Structural aspects in ultrathin cellulose microfibrils followed by C-13 CP-MAS NMR

C-13 CP-MAS NMR was used to study the ultrastructural aspects of ultrathin microfibrils extracted from sugar beet pulp. Depending on the stocking cond ition, the cellulose microfibrils contained different amounts of the polymo rphs I alpha and I beta. Structural changes were followed after a purificat ion treatment. It was found that the crystallinity, as measured by solid-st ate NMR, increases as the purification proceeds. This is primarily due to t he removal of non-cellulosic polysaccharides during the di:different treatm ents. This was confirmed by neutral sugar analysis. A crystallite size of 4 nm is derived from the NMR results which is in good agreement with the TEM observations. To avoid any underestimate of the microfibrils size, most of the hemicelluloses tightly bound to the cellulose microfibrils has to be r emoved. (C) 1999 Elsevier Science Ltd. All rights reserved.