The small and broad peak at 2 _ = 34.5◦ represents the contribution of (040) plane . The peak intensity corresponding to (002) lattice planes increased and became sharper as a result of the chemical treatment, which was related to an increase of the crystallinity in the material. The crystallinity index (CrI) of the materials was obtained by the peak height method and is summarized in . Several authors have mentioned the limitations of this method ,particularly due to the underestimation of the contribution of the amorphous region, resulting in an overestimation of the CrI. Despite its limitation, the peak height method has been extensively used for the calculation of the CrI and it was therefore used in the present work to allow a comparison with reported data. The crystallinity increased significantly from 37.4% to 68.8%. The higher crystallinity index of BGS compared to GS (37.4 vs. 47.1%) could be well understood as a result of the removal of amorphous non-cellulosic compounds, induced by the purification treatment (alkali and bleaching treatments) performed to purify cellulose. Furthermore, after acid treatment, most of the amorphous regions were removed, leading to a significant increase of crystallinity for CNC-GS sample. During the hydrolysis process, sulfite ions can penetrate the more accessible amorphous regions of cellulose and allow the hydrolytic cleavage of glycosidic bonds, which eventually releases individual crystallites . In addition, during the preparation of cellulose nanocrystals the growth and realignment of monocrystals might occur simultaneously and thus can improve the cellulose crystallinity . This phenomenon could serve to explain the narrowing of the diffraction peaks. This increase in the cellulose fibers crystallinity was also expected to enhance their stiffness and rigidity, and therefore the strength. Thus, it would be assumed that the potential mechanical properties and reinforcing capability of treated fibers should increased . The CrI of the CNC-GS was comparable with the values in the range of 50–90%reported for nanocrystals isolated from marine biomass Posidonia oceanica , coconut husk and rice husk . The average cross-sectional dimension of the elementary cellulose crystallites was determined from X-ray diffractograms by applying Scherrer’s expression as described in Section 2. Since Scherrer’s equation is restricted to samples of high crystallinity and without any broadening of peaks ,this calculation was made only for CNC-GS, and the value found was 6.4 nm.