Effect of increasing core layer particle thickness on lightweight particleboard properties

To reduce the raw material content in particleboards, the influence of core layer particle geometry on panel properties was compared for lightweight particleboards (500 kg/m³) and conventional panels (650 kg/m³). Specifically, the bending strength and modulus of elasticity, internal bond strength, thickness swelling, water absorption, and density distribution perpendicular to the plane direction were evaluated. Industrial core layer reference particles were obtained and compared to laboratory-made particles by varying the cutting blade projection of the knife ring flaker during chipping. The particles were then classified as Thin, Normal, or Thick after assessment by manual gauging. Additionally, sieve analysis and image analysis were applied for particle size or particle dimension measurement. Based on particle surface calculations (in square metres per mass of dry particles) and the mass of solid adhesive in relation to the mass of dry wood, the surface-specific adhesive amount was calculated. As the cutting blade projection during particle preparation determines the particle dimensions, it also controls the surface-specific amount of adhesive. With increasing particle thickness, the internal bond strength for both conventional and lightweight panels also increased. Normal particles showed the best mechanical results, whereas other correlations between mechanical properties and particle thickness were insignificant. Moreover, most laboratory-made particle variations outperformed the industrial reference. Thickness swelling of the lightweight panels, particularly after 24 h, was either equal to or less than that of conventional panels. The density profile was predominantly unaffected by the core layer particle thickness. Overall, these results suggest that the core layer particle thickness and the thickness-related changes of adhesive coverage of the core layer particles have only little effect on the key physical and mechanical properties of lightweight panels. In practical application, an increase in core layer particle thickness seems to be unable to maintain bending properties in wood-reduced particleboards on the same level as in conventional density particleboards.