Development of environmentally benign pressure-sensitive adhesive systems via modification of substrate properties

Results are presented from a study on a novel approach for reducing the negative impact of pressure-sensitive adhesive (PSA) contaminants on paper recycling. Paper substrates are developed that can be easily removed from the recycling process via screening operations and retain their attached PSAs. A model series of hot-melt PSAs consisting of a styrene-isoprene styrene/styrene-isoprene (SIS/SI) linear triblock, diblock copolymer blend, a pentaerythritol ester of rosin tackifying resin, and a naphthenic process oil were blended in combinations to produce a range of properties. These PSAs were attached to paper substrates with bulk and surface properties that were manipulated using commercial papermaking chemicals and dosages. A poly(amide epichlorohydrin) wet-strength resin was used to inhibit the fiberization of substrates. Removal efficiencies for PSAs coated on this paper were increased, but poor adhesion between the PSA. films and paper substrates during repulping limited the improvement. It was found that the retention of the PSA increased linearly with its mechanical loss tangent indicating that properties of the PSA film could be manipulated to optimize removal efficiencies. It was also found that PSA-paper adhesion could be enhanced without restricting PSA properties by introducing an alkenyl ketene dimer size to the paper. The increased adhesion between PSA films and paper in an aqueous environment was achieved by raising the cellulose-water and lowering the cellulose-PSA interfacial energies. Removal efficiencies for PSAs attached to the sized, wet-strength paper substrates were >90% for all of the experimental hot-melt PSAs. Results of this study indicate that minor modifications made with common papermaking additives to paper used in PSA products can significantly reduce their impact on paper recycling.