Adhesion behaviour of benzoyl peroxide-cured epoxidized natural rubber (ENR 25)/ acrylonitrile-butadiene rubber (NBR) blend adhesive with natural tackifier

Abstract

The loop tack, peel, shear strength and morphology of crosslinked epoxidized natural rubber (ENR 25) acrylonitrile-butadiene rubber (NBR) blend adhesive were investigated. Gum rosin, toluene and benzoyl peroxide were used as the tackifier, solvent and crosslinking agent, respectively, throughout the study. Benzoyl peroxide loading was varied from 1 to 5 parts per hundred parts of rubber (phr), whereas the gum rosin concentration was fixed at 40 phr. Polyethylene terephthalate (PET) substrate was coated at 30 µm and 120μm coating thickness using a SHEEN hand coater. ENR 25/NBR adhesive was crosslinked at 80°C for 30 min. Loop tack, peel and shear strength were determined by a Lloyd adhesion tester operating at 30 cm/min. The result showed that loop tack and peel strength of the ENR 25/NBR blend adhesive indicated a maximum value at 2 phr of benzoyl peroxide. This observation was attributed to the effect of optimum crosslinking of rubber chain. However, shear strength increased with increasing loading of benzoyl peroxide, an observation associated with the steady increase in the cohesive strength. In all cases, the adhesion properties increased with increasing coating thickness. Scanning electron microscope (SEM) was used to investigate the morphology of the ENR 25/NBR blend adhesive on base stock after 90° peel test. The micrograph showed little adhesive left at 0 phr compared to 2 phr benzoyl peroxide loading. This observation was due to the increasing peel strength when 2 phr benzoyl peroxide was added into the system.