Search

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]

Liquefied wood is a naturally based product which has the potential to be used as an adhesive. The bonding of wood with liquefied wood requires a high enough temperature to cure the liquid polymers and achieve bond strength. Dielectric analysis, rheometry and differential scanning calorimetry were used to analyse the curing process of low solvent liquefied wood. For the liquefaction, ethylene glycol was used as a solvent and sulphuric acid was used as a catalyst. The dielectric analysis was used for in situ measurements of the curing of liquefied wood during the bonding of wood. It was found that curing started after a temperature of 100 °C had been reached in the bond. This is correlated with the water evaporation and the diffusion of water and ethylene glycol from the liquefied wood into the wood substrate. Rheological measurements proved the influence of the substrate on the curing of the liquefied wood during bonding. Differential scanning calorimetry showed that the curing of liquefied wood occurs in two parts: first, the initial elimination of water and ethylene glycol from the liquefied wood, and then the chemical reaction of the liquefied wood at higher temperatures. [ABSTRACT FROM AUTHOR]