## 4 Discussion
This led to the conclusion that the treatments did not considerably improve the adhesion between the PHB matrix and the fibers. But PHB became more flexible when curaua fibers were added. However, according to this study [26], both the orientation and length of the fibers are intrinsically linked to the mechanical properties of a composite, as this work concluded that the fibers must be long and perpendicular to the applied load so that the mechanical resistance of the fibers can be used more effectively. However, as the curaua fibers were randomly dispersed in the composites, only fibers oriented parallel to the applied load reinforced the composites. According to this other work [64], short fibers act not as reinforcement but as filler. Also, according to statistics, the PHB matrix differed considerably from all other composites in terms of flexural modulus. SEM images show that the chemical treatments of the fibers mainly affected the matrix's fiber distribution and the composite's brittleness. No significant improvement in adhesion was observed for any of the fiber treatments. The recent study [65] that used banana fiber as polymer reinforcement and chemically treated it showed similar behavior to that observed. However, it suggests that the strong bond between the fiber and the surrounding matrix can strengthen the composites. TGA and DSC thermal analyses evaluated the degradation and crystallization stability of the PLA and PHB composites. It was observed that the PLA composites exhibited the same thermal behavior as pure PLA with only one degradation stage; however, all PLA composites showed a reduction in thermal stability, but PHB composites showed a higher decomposition rate than PLA because the fibers added to the polymer leads to a decrease in polymer degradation, thus improving its thermal stability. Also, this reduction in the thermal stability of PLA composites was reported in this other study [66] that developed PLA composites reinforced with curaua fiber, suggesting hemicellulose and lignin degradation. Crystallinity in PLA composites increases proportionally to the amount of filler due to fiber/matrix interaction during the cold crystallization process, which influences the formation of a crystalline structure. In contrast to PHB composites, which do not undergo cold crystallization, such fiber/matrix interaction does not occur, and crystallites are not formed. The results suggest that, although chemical treatments can alter the structure of fibers and reduce lignin content, this does not necessarily translate into improvements in all composite properties. For instance, while there was an improvement in the flexural of PHB composites, tensile strength did not improve, pointing to the need for methods that promote better chemical integration between the fiber and the polymer matrix. Therefore, it is necessary to develop research on chemical treatments or compatibilizers that can enhance adhesion between curaua fibers and polymer matrices, especially for PLA and PHB. Furthermore, investigating combinations of treatments that can maximize lignin removal without compromising fiber integrity is crucial. Accelerated aging studies should also be conducted to understand better how chemical treatments and fiber addition affect the durability and degradation of composites over time. Comparing the behavior of other natural fibers treated under the same conditions can help identify best practices and treatments applicable to a broader range of fibers. In summary, although sodium hypochlorite treatments significantly reduced lignin content and altered fiber structure, their impact on the mechanical properties of curauau-reinforced composites was limited. Improving matrix-fiber adhesion remains crucial for developing stronger and more durable composites.