Dependence of Adhesion Property of SMR L-based Adhesives on Antioxidants

The viscosity, tack, peel, and shear strength of Standard Malaysian Rubber (SMR L grade)-based pressure-sensitive adhesives was studied in the presence of two types of antioxidants, that is, 2,6-di-tert-butyl-p-cresol (BHT) and 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) using coumarone-indene resin and toluene as the tackifier and solvent, respectively. The concentration of antioxidant was varied from 1 to 4 parts per hundred parts of rubber (phr). A SHEEN hand coater was used to coat the adhesive on polyethylene terephthalate substrate to give a coating thickness of 90 μm. Viscosity was determined by a HAAKE Rotary Viscometer. Tack, peel, and shear strength were measured using a Lloyd Adhesion Tester operating at 30 cm/min. Results indicate that the viscosity and shear strength decreases with increasing antioxidant concentration, an observation that is attributed to the plasticizing effect of the antioxidants. However, tack and peel strength shows the reverse behavior, a phenomenon that is associated to the increasing wettability and compatibility of adhesive on the substrate as antioxidant concentration is increased. Except for the shear strength, BHT antioxidant consistently exhibits a higher viscosity, tack, and peel strength compared to TMQ antioxidant.