Manufacture and properties of high-performance oriented strand board composite using thin strands

Three-layered composite oriented strand boards were manufactured using very thin hinoki (Japanese cypress, Chamaecyparis obtusa Endl.) strands oriente d in the faces and mixtures of sugi (Japanese cedar, Cryptomeria japonica D . Don.) and hinoki particles in the core. The boards were composed of two d ensity levels, with 1:8:1, 0.5:9:0.5, and 0:10:0 face:core:face ratios. Pol ymeric and emulsion type isocyanate resins were used. The resin contents fo r the strands in the face and particles in the core were 10% and 5%, respec tively. The steam-injection press was applied at 0.62 MPa (160 degrees C), and the steam-injection time was 2 min. The mechanical and physical propert ies of the boards were evaluated based on the Japanese Industrial Standard. The parallel moduli of rupture and elasticity along the strand orientation direction and the wood screw retaining force increased with increasing fac e/core ratios. Incorporation of 10%-20% of thin strands in the face of the boards improved the parallel moduli of rupture and elasticity by 47%-124% a nd 30%-65%, respectively. In addition, the thickness swelling after water-s oaking at 20 degrees C for 24h, and the parallel linear expansion after boi ling for 2 h and water-soaking at 20 degrees C for 1 h, of the three-layere d composite boards were below 8% and 0.15%, respectively, despite a short s team-injection press time. The thickness swelling of the boards decreased w ith increasing face/core ratios. In contrast, the presence of face strands seems to have a minimal effect on the moduli of rupture and elasticity alon g the perpendicular direction of the three-layered composite boards. A simi lar trend was observed for the internal bond strength, hardness, and linear expansion along the perpendicular direction.