*3.3. Structure of Raw OPEFB Fiber, Treated Cellulose, Microcrystalline Cellulose and Nano-Bentonite as Observed by XRD*

The XRD patterns of raw OPEFB fiber, treated OPEFB cellulose and OPEFB microcrystalline cellulose are shown in Figure 5. The XRD diffractograms of all the samples revealed a broad amorphous hump and crystalline peaks, indicating that OPEFB is a semi-crystalline material in nature. Generally, all samples show peaks at around 2θ = 15–16◦ , 2θ = 21–22◦ and 2θ = 34–35◦ , which indicates that the OPEFB contains a crystalline structure of cellulose I with (110), (200) and (004) diffraction planes, respectively, which is typical for natural plant cellulose [25]. The lowest intensity peak at 2θ = 18◦ is related to amorphous region arrangement, while 2θ = 22◦ is related to the crystalline structure of cellulose. The CrI was calculated based on the Segal formula [26]. The raw OPEFB possesses 37.80% CrI value, which is the lowest among all samples. This can be associated with its high amorphous region. Conversely, the microcrystalline cellulose possesses the highest CrI value, which is 65.9% due to the removal of the amorphous phase from its structure.

*3.3. Structure of Raw OPEFB Fiber, Treated Cellulose, Microcrystalline Cellulose and* 

The XRD patterns of raw OPEFB fiber, treated OPEFB cellulose and OPEFB microcrystalline cellulose are shown in Figure 5. The XRD diffractograms of all the samples revealed a broad amorphous hump and crystalline peaks, indicating that OPEFB is a semicrystalline material in nature. Generally, all samples show peaks at around 2Ɵ = 15–16°, 2Ɵ = 21°–22° and 2Ɵ = 34°–35°, which indicates that the OPEFB contains a crystalline structure of cellulose I with (110), (200) and (004) diffraction planes, respectively, which is typical for natural plant cellulose [25]. The lowest intensity peak at 2θ = 18° is related to amorphous region arrangement, while 2θ = 22° is related to the crystalline structure of cellulose. The CrI was calculated based on the Segal formula [26]. The raw OPEFB possesses 37.80% CrI value, which is the lowest among all samples. This can be associated with its high amorphous region. Conversely, the microcrystalline cellulose possesses the highest CrI value, which is 65.9% due to the removal of the amorphous phase from its structure.

*Nano-Bentonite as Observed by XRD* 

**Figure 5.** X-ray diffraction (XRD) pattern of raw OPEFB cellulose, treated cellulose and microcrystalline cellulose. **Figure 5.** X-ray diffraction (XRD) pattern of raw OPEFB cellulose, treated cellulose and microcrystalline cellulose.

The low Crl value of the raw OPEFB indicates that it contains a high content of hemicellulose and lignin. The same results were obtained through previous studies [27]. As expected, crystallinity of the OPEFB increased after the removal of lignin and hemicellulose. After the alkaline and bleaching pre-treatment, the peak of the treated OPEFB cellulose became sharper and more intense than the raw OPEFB, suggesting that the crystallinity of the treated OPEFB cellulose becomes higher after the treatment. However, the CrI value has been further increased when the treated OPEFB cellulose was acid hydrolyzed to form microcrystalline cellulose. This clearly indicates that more amorphous linkages within the cellulose structure have been broken down, releasing the high crystalline cel-The low Crl value of the raw OPEFB indicates that it contains a high content of hemicellulose and lignin. The same results were obtained through previous studies [27]. As expected, crystallinity of the OPEFB increased after the removal of lignin and hemicellulose. After the alkaline and bleaching pre-treatment, the peak of the treated OPEFB cellulose became sharper and more intense than the raw OPEFB, suggesting that the crystallinity of the treated OPEFB cellulose becomes higher after the treatment. However, the CrI value has been further increased when the treated OPEFB cellulose was acid hydrolyzed to form microcrystalline cellulose. This clearly indicates that more amorphous linkages within the cellulose structure have been broken down, releasing the high crystalline cellulose [28].

lulose [28]. Figure 6a displays the XRD pattern of the nano-bentonite (before and after ultra-sonication) in the region of 2Ɵ = 5° to 50°. However, the signal from 5° to 10° was focused to clearly observe the changes in d001 basal spacing of the nano-bentonite upon ultra-sonication (Figure 6b). The nano-bentonite's basal spacing represents the stacking distance and order between its platelets and provides information about the platelets dispersion. Figure 6b exhibits that the d001 basal spacing of raw nano-bentonite is 1.44 nm. However, Figure 6a displays the XRD pattern of the nano-bentonite (before and after ultrasonication) in the region of 2θ = 5◦ to 50◦ . However, the signal from 5◦ to 10◦ was focused to clearly observe the changes in d<sup>001</sup> basal spacing of the nano-bentonite upon ultrasonication (Figure 6b). The nano-bentonite's basal spacing represents the stacking distance and order between its platelets and provides information about the platelets dispersion. Figure 6b exhibits that the d<sup>001</sup> basal spacing of raw nano-bentonite is 1.44 nm. However, the d<sup>001</sup> of the nano-bentonite has been increased to 1.47 nm after the ultra-sonication process. This indicates that the ultra-sonication process does slightly increase the d<sup>001</sup> of the nano-bentonite, by altering the bentonite layer's stacking through de-agglomeration of the bentonite's tactoids. The small increase in the basal spacing of bentonite can facilitate the intercalation of the TPS chain during the mixing process and improve the film's strength. This outcome was the same with the result of Abdul Hamid et al., where they showed that the ultra-sonication process could produce more loosely packed MMT and encourage the copolymer chains' intercalation inter-platelets [29].

Apparently, there are clear changes in the XRD pattern of the nano-bentonite after it is subjected to the ultra-sonication process (Figure 6a). The diffraction peaks at 2θ = 21.8◦ , 25.4◦ and 26.6◦ disappeared, suggesting that the ultra-sonication process has successfully and effectively disrupted and at a certain level destroyed the organization of the nanobentonite platelets [30]. Moreover, the diffraction peaks at 2θ = 19.76◦ and 35◦ are shifted to lower angles to 18.9◦ and 34.0◦ , respectively, due to the expanding of basal spacing of the nano-bentonite platelets.

copolymer chains' intercalation inter-platelets [29].

the nano-bentonite platelets.

the d001 of the nano-bentonite has been increased to 1.47 nm after the ultra-sonication process. This indicates that the ultra-sonication process does slightly increase the d001 of the nano-bentonite, by altering the bentonite layer's stacking through de-agglomeration of the bentonite's tactoids. The small increase in the basal spacing of bentonite can facilitate the intercalation of the TPS chain during the mixing process and improve the film's strength. This outcome was the same with the result of Abdul Hamid et al., where they showed that the ultra-sonication process could produce more loosely packed MMT and encourage the

Apparently, there are clear changes in the XRD pattern of the nano-bentonite after it is subjected to the ultra-sonication process (Figure 6a). The diffraction peaks at 2θ = 21.8°, 25.4° and 26.6° disappeared, suggesting that the ultra-sonication process has successfully and effectively disrupted and at a certain level destroyed the organization of the nanobentonite platelets [30]. Moreover, the diffraction peaks at 2θ = 19.76° and 35° are shifted to lower angles to 18.9° and 34.0°, respectively, due to the expanding of basal spacing of
