Laboratory High Consistency Dispersion Studies of Mixed Office Waste Paper and Comparison With Recycle Mill Samples

A laboratory study is presented of high consistency dispersion using a bench scale hand fed 12 inch refiner. The study consists of several parts: (1) preliminary trials using refiner-type and knuckle-type plates; (2) dis-persion of furnishes repulped at three consistencies, 6, 12 and 18%; and (3) dispersion of a furnish repulped at 12% consistency and subjected to three consecutive passes. Samples from two recycle mills were also examined. Results consist of toner particle size and area distribution curves obtained by image analysis, and fiber/toner detachment information obtained by visual microscopic examination. The particle size distributions of the furnishes repulped at 6, 12 and 18% consistency are very different, with the 6% sample having many more larger and fewer small particles compared to the 12%, and especially the 18%, samples. After dispersion, especially after the smallest plate gap sepa-ration used, the distributions are very similar or nearly identical. However, the ratios of clean-to-hairy particles for each repulped furnish remain virtually unchanged. It appears that the repulping consistency determines which fiber/toner “bonds” will be broken, and although dispersion is effective in further breaking down toner particles, it is not effective (at the tempera-ture of these trials) in further detaching toner from fiber. The influence of consecutive passes of the same gap setting is to approach a unchanging distribution of toner particle sizes. [