Optimizing the monomer composition of acrylic water-based pressure-sensitive adhesives to minimize their impact on recycling operations

Results are reported on a study of the variables controlling the impact that acrylic water-based pressure-sensitive adhesive (PSA) has on paper recycling operations. Surface, bulk, and performance properties of 25 commercial acrylic water-based PSAs were characterized and compared against their laboratory-measured screening removal efficiencies. No correlation was discernible. However, the results did indicate that the use of both vinyl acetate and acrylic acid monomers produced adhesives that readily fragment during repulping operations, resulting in little or no removal via screening. Study of a model system developed to further examine this phenomenon demonstrated that replacing these monomers with those possessing greater hydrophobicities, gauged here with their octanol-water distribution coefficients, produced a substantial increase in measured removal efficiencies. The improvements correlate with the wet tensile strengths of water-soaked adhesive films. The measured dependency of removal efficiencies and tensile strengths on soaking times indicates that the kinetics of water penetration into PSA films is not a controlling factor in determining the observed behavior; rather the films fragment in their water-saturated form during the repulping process. The data presented indicate that in formulating benign PSA it is important to avoid the combination of vinyl acetate and acrylic acid, and in general, increase the residual strength in water-saturated films through a prudent choice of monomer combinations.