End-grained wood-polyurethane composites, 1 synthesis, morphology and characterization

In order to improve the dimensional stability of end-grained wood upon environmental humidity variations, a two-step procedure was thoroughly studied which involved the osmotic impregnation of native poplar wood by PEG, followed by the reactive impregnation with HMDI, leading to polymer chain extension and polyurethane formation. It came out that the efficiency of PEG and/or polyurethane grafting within ligno-cellulosic cell walls was intimately related to parameters such as concentration of the PEG impregnation bath, PEG molar mass, time and temperature of impregnation steps. Based on the different sample characterizations, Soxhlet extraction and density measurements, it came out that adequate experimental conditions are to carry out osmotic impregnation at 20 °C for 24 h starting from an aqueous solution of PEG ([PEG] = 0.5 mol · L^-1 and M̄_nPEG = 400 or 1 000) and reactive impregnation in bulk with a large excess of HMDI at 20 °C for 2 h. Combining scanning electron microscopy and mercury porosimetry demonstrated the selective impregnation of cell wall and wood rays which were collapsed in native wood and expanded in wood polyurethane composites.