Assembling and Redispersibility of Rice Straw Nanocellulose: Effect of <i>tert</i>-Butanol


Self-assembling of sulfuric-acid-hydrolyzed cellulose nanocrystals (CNCs, 6.4 nm wide) and TEMPO oxidized cellulose nanofibrils (CNFs, 2.1 nm wide) from aqueous suspensions was induced by rapid freezing (−196 °C, 10 min) and slow lyophilization (−50 °C, 0.05 mbar, 2 days). The assembled structures contain submicron (200–700 nm) wide and tens of micrometer long fibers at up to 0.1–0.5% and 0.01–0.05%, the critical fiber-to-film transformation concentrations for CNCs and CNFs, respectively. The assembled fiber widths were significantly reduced to ∼40 nm, that is, by 1 order of magnitude, when 10% of the aqueous media was replaced with <i>tert</i>-butanol. Further increasing <i>tert</i>-butanol contents in the media to 93/7 (CNCs) and 50/50 (CNFs) <i>tert</i>-butanol/water, both at 0.1% nanocellulose concentration, reduced longitudinal assembling for CNCs and lateral assembling for CNFs as well as increased critical fiber-to-film transformation concentration for CNFs. While all assembled structure could be redispersed in water, those from <i>tert</i>-butanol/water could also be easily redispersed in DMF aided with brief 2 min ultrasonication. None of the assembled structures could be redispersed in the lower dielectric constant ethanol, acetone or chloroform

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