Water-Soluble/Dispersible Cationic Pressure-Sensitive Adhesives. I. Adhesives from Solution Polymerization Zegui Yan, Yulin Deng Institute of Paper Science and Technology, 500 10th Street, NW, Atlanta, Georgia 30332-0620 Received 6 September 2002; accepted 27 January 2003 ABSTRACT: Pressure-sensitive adhesives (PSAs) have long been a problem as sticky contaminants for paper recy- cling mills. The main problem associated with such stickies is that the PSAs in the waste papers deposit on the felts, press rolls, and drying cylinders of paper machines, and this creates problems with paper formation, reducing the paper quality and paper machine runnability. The annual cost of stickies to the U.S. paper industry is estimated to be about $600,000,000 – 650,000,000. To solve this problem, a series of cationic water-soluble/dispersible PSAs have been synthe- sized by the free-radical solution polymerization of butyl acry- late and [3-(methacryloylamino)propyl]trimethylammonium chloride in ethanol. The PSA end-use properties, repulpability in paper recycling, and the effects on the properties of recycled paper products have been studied. The cationic PSAs can be dissolved or dispersed in water if the cationic charge density in the PSA backbone is controlled, and so they do not deposit as stickies during recycling and papermaking processes. Because the PSAs are cationically charged, they can easily be removed from the papermaking system by adsorption onto the nega- tively charged fibers and fine surfaces. Furthermore, the ad- sorbed colloidal or dissolved PSAs have little effect on the final paper properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1624 –1630, 2003 Key words: adhesives; recycling; solution properties; fibers INTRODUCTION Pressure-sensitive adhesives (PSAs) are widely used for self-adhesive stamps, tapes, labels, and paper coat- ings. PSAs have long been a problem as sticky con- taminants for paper recycling mills. 1–4 The main prob- lems associated with such stickies include deposition on the felts, press rolls, and drying cylinders, which creates problems with paper formation, reducing the paper quality and paper machine runnability. The annual cost of stickies to the U.S. paper industry is estimated to be about $600,000,000 – 650,000,000. 5,6 Many researchers have focused on understanding and resolving the problem of stickies in waste-paper recycling and papermaking. Two approaches have been made to solve these problems: sticky control and new adhesive development. The technologies that have been developed or studied for sticky control include: (1) treating machine surfaces with surface- active agents to protect the deposition of sticky parti- cles; (2) using talc, clay, or precipitated calcium car- bonate (PCC) to stabilize the sticky particles and pro- tect against their deposition; (3) using detackification agents to reduce the tackiness of stick particles; (4) using dispersion agents such as surfactants or poly- mers to stabilize stickies; (5) adding chelating agents to reduce the concentration of some metal ions to reduce the precipitation of stickies; (6) enzymatic treatment; (7) using washing, cleaning, screening, and flotation tech- niques to remove stickies; and (8) modifying or washing paper-machine forming fabrics and felts to reduce their affinity for stickies. Although problems with stickies can be reduced by one or another of the techniques listed, the techniques that work well in one paper mill may not work for others because of the differences in the adhe- sives, pulps, and papermaking conditions. To fully solve the problems of stickies for the paper recycling industry, new adhesives that are repulpable and easily removable must be developed. For this reason, the development of repulpable PSAs is of great interest to the paper indus- try. 6–8 The technologies currently being evaluated by ad- hesive manufacturers in an effort to make repulpable adhesives can be divided into two categories: recov- erable (or screenable) and dispersible/soluble adhe- sives. 9 Two different approaches have been employed in recoverable adhesive development: (1) adhesives that have a high glass-transition or melting tempera- ture and will not soften and break down under repulping conditions and (2) adhesives that have a density significantly lower or higher than that of water and fibers. Unfortunately, polymers with high glass- transition or melting temperatures can only be used for hot melts but not for PSAs. Although some high- or low-density polymers have been used for PSA, only a limited number of polymers can meet this unique requirement. In contrast to recoverable PSAs, water- Correspondence to: Z. Yan (zegui.yan@ipst.edu). Contract grant sponsor: U.S. Department of Energy. Journal of Applied Polymer Science, Vol. 90, 1624 –1630 (2003) © 2003 Wiley Periodicals, Inc.