Mini-Encyclopedia of Papermaking Wet-End
Additives and Ingredients, their Composition, Functions, Strategies for Use
Composition: Stickies are one of the things you get when you recycle mixed waste paper. Actually, stickies are many things. A key component is likely to be polyvinylacetate (PVAc), a material that is widely used for self-stick labels. Stickies encountered in a mill using recycled paper are likely also to contain wood pitch, oils, sizing agents, antifoam, etc. It is the nature of stickies to be highly deformable, somewhat water-hating, and, well, "sticky."
Function: Stickies can hurt product quality when they appear as spots or when they cause pick-outs. They can hurt paper machine efficiency due to the downtime required to clean the wet-press section or other parts of the paper machine where they decide to accumulate.
Strategies for Use: The best strategy is prevention - get it out of the furnish before the paper machine system. Sorting of waste paper is the most effective strategy, but it can be very expensive. The next line of defense is to remove stickies by screening operations. Screening of stickies often is made more difficult after pulping because the particles are broken down. Even in cases where the stickies remain intact, they still can extrude themselves through the narrow slots of a pressure screen. The fact that stickies usually have a density similar to water means that hydrocyclone cleaning is unlikely to be effective as a separation tool. However, the water-hating nature of some stickies can help promote their removal during a froth-floatation stage of a de-inking process. Some strategies to consider on the paper machine include maintenance of good retention, use of talc, continuous chemical cleaning of the wet-press felts, and use of doctor blades to keep dryer can surfaces clean.
Cautions: Solvents used for cleaning of tacky materials from papermaking equipment may be hazardous. Safe cleaning procedures should be followed.
|Schematic showing how stickies can be extruded through a screen that would exclude most non-sticky particles of similar size|
PLEASE NOTE: Users of the information contained on these pages assume complete responsibility to make sure that their practices are safe and do not infringe upon an existing patent. There has been no attempt here to give full safety instructions or to make note of all relevant patents governing the use of additives. Please send corrections if you find errors or points that need better clarification.
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This page is maintained by Martin Hubbe, Associate Professor of Wood and Paper Science, NC State University, firstname.lastname@example.org .