Cleaning and screening[edit]
Centrifugal cleaning is spinning the pulp slurry in a cleaner, causing materials that are denser than pulp fibers to move outward and be rejected. Screens, with either slots or holes, are used to remove contaminants that are larger than pulp fibers.
Materials which are more difficult to remove include wax coatings on corrugated cartons and stickies, soft rubbery particles which can make deposits and contaminate the recycled paper. Stickies can originate from book bindings, hot melt adhesives, PSA adhesives from paper labels, laminating adhesives of reinforced gummed tapes, etc.