MECHANISTIC BEHAVIOR OF LIGNIN MODEL COMPOUNDS: INVESTIGATION ON THE LOWER BLEACHABILITY OF SODA/ANTHRAQUIONE (SAQ) PULP (original) (raw)

ABSTRACT Laboratory study on bleaching of soda/anthraquinone (SAQ) pulp suggests that AQ catalyzed soda pulp is less responsive towards bleaching chemicals compared to kraft pulp. In this context, shortening of the H-Factor is considered to be one possible strategy to improve bleachability of the SAQ hardwood pulp. To investigate the poorer bleachability, soda, SAQ and kraft pulping were carried out using eight commercially available lignin model compounds representing mostly the reactive species generated during pulping. The investigation indicated that these reactive species vigorously participated in base induced condensation reaction. From GC, GC-MS and solid sample introduction MS analysis, vinylogous compounds were found to undergo Michael addition to repolymerize. Correlating the rate of condensation with alkalinity, some lignin model compounds were found to undergo condensation at a lower rate at 0.6 M NaOH compared to 0.2 M NaOH; which explains the improved final brightness by shortening the pulping time of SAQ/SMAQ pulp. Evidence was also found that the pre extraction (hot water, carbonate or acetate extraction) process removed hydrolysable compounds that could influence pulping and bleaching. Keyword: Anthraquinone, alkaline pulping, lignin condensation, quinone methide, carbanion, Michael addition, preextraction.