Viscosity, tack and, peel and shear strengths of ethylene-propylene-diene rubber (EPDM)/standard Malaysian rubber (SMR L) blend adhesive were studied using various blend ratios of the two rubbers, ranging from 0 to 100% EPDM. Coumarone-indene resin, toluene, and poly(ethylene terephthalate) (PET) were used as the tackifier, solvent, and coating substrate, respectively. The tackifier content was fixed at 40 parts per hundred parts of rubber (phr). A SHEEN hand coater was used to coat the adhesive on PET film at four coating thicknesses, that is, 30, 60, 90, and 120？μm. The viscosity and adhesion properties were determined by a Brookfield viscometer and a Lloyd Adhesion Tester, respectively. Results show that the viscosity, loop tacks and peel strength of blend adhesives decrease gradually with increasing % EPDM. This observation is attributed to dilution effect and lowering in wettability and compatibility. Shear strength, however, passes through a maximum at 20–40% EPDM blend ratio, an observation which is ascribed to culmination of cohesive strength at the optimum EPDM blend ratio. Increasing coating thickness increases the adhesion properties in all blend ratios in this study. 1. Introduction Natural rubber is widely used to prepare pressure-sensitive adhesives. However, natural rubber alone has a very low tack and adhesion to surfaces [1]. Hence, it is necessary to add tackifier to the elastomer to produce the required balance of tack, peel adhesion, and resistance to shear forces. In formulating a rubber-based pressure-sensitive adhesive, an elastomer provides the elastic component whereas a low molecular weight tackifier imparts the viscous component. The adhesion properties of natural-rubber-based adhesives have been investigated by several researchers. Leong et al. [2] have studied the viscoelastic properties of natural rubber pressure-sensitive adhesive using acrylic resin as a tackifier. Fujita et al. [3, 4] reported the effects of miscibility and viscoelasticity on peel strength and shear creep resistance of natural-rubber-based pressure-sensitive adhesives. However, most of the rubber-based adhesives are prepared using one type of elastomer. Research works on rubber-blend-based adhesives are not widely reported. Phillips et al. [5, 6] have studied the nano- and bulk-tack adhesive properties of stimuli-response and fullerene-polymer blends containing polystyrene-block-polybutadiene-block-polystyrene and polystyrene-block-polyisoprene-block-polystyrene rubber-based adhesives. It was found that the presence of oxygen was essential to the
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