Effect of molecular weight and testing rate on peel and shear strength of epoxidized natural rubber (ENR 50)-based adhesives

The dependence of peel strength and shear strength of epoxidized natural rubber (ENR-50)-based pressure sensitive adhesive on molecular weight and rate of testing was investigated using coumarone-indene as the tackifying resin. Toluene and polyethylene terephthalate were used as the solvent and substrate respectively, throughout the study. A SHEEN hand coater was used to coat the adhesive on the substrate at a coating thickness of 120 μm. All the adhesion properties were determined by a Llyod Adhesion Tester operating at different rates of testing. Result shows that peel strength and shear strength increases up to an optimum molecular weight of 4.2 × 10⁴ of ENR 50. For peel strength, the observation is attributed to the combined effects of wettability and mechanical strength of rubber at the optimum molecular weight, whereas for the shear strength, it is ascribed to the optimum cohesive and adhesive strength which enhances the shear resistance of the adhesive. Peel strength and shear strength also increases with increase in rate of testing, an observation which is associated to the viscoeslastic response of the adhesive. DSC and FTIR study confirms the miscibility of tackifier and the ENR 50.