X-ray diffraction (XRD)

The crystallinity index (CrI) of pretreated solids was determined using XRD. Diffractograms were collected with a D8 Advance instrument (Bruker-AXS, Karlsruhe, Germany) in θ-θ mode using Cu Kα1,2 radiation and a Våntec-1 detector. Samples were mounted on a low background Si sample holder. Continuous scans were applied within the 2θ range of 10°–40°. The data was collected until diffractograms appeared smooth. First, background removal of collected diffractograms was performed. The points for I_AM and I₀₀₂ were identified with support of a 4th degree polynomial fit as these are required for calculation of CrI. CrI was calculated based on the intensity ratio between I_AM and I₂₀₀ expressed as counts per seconds, using Eq. 5 [38]:

In Eq. 5, "I_AM" represents the intensity of diffraction of non-crystalline material, which is defined as the minimum of the valley between the main cellulose peaks (specifically the range 17.8°–19.8°). "I₀₀₂" refers to the maximum intensity of the peak that corresponds to the plane with the Miller indices 002 at a 2θ angle of 22°–24°.