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

13C CP-MAS NMR was used to study the ultrastructural aspects of ultrathin microfibrils extracted from sugar beet pulp. Depending on the stocking condition, the cellulose microfibrils contained different amounts of the polymorphs Ialpha and Ibeta. Structural changes were followed after a purification treatment. It was found that the crystallinity, as measured by solid-state NMR, increases as the purification proceeds. This is primarily due to the removal of non-cellulosic polysaccharides during the different treatments. 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 removed.