THE EFFECTS OF ADHESIVE PROPERTIES ON THE REMOVAL OF PRESSURE SENSITIVE ADHESIVE CONTAMINANTS IN PAPER RECYCLING

Pressure sensitive adhesive (PSA) materials have significant negative impact on paper recycling. PSA materials are hard to remove in recycling and deposit on equipment and are retained in the product, severely hampering operations. This research had as an objective to evaluate if some PSA properties could be predictors of the removal of PSA materials with pressure screens in paper recycling. Several PSA materials were pulped, characterized for particle size and then subjected to a single slot screening experiment. The PSA materials properties of glass transition temperature, contact angle, yield strain, yield stress, and modulus were determined. Statistical modeling determined that the particle size after pulping was not significantly related to any individual PSA property. Statistical modeling determined that particle passage in a pressurized screen was negatively related to both yield stress and particle dimensions. A hot melt adhesive PSA had a very different screenability than did acrylate based adhesives. The hot melt adhesive was found to fold upon itself into a more spherical shape and to also to contain more attached fibers, in agreement with a higher tack for this adhesive than acrylate adhesives. The passage of the PSA adhesives particles could be modeled with moderate accuracy using a simple extrusion model. The model had yield stress as a fitting parameter and the calculated yield stress from the model was in agreement with the yield stresses measured for the PSA materials. These findings indicate that particle size and cohesive energy are critical to the design of PSA materials that will not extrude through a pressurized screen