# Evaluation of Impact Energy Absorption by Natural Fiber Composites in Motorcycle Helmets
## 5 Conclusions  
This study evaluated the effect of an impact absorption test on composites reinforced with natural fibers. Based on the data obtained, one can conclude that there are statistically significant differences in impact absorption between pure polyurethane (PU) prototypes and composites enhanced with natural fibers. Furthermore, this study highlights that including natural fibers improves impact absorption performance, corroborating previous research findings. The results confirm that natural fibers, such as coconut, sugarcane bagasse, and sisal, are effective reinforcements in polymers, enhancing the impact absorption capabilities of the composites. It was observed that sugarcane bagasse and coconut fibers performed better at lower proportions, while sisal fiber demonstrated greater effectiveness at an intermediate proportion. The analysis further quantified the effect of filler content, showing that sugarcane bagasse and coconut fibers performed better at lower concentrations (5-10%), while sisal fiber demonstrated greater effectiveness at an intermediate proportion (10%). These findings contribute to the body of knowledge on natural-fiber-reinforced composites and their application in enhancing impact absorption for protective equipment, such as motorcycle helmets. The results emphasize the importance of producing composites with varying proportions and types of natural fibers to achieve optimal impact absorption performance. However, it is crucial to note that further research is needed to expand knowledge in this area. Future studies could explore additional aspects of these composites, such as mechanical strength and durability, as well as the effects of processing and the overall characteristics of the materials, besides comparing the impact absorption properties of natural-fiber-reinforced composites with polystyrene. This analysis can highlight the reasons why one type of fiber is better than another. Furthermore, such investigations would provide a more comprehensive and in-depth understanding of natural-fiber-reinforced composites and their applications in protective equipment. Another promising direction for future work is the development of a biodegradable foam matrix reinforced with natural fibers. In addition, we recommend estimating the cost of the PU pad or helmet with the addition of the individual natural additives mentioned, as well as the cost of the pad with out these additives. Additionally, it would be useful to analyze how much the inclusion of natural fibers increases the cost of the helmet or helmet pad and analyze the failure status of the helmets in different configurations. Conceptualization, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; methodology, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; software, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; validation, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; formal analysis, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; investigation, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; resources, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; data curation, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; writing--original draft preparation, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; writing--review and editing, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; visualization, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; supervision, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; project administration, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. ; funding acquisition, T.B.d.A., C.R.H.B., R.M.M., E.P.E., and E.C.d.O. All authors have read and agreed to the published version of the manuscript. The authors express their thanks for the financial support provided by the scholarship from the Brazilian agency CNPq (305479/2021-0). This study was financed in part by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior--Brasil (CAPES)--Finance Code 001. Not applicable. Data Availability Statement: Data are contained within this article.