It is well known that cellulose microfibrils of plant cell-walls have disordered regions periodically present along each cellulose microfibril, which have been indirectly shown from the leveling-off degrees of polymerization (DP, 200-300) obtained from such celluloses by dilute acid hydrolysis. However, it is unknown whether such disordered regions are originally present in nascent cellulose microfibrils formed by biosynthesis process or artificially formed during delignification and/or drying processes.<br/>In this paper, disordered regions of plant cellulose microfibrils are studied in terms of two aspects. One is dilute acid hydrolysis of wood meals, de-waxed wood meals, wood holocellulose and wood celluloses for dried or never-dried samples, to study the conditions to form the leveling-off DPs and to determine DP values after dilute acid hydrolysis. The results showed that the leveling-off DPs varied, depending on the delignification and drying processes, indicating that such leveling-off DPs are formed artificially during pulping and drying processes. The presence of glucomannan was also the key factor to form the leveling-off DPs in the case of softwood cellulose.<br/>Another method was a layer-by-layer peeling of surface cellulose microfibrils, in which glucoronate units were densely and position-selectively formed on the microfibril surfaces by TEMPO-mediated oxidation. The surface molecules containing both glucose and glucoronate units present on each TEMPO-oxidized cellulose microfibril were removed by alkali treatment at a high temperature. Solid-state <sup>13</sup>C-NMR, X-ray diffraction and AFM analyses were carried out to the layer-by-layer peeled TEMPO-oxidized cellulose samples. The results showed that algal celluloses with larger cellulose microfibril sizes and higher crystallinities had rather perfect crystallites without any disordered regions on the microfibril surfaces. All the C6-OH groups in microfibril surface molecules, facing outside from the microfibril surface, had g-g conformation, whereas those facing inside the crystallite had g-t conformation. All the C6-OH groups present inside crystallites had t-g conformation. These different C6-OH conformations remained after repeated removal of the surface layers of algal cellulose microfibrils. In contrast, wood cellulose microfibrils indicated to have somewhat disordered structures from two layers from the microfibril surface, probably because of smaller microfibril widths.

Disordered structures in plant cellulose microfibrils in terms of leveling-off DP and layer-by-layer surface peeling of microfibrils

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.