||June 30, 2008
Single-stage blending of natural rubber and high acrylonitrile-butadiene rubber (NBR) was carried out in an intermeshing rotor internal mixer according to a two-level, two-variable factorial mixing experiment. Mixer rotor speed and initial mixing temperature of NBR were taken as the two variables. This paper reports on the effect of these two variables on properties of NR/NBR/carbon black composites via domain size. Transmitted light micrographs obtained from thin sections of carbon black loaded NR/NBR vulcanizates have shown that domain size decreases with increasing mixer rotor speed. This was mainly attributed to the reduction in the difference between the viscosities of component elastomers as a result of high shear rate coupled with rapid rise in batch temperature. However, initial mixing temperature of NBR does not exert a significant effect on morphology. The cure rate and tensile strength of fine textured blends were higher than those of the coarse textured ones. The increase in tensile strength of fine textured blends can be attributed to increased crack deviation around the smaller domains.
Further, results have shown that viscosity, tensile moduli, tear strength and oil/fuel resistance of the composites are not significantly affected by morphology.