Fragmentation of brittle polymeric toner line caused by swelling of paper substrate during immersion in water / a dissertation submitted by Joel C. Panek.

by Panek, Joel C.

Recycling of paper that was printed with polymeric toner (laser printing, photocopying) consists of repulping the paper then removing the toner from the paper fiber. Repulping involves immersing the paper in water and applying mechanical forces to disintegrate the paper into an aqueous slurry of toner particles and fiber. The ability to remove the toner from the slurry is affected by the size and shape of toner particles. This thesis addressesthe fragmentation of the toner into smaller particles during the initial immersion of paper in water before mechanical forces are applied. Toner on paper was modeled as composite consisting of a brittle, hydrophobic line on a ductile, hygroscopic substrate. The line fractures into segments (fragmentation) due to stresses that develop from expansion of the substrate due to absorption of water. The fragmentation of the toner line on paper was best described with a bond-site model that was developed in this thesis. The bond-site model is based on the Kelly-Tyson stress transfer model in which the interface is assumed to yield plastically. This model includes discrete bond-sites to account for the discontinuity of the toner-paper interface. Based on the model, the average segment length after fragmentation increaseswith: 0 increasing effective thickness of the toner line a increasing tensile strength of the toner line 0 increasing distance between toner-paper bonds l decreasing effective length per toner-paper bond l decreasing shear strength of the toner-paper bond Fragmentation was experimentally quantified using model samples of toner lines on paper and cellulose acetate. The samples were immersed in water and distance between cracks (segment length) was measured. The average segment length ranged from 100 to 400 microns and the coefficient of variation was approximately 54% for all sample sets. The segment length distribution was empirically fitted with a gamma curve, using parameters calculated from the mean and variance of the data. The fragmentation experiments showed that cellulose acetate cannot be used as a model substrate for studying the fragmentation of toner on paper. The toner-cellulose acetate interface is elastic and cleanly fractures rather than yields, prohibiting transfer of the results.