Changes in cellulose supramolecular structure and molecular weight distribution during steam explosion of aspen wood

We have studied the cellulose supramolecular structure in pulps obtainedby steam explosion of aspen wood. The pulps were bleached with hydrogenperoxidein an OQP-sequence and characterised by size exclusion chromatography and¹³C cross polarisation magic angle spinning (CP/MAS)NMR-spectroscopy. With CP/MAS-NMR-spectroscopy and chemometrics we were able toseparate the supramolecular structural changes taking place during steamexplosion into two independent processes. One process was related to the extentof processing and showed degradation and dissolution of cellulose,hemicelluloseand lignin accompanied by an increase in cellulose content. The second processwas displayed by pulps having molecular weights below approximately 100000 andwas interpreted as showing the removal of dislocations and an increase incrystalline and/or paracrystalline cellulose in the cellulose fibrils.