Breakage of Pressure Sensitive Adhesive Contaminants in Paper Recycling Operations, 2000 Pulping / Process & Product Quality Conference Proceedings

B. E. Lucas, R. A. Venditti, H. Jameel--It has been found previously that an industrial pressure screen broke down pressure sensitive adhesive (PSA) contaminants, while laboratory screens did not. It was suspected that the high shear and pressure gradients in the pressure screen caused the breakage. To investigate the effect of recycling conditions on breakage in pressure screens and other recycling operations, statistically designed experiments were conducted in a laboratory high shear device. A single type of acrylate based PSA label was applied to copy paper, pulped and then processed in the high-shear device. The operating variables in the shear device studied were consistency, time, initial temperature, and rotor speed. Dyeing and image analysis of the treated and untreated adhesive contaminants was performed to obtain the parts per million (PPM), average particle size, and number of particles in 1 m 2 . Statistical analysis of the data showed that consistency, time, and initial temperature affected the breakage of the adhesive material, whereas rotor speed did not. Empirical models for the average particle size and the number of particles in 1 m 2 were developed using a backward elimination program in the SAS System. Further experiments in which the consistency was varied revealed that at consistencies less than 6%, minimum breakage occurred, but at consistencies greater than 9%, breakage increased as the consistency increased. Increasing the consistency from 9 to 14% reduced the average particle size by half and more than doubled the number of particles in 1 m 2 . Also, increasing the initial temperature from 25 to 75 o C increased the breakage and almost doubled the number of particles in 1m 2 . These findings provide operational information that is useful in the analysis of recycling equipment with respect to the removal of adhesive contaminants.