X-ray diffraction (XRD) was conducted to ascertaining the crystallinity of the garlic straw fibres after different treatments (GS, ATGS, BGS and CNC-GS samples). Each material in the form of milled powder was placed on the sample holder and levelled to obtain total and uniform X-ray exposure. The samples were examined using an X-ray diffractometer (D8-Advance Bruker AXS GmbH) at room temperature with a monochromatic Cu K radiation source ( = 0.154 nm) in the step-scan mode with a 2 angle ranging from 10◦ to 50◦ with a step of 0.04 and scanning time of 5.0 min. The crystallinity index CrI, was determined using the method described by Segal et al. (1959). Moreover, the average thickness of cellulose crystallites was estimated also from the XRD patterns by using Scherrer’s Eq. (1):