Effect of the polystyrene granules type and content on the physical and mechanical properties of the lightweight wood-based panels

Background and objectives: Nowadays, production of wood-based panels with lower density (about 25% lower compared to those conventional panels) gained more interest all over the world due to increased price of raw wood and the market needs for lightweight panels. Several methods and materials were used to produce lightweight panels in recent years. Among all, using of light and voluminous materials like polymeric granules were attracted more interest to reduce the panels density. Simultaneous use of the unique properties of two or more conventional wood products can influence the final characteristics of the lightweight wood-based panels. The aim of the current study was the production of lightweight wood-based panels using wood fiber as the surface layers and a mixture of wood particles and polystyrene granulate as the core layer. A comparative study was done to see the effect of two types of polystyrene granules (expandable and pre-expanded granules) and the granules percentage on the physical and mechanical properties of the lightweight wood-based panels. Materials and methods: Hybrid-lightweight panels (520 kg/m³) were produced using wood fiber as surface layers and a mixture of wood particles and polystyrene granulate as core layer. The granules type were pre-expanded and expandable granules with different percentage (5, 10 and 15% based on oven dry mass of wood coarse particles). In this study, mechanical (bending strength, modulus of elasticity, internal bond, and screw withdrawal resistance) and physical properties (thickness swelling and water absorption) of the panels were evaluated. Results: The results showed that the physical and mechanical properties of panels were improved using polystyrene granules compared to that of reference panels (no granules). The modulus of elasticity was nearly doubled in case of pre-expanded granules, while other properties were nearly the same. Increasing the granules content up to 15 percent has a significant effect on the internal bond value, edge screw withdrawal resistance and physical properties (thickness swelling and water absorption). Thickness swelling and water absorption was significantly reduced with substitution of wood particles with polystyrene granules. Conclusion: The results showed that with increasing of polystyrene granules the internal bond and screw withdrawal resistance were improved. The results also showed that the granules types (expandable and pre-expanded granules) had no significant influence on the panels’ properties, except the modulus of elasticity and internal bond. As final conclusion, using of expandable granules can be favored for panels’ production due the elimination of pre-expansion process and increased binder effectiveness.