Optimized condition for eco-friendly wood composites manufactured from castor oil-based polyurethane

Castor oil is used as polyurethane (PU) polyol raw material with three kinds of isocyanate. In this study, polymeric diphenylmethane diisocyanate (PMDI), Desmodur L and Desmodur N were used to compare the structures of aromatic isocyanate oligomers, aromatic isocyanate trimers and aliphatic isocyanate trimers. Water, organosiloxane and dibutyltin dilaurate were used as the bubble agent, surfactant and catalyst to manufacture PU resin with molar ratios of NCO/OH of 1/1, 1.5/1 and 2/1, respectively. The results show that increasing the NCO/OH molar ratio increases the water absorption and hard segment content of PU resins. PMDI-based PU and Desmodur N-based PU resins have high thermal stability. The low-density composites of ca. 450 Kg/m3 were prepared successfully from a mixture of PU resin and China fir (Cunninghamia lanceolata) particles. The results demonstrated that increasing the NCO/OH molar ratio and using Desmodur L are optimal and beneficial to improving the composites' dimensional stability and internal bonding strength. The composites prepared with bio-based PU resins have lower thickness swelling rates and higher internal bonding strengths than formaldehyde-based and commercial PU-based resins. Bio-based PU composites can be used as eco-friendly building materials and replace formaldehyde-based manufacturing composites.