A study of thermo-hydro-treated (THT) birch wood by chemical analysis and Py-GC/MS

The chemical changes in birch wood occurring at thermo-hydro treatment (THT) was studied at temperatures (T) of 150, 160 and 170 degrees C by analytical pyrolysis [Py-gas chromatography/mass spectrometry/flame ionisation detector (GC/MS/FID)], elemental analysis and traditional wet-chemical analysis. THT wood (THTW) was also extracted with acetone. Mass losses (ML) due to THT and acetone extraction of THTW were considered for material balance calculations. The holocellulose and hemicellulose (HC) contents decrease with increasing THT temperature (THTT), thus the apparent lignin content is elevated by ca. 20%. The HC degradation begins at 150 degrees C, while that of alpha-cellulose modification at 170 degrees C. Compared to unmodified birch, the THT170 degrees C material contains ca. 10% less alpha-cellulose and up to 40% less HC. The Py-GC/MS also indicates decreasing amounts of volatile products from polymeric carbohydrates (CHs) and lignin origin as a function of increasing THTT. The identified CH-based Py products of THT170 degrees C of non-extracted (ne) and extracted (e) materials resulted in 13 and 22% weight decrements, respectively, while the lignin-type Py products were reduced by 13 and 49%, respectively. With increasing THTT, the total content of CO2, water and methanol decreases, and the amount of unidentified compounds increases by 30%.