Cellulose nanofibers from white and naturally colored cotton fibers
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Suspensions of white and colored nanofibers were obtained by the acid hydrolysis of white and naturally colored cotton fibers. Possible differences among them in morphology and other characteristics were investigated. The original fibers were subjected to chemical analysis (cellulose, lignin and hemicellulose content), X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM). The nanofibers were analyzed with respect to yield, elemental composition (to assess the presence of sulfur), zeta potential, morphology (by scanning transmission electron microscopy (STEM)) and atomic force microscopy (AFM), crystallinity (XRD) and thermal stability by thermogravimetric analysis in air under dynamic and isothermal temperature conditions. Morphological study of several cotton nanofibers showed a length of 85–225 nm and diameter of 6–18 nm. The micrographs also indicated that there were no significant morphological differences among the nanostructures from different cotton fibers. The main differences found were the slightly higher yield, sulfonation effectiveness and thermal stability under dynamic temperature conditions of the white nanofiber. On the other hand, in isothermal conditions at 180 °C, the colored nanofibers showed a better thermal stability than the white.
KeywordsNaturally colored cotton fibers Colored cellulose nanofibers AFM STEM
The authors gratefully acknowledge the supply of cotton fiber samples by Dr. Odilon R. R. F. Silva and Dr. Luiz P. de Carvalho (Embrapa Algodão, Brazil) and financial support provided by FAPESP (Process No. 07/50863-4), FINEP, CNPq and EMBRAPA.
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