Optimizing kenaf fibre sodium hydroxide treatment to enhance the mechanical properties of treated kenaf fibre lightweight foamed composites

The established efficacy of sodium hydroxide (NaOH) alkali treatment in addressing the intrinsic bonding and compatibility challenges of Kenaf Fibre (KF) as a composite reinforcement material provides the scientific basis for this investigation. This research aims to optimise NaOH concentration and treatment duration to enhance the fibre–matrix interfacial bonding and mechanical performance of Treated Kenaf Fibre Lightweight Foamed Composites (TKFLFC). A comprehensive 12 × 8 factorial experimental design was implemented to examine the combined effects of low (0.25–1.0 M) and high (1.25–2.0 M) alkali concentrations across various exposure durations (2–24 h) , comprising 96 distinct treatment configurations, each tested with 20 fibre specimens, resulting in a total of 1920 specimens. Mechanical, interfacial, and chemical characterisation, comprising single-fibre tensile, fibre pull-out, Scanning Electron Microscopy coupled with Energy Dispersive X-ray spectroscopy (SEM–EDX), and Fourier Transform Infrared Spectroscopy (FTIR) was conducted to establish correlations between fibre treatment conditions and performance behaviour. Results indicate that higher NaOH concentrations required shorter exposure times to achieve optimal performance, whereas lower concentrations benefited from prolonged durations. The optimal conditions, identified as 0.75 M for 20 h (low) and 1.5 M for 12 h (high), yielded the highest tensile strengths of 582.87 MPa and 600.88 MPa, respectively, and enhanced fibre pull-out interfacial strength by approximately 36% compared to untreated fibres. SEM–EDX and FTIR analyses confirmed substantial removal of non-cellulosic components and improved surface roughness conducive to mechanical interlocking. When incorporated into LFC, these optimised fibres improved compressive, tensile, and flexural strengths with a minor reduction in workability. Overall, the study establishes a direct linkage between alkali treatment optimisation and macro-scale composite performance, underscoring the potential of TKF in advancing sustainable, high-performance lightweight composites.