Role of Specific Gravity on Removal of Hot Melt Adhesives in Recyclable Grades, 1992 Hot Melt Symposium Proceedings

As recycling gains momentum in the 90’s paper manufacturers will be seeking new methods of contaminant removal. One group of contaminants, hot melt adhesives or "stickies", has long been a nemesis which requires extensive capital investment to control. Removing hot melt adhesives can be efficiently improved if we attack the problem at its roots; that is, to encourage packagers to specify hot melt adhesives with specific gravities that readily lend themselves to being removed by centrifugal cleaners. Hot melt adhesives fall into three categories: light rejects, removable with through-flow or reverse cleaners; and heavy rejects, removable with forward cleaners; and those which fall into a critical range of specific gravities which defy the principles of centrifugal cleaning. Our work identifies 0.980 as the maximum specific gravity of light rejects efficiently removed with through-flow or reverse cleaners. We identified 1.050 specific gravity as the lightest material removable by forward cleaning. Staying out of the 0.980-1.050 critical range allows mill with forward and reverse cleaners to remove over 90% of hot melt contamination in one pass. Much improvement can be made in the cleanliness of recycle if we can encourage the industry, as a whole, to specify hot melt adhesives that fall outside this critical range.