*2.5. Structural Characterization*

X-ray diffraction (XRD) patterns were recorded on a Rigaku SmartLab X-ray powder diffractometer equipped with a 9 kW CuKα rotating anode (Rigaku, Tokyo, Japan), operating at 40 kV and 150 mA. A Göbel mirror was used to convert the divergent X-ray beam into a parallel beam and to suppress the Cu Kβ radiation. The specimens were analyzed at room temperature using a zero diffraction quartz sample holder. XRD data analysis was carried out using PDXL 2.1 software from Rigaku. The crystallinity index (*CrI*) was determined by using the empirical method proposed by Segal et al. [55]:

$$CrI(\%) = \frac{I - I'}{I} \times 100$$

where *I* is the intensity of the peak assigned to (002) crystal plane of cellulose located at 21−23◦ and *I* is the intensity of the diffractogram of the amorphous cellulose at 18−19◦. In addition, the crystallite size of cellulose (*D*) was estimated by Scherrer's Equation:

$$D = \frac{K\lambda}{\beta \cos \theta}$$

where *K* is a constant of value 0.94, *λ* is the X-ray wavelength (0.15418 nm), *θ* is the diffraction angle for the (200) plane, and *β* is the peak width at half the maximum intensity (calculated from peak deconvolution when necessary).

## *2.6. Mechanical Characterization*

The mechanical properties of the films were measured by uniaxial tensile tests on a dual column Instron 3365 universal testing machine. Dog-bone-shaped samples were stretched at a rate of 5 mm/min. All the stress–strain curves were recorded at 25 ◦C and 44% RH. Ten measurements were conducted for each sample and the results were averaged to obtain a mean value. From the stress–strain curves, Young's modulus, yield stress, elongation at the break, and fracture energy (area below the curve) were calculated.
