DYNAMIC MECHANICAL-PROPERTIES OF SILICA-FILLED ETHYLENE VINYL-ACETATE RUBBER

Dynamic mechanical studies of ethylene vinyl acetate rubber indicated the presence of different transitions: the alpha-transition or glass-rubber transition temperature (T(g)) at -17-degrees-C, the beta-transition around -60 to -70-degrees-C observed as a shoulder, and the gamma-transition in the temperature region of -127 to -135-degrees-C, apart from a high-temperature transition (T1,1) at +69-degrees-C. The alpha-transition temperature did not shift its position with incorporation of silica filler, but there was gradual sequential lowering of tan delta peak values at T(g) with increase in filler loading. Such sequential dependence of tan delta values on filler incorporation was not observed in the cases of beta- and gamma-transitions. The T1,1 transition was found to be less prominent in the presence of filler, particularly at high concentration. Treatment of the filler with a silane coupling agent caused a shift in the alpha-transition temperature to higher temperature by about 4-degrees-C. Studies on dynamic mechanical properties under isothermal conditions have shown that the coupling agent caused a breakdown of silica agglomerates during mixing. An increase in frequency caused a shift of tan delta peak positions in the alpha- and gamma-transition regions toward higher temperature. Although frequency did not have a significant effect on the tan delta value at the alpha-transition, increase in frequency caused sequential lowering of tan delta value at the gamma-transition. In the high-temperature region, the T1,1 peak exhibited by the gum compound gradually disappeared with increasing frequency.