STUDIES ON THE EFFECT OF BLEND RATIO AND CROSS-LINKING SYSTEM ON THERMAL, X-RAY AND DYNAMIC-MECHANICAL PROPERTIES OF BLENDS OF NATURAL-RUBBER AND ETHYLENE-VINYL ACETATE COPOLYMER

Differential scanning calorimetry (d.s.c.), X-ray, dynamic mechanical and microscopy studies were carried out using a series of blends of na tural rubber (NR) and ethylene-vinyl acetate copolymer (EVA) in the cr osslinked and uncrosslinked states. The crosslinking system (sulfur, p eroxide and mixed) and blend ratio do not influence significantly the melting temperature (T(m)) of EVA. The decrease in percentage crystall inity of EVA with NR content is related to the incomplete crystallizat ion, as indicated by the lower heat of fusion (DELTAH). The glass tran sition temperature (T(g)) of NR in the uncrosslinked blend did not cha nge substantially and this indicated incompatibility. However, in the case of crosslinked systems, depending on the type of crosslinking age nts used, the T(g) of the NR phase in the blend was shifted to higher temperatures. This has been explained with reference to the predominan t crosslinking of the NR phase. From X-ray diffraction patterns, the i nterplanar distances (d values) were calculated. With the addition of NR there was a tendency for the d values to increase in all systems. T he crystallinity was measured by X-ray and the results were in line wi th those of d.s.c. measurements. The dynamic mechanical properties suc h as tan delta, storage modulus and loss modulus of the blends were ev aluated. The existence of separate T(g) values in dynamic mechanical t hermal analyser studies indicates that the blends are incompatible. Th e morphology of the uncrosslinked blends has been studied by scanning electron microscopy.