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Experimental study of the effect of a laser beam on the morphology of wood surfaces

: Wust, H.; Haller, P.; Wiedemann, G.

Militz, H. ; Univ. Göttingen, Institut für Holzbiologie und Holztechnologie:
Wood modification: processes, properties and commercialisation : The Second European Conference on Wood Modification, ECWM 2005. October 6th/7th, 2005, Göttingen, Germany
Göttingen: Univ. Göttingen, 2005
ISBN: 3-00-017207-6
European Conference on Wood Modification (ECWM) <2, 2005, Göttingen>
Fraunhofer IWS ()
Holz; CO2-Laser; Neodym-YAG-Laser; Laserbestrahlung; Oberflächenmorphologie; Laserschmelzen; Wasserdichtheit

Wavelength, power density, pulse duration, repetition rate of laser irradiation for modification of wood and surface melting processes by laser beam that can be seen from microscopic observations (SEM) were studied. The absorption of the laser beam varies with the changing wood structure during irradiation. The chemical composition, particularly the distribution of cellulose, hemicelluloses and lignin in the cell wall, leads to the observed changes of the threshold values for intensity and interaction time. A field of irradiation parameters has been determined which guarantees melting of wood without pyrolysis. The surface temperature is assumed to be not higher than 200 deg C because above this temperature carbonising of hemicellulose and lignin is expected. It has been found that irradiation with Nd:YAG-laser (1,064 micron) requires an 8 to 1000 times higher beam intensity than irradiation with CO2- laser (10.6 micron), depending on irradiation time, to obtain about the same effect. Both wetting behaviour and water absorption of all wood species tested here were changed by laser irradiation. The largest effect of laser irradiation was observed with spruce whereas only slight changes were obtained with sapeli. Until recently laser application in wood technology has been restricted to a few techniques of cutting, perforating and engraving of wood and wood products. In view of this state of art it is highly justified to apply contemporary methods of material science to wood for better understanding of its structure and diverse properties in order to modify them with the aim of extended use.