Structure-property correlation of heat shrinkable EVA/CSM blends in presence and absence of curatives

Heat shrinkability, a collective property of the polymer, is being utilized 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 chlorosulfonated polyet hylene elastomer (CSM), without curatives and by incorporation of metal oxi de as curatives, were studied with reference to their shrinkability. With i ncrease in elastomer content and cure time the shrinkage was found to incre ase. Again, high-temperature (H-T) stretched samples showed higher shrinkag e than room-temperature (R-T) stretched samples, the shrinkage at 150 degre esC being the highest. Generally, the crystallinity of stretched (R-T and H -T) samples were higher than that of the usual unstretched sample. For the metal oxide-cured system, R-T stretched samples of both plastic-rich and el astomer-rich blends showed higher crystallinity than corresponding H-T stre tched samples, unlike the elastomer-rich blends with curatives. From high-t emperature DSC it was found that, with increase in CSM content, stability t oward oxygen was increased in absence of curatives, but in presence of cura tives stability is decreased, which is obvious from the heat-of-degradation values. For H-T shrunk samples, the initial decomposition temperature was found higher than corresponding unstretched samples for both the systems. T he H-T shrunk sample showed faster degradation initially then beyond 50% de composition the rate started going down compared to usual unstretched sampl e for both the systems.