Hydroxyapatite functionalized natural fiber‐reinforced composites: Interfacial modification and additive manufacturing

Abstract Natural fibers are lightweight, cost‐effective, readily available, and eco‐friendly materials. However, natural fiber‐reinforced composites are constrained by biological inconsistency and inferior fiber‐matrix interfacial properties, which restrict effective processing using advanced additive manufacturing methods. In this study, we develop a novel concept for natural fiber composite interfaces by growing hydroxyapatite (HAP) nanocrystals on jute fibers. The resulting hybrid composite is characterized using mechanical testing, nanoindentation, and modulus mapping. The interfacial region suggests a 31.4% increase in stiffness and possesses a storage modulus of up to 7.5 GPa. The tensile modulus and strength of the hybrid composite improves by 30% and 33%, respectively. Furthermore, we develop a novel process for the additive manufacturing of jute fiber thermoset composites through a direct writing (DW) process. The HAP modification increases thermal conductivity, consequently improving the curing process during DW and enhancing composite manufacturability. We demonstrate that the DW process enables the printing of intricate multilayer geometries with varying fiber content. Highlights Hydroxyapatite is used for natural fiber composite interfacial modification. Nanoindentation shows the interfacial region exhibits 31.4% higher stiffness. Modified composites possess superior mechanical performance. Jute fibers are thermally functionalized for composite additive manufacturing. A direct writing method is developed for continuous functionalized jute fiber.