Physical Properties and Dimensional Stability of Starch-Bonded Mixed-Species Particleboards from Selected Tropical Hardwoods

Abstract

This study examined how species composition and particle size influence the physical performance of starch‑bonded particleboards made from tropical sawmill residues. Mixed furnish from Gmelina arborea, Tectona grandis, Khaya senegalensis and Daniellia oliveri was prepared at three blending ratios (25:25:25:25, 40:20:20:20 and 55:15:15:15) and particle sizes (1.70, 2.36 and 3.35 mm). Board density remained narrowly constrained (0.41–0.45 g/cm³) across all treatments, indicating robust mat consolidation under constant pressing conditions despite changes in species proportion and granulometry. Impact‑related properties were highly composition‑sensitive. Shatter index decreased from approximately 26–38% in boards with equal or moderate Khaya senegalensis content to 5–9% in boards dominated by K. senegalensis, while shatter resistance increased from roughly 62–74% to 91–95%. Strong, significant correlations among responses at different particle sizes (r ≈ 0.94–0.97) showed that performance trends at one sieve class were closely mirrored at the others, and regression modelling indicated that particle‑size parameters explained over 80% of the variance in a composite response measure (R² = 0.807). Correlations among physical properties revealed that density was only weakly linked to impact behaviour, whereas shatter index and shatter resistance were almost perfect inverses (r = -0.999), demonstrating that they form a tightly coupled diagnostic pair for toughness. A multiple regression using density and the two-shatter metrics accounted for 56.4% of response variability, emphasising impact‑related properties as dominant predictors of board performance. In conclusion, increasing the proportion of Khaya senegalensis and controlling particle‑size distribution offers a clear route to designing durable, fully bio‑based particleboards from under‑utilised hardwood residues.