Characterisation of cellulose treated by the steam explosion method. Part 1: Influence of cellulose resources on changes in morphology, degree of polymerisation, solubility and solid structure

Abstract

Abstract Steam explosion treatment was carried out on almost pure natural celluloses (wood pulps and purified cotton linter) to obtain alkali‐soluble cellulose and to clarify the effect of cellulose resources on the changes in morphology, viscosity‐average degree of polymerisation P v , solubility towards aqueous alkali solution S a , and supermolecular structure of the celluloses. Soft wood pulp was most effectively treated in view of the changes in morphology and P v , but cotton linter was found to be resistant to the treatment. The degree of breakdown of intramolecular hydrogen bonding at C 3 and C 6 ( X am ( C 3 ) and X am ( C 6 ), respectively), as determined by solid‐state cross‐polarisation/magic angle sample spinning (CP/MAS) NMR, had a tendency to increase for soft wood pulp by the steam treatment employed here. Contrary to this, the crystallinity and the average crystal size estimated by X‐ray diffraction increased. Solubility of the treated wood pulps towards aqueous alkali solution can be improved to 100% when suitable conditions for the steam explosion are chosen to give P v less than 400 and X am (C 3 ) greater than 44% and X am (C 6 ) greater than 33%. Solid‐state NMR analysis may suggest that hydrogen bond formation at the C 2 hydroxyl group may first take place in the structural change of cellulose during the steam explosion.