Chemical modification of poplar wood with foaming polyurethane resins

This study was devoted to chemically modifying poplar wood with foaming polyurethane (PU) resin, which improved both dimension stability and mechanical property of wood. The controlled tests demonstrated the poplar wood treated with only solvent acetone had decreases of both dimension stability and mechanical property, while the wood modified with solution of polymetric methylenebis(phenylisocyanate) in acetone had an excellent improvement of dimension stability but a little strength loss. Seven foaming PU resins with NCO/OH mole ratio from 12 to 2.5 were used to chemically modified wood, of which the mole ratio 3.0 gave best balance between dimension stability and mechanical property. The 24‐h volumetric swelling coefficient (VSC24 h) and 24‐h water absorption coefficient (WAC24 h) of the modified wood reduced 34.29% and 57.60% and the modulus of rapture and modulus of elasticity improved 39.89% and 37.15%, respectively. The improvements of dimension stability were contributed to that of the hydrophilic hydroxyl groups in wood were blocked by isocyano groups and water movement was hindered by successive cued PU deposit on the surface of vessels. The improvements of mechanical property were owed to the reinforcement of foamed PU on the cell wall and void space of wood. Four morphologic models of foamed PU within wood were discovered by SEM.