An investigation of thermochemical changes in Canadian hardwood species during wood welding

Thermochemical changes during wood-dowel welding were investigated in two Canadian hardwood species commonly used for indoor appearance applications: sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis). The original reference wood sample and the welded interface between two bonded wood pieces, a dowel and a substrate, were compared to explain differences in mechanical properties between species. Pyrolysis gas chromatography–mass spectrometry (Py-GC/MS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) were used. The gases emitted during wood welding were determined by Py-GC/MS and gas chromatography coupled with a thermal conductivity detector and a flame ionization detector (GC-TCD/FID). Results showed that thermal welding of birch and maple woods degrades hemicelluloses and affects lignin polymer through depolymerisation. Welding effectiveness is therefore directly associated with the properties of the original wood constituents, primarily lignin and carbohydrates. The lignin-related changes at the welded interface were greater for sugar maple than for yellow birch, corroborating mechanical property differences observed between the two species. The gases proportions were similar for both species and no harmful gases were detected in the smoke released during welding process.