Stickie Removal Using Neutral Enzymatic Repulping and Pressure Screening, 1998 Recycling Symposium Proceedings

Removal of stickie contaminants is currently a major focus of paper recycling research. Medium consistency alkaline repulping followed by pressure screening has proven to be effective for stickie removal. There is, however, an alternate method that is equally effective and more environmentally benign. This study compares the effectiveness of this alternative method, neutral enzymatic, repulping, with conventional alkaline repulping for contaminant removal from a controlled office paper furnish spiked with typical pressure-sensitive adhesives. Neutral repulping on a pilot scale was performed using a mixture of cellulase and lipase preparations at the ambient pH of the paper furnish. Sequential pressure screenings, flotation, and washing comprised the deinkmg process, and contaminant count on handsheets prepared after each step was used for these evaluations. We found that pressure screening was substantially more effective for contaminant removal when the pH was neutral. The enzyme mixture further enhanced both the freeness and brightness of the deinked pulp. Process water from the enzyme treatment also contained fewer microstickies, an added benefit for improved water quality and mill performance.