Abstract
Cellulose nanowhiskers as one kind of renewable and biocompatible nanomaterials evoke much interest because of its versatility in various applications. Herein, the sisal cellulose nanowhiskers with ultrathin diameter of 5–10 nm, high crystallinity of 74% and C6 carboxylate groups converted from C6 primary hydroxyls were prepared via a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)/NaBr/NaClO system selective oxidization combined with mechanical homogenization. The effects of sodium hydroxide concentration in alkali pretreatment on the final sisal cellulose nanowhiskers were explored. It was found that with the increase of sodium hydroxide concentration, the sisal fiber crystalline type would change from cellulose I to cellulose II. The versatile sisal cellulose nanowhiskers would be particularly useful for applications in the nanocomposites as reinforcing phase, as well as in tissue engineering, filtration, pharmaceutical and optical industries as additives.
Highlights
A number of new nanomaterials with various excellent properties have been found and prepared in order to satisfy the development of social industry (Roduner 2006)
It could be seen that when the alkali concentration was 15 %, the X-ray diffraction had both the characteristic peaks of cellulose typeIand II, and the fiber at this time was a mixture of cellulose Iand II, indicating that with the increase of the alkali concentration, the cellulose in sisal fiber would gradually transform from cellulose I to cellulose II, which was basically consistent with previous studies on this aspect (Yu et al 2014)
The absorption peak at 1110 cm− 1 was caused by the C-O stretching vibration of the cellulose six-membered ring framework, and the absorption peak was nearly disappeared with the increase of alkali concentration, which was related to the change of hydrogen bond
Summary
A number of new nanomaterials with various excellent properties have been found and prepared in order to satisfy the development of social industry (Roduner 2006). Some bacterias could even use toxic compounds generated after industrial activities as carbon source to form cellulose (Marín et al 2019). Enzymatic hydrolysis is another interesting pathway to produce nanocellulose (Karim et al 2017), which mainly used the specificity of cellulase to hydrolyze the amorphous area in the fiber to prepare nanocellulose. Biological method and enzyme hydrolysis did not generate toxic residues as acid hydrolysis did, which were normally held in mild thermal and pressure conditions, resulting in a lower energy-intensive process (Fritz et al 2015) but low efficiency
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