In-fluence of mixing schemes on ageing, swelling and permeability properties of vulcanizates from blends of natural rubber and low molecular weight natural rubber in petroleum fuels and organic solvents

Blends of natural rubber (NR) and low molecular weight natural rubber (LMWNR) were compounded using three different mixing schemes by adopting the semi-efficient sulphur vulcanization compounding formulation. In scheme 1, the natural rubber and LMWNR were first mixed before adding the compounding ingredients. In scheme 2, the compounding ingredients were first mixed with the NR before adding the LMWNR and in scheme 3 the compounding ingredients were first mixed with the LMWNR before adding the NR. Properties of the vulcanizates from the three mixing schemes viz-a-viz: chemical resistance, ageing and physico-mechanical properties were investigated and compared. The physico-mechanical results of all the vulcanizates were found to be within the accepted level for NR compounds. The ageing results from all the mixing schemes were found impressing. Vulcanizates from mixing scheme 1 restricted penetration of petroleum fuels and organic solvents best, followed by scheme 2 and the least was scheme 3. The activation energy and free energy change were found to be highest with scheme 1, thereby making mixing scheme 1 being more technologically advantageous than other mixing schemes.