Adhesives Containing Pine Bark Tannin for Bonding Nylon Cord to Rubber

Abstract

Purified loblolly pine bark tannin was studied as an additive in resorcinol-formaldehyde latex (RFL) adhesive dips for bonding nylon to a styrenebutadiene-rubber (SBR) vulcanizate. The viscosity of the adhesive and its bonding characteristics depended on the order in which ingredients were combined in adhesive preparation. Pre-dilution before combining reactive components led to increased viscosity, higher pullout forces, and prevention of precipitate formation when compared to the addition of water after mixing resorcinol, tannin, formalin, and NaOH (post-dilution). Viscosity increased as the resin solids content of the adhesive increased. Stress-strain measurements indicated an initial toughening of the adhesive as resorcinol was replaced by tannin, but at sufficiently high substitutions, a marked softening and reduction in toughness occurred. Pullout forces with nylon 66 cord were increased if the adhesive was applied without prior aging. Pullout forces could be optimized by varying the formaldehyde concentration and latex-to-resin ratio in the tannin-containing adhesives.