Effect of fish scale-derived biofiller loading on the mechanical, microstructural and moisture-resistance behavior of snake plant fiber/epoxy composites.

Sustainable composites based on natural fibers and bio-derived fillers offer a promising alternative to conventional synthetic materials. This study systematically investigates the influence of fish scale (FS) bio-filler incorporation on the mechanical performance, microstructural characteristics, and moisture-uptake behavior of snake plant (SP) fiber-reinforced epoxy composites. Composites were fabricated using the hand lay-up technique with a constant SP fiber content (20 wt%) and varying FS filler loadings (0-20 wt%). Mechanical properties, including tensile, flexural, impact, and hardness behavior, as well as fracture morphology, chemical interactions, and water-absorption kinetics and apparent Fickian diffusion behavior, were evaluated. Results showed that the filler-free composite exhibited superior overall mechanical performance, achieving the highest tensile strength (87.66 MPa) and modulus (4.78 GPa), flexural strength (114.28 MPa) and modulus (6.45 GPa), and impact strength (20.12 kJ m-2), attributed to effective fiber-matrix interaction and matrix continuity. Increasing FS content caused a gradual decline in tensile, flexural, and impact properties, particularly at higher filler loadings, due to weakened interfacial adhesion and increased defect formation. However, hardness improved with FS incorporation, reaching a maximum value of 72.54 Shore D at 10 wt% FS. SEM analysis revealed a transition from rough, well-bonded fracture surfaces to brittle, crack-dominated morphologies with increasing filler content, while FTIR indicated physical interactions without new chemical bonds. At 120 h, water absorption decreased by 36%, from 17.50% in S1 to 11.20% in S5. However, apparent diffusion coefficients showed no consistent trend, indicating reduced moisture retention but not necessarily slower transport. Overall, 5-10 wt% FS provided the best performance balance, although long-term moisture durability requires further validation. These findings support the development of lightweight, sustainable composites for non-load-bearing and semi-structural applications.