Structural characterization of carboxyl cellulose nanofibers extracted from underutilized sources

Two different chemical methods, TEMPO-oxidation and nitro-oxidation, were used to extract carboxylcellulose nanofibers (CNFs) from non-wood biomass sources (i.e., jute, soft and hard spinifex grasses). The combined TEMPO-oxidation and homogenization approach was very efficient to produce CNFs from the cellulose component of biomass; however, the nitro-oxidation method was also found to be effective to extract CNFs directly from raw biomass even without mechanical treatment. The effect of these two methods on the resulting cross-section dimensions of CNFs was investigated by solution small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The UV-Vis spectroscopic data from 0.1 wt% TEMPO-oxidized nanofiber (TOCNF) and nitro-oxidized nanofiber (NOCNF) suspensions showed that TOCNF had the highest transparency (> 95%) because of better dispersion, resulted from the highest carboxylate content (1.2 mmol/g). The consistent scattering and microscopic results indicated that TOCNFs from jute and spinifex grasses possessed rectangular cross-sections, while NOCNFs exhibited near square cross-sections. This study revealed that different oxidation methods can result in different degrees of biomass exfoliation and different CNF morphology.