Formation of disordered regions is caused by drying in cellulose microfibrils of Egeria densa

Abstract

Periodically disordered regions can be induced by drying in cellulose microfibrils of several plant species. In this study, cellulose nanocrystals were prepared from never-dried and oven-dried cellulose samples from Egeria densa by sulfuric acid hydrolysis and observed with transmission electron microscopy. Cellulose nanocrystals from never-dried samples were long (> 1 μm in length), curved smoothly, and had very few kinks. In contrast, cellulose nanocrystals from oven-dried samples were shorter (50–600 nm in length) and were almost entirely straight. These results indicated that never-dried cellulose microfibrils lacked the disordered regions along the microfibril and exhibited a continuous, low bending rigidity. Never-dried and oven-dried cellulose samples from E. densa were subjected to acid hydrolysis, dissolution in 1% LiCl/dimethylacetamide, and size-exclusion chromatography–multi-angle laser-light scattering analysis. After acid hydrolysis, oven-dried samples showed a significantly lower degree of polymerization than never-dried samples. In addition, oven-dried samples showed a unimodal and narrow molar mass distribution, whereas never-dried samples showed a bimodal distribution after acid hydrolysis. These results indicated that oven-drying induces the disordered regions along the cellulose microfibril and that the disordered regions are cleaved by acid hydrolysis.