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

We have studied the cellulose supramolecular structure in pulps obtained by steam explosion of aspen wood. The pulps were bleached with hydrogen peroxide in an OQP-sequence and characterised by size exclusion chromatography and (1)3C cross polarisation magic angle spinning (CP/MAS) NMR-spectroscopy. With CP/MAS-NMR-spectroscopy and chemometrics we were able to separate the supramolecular structural changes taking place during steam explosion into two independent processes. One process was related to the extent of processing and showed degradation and dissolution of cellulose, hemicellulose and lignin accompanied by an increase in cellulose content. The second process was displayed by pulps having molecular weights below approximately 100 000 and was interpreted as showing the removal of dislocations and an increase in crystalline and/or paracrystalline cellulose in the cellulose fibrils.