Shive and knot elimination with TCF and ECF bleaching sequences

Comparisons were made between bleaching stages that include hydrogen peroxide (P), peracetic acid (T), ozone (Z), and chlorine dioxide (D). Shives or knots were added to particle free pulp before bleaching. The efficiencies of particle removal in totally chlorine free (TCF) and elemental chlorine free (ECF) sequences were compared. Using a QPQ(PO) * sequence, it is possible to obtain the same degree of shive elimination as with ECF bleaching. Other TCF sequences do not show the same capacity for reducing particles. If an ozone or peracetic acid stage precedes a final hydrogen peroxide stage, problems with cleanliness may occur in the final pulp. However, mechanical treatment after final bleaching improves shive elimination in all TCF sequences. Application : the elimination of shives in TCF bleaching can be as effective as shive reduction in ECF bleaching.