Evaluation of lightweight fiberboard using recycled polystyrene as a part of binder

Background and objectives: Nowadays, production of lightweight fiberboard with density lower than 500 kg/m3 gained a lot of interests for both non-structural and insulation applications in buildings. Environmental friendliness, lower price, recyclability, superior thermal and sound insulation, and desirable mechanical properties are some of the advantages of lightweight fiberboard compared to those of polymeric (polystyrene and polyurethane foams) and mineral-based (glass and mineral wool) insulation boards. Replacement of isocyanate and improving the board flexibility are in major focus for such panel’s producers. Hence, the aim of this study was to evaluate the production capability of lightweight fiberboard by replacing the isocyanate with polystyrene resin obtained from foam dissolution in methylene chloride solution. To this end, the effect of press temperature, solvent to foam weight ratio, different percentages of isocyanate replacement with polystyrene adhesive and board density on the physical and mechanical properties of lightweight fiberboard were investigated.

Materials and methods: Lightweight fiberboard (10 mm thick) with density from 200 – 300 kg/m3 were produced using wood fiber with combination of isocyanate and polystyrene as adhesive. In this study, mechanical (bending strength, modulus of elasticity, compression strength and tensile strength perpendicular to panel surface (internal bond)) and physical properties (thickness swelling and water absorption) of the panels were evaluated.

Results: The best modulus of elasticity, tensile and compressive strength was observed in boards made at 160°C. Increasing the weight ratio of solvent (methylene chloride) to polystyrene foam had a negative effect on these properties. Also, changing the solvent to foam ratio did not have a significant effect on the physical properties (thickness swelling and water absorption) of lightweight fiberboard. Increasing the percentages of isocyanate replaced with polystyrene adhesive (from 15 to 45% (based on the amount of isocyanate used)) improved the bending and physical properties and weakened the compressive and tensile strengths perpendicular to the panel’s surface. Mechanical properties (bending strength, modulus of elasticity, compressive and tensile strength) of the lightweight fiberboard as well as the swelling thickness of samples have increased significantly with increasing the board’s density.

Conclusion: In this study, lightweight fiberboard was developed using isocyanate as an expensive and toxic adhesive replaced with adhesive made from recycled polystyrene foams. The results showed good performance of boards made with 45% isocyanate replaced with polystyrene adhesive. Generally speaking, a promising alternative for recycling of polystyrene foams (used as adhesives for wood-based panels industries) was presented in this research while lightweight fiberboard was also produced as non-structural and insulating applications having less isocyanate consumption.