level and beyond this shrinkability was decreased. Temperature has a profound effect on the shrinkability. High temperature (H-T) stretched samples showed higher shrinkage than room temperature (R-T) stretched one. Generally, the crystallinity of high temperature (H-T) stretched sample was higher than that of room temperature (R-T) stretched sample, which was again higher than that of original unstretched sample, for a particular blend. At room temperature (R-T), stretching nucleation is favoured but at high temperature (R-T) stretching crystal growth is favoured. From SEM, it was seen that elastomer phase in H-T stretched sample was more elongated than that in R-T stretched one and in shrunk sample elastomer phase was More spherulitic than that of the original unstretched one.