The influence of the structure of three-layer particle boards on the thickness and density of surface layer

In this research the influence of the structure of surface layer on the density and thickness of surface layer of three-layer particleboard was examined. Four wood species (spruce, beech, oak and poplar) and their mixture were used to evaluate their influence. The structure of wood particles with regard to wood species was altered only in the surface layer, while its composition in the core layer remained unchanged. For particleboard manufacturing urea-formaldehyde resin was used. The thickness, length, slenderness ratio and specific surface of particle used were determined by using the image analysis and the absorption method. Vertical density distribution was determined by using device for vertical density distribution measurement. From the data obtained by this device, the thickness and density of surface layer was determined. Particle geometry is strongly influenced by density of wood species used. Spruce wood particles are the thinnest with the highest slenderness ratio and specific surface area. Among the wood of deciduous trees, poplar particles are the thinnest; those of oak are a bit thicker, and particles of beech are the thickest. Slenderness ratio and specific surface area are smaller when using thicker wood particles. Wood species used in the surface layer strongly influence the thickness and density of surface layer. By increasing the share of spruce, oak and poplar particles the thickness of surface layer decreases while with increasing fhe share of beech particles the thickness increases. By decreasing the share of beech particles the density of surface layer increases, while with decreasing the share of spruce, oak and poplar the densitv of surface layer decreases. Increasing of thickness of the surface layer leads to a decrease of thickness of the core layer. If the surface layer is thinner, its density is higher.