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Molecules 2021, 26, 5276 14 of 22 The results of the XRD analysis of PLA/chitin-, B-CNF-, and C-CNF-reinforced bio- composites is presented in Figure 7. The result shows peaks between 2θ = 16◦ to 22◦, with the highest peak at 2θ = 16◦. The neat PLA used in this study was semicrystalline, and these peaks are due to the crystalline parts. The remaining part of the graph, without any peaks in the amorphous region, shows that the biocomposite was more amorphous, as shown by the span of the non-peak region. The addition of chitin to neat PLA is shown with sample P9010, which reduced the XRD peak height compared to PLA/chitin/CNF [57]. However, as was reported in previous studies, the three peaks in the neat PLA were still maintained only to reduce the intensity [58]. Furthermore, similar peaks were observed throughout the biocomposite with B-CNF and C-CNF loading, with slightly higher peaks than the P9010 (control sample) [59]. The peaks were mostly similar in all the biocomposite regions, probably due to the high percentage of PLA present in the biocomposites. The B-CNF-reinforced biocomposite peaks had a higher peak intensity than the C-CNF-reinforced biocomposites with the same percentage loading. This was expected, since there is a significant difference between the crystallinity indices of these two types of CNF. The XRD crystallinity of the bamboo CNF was 75.68%, which is greater than that of the commercial CNF, 70.67% (Figure 2b). This is important because it has a significant effect on their reinforcement ability. A higher crystallinity index means a higher reinforcement effect in composite materials. Cellulose and polylactic acid have been reported to have similar crystalline peak regions in XRD analysis [60], and the peak is maintained or increased with the addition of CNF loading [61]. 2.6. The Thermal Properties of Bamboo and Commercial CNF-Reinforced PLA/Chitin Bionanocomposites The thermogravimetry analysis results ae shown in Figure 8. The Figure shows two degradation steps: initial and significant degradation. The onset temperature shows the beginning of the degradation process of the material content. The initial degradation occurred below 50–65 ◦C for the PLA/chitin-, B-CNF-, and C-CNF-reinforced biocompos- ites. The thermal degradation of the samples began with the initial step, which can be attributed to the evaporation of water and the volatile content (vaporisation of moisture) of the composites. The second degradation onset of PLA/chitin was ~285 ◦C. Thermal stability tends to improve with the addition of the two types of CNF fibres. The onset temperature of 5% CNF biocomposite was the highest. The second degradation shown on the graph occurred at a temperature between ~300 and 310 ◦C for the B-CNF biocomposites and between 290 and 300 ◦C for the C-CNF biocomposites. As was observed from this range of values, the B-CNF biocomposites had a higher onset temperature than the C-CNF biocomposites. The major decomposition peaks observed on the DTG graph (Figure 8b) show that the B-CNF biocomposites’ peak degradation temperature ranged from ~360 to 380 ◦C, which was greater than that of the C-CNF biocomposites, at ~340–354 ◦C peak temperature. These values probably show that B-CNF reinforced biocomposites have better thermal stability than C-CNF-reinforced biocomposites [62]. However, both biocomposites had percentage degradation values above 80% of the weight loss decomposition point of biocomposites [63]. PLA/chitin reinforced with B-CNF has a higher thermal stability than when it is reinforced with C-CNF, probably due to the difference between the crystallinity properties of the CNFs [64].PDF Image | Supercritical Carbon Dioxide Isolation of Cellulose Nanofibre
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