Dependence of Peel Adhesion on Molecular Weight of Epoxidized Natural Rubber

The effect of molecular weight of two grades of epoxidized natural rubber (ENR)—i.e., ENR 25 and ENR 50—on the peel strength of an adhesive is studied using coumarone-indene resin, gum rosin, and petro resin as tackifiers. Toluene and polyethylene terephthalate (PET) film acted as the solvent and substrate, respectively. A SHEEN hand coater was used to coat the adhesive on the substrate to give coating thicknesses of 30, 60, 90, and 120 µm. The peel strength of adhesive was determined using a Lloyd Adhesion Tester operating at 30 cm/min. Results show that peel strength has a maximum value at a molecular weight of 6.8 × 10⁴ and 3.9 × 10⁴ for ENR 25 and ENR 50, respectively, an observation which is attributed to the combined effects of wettability and mechanical strength of the rubber at the respective optimum molecular weight of ENR. Peel strength increases with coating thickness for all the tackifiers investigated, with a gum rosin-based adhesive exhibiting the highest peel strength.