Technical Perspective of the Effect of Hot Melt Adhesives on the Recycling of Post Consumer Recovered Paper/Paperboard Materials, 1992 Hot Melt Symposium Proceedings

When I was asked to participate in this Hot Melt Mini-Seminar, I was immediately reminded of an experience in the early 1970s. I was working as a Technical Director in a paper mill that produced linerboard which was shipped to box plants for the manufacture of corrugated containers. A recycling plant had been started up at this mill to recycle old corrugated containers (OCC). The goal of the mill was to recycle enough OCC to produce 300 Tons per Day of recycled fiber for use in the manufacture of the linerboard.

Two problems were encountered. The first was spots in the sheet that grew in size whenever heat was applied to the linerboard particularly when the linerboard was run over heated rolls in the box plants. These spots ranged in size from l/8 to l/2 inches in diameter after heating. The paper testers at the mill quickly learned that these spots could be detected by heating test sheets of the linerboard in a convective air drying oven which was set at 220 F. The number of the spots in a given area could be counted to provide a relative measure of the severity of the problem.

Complaints began to come in from the box plants. The spots were degrading the appearance of the finished corrugated containers and upsetting customers who expected a clean surface for printing on the containers. I became involved in extensive trials with the goal to eliminate or reduce these spots. It was determined that these spots were composed of materials derived from Hot Melt Adhesives (HMAs) or wax coatings. The OCC supply was carefully inspected for containers with wax coatings to be sure that these coatings were not causing the spot problem. This close inspection revealed that containers with wax coatings were not encountered frequently. The spot problem persisted and it was concluded that the problem was being caused by Hot Melt Adhesives HMAs). Since HMAs were being used by almost all of the box consumers, it was not feasible to reject containers with HMAs applied to them.

The second problem, encountered sometime after the snot problem involved slippery linerboard. The box plants had difficulty in handling stacks of the finished corrugated sheets; the sheets would tend to slide over one another and sheet stacks would collapse. The box customers would complain that the corrugated containers, when filled with their products, would not stack well. The filled corrugated containers would tend to slide over each other too easily. Some customers also complained of filled corrugated containers that slid off conveyors too easily.