Multi-response Optimization of Alkali Treatment and Powdered Bamboo Loading in Epoxy Composites Using Box-behnken Response Surfaces

Abstract

Aims: This study developed powdered bamboo/epoxy composites and evaluated the joint effects of sodium hydroxide (NaOH) concentration, treatment time and bamboo loading on mechanical performance and water absorption. Study Design: A three-factor, three-level Box–Behnken response-surface design comprising 15 runs, including three centre points, was used. Place and Duration of Study: Department of Mechanical Engineering, University of Cross River State, Calabar, Nigeria; experimental work was completed in 2025. Methodology: Bamboo powder was treated with 0–15% NaOH for 0–9 h and incorporated into epoxy at 10–20 wt.%. Composites were fabricated by hand lay-up and consolidated under a constant 10 kg load. Tensile, flexural and compressive strengths, Shore D hardness and water absorption were measured. Full quadratic models were fitted in coded variables, and equal-weight desirability optimisation maximised the four mechanical responses while minimising water absorption. Results: All five models were significant (four at P < .001; water absorption at P = .002), with R² values of .971–.991 and adjusted R² values of .920–.974. The strongest tested formulation, comprising 15% NaOH, 4.5 h treatment and 20 wt.% bamboo, produced tensile, flexural and compressive strengths of 79.576, 103.63 and 89.44 MPa, respectively, with hardness of 43.6 Shore D. Minimum water absorption was 2.78% at 15% NaOH, 4.5 h and 10 wt.% bamboo. The predicted simultaneous optimum was 15% NaOH, 5.68 h and 20 wt.% bamboo, with an overall desirability of .929. Conclusion: The results demonstrate a strength–moisture trade-off and identify a model-based process window requiring confirmatory validation before structural application.