Physical Structure Selectivity of Universal Alkaline Periodate Oxidation on Lignocellulose for Facile Isolation of Cellulose Nanocrystals.

In this work, we report for the first time the alkaline periodate oxidation on lignocelluloses for the selective isolation of cellulose nanocrystals (CNCs). With the high concentrations as potassium salt at pH 10, periodate ions predominantly exist as dimeric orthoperiodate ions (H2I2O104-). With reduced oxidizing activity in alkaline solutions, dimeric orthoperiodate ions preferentially oxidized non-ordered cellulose regions. The alkaline surroundings promoted the degradation of these oxidized cellulose chains via β-alkoxy fragmentation and generated CNCs. Obtained CNCs were uniform and generally contain carboxyl groups. Furthermore, the reaction solution could be conveniently reused after the regeneration of periodate with ozone gas. This method allowed us to directly produce CNCs from diverse sources, in particular lignocellulosic raw materials including sawdust (European beech and Scots pine), flax and kenaf in addition to microcrystalline cellulose and pulp.