Adhesive properties of neoprene-phenolic-EPN blends

This study investigates the adhesive properties of neoprene-phenolic-EPN blends for SBR-SBR and Al-Al bonding. The effect ofvarying the phenolic: EPN ratio on adhesive properties was studied. The first part (Case A) brings out the significance of blending a phenolic copolymer with epoxidized phenolic novolac (EPN) resin and neoprene rubber. The phenolic resin was the product of condensation of a mixture of phenol and cardanol with formaldehyde. Cardanol, a meta-substituted phenol, is the main ingredient of cashew nut shell liquid (CNSL), a renewable resource. In the second part (Case B), the phenolic resin used was a commercial resin based on p-tertiary butyl phenol. For SBR-SBR bonds, 30 phr EPN in the phenolic/EPN blend leads to optimal shear and peel properties for both Cases A & B. For Al-Al bonds, on the other hand, 60-80 phr EPN in the phenolic/EPN blend gives optimal properties for shear and peel properties for both cases. The formulation containing cardanol performs better on Al-Al bonds while the t-butyl phenol based formulation is better suited for SBR-SBR bonds. Morphological studies using SEM indicate greater energy absorption and improved bond strength on addition of EPN into neoprene-phenolic formulations for both for SBR-SBR and Al-Al bonding. The successful application of cardanol, a renewable resource, for adhesive formulation is of significance.