## 3 Results
### Thermogravimetric Analysis (TGA) and Different Scanning Calorimetry (DSC) of Curua/Composites
There is also the third stage of degradation related to the PHBV copolymer present in the PHB. The DSC analysis (Figure 7) was carried out to investigate the crystalline percentage in the polymers and composites. A high portion of the crystalline structure is wanted for most polymers/composites since the crystalline microstructure improves the mechanical resistance of polymers [52; 53]. The results of the DSC analyses are shown in Figure 7.  
The DSC curves of all PHB-containing materials (Figure 7A) show three endothermic peaks. The first one occurs at a temperature of 174 \({}^{\circ}\)C. The mentioned temperature indicated the melting point of the polymer [54]. The second, more pronounced peak at 295 \({}^{\circ}\)C, is related to the degradation of PHB [55]. At 325 \({}^{\circ}\)C, the degradation of the curaua fibers generates the third endothermic event [56]. Figure 7B shows more thermal events of the PLA-containing materials. The first thermal change is recognizable at approximately 60 \({}^{\circ}\)C. This peak is related to the glass transition of PLA [57]. A crystallization reaction generates the following exothermic peak. This event is typical for PLA and is known as cold crystallization. Here, the mobility of the polymer chain increases, and parts of the initially amorphous structure change to crystalline [58]. At 160 \({}^{\circ}\)C, the polymer melts, degrading between 340 and 360 \({}^{\circ}\)C [54]. Whereas the first three thermic events occur at nearly the same temperature, strong shifts of the maximum degradation temperature are visible for the investigated composites. The highest degradation temperature was found for the neat PLA. In general, the following tendency was found: The higher the filling degree of the composite, the lower the peak intensity and the stronger the shift of the degradation peaks to lower temperatures. This tendency, together with the fact that no longstanding thermal event for the degradation of the curaua fibers occurred, makes it evident that the matrix's degradation peak overlays the fibers' degradation peak. As the degradation of the pure polymer starts at approximately 315 \({}^{\circ}\)C, premature degradation can be observed for all composites. Hence, the degradation of the fibers initiates the degradation of the entire composite. Also, the crystallinity of the polymers and composites was calculated using the enthalpy of the melting peak found in the DSC analyses, the enthalpy of a PHB polymer with 100% crystallinity (PHB = 146 J/g; PLA = 93 J/g), and the weight fraction of the polymer of the composites. A more detailed description of the calculus method can be found elsewhere [59]. The calculated crystallinity values (X\({}_{\rm c}\)) for all composites are listed in Table 3.  
Comparing the crystallinity percentage in the tested polymers/composites revealed that PHB contains more than double the number of highly ordered structures than PLA. On the other hand, it can be observed that the filling with curaua fibers strongly affected the PLA composites. Nevertheless, the generally low amount of crystallinity in the PLA matrix cannot explain the pronounced crystallinity increase in the PLA composites. Other effects are involved in comparing the maximum percentage increase in crystallinity in the  
Figure 7: Comparative DSC curves of untreated and treated curaua fibers with different percentages in PLA matrix (**A**) and PHB matrix (**B**). CF: untreated curaua fibers; CWM: curaua treated with hot water and mercerized; CHM: curaua treated with hypochlorite and mercerized. PHB (9%) with the maximum percentage increase in the PLA (104%). One reason might be the cold crystallization mentioned during the DSC measurement's heating process [60]. As the fibers are already more or less equally distributed in the polymer matrix, the cold crystallization is influenced by the presence of the curaua fibers. As the PHB material does not present cold crystallization, such interaction between fibers and matrix does not occur.