Application Of Fluorescent Whitening Agent In Papermaking Process

Fluorescent whitening agent, which is also called white dye, is a fluorescent dye. It is widely used in many fields including textile industry, paper-making, detergent, soap, rubber, plastic, pigments and paint et al. It can absorb invisible UV radiation and re-emit this energy as visible violet -blue light, which increases the total amount of reflection lights, brightening/whitening the applied products.Paper whiteness is still an important index for printing paper, culture paper and industrial paper. Bleaching is the treatment of wood and other lignocelluloses pulps with chemical agents, such as chlorine bleaching, hydrogen peroxide etc., to increase their brightness. But a higher level of whiteness is required. Fluorescent whitening agent, which is used as an additive to improve paper whiteness, is added to the wet end of the papermaking process to increase the whiteness of the paper by physical method. In this study, by analysis of handsheet whiteness, the relationship between whitening effects and influence factors, such as charge level of fluorescent agent, pulp brightness, water hardness, water temperature, stock consistency, contact time, pH value /acid content, alum, fillers, cationic polymers, acid vs. neutral sizing, oxidative vs. reductive bleaching et al., were investigated. The influences of various additives and their addition methods on the whitening efficiency of the fluorescent whitening agent were analyzed. The results obtained were applied in papermaking process to validate effectiveness in practical production.The results show that higher whitening efficiency of the fluorescent agent was obtained under the following conditions: the higher the pulp brightness, less calcium chloride content (less than 500mg/L in process water), reaction temperature less than 35℃between pulp and fluorescent whitening agent, higher stock consistency, about 10 minutes of contact time between pulp and fluorescent whitening agent, pH 7.5, employing suitable amount of cationic polyacrylamide. In addition, fluorescent whitening agent are stable to peroxide bleaching pulp, and are adversely affected by chlorine or hypochlorite bleaching pulp which containing a small amount of residual chlorine. AKD has less adverse effect than rosin size while calcium carbonate is more favorable than talc powder on improving the effect of the fluorescent whitening agent.The above experimental results were applied to practical production. The dosage of the fluorescent whitening agent has been reduced from 15-16 kg per ton of paper to 8-10kg per ton of paper.