Mini-Encyclopedia of Papermaking Wet-End
Additives and Ingredients, their Composition, Functions, Strategies for Use
MIXED OFFICE WASTE (MOW)
Composition: "Engine blocks, dead cats, dead skunks, you name it " But the main contents of mixed office waste are xerographic papers and offset papers. Inks are the first types of contaminants to consider. Other common contaminants of "MOW" include labels, carbonless forms, unbleached kraft, paper made from mechanical pulp, and colored papers. The contaminants present in the second list make a difficult situation worse, and many recyclers take great pains to sort their incoming supply. The usual approach is to disperse the bales of MOW in a hydropulper, remove very large and heavy contaminants with the centrifugal action of a large hydrocyclone, screen the pulp, wash it, and possibly use flotation to remove fine particles. Since it is difficult to remove all of the ink, mixed office waste is often bleached with hydrogen peroxide. Xerographic toner, especially when it is applied by computer-generated "laser printers," can be difficult to detach from fibers. Various surface-active materials are used to promote release and either disperse the particles or cause them to agglomerate. Even this brief review of the steps in de-inking of mixed office waste should make it evident that the product of de-inking might be quite different from the bleached kraft pulp that was used to make most of the original products that were the sources of the fiber. Some materials that are likely to be present in de-inked MOW include residual toners and ink, stickies (from labels and binding of magazines), surfactants, hydrogen peroxide bleach residual (if de-inked on-site), silicates (a stabilizer for peroxide), and some mineral filler that makes it through de-inking.
Function: The goal of most papermakers is to use recycled MOW pulp in place of some or all of the virgin bleached kraft fibers in various grades of paper.
Strategies for Use: Some of those who have done the most careful life-cycle analyses of paper recycling have suggested that office waste should be burnt in highly efficient incinerators, taking the place of fossil fuels that otherwise might be expended for the generation of energy. However, others point to the fact that the fibers contained within mixed office waste represent the culmination of a capital-intensive pulping process, and it is wasteful to just throw such valuable fibers away. Because of the many steps needed to "clean up" mixed office waste, the process can produce an amount of sludge that is about equal to the weight of paper product. Increased dosages of such additives as talc (to detackify stickies), biocides, and defoamers may be needed to keep the system running efficiently when the content of de-inked MOW is increased. Sizing agent dosages may have to be increased as well in order to overcome the effect of surfactants.
Cautions: Mixed office waste may contain decaying food products and other substances that carry germs.
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 .