## 5 Conclusions  
The lignocellulosic characterization of treated curaua fibers revealed that the two chemical treatment routes remove the fiber's non-structural components. The curaua treated with hot water and mercerized fiber presented 68% cellulose, while the curaua treated with chlorite and mercerized fiber presented 71% cellulose. Both values of the cellulose contents show that the route using hot water treatment is more efficient because it uses fewer chemical reagents to produce similar results to curaua treated with chlorite and mercerized and curaua treated with hot water mercerized. The treated process with NaClO is very vigorous and degrades part of the fiber cellulose, resulting in more fragile fibers. The removal of the non-structural components of the fibers promotes the increase in the crystallinity of the fibers, as observed in the XRD assay, with the fiber being more crystalline and the curaua being treated with chlorite and mercerized.  
Curaua fiber stands out among other natural fibers for its low lignin content, around 8%, which is a significant advantage. According to the results of this study, this low lignin content favors better mechanical anchoring between the fiber and the matrix, resulting in composites with more robust mechanical properties. The thermal behavior of the composites was similar to the thermal behavior of the alone polymers (PLA or PHB) in which the only noticeable difference is the displacement of degradation stages due to the presence of the fibers in concentrations of 10 and 20 wt%. The crystallinity of PLA composites increased with the insertion of curaua fiber due to the high crystallinity of this fiber, which favored the crystallization of the composite. In contrast, PHB composites showed similar crystallinity to pure PHB.  
The composites reinforced with curaua fibers presented good mechanical properties with the pure polymer. The composites curaua treated with hot water and mercerized 20%/PHB and curaua treated with hot water and mercerized 20%/PLA showed higher tensile and flexural properties compared to pure polymer, higher crystallinity, and better adhesion interfacial bonding, evidencing the fact that the fiber and matrix break together, with little slippage and detachment of fibers in the rupture; that is, the fiber with less intense treatment is better concerning the adhesion between fiber and matrix.  
Therefore, these composites can be considered viable for industrial applications, especially coatings in the automotive industries, where their thermal and mechanical characteristics are required. Thus, these composites can be used in engineering applications to substitute conventional materials with biodegradable composites with similar mechanical and thermal properties.  
Conceptualization, J.M.d.O., V.M.Z.S. and S.M.d.L.; methodology, J.M.d.O., V.M.Z.S. and S.M.d.L.; software J.M.d.O. and V.M.Z.S.; validation J.M.d.O., V.M.Z.S. and S.M.d.L.; formal analysis, R.M.L. and L.A.T.; investigation J.M.d.O. and V.M.Z.S.; resources, S.M.d.L.; data curation, J.M.d.O., V.M.Z.S. and S.M.d.L.; writing--original draft preparation, J.M.d.O. and V.M.Z.S.; writing--review and editing, L.A.T., V.F.S. and R.C.M.S.-C.; visualization, J.M.d.O. and V.M.Z.S.; supervision, S.M.d.L.; project administration, S.M.d.L.; funding acquisition, R.C.M.S.-C. and S.M.d.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Decanato de Pos-Graduacao University of Brasilia (DPG-UnB), FAPDF (Fundacao de Amparo a Pesquisa do Distrito Federal)--Project number 0193.001251/2016, CAPES (Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior), and CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico)--Project number 310284/2021-0.  
Not applicable.