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A close-up of some fingers peeling off a stamp from a self-adhesive book.

Self-adhesive stamps are an example of "the stickies" that can cause problems during the recycling process.

New hope for sticky situation

By Sarah Finley

From eNews, July 21, 2005

Remember the days when you had to actually lick stamps? OK, maybe those days weren't that long ago. The early 1990s were probably the last time the majority of postal service patrons used lick-and-stick postage, right before the pressure-sensitive adhesive stamp went into full-scale production. Today, it's estimated that 96 percent of all stamps are of the peel-and-stick variety.

But while most consumers would agree that no-lick technology has improved stamps and other paper products such as envelopes and address labels, pressure-sensitive adhesives (PSA) are anything but popular with the paper recycling industry.

Most paper recycling systems use water to transform recovered paper into pulp, which is then transformed back into paper. PSAs do not dissolve in water, instead they break down into small particles that cleaners and screens can't remove effectively. These tiny particles make their way into the final paper product and degrade its quality, or they eventually gum up recycling mill equipment, causing expensive downtime. According to the California Integrated Waste Management Board, stickies cost the paper recycling industry about $700 million a year in paper mill maintenance and recovered paper collection costs.

The recycling industry, along with the U.S. Postal Service, has investigated many approaches for controlling stickies, including new methods for monitoring and cleaning recycled paper sources, new equipment to aid in contaminant removal, additives for protecting key process sites, and techniques for making contaminants less harmful. Steve Severtson, associate professor in the Department of Bio-based Products, believes there's another solution. "The best way to minimize these problems is to redesign PSA products," he says.

Backed by the Department of Energy's Industrial Technologies Program, with matching funds from several industrial research partners, Severtson has devoted considerable time during the past five years to developing PSAs that are more compatible with recycling operations. While several research groups around the nation have been pursuing the same objective, most have focused on adhesive film or the materials used to make the adhesive. Severtson is interested in the paper facestock-the paper used to make the PSA.

Severtson and his research team worked with St. Paul-based H.B. Fuller Co., a leading adhesive and sealant manufacturer, to develop a self-adhesive laminate that would be environmentally friendly and easy on recycling equipment. The team worked with hot-melt PSAs, and their goal was to find an affordable solution.

"Thermoplastic or hot-melt PSAs are less complex and better suited for research," Severtson says. "They are easier to formulate and coat, and you can usually achieve the same performance properties as those demonstrated by other types of PSAs." Hot-melt PSAs make up from 15 to 20 percent of the PSA currently on the market. Acrylic and rubber adhesives are the other types available.

They blended the ingredients of hot-melt PSAs in combinations to produce a range of adhesive properties, and then attached them to facestocks modified with a wet-strength resin and a sizing agent that increased the PSAs adhesion and ability to break down into particles large enough for recycling mill cleaners and screens to catch.

"Our findings demonstrate that for most PSAs, the adhesive film alone can't be certified as [environmentally] benign," he says. "The entire laminate, [which consists of the adhesive, a release liner, and the facestock] has to be considered."

They also found that PSAs made with untreated or uncoated paper (such as general office paper or paper without the glossy finish) were up to 70 percent easier to remove during the repulping process than those produced with the common or coated facestocks.

H.B. Fuller is currently working with its customers to market the new product. Meanwhile, Severtson and his team will be applying what they've learned to water-based PSAs and develop a screenable wax coating for cardboard (the paraffin wax used to coat cardboard can gum up recycling mill equipment and decrease product quality).