Analysis of the effect of molecular weight and testing rate on shear strength of epoxidized natural rubber-based adhesives with a statistical model

The effect of the molecular weight and testing rate on shear strength of epoxidized natural rubber (ENR 25)-based adhesives with statistical model was investigated using gum rosin as the tackifying resin. Toluene and polyethylene terephthalate (PET) 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 Lloyd Adhesion Tester operating at different rates of testing. Result shows that shear strength increases up to an optimum molecular weight of 6.5 ×?10⁴ ENR 25. Shear strength increases with coating thickness, an observation that is ascribed to the increasing amount of adhesive present in the coating layer, which enhances the shear resistance of the adhesive. It also increases with increase in rate of testing, a phenomenon that is associated with the viscoelastic response of the adhesive.