Mechanism of microfibril contraction and anisotropic dimensional changes for cells in wood treated with aqueous NaOH solution

Abstract

Anisotropic swelling of wood samples was observed upon treatment with an aqueous NaOH solution with 0-0.20 fraction concentrations. At NaOH concentrations less than 0.10, the swelling occurred only along the tangential axis (T) and not along the radial (R) or longitudinal (L) axes. At greater NaOH levels, the swelling was even more pronounced along T with shrinkage along the other axes. These anisotropic changes along R and L were closely related to the crystallinity of microfibrils in the wood cell wall and simulated with a cell structure model. This exercise revealed microfibril contraction and matrix swelling in the wood cell wall upon NaOH treatment. The observed anisotropy in cross section was caused by differences in the microfibril angles (LR and LT) with the cell wall.

Formation of hydrogels from cellulose nanofibers

“…Previous studies support this possibility, and reported that the strong alkali treatment (mercerization) caused the longitudinal contraction of wood samples (Ishikura & Nakano, 2007;Nakano, Sugiyama, & Norimoto, 2000) and the in-plane contraction of cellulose samples, including a wet sheet of bacterial cellulose (Shibazaki et al, 1997) and a dry sheet of microfibrillated cellulose (Nakagaito & Yano, 2008). As an explanation for these behaviors, Nakano et al proposed that the contraction is related to the entropy elastic force of cellulose microfibrils (Nakano, 2010;Nakano et al, 2000). Because the cellulose nanofiber isolated in this study corresponds to the cellulose microfibril aggregates (or bundles) in wood cell walls (Donaldson, 2007;Fahlén & Salmén, 2005;Tarashima et al, 2010), their proposal may be applied to our example.…”

“…The procedure basically followed the method we used in previous studies (Abe et al, 2007;Abe & Yano, 2009, 2010. Wood powder was purified by a series of chemical treatments as follows.…”

“…We have also reported an isolation method in which plant fibers are ground in an undried state, and have prepared cellulose nanofibers from various sources such as softwood, rice straw, potato tuber and bamboo (Abe, Iwamoto, & Yano, 2007;Abe & Yano, 2009, 2010. In our previous study, a wood sample was homogeneously fibrillated by just one-time grinding, and the resultant nanofibers had a uniform width of approximately 15 nm and a length of more than several micrometers (Abe et al, 2007).…”

Wood Waste Turned Into Value Added Products: Thermal Plasticization by Benzylation Process

“…In order to increase reactivity and swell lignocellulosic materials before modifi cation, the material was treated with alkaline solution. Alkaline treatments contracts microfi brils in the cell wall and changes the dimension (Nakano, 2010). The mechanism of microfibril contraction and anisotropic dimensional changes of cells in wood are treated with aqueous NaOH solution.…”

“…In contrast to that, LOI increased with the NaOH, KOH and LiOH concentration. It is probably due to the transition between cellulose polymorph and the effect of alkali ion (Nakano, 2010;Borysiak and Doczekalska, 2005). The lowest TCI and LOI values were observed on untreated materials, which may indicate that the amorphous region is higher in untreated materials than after alkali treatment when mercerization takes place.…”