Sustainable Phoenix sp. Chopped‐Fiber Epoxy Composites: Length–Loading Optimization via <scp>ASTM</scp> Testing and Diffusion Kinetics

ABSTRACT Sustainable natural‐fiber‐reinforced epoxy composites are attractive for lightweight components, yet their design is constrained by the coupled effects of the chopped‐fiber architecture on mechanical performance and moisture ingress. In Phoenix sp. for fiber/epoxy systems, a unified work linking fiber length, fiber loading, and water‐uptake kinetics under consistent processing and standardized testing has remained limited. This work establishes a design window for chopped Phoenix sp. fiber–reinforced epoxy composites by quantifying the combined effects of fiber length and fiber weight fraction on mechanical response and immersion‐driven transport descriptors. Alkali‐treated Phoenix fibers (10–30 mm) were incorporated into a DGEBA epoxy using hand lay‐up, followed by compression consolidation and staged curing. Specimens were characterized using ASTM tensile, flexural, impact, and hardness tests, and ASTM D570 immersion testing at controlled temperatures with diffusion‐kinetic fitting. A distinct optimum was obtained at 15 mm and 20 wt%, where tensile strength increased from 35.2 ± 2.1 MPa for neat epoxy to 58.7 ± 2.8 MPa and impact strength reached 24.3 ± 1.9 kJ·m −2 . At higher fiber packing, reduced wetting continuity and defect sensitivity were reflected by a decline in tensile strength to 44.6 ± 3.8 MPa at 50 wt% (15 mm). Water uptake increased strongly with fiber fraction, with saturation rising from 0.45% for neat epoxy to 9.58% at 50 wt% under the reported immersion condition. These results define an actionable length–loading window for selecting Phoenix fiber/epoxy formulations and provide transport descriptors for durability screening in moisture‐exposed service conditions.