Developing Pressure-Sensitive Adhesives that can be Removed During Paper Recycling Operations, 2000 Recycling Symposium Proceedings

Paul C. McCaslin --One of the contributors to the formation of stickies in recycled paper is the presence of pressure-sensitive adhesives (PSAs) in the furnish. Much effort has gone into understanding the impact of PSAs in stickies formation and developing ways of minimizing their impact. From the PSA development side, two strategies have been explored for stickies reduction. One approach is to design the PSA to agglomerate during repulping so that the resulting clusters of polymeric material in which the PSA is typically found can be captured during pulp screening. Another approach is to tailor the PSA properties so that it is dispersed in the aqueous phase during repulping and separated from the paper when the water is removed. The advantages and disadvantages of these two approaches will be discussed. Although efforts have been made to develop a single standardized test for characterizing stickies levels in recycled paper, it is important to recognize that one characterization test cannot satisfy all applications. Specifically, recycled paper mills want to determine whether the pulp is acceptable for the paper machine, while PSA manufacturers want the test to show how the PSAs behave under simulated repulping conditions. The differences in approach between these two concerns will be presented. Some of the methods developed by Avery Dennison for characterizing PSAs based on their behavior during pulp recycling will be described. These methods include paper pulping, handsheet formation, dyeing of stickies, and characterization of their size distribution.