The small and broad peak at 2 _ = 34.5◦represents the contribu-tion of (040) plane . The peak intensity correspondingto (002) lattice planes increased and became sharper as a resultof the chemical treatment, which was related to an increase ofthe crystallinity in the material. The crystallinity index (CrI) of thematerials was obtained by the peak height method and is sum-marized in . Several authors have mentioned thelimitations of this method ,particularly due to the underestimation of the contribution of theamorphous region, resulting in an overestimation of the CrI. Despiteits limitation, the peak height method has been extensively usedfor the calculation of the CrI and it was therefore used in thepresent work to allow a comparison with reported data. The crys-tallinity increased significantly from 37.4% to 68.8%. The highercrystallinity index of BGS compared to GS (37.4 vs. 47.1%) couldbe well understood as a result of the removal of amorphous non-cellulosic compounds, induced by the purification treatment (alkaliand bleaching treatments) performed to purify cellulose. Further-more, after acid treatment, most of the amorphous regions wereremoved, leading to a significant increase of crystallinity for CNC-GS sample. During the hydrolysis process, sulfite ions can penetratethe more accessible amorphous regions of cellulose and allow thehydrolytic cleavage of glycosidic bonds, which eventually releasesindividual crystallites . In addi-tion, during the preparation of cellulose nanocrystals the growthand realignment of monocrystals might occur simultaneously andthus can improve the cellulose crystallinity . Thisphenomenon could serve to explain the narrowing of the diffrac-tion peaks. This increase in the cellulose fibers crystallinity was alsoexpected to enhance their stiffness and rigidity, and therefore thestrength. Thus, it would be assumed that the potential mechan-ical properties and reinforcing capability of treated fibers shouldincreased . The CrI ofthe CNC-GS was comparable with the values in the range of 50–90%reported for nanocrystals isolated from marine biomass Posido-nia oceanica , coconut husk and rice husk . The average cross-sectionaldimension of the elementary cellulose crystallites was determinedfrom X-ray diffractograms by applying Scherrer’s expression asdescribed in Section 2. Since Scherrer’s equation is restricted tosamples of high crystallinity and without any broadening of peaks,this calculation was made only for CNC-GS, and the value foundwas 6.4 nm.