Improving core bond strength of particleboard through particle size redistribution

Novel particleboard furnish mixtures were formulated to improve the core-bonding and screw-holding of industrial particleboard without increasing resin content or board density. Single-layer (uniform vertical density with core furnish only) and conventional 3-layer particleboards were manufactured at two density levels from four novel mixes plus control (unscreened industrial core furnish). Board mean and core density, internal bond strength, edge screw withdrawal resistance, and moduli of rupture and elasticity were measured. The core of commercial furniture-grade particleboard appears to contain too many fine particulates and insufficient coarser particles. Uniform density profile single-layer boards containing novel mixes with higher-coarse (>2 mm) and lower-fines (<1-2 mm) fractions than industrial furnish had higher bond strength and screw-holding. In three-layer boards of low target density, replacing 20% fines particle content of the total furnish with coarse particles increased internal bond strength by 40% and screw-holding by 18%. The results from this study suggest that not only fines content but also the ratio of all particle-size fractions strongly affect particle packing-efficiency and bond strength. This suggests that industrial particleboard core furnish be screened into three size-fractions, and some of the fines replaced with two coarser-particle fractions.