Influence of nanoclay on adhesion of EPDM vulcanizate

The influence of unmodified clay, Cloisite Na+ on adhesion between prevulcanized EPDM rubber and unvulcanized EPDM rubber containing nanoclay was investigated using 180° peel test. The rubber showed improvement in peel strength with increasing clay concentration up to 4 phr, beyond which it decreased. A maximum of 51% improvement in peel strength was obtained for 4 phr Cloisite Na+. This was attributed to enhanced tensile strength, monomer friction coefficient, marginal improvement of polarity and micro-roughness of the clay filled rubber. At higher clay loading (8 phr), the peel strength reduced due to formation of boundary layer of Zn-stearate, accelerators and clay on the outermost surface, diffusion of the fewer rubber chains, agglomeration of the clay particles and increased modulus of the rubber.