FAS (THIOUREA DIOXIDE) BLEACHING OF RECYCLED PULP

The use of recycled fibre (RCF)for high brightness paper grades has in creased the demand for bleaching chemicals. The move away from chlorin e based bleaching agents has meant that FAS, sodium hydrosulfite and h ydrogen peroxide have taken up most of this demand. Two case studies i n which FAS is used for the bleaching of RCF pulp are discussed. The f irst study focuses on the optimum conditions for FAS bleaching of wood free waste (WFW). The effect of bleaching time, temperature and FAS o n brightness development of WFW is examined. Study two considers the e ffect of post bleaching wood containing waste with FAS. In particular the effect of FAS dose is examined in relation to pulp treated at vari ous levels of peroxide in the pulper. Finally a comparison is made bet ween FAS and hydrosulfite as reducing agents for RCF pulp, focusing on bleaching performance, handling, safety, environmental concerns and e conomics.