MECHANICAL DEVULCANIZATION OF CARBON BLACK FILLED NATURAL RUBBER VULCANIZATES: EFFECT OF CROSSLINK DENSITY

摘要

The present study aims to find the correlation between the crosslink density of the freshly prepared sample to be devulcanised and the efficiency of mechanical devulcanization in a two roll mill. Efficiently vulcanized (EV) carbon black filled natural rubber vulcanizates with varying crosslink densities were mechanically devulcanised on a two-roll mixing mill and the efficiency of devulcanization was determined from the residual crosslink densities of the devulcanized samples and the corresponding revulcanizate properties. With increasing crosslink density of the starting material, the tear and tensile strengths of the sample first increased, reached a maximum and then decreased. The percent devulcanization associated with these samples on mechanical devulcanization ranged between 70-80 per cent irrespective of their difference in original crosslink density. Hence, the absolute value of the residual crosslink density is high when the original crosslink density is high leading to poor revulcanizate properties irrespective of the higher per cent devulcanization attained. Thus, the original crosslink density of the sample to be devulcanized appears to be one of the most important factors that defines the revulcanizate properties of the devulcanized samples.