Multi-response Optimization of Alkali Treatment and Powdered Bamboo Loading in Epoxy Composites Using Box-behnken Response Surfaces
Innocent Iwara Ibiang *
Department of Mechanical Engineering, Faculty of Engineering, University of Cross River State, Calabar, Nigeria.
Friday Aje Ovat
Department of Mechanical Engineering, Faculty of Engineering, University of Cross River State, Calabar, Nigeria.
Dodeye Inah Igbong
Department of Mechanical Engineering, Faculty of Engineering, University of Cross River State, Calabar, Nigeria.
*Author to whom correspondence should be addressed.
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.
Keywords: Alkali treatment, bamboo powder, Box-Behnken design, epoxy biocomposite, multi-response optimisation, response surface methodology