Action FP0802 Changes of the crystalline volume fraction during wood thermal modification Wiesław OLEK 1) and Jan T. BONARSKI 2) 1) Faculty of Wood Technology, Poznań University of Life Sciences, Poland 2) Institute of Metallurgy and Materials Science, Polish Academy of Sciences Kraków, Poland Workshop Wood Structure/Function-Relationships Hamburg-Bergedorf, October 5-8, 2010
Introduction Thermal modification is used to improve the dimensional stability of wood as well as to increase its decay resistance. The improvement is mainly obtained due to changes of the hygroscopic properties, which depend on water accessibility to the sorption sites. The alteration of wood ultrastructure is often recognized as a factor influencing the accessibility. The traditional methods for the MFA measurements are unable to determine the changes in wood ultrastructure.
30 25 unmodified modified @ 220 C 20 EMC; % 15 10 5 0 0 20 40 60 80 100 H; % Sorption isotherms of beech wood. Solid dots desorption, empty dots adsorption, H-H model (solid lines)
Objective To apply the crystallographic texture function to quantify changes in the ultrastructure due to the thermal modification.
Thermal modification: Experimental poplar and European beech wood, laboratory process made in moist air, superheated steam added at ca. 130 C, target temperature 220 C, cooling firstly done in steam then in moist air only.
Experimental Texture experiment measurements: X-ray diffraction technique, texture goniometer, filtered CoK radiation, set of incomplete, back-reflection pole figures registered for (101), (002) and (040) lattice planes.
Experimental Texture experiment measurements: pole figures measured in the range of = 0-75 and = 0-360 by the Equal Solid Angle measurement grid with 642 points at the pole figure window D /D = 1. unmeasurable area 642 positions of a sample during a measurement = area of incomplete pole figure
Experimental Texture experiment measurements: 642 diffraction spectra registered during a single experiment
Experimental Texture experiment measurements: pole figure of the amorphous phase beech poplar
Experimental Texture experiment calculations of Orientation Distribution Function: discrete, Arbitrarily Defined Cells (ADC) method, complete pole figures (101), (001) and (010), inverse pole figures for anatomical directions (L T R).
Experimental Calculated 3D Orientation Distribution Function Φ φ 2 φ 1
Results Beech wood Crystalline volume fraction (GC-AS method) Crystallinity (Segal method) Unmodified Modified at 200ºC 0.563 ± 0.028 0.587 ± 0.026 0.611 ± 0.023 0.662 ± 0.021
Results Poplar wood Crystalline volume fraction (GC-AS method) Crystallinity (Segal method) Unmodified Modified at 200ºC 0.678 ± 0.024 0.578 ± 0.025 0.586 ± 0.025 0.631 ± 0.022
Results Texture index Unmodified Modified at 200ºC Beech wood 0.84 0.62 Poplar wood 0.79 0.81
Unmodified Modified at 220 o C Unmodified + Modified at 220 o C Skeleton profiles (intensity vs. φ 1 angle of Euler s orientation space) of the 3D Orientation Distribution Function of beech wood - unmodified and modified at 220 C. 10 - spreading over elementary subarea (Dj 1 DF Dj 2 ) of the orientation space was assumed
Unmodified Modified at 220 o C Unmodified + Modified at 220 o C Skeleton profiles (intensity vs. φ 1 angle of Euler s orientation space) of the 3D Orientation Distribution Function of poplar wood - unmodified and modified at 220 C. 10 - spreading over elementary subarea (Dj 1 DF Dj 2 ) of the orientation space was assumed
Concluding remarks 1. Crystalline volume fraction as well as crystallinity do not properly characterize changes of wood ultrastrucure caused by thermal modification. 2. The crystallographic texture is very sensitive measure of the changes. The texture component {001} significantly decreases during the modification while the {100} one increases. 3. The texture sharpness did not change significantly as the texture index varied insignificantly. However, the texture components were significantly changed.