Contaminant Removal
Quantitative measure of the percentage of printing ink removed from recovered paper during the recycling process. Achieving a high de-inking efficiency is essential for producing high-quality recycled pulp used in graphic papers and white-lined chipboard. This metric determines the brightness and purity of the recycled fibres before they are formed into a new paper web.
Separation Dynamics
Removal of ink involves two sequential stages, which are the detachment of ink particles from the cellulose fibres and their subsequent separation from the pulp slurry. During the repulping phase, chemical surfactant packages assist in breaking the ink binders and dispersing the released particles. These dispersed particles are then gathered by air bubbles in flotation cells, which carry them to the surface where they are skimmed off as foam.
When de-inking efficiency falls below target levels, the remaining ink particles cause grey spots and reduce the brightness of the finished paper.
Measurement Standard
Laboratory evaluations of this metric compare the brightness of the pulp sheets before and after the washing or flotation processes. These tests utilize spectrophotometers to measure light reflectance at specific wavelengths, which provides an objective rating of ink removal. Maintaining high efficiency minimizes the need for chemical bleaching.
