Evaluation of natural rubber latex-based PSAs containing aliphatic hydrocarbon tackifier dispersions with different softening points—Adhesive properties at different conditions

Natural rubber latex-based water–borne pressure sensitive adhesives (PSAs) have been formulated with three aliphatic hydrocarbon water-based dispersions (varying softening points) at two different resin addition levels (25% and 50%). Time–temperature superposition analysis using WLF approximations for adhesive peel has revealed that the adhesives formulated with 50% resin addition level show good adhesive behavior. It has also been determined from time–temperature superposition analysis that peel force increases systematically with softening point and peel rate. Correlation of viscoelastic behavior with adhesive properties suggests that at least 50% resin addition level is needed to bring the natural rubber-based formulations into PSA criteria as defined by Dahlquist and others. Adhesive property evaluations performed on a high surface energy substrate (stainless steel) and low surface energy substrate (LDPE) suggested that optimum tack, peel and shear properties at room temperature were obtained for a formulation containing a higher softening point dispersion (95 °C) at 50% resin addition level. Adhesive peel and tack tend to follow softening point trends as well. A 25% tackifier dispersion addition level did not provide any significant adhesion. Humid aging (50 °C and 100% relative humidity) evaluations of the water–borne adhesives seem to correlate well with the room temperature adhesive property observations.