Optimisation of areca nut husk-derived cellulose nanofibers for enhancing the mechanical properties of epoxy composites using response surface methodology

Areca nut husk, a widely available yet underutilised agro-waste, is explored in this study as a novel and sustainable source of cellulose nanofibers (CNFs), addressing both environmental concerns and the growing demand for bio-based reinforcements in polymer composites. CNFs were extracted using alkali and bleaching treatments followed by ultrasonication, yielding fibres with a mean diameter of 35.84 nm. Epoxy composites were fabricated with CNF loadings ranging from 0.1 to 1.0 wt%, while key processing parameters, including mixing time (10–30 min) and curing temperature (60–100 °C), were optimised using Response Surface Methodology (RSM) based on a Box–Behnken Design. The developed regression models exhibited high predictive accuracy, with R2 values of 99.63% for tensile strength and 99.80% for flexural strength. Analysis of variance (ANOVA) identified CNF content as the most influential factor (F = 934.48 and 1646.71 for tensile and flexural strength, respectively), followed by mixing time and curing temperature. Optimised conditions of approximately 1.5 wt% CNF, 22 min mixing, and 80 °C curing yielded experimentally validated tensile and flexural strengths of 61.88 MPa and 74.36 MPa, respectively, deviating by only 5.27% and 2.76% from model predictions. These results confirm the effectiveness of process-optimised CNF incorporation in enhancing mechanical performance and highlight the potential of areca nut husk as a viable, high-performance bio-reinforcement for next-generation green composites.