Changes in the degree of polymerization of wood celluloses during dilute acid hydrolysis and TEMPO-mediated oxidation: Formation mechanism of disordered regions along each cellulose microfibril.

Most commercially available plant celluloses, such as kraft pulps and cotton celluloses, have so-called leveling-off degrees of polymerization (LODPs) when subjected to dilute acid hydrolysis. The formation of LODPs is hypothesized to be caused by disordered regions that are present periodically along each cellulose microfibril in plant celluloses. Here, we prepared never-dried wood cellulose, and wood celluloses at different drying stages, and subjected them to dilute acid hydrolysis. The viscosity average degrees of polymerization (DPv) of the wood celluloses decreased in DPv with increasing dilute acid-hydrolysis times. However, the DPv values after 4h of acid hydrolysis differed from those of softwood bleached kraft pulp (SBKP), which showed typical patterns of LODPs. Thus, the disordered regions corresponding to LODPs that were observed for SBKP are probably not synthesized in the native wood. Instead, such disordered regions are formed secondarily or artificially during the isolation/purification and/or drying processes of plant cellulose fibers. The results of the dilute acid hydrolysis and the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation of SBKP and softwood unbleached soda-anthraquinone pulp showed that the structures of disordered regions can be controlled via the preparation and drying conditions of wood cellulose used as starting materials.

Dynamic Viscoelastic Functions of Liquid-Crystalline Chitin Nanofibril Dispersions.

The dynamic viscoelastic functions of aqueous chitin nanofibril (ChNF) dispersions are defined by their liquid-crystalline fibril arrangement. Four ChNF dispersions with different structures were prepared from squid-pen ß-chitin, by sonication in aqueous acetic acid at pH 3 for 4-40 min. Squid-pen ß-chitin was disintegrated into randomly oriented bundles of ChNFs during the initial stage of sonication and then became more finely dispersed with further sonication up to 8 min. The additional sonication resulted in the individualization of the approximately 3 nm-wide ChNFs. The individual ChNFs self-organized into a nematic liquid crystalline phase. All ChNF dispersions showed power-law concentration c dependences of their storage moduli G' at a certain angular frequency ω (Gω' = Acα). The front factor A was positively correlated with the degree of disintegration. The exponent α increased from 2.7 to 3.8-3.9, as the ChNF dispersion self-organized from the randomly dispersed structure into the nematic-ordered fibril arrangement. This demonstrated an enhancement in the solid concentration dependence.