DETERMINATION OF COLOURANTS THAT CAUSE RED DISCOLOURATION IN DEINKED PULP AND MODELLING THEIR INFLUENCING CONDITIONS DURING RECYCLED FIBER PROCESSING

摘要

The occasional appearance of a red shadernin deinked recycled fibers limits the use of deinkedrnpulp (DIP) for high-quality graphic paper grades.rnPrevious investigations have identified red colourantsrncausing red discolouration in terms of three pigmentsrnand one dye. In this work the influence of sevenrnprocess and chemical conditions during recycledrnfiber processing on red discolouration is simulated onrna lab scale. By means of a modified chemicalrnanalysis (visible extinction spectroscopy)rnconcentrations of colourants before and afterrnflotation were quantified. The NaOH dosage has thernmost important effect due to the fact that it influencesrnthe ink particle distribution of red colourants resultingrnin a poorer deinkability. Independent of NaOHrnaddition, all filtrates are strongly coloured red.