New Insights Into Lignin Modification During Chlorine Dioxide Bleaching Sequences (Iv): Modifications in (Ep) and (Eop) Stages, and Its Impacts on the D1 Stage, 2004 Engineering, Pulping, and PCE&I Conference

Peroxide-reinforced extractions ((EP) or (EOP)) of D0 pulps lower both post-extraction kappa numbers and Klason lignins than either E or (EO). An oxygen-reinforced extraction (EO) results in lower kappa numbers, but affords comparable Klason lignins as an E stage (~1.2% lignin). Quinonoid structures in (EO) stocks are similar to that of the D0 (~1.7 mmol/g lignin). Peroxide inclusion in (EP) and (EOP) was found to eliminate both quinonoid and muconic moieties; these observations were confirmed with the (EP) treatment of reference pulps (periodate or periodate-peracetic acid) that contain significant levels of either quinones or muconic entities. The D1 bleachability order, from easiest to hardest, was D0(EOP) > D0(EP) ≈ D0(EO) > D0E. An identical order was found for how quickly the yellow chromophores (b* value) are eliminated. All extracted pulps, regardless of the type of extraction employed, approach a common D1 asymptotic brightness (~86 ISO) and b* value (~4). This indicates these pulps have similar residual D1 chromophores limiting the brightness ceiling.