Improved strength properties of three-layered particleboards with different core and surface layers based on kiri wood (Paulownia spp.)

The kiri tree produces low-density wood, which serves as an excellent material for particleboards (PB) due to the correspondingly low bulk density of the particles and better glue utilization. In this study, kiri particles (KPs) are used in surface and core layers to explicitly improve certain strength properties of three-layered PBs. Six variants of three-layered PBs were produced from KPs and industrial particles (IPs) with a target density of 500 kg m⁻³. The composition of the PBs was 100% KPs, 100% IPs, KPs in the surface layer with IPs in the core layer and vice versa, and KPs and IPs, respectively, in the surface layer with a 50/50% mixture of KPs and IPs. KPs in the surface layer improved bending strength and bending MOE for all different core layers. The internal bond strength increased accordingly with the amount of KPs in the core layer. Thickness swelling was lower with KPs in the surface layer for panels with all different core layers. Water absorption was lower with KPs in the surface layer for most of the panels. Density profiles reveal that the variants with lowest density in the core layer do not necessarily show the lowest IB results, which indicates that IB is more dependent on the compression of the particles and resulting enhanced adhesion than on density alone. Screw withdrawal resistance was not affected by the surface layer, but it increased with the overall amount of KPs in the PB.