Abstract
A high yield of lignin was generated when solid alkali (MgO) and active oxygen (O2 and H2O2) were used in bagasse cooking as a pretreatment for lignin conversion. In the present work, the lignin present in raw material, pulp, and yellow liquor was characterized by Fourier transform infrared spectroscopy (FTIR) and heteronuclear single-quantum coherence (HSQC) NMR. The results showed that 95.4% of the lignin was obtained from the raw material and present in the yellow liquor. The syringyl (S/S′/S″) units could be changed completely and removed from the raw material, and a novel G′ unit with a carbonyl group was generated through an oxidizing reaction. The phenolic structures had a high reactivity during the cooking process, and the β-O-4′ (A/A′/A″) structures had different levels of reactivity. Moreover, the H unit, P structure, and nonphenolic β-5′ and β–β′ structures were stable throughout the cooking process.
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