The formation of LC and other aromatic end-group structures in O-alkyl-substituted cellulose during kraft pulping conditions

Abstract

Ultraviolet resonance Raman spectroscopy (UVRRS) was used to study the formation of aromatic and/or lignin-carbohydrate (LC) structures at the reducing end groups of O-alkyl-substituted cellulose under conditions simulating the initial phase of kraft pulping. The derivatives studied were methyl cellulose (MC) with degree of substitution (DS) of 1.64–1.95, carboxymethyl cellulose (CMC) with DS ∼0.6, and a lignin model compound, creosol. The total alkali concentrations in the treatments were 0.1 M and 0.5 M and the sulfidities were 1%, 10%, and 30%. HS− ions and creosol are both strong nucleophiles and they compete for the hot-alkali-generated unsaturated electrophilic reaction sites in the reducing end groups of the polysaccharides. The results indicated that conditions similar to those in the initial phase of conventional kraft cooking (high OH− and low HS− ion concentrations) increased the aromatic nature of the end groups and conditions similar to those in the initial phase of super batch cooking (low OH− and high HS− ion concentrations) partly inhibited the formation of aromatic and LC end groups.