Surface modification of solid wood using different techniques

The rising demand for consistent, high quality, as well as high density wood species has raised interest in diff erent wood modifi cation techniques. One modifi cation method is wood densifi-cation, where solid bulk wood can be compressed, following softening, until its density reaches that of the cell wall (1.50 g/cm 3). It is well known that many of the properties of solid wood correlate with its density and as such can be enhanced by increasing the density. By targeting the compression to the surface of solid wood only, the surface properties can be enhanced. The main aim of this thesis was to evaluate the eff ect of diff erent wood surface densifi cation methods on surface properties. Three methods were evaluated; (i) a lamination technique, where low density wood was laminated to a high density compressed wood surface, (ii) surface modifi cation where densifi cation was accomplished using a single sided heated press and (iii) with a single sided heated press assisted by frictional heating. With the lamination technique, it proved easy to generate the desired hard surface, but an adhesive is needed. The diff er-ence between compression with and without friction is that when using friction the process temperature is rather diffi cult to control, but an even layer of extractives are formed on the surface. Without friction, however, extractive spots are seen on the surface. The results show that the process parameters used in surface densifi cation have a signifi cant infl uence on the vertical density profi les, which in turn have an infl uence on surface hardness. On the other hand hardness correlates with the degree of densifi cation and the thickness of the densifi ed surface. Moreover, wettability decreased signifi cantly, caused by the closure of lumens, a smooth surface and an extractive layer on the surface. The extractives on the surface were analysed by FTIR-ATR spectroscopy and X-ray photoelectron spectroscopy. Using FTIR-ATR spectroscopy there was no trace of extractives, but with X-ray photoelectron spectroscopy an extractive layer was identifi ed, this was most probably due to the penetration depth of the IR-beam, which is rather high, compared to X-ray photoelectron spectroscopy, which is highly surface sensitive. The extractive layer could provide a natural coating and reduce the need for further coating. Furthermore, a potential measure error was found when measuring the vertical density profi le of composites with large diff erences in densities, …