Grafting of perfluoroalkyl chains onto wood using blocked isocyanates

Chemical modification of wood was investigated using blocked isocyanates prepared from reaction of 4,4′-diphenylmethane diisocyanate (MDI) with 1 equivalent of 2-perfluorohexyl ethanol followed by addition of 1.1 equivalent of methyl ethyl ketoxime (MEKO). Thermal dissociation of the urethane linkage bearing a methyl ethyl ketoxime group allows generation of free isocyanate which reacts with alcohols like cyclohexanol or benzyl alcohol. The reaction was then extended to the hydroxyl groups of wood in order to bind perfluoroalkyl chains. Reaction was first studied on wood meal before grafting on blocks. Such modified blocks possess improved dimensional stability compared to untreated ones. Contact angle measurements were also performed. σ values obtained for modified blocks were greater and did not decrease with time compared to those obtained with unmodified blocks.