Abstract
Peroxide‐reinforced extractions ((EP) or (EOP)) of D0 pulps lower both post‐extraction kappa numbers and Klason lignins more 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 those of the D0 pulps (1.7 mmol/g lignin). Peroxide inclusion in EP and EOP appeared to eliminate both quinonoid and muconic acid moieties. These observations were confirmed with (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 (∼4.2) when excess ClO2 is applied. The main difference among these pulps was how quickly the asymptotic limits are approached as a function of ClO2 consumed. The bleachability study indicates that various extracted pulps have similar residual D1 chromophores limiting the brightness ceiling. *Dedicated to Drs. Donald R. Dimmel and Thomas J. McDonough on their retirement from the Institute of Paper Science and Technology.
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