## 3 Results and Discussion
### Biochar Composites Characterisation  
#### 3.2.1 Thermal Behaviour of the PLA/PBAT/BC Composites  
Figure 4 represents the DSC thermograms from the second heating-cycle of the PLA/PBAT blend and PLA/PBAT/BC composites. Here, two distinct transitions are observed: the cold-crystallisation exotherm at \(\sim\)101.5 \({}^{\circ}\)C and a melting endotherm at \(\sim\)176 \({}^{\circ}\)C for PLA/PBAT blend. The glass transition of the PLA/PBAT blend and composites appear around \(\sim\)65 \({}^{\circ}\)C. The biochar addition into the PLA/PBAT blend decreases the cold-crystallisation temperature of the composites by (\(\sim\)5 \({}^{\circ}\)C) with 1 wt% of biochar content. Moreover, the crystallinity of neat PLA improves with filler addition, where fillers act as nucleating agents. These nucleating agents lower the cold-crystallisation temperature and improve the percentage crystallinity of PLA [48]. In PLA/PBAT/BC composites, the decrease in cold-crystallisation temperature can be attributed to the nucleation effect of the biochar particles, something which has also been observed in other biochar-based polymer composites [45; 49]. Table 2 shows the thermal properties of the PLA/PBAT blend and PLA/PBAT/BC composites. The melting temperature (\(T_{m}\)), crystallisation temperatures (\(T_{c}\)) and total crystallinity (\(X_{c}\)) of the blend and composites have been calculated. The PLA/PBAT (80/20) blend has a melting point of 176.05 \({}^{\circ}\)C. It should be noted that adding even 1 wt% of biochar increases the composites' melting point by \(\sim\)2 \({}^{\circ}\)C. The increase in melting temperature of the composite is due to an increase in the growth of the PLA crystalline phase [50]. However, introducing biochar into the PLA/PBAT blend dramatically improved the percentage crystallinity of the composites by \(\sim\)40.6% in PLA/PBAT/BC (85/10/5), compared to that of the PLA/PBAT (80/20) blend. As expected, the total crystallinity also decreased as the PLA content in the composite decreased (Table 2). A high concentration of PBAT in the PLA/PBAT blend reduced the crystal nuclei number and spherulite growth rate, leading to a decline in the degree of crystallinity [51]. Moreover, the lowering of crystallinity in PLA/PBAT composites with the increase in PBAT may be attributed to the low crystallinity of PBAT. Furthermore, the phase separation of PLA and PBAT restricted the PLA-polymer-chain alignment [52], although adding biochar into the PLA/PBAT blend improved the total crystallinity of the composites. Figure 3: XRD pattern of coconut shell biochar. Figure 5 depicts the TGA and DTG of the PLA/PBAT/BC composites. Table 3 summarises the onset of degradation temperature (T\({}_{5}\), a temperature at which 5 wt% degradation occurs), maximum degradation (T\({}_{\text{max}}\)) and percentage of char formed at 550 \({}^{\circ}\)C. Thermal degradation mainly appears between 300 \({}^{\circ}\)C and 500 \({}^{\circ}\)C, because of two main constituents. The first weight loss corresponds to PLA, and the second to the PBAT between 400 \({}^{\circ}\)C and 450 \({}^{\circ}\)C [53]. The biochar in the composites is thermally stable, and shows no degradation even at 600 \({}^{\circ}\)C, which is expected, as the pyrolysis temperature was 800 \({}^{\circ}\)C. The char-residue percentage at 550 \({}^{\circ}\)C (Table 3) confirms the content of biochar in the composites. The onset of degradation (T\({}_{5}\)) and the maximum degradation temperatures of different composites are shown in Table 3. The onset of degradation started at 346.98 \({}^{\circ}\)C for PLA/PBAT (80/20) and moderately improved, with an increase in PBAT and biochar content, reaching a maximum of 351.45 \({}^{\circ}\)C for PLA/PBAT/BC (70/20/10). Unlike in the biochar poly(propylene) composites, the onset of degradation does not show any considerable improvement with biochar addition; this is crucial in determining the nozzle temperature for the 3D printing process [39].