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This paper is an overview of our recent investigations of liquefied wood (LW) for preparation and application of wood adhesives and wood surface finishes. For the purpose of wood bonding, poplar wood (Populus nigra L.) was liquefied with ethylene glycol (EG) and sulphuric acid. The process of the curing of LW at different conditions was characterized using differential scanning calorimetry (DSC). The effect of the press temperature and the pressing time on the shear strength of bonds was monitored after the bonding of 5mm thick beech (Fagus sylvatica L.) lamellas. According to the results of DSC measurements, the curing process of the LW took place in two phases. In the initial physical phase the removal of water and EG from the LW occurred. This phase was followed by an exothermic chemical reaction. It was found that the optimum conditions for bonding beech lamellas were: a ratio between poplar and EG of 1:1, a press temperature of 180°C, and a pressing time of 12 minutes. Using such conditions it was possible to obtain bonds with a dry shear strength of about 7N/mm². For preparation of polyurethane wood coatings, poplar wood was liquefied with diethylene glycol (DEG) and the excessive DEG was removed from the reaction mixture prior to curing with isocyanate type hardener. For the purpose of preparation of light-coloured polyurethane coatings from bleached liquefied wood, liquefaction of wood was conducted with a mixture of polyethylene glycol (PEG) and glycerol (GLY) at a 9:1 ratio. Both LW based PU coatings and bleached LW based PU finishes were in the most relevant properties comparable to commercial polyurethane wood coatings. [ABSTRACT FROM AUTHOR]

The bonding of beech (Fagus sylvaticaL.) with liquefied wood (LW) causes deterioration of the wood surface, resulting in a high percentage of wood failure at a relatively low bond shear strength. Light microscopy, scanning electron microscopy, FT-IR micro-spectroscopy and elemental carbon, nitrogen and sulphur (CNS) analysis techniques were used to investigate the formation of such bonds. It was assumed that the degradation of lignin, hemicelluloses and parts of the cellulose occurred in the cells of the wood surface where the LW had been applied. At the elevated temperatures occurring during the bonding process, the deteriorated cells were carbonised to some extent. The weak boundary layer of the bond was determined to be a layer of delignified cells located between the zone of partly carbonised cells on the one side and the cells of the undamaged wood of the adherend on the other side. The bonds which formed during the bonding of wood with LW were found to be very untypical compared to bonds formed by synthetic wood adhesives. No adhesive film was formed, the adhesive-adherend interface was not clear and the cells of the adherend subsurface were damaged. [ABSTRACT FROM AUTHOR]