Study of the effect of bleaching agents on the crystalline index of cellulose-based materials derived from corn husk by CP/MAS 13C NMR and FT-IR spectroscopies

This work proposes an evaluation of the Crystalline Index (CrI) in function of the bleaching process employed during cellulose extraction from corn husk, for further characterization using CP/MAS C-13 NMR, XRD, and FT-IR. In that sense, CrI values were calculated by FT-IR and the bands associated with the crystalline and amorphous regions were observed at 1424 cm(-1) and 896 cm(-1), respectively. Similarly, the signals due to ordered (89.1 ppm) and disordered (84.2 ppm) cellulose chains were detected by solid-state C-13 NMR, while the Segal equation was only used for comparison purposes. Additionally, PCA studies showed consistent results attributed to the crystalline region in cellulose domains analyzed by both, FT-IR and solid-state C-13 NMR. The results revealed the coexistence of cellulose I/cellulose II and its effect on CrI, as well as the incomplete mercerization process, in some cases non-cellulosic residues can cause an overestimation of CrI. Additionally, the thermal stability and the glass transition temperature were determined by TGA/DTA and DSC analyses. Finally, a partially fibrillated network morphology with a diameter of 20.47 +/- 2.77 mu m was observed in cellulose bleached with peracetic acid, whereas organosolv method provides flexible and clean microfibrils with diameter sizes between 10 and 9 mu m.