Curaua nanofibers extracted under different conditions were investigated. The raw fibers were mercerized with NaOH solutions; they were then submitted to acid hydrolysis using three different types of acids (H 2 SO 4 , a mixture of H 2 SO 4 /HCl and HCl). The fibers were analyzed by cellulose, lignin and hemicellulose contents; viscometry, X-ray diffraction (XRD) and thermal stability by thermogravimetric analysis (TG). The nanofibers were morphologically characterized by transmission electron microscopy (TEM) and their surface charges in suspensions were estimated by Zeta-potential. Their degree of polymerization (DP) was characterized by viscometry, crystallinity by XRD and thermal stability by TG. Increasing the NaOH solution concentration in the mercerization, there was a decrease of hemicellulose and lignin contents and consequently an increase of cellulose content. XRD patterns presented changes in the crystal structure from cellulose I to cellulose II when the fibers were mercerized with 17.5% NaOH solution. All curaua nanofibers presented a rod-like shape, an average diameter (D) of 6-10 nm and length (L) of 80-170 nm, with an aspect ratio (L/D) of around 13-17. The mercerization of fibers with NaOH solutions influenced the crystallinity index and thermal stability of the resulting nanofibers. The fibers mercerized with NaOH solution 17.5% resulted in more crystalline nanofibers, but thermally less stable and inferior DP. The aggregation state increases with the amount of HCl introduced into the extraction, due to the decrease of surface charges (as verified by Zeta Potential analysis). However, this release presented nanofibers with better thermal stability than those whose acid hydrolysis was carried out using only H 2 SO 4 .
There is growing interest in cellulose nanofibres from renewable sources for several industrial applications. However, there is a lack of information about one of the most abundant cellulose pulps: bleached Eucalyptus kraft pulp. The objective of the present work was to obtain Eucalyptus cellulose micro/nanofibres by three different processes, namely: refining, sonication and acid hydrolysis of the cellulose pulp. The refining was limited by the low efficiency of isolated nanofibrils, while sonication was more effective for this purpose. However, the latter process occurred at the expense of considerable damage to the cellulose structure. The whiskers obtained by acid hydrolysis resulted in nanostructures with lower diameter and length, and high crystallinity. Increasing hydrolysis reaction time led to narrower and shorter whiskers, but increased the crystallinity index. The present work contributes to the different widespread methods used for the production of micro/nanofibres for different applications.
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