Mechanism study on Betula wood dowel rotation welding into larch and enhanced mechanism of treating with CuCl2

Abstract

Mechanical properties and chemical changes of wood dowel welding were studied using untreated and copper chloride (CuCl2)-treated Betula wood dowels. The effects of the welding times (3 s, 5 s, and 7 s) and the highest temperatures in the welding interface were also studied. The treated wood dowels with a welding time of 3 s and the highest temperature of 265.6 °C had the best pullout resistance. Wood constituents were pyrolyzed by the frictional heat generated from rotational welding to form oxygen-containing materials, most of which were C-O materials. With the extension of welding time, welding interface materials were pyrolyzed deeper, but the rate of pyrolysis decreased, which indicated that the pyrolysis of hemicellulose and cellulose might have occurred in the prior period of the welding process. Acid hydrolysis of hemicellulose and cellulose of the wood dowel treated with CuCl2 might have occurred during immersion, which promoted the formation of molten materials by the depolymerization and pyrolysis of wood constituents. With the same welding time, the content of oxygen-containing materials with treated samples was higher than with untreated samples, which might indicate that more pyrolysis and molten reactions occurred in the treated welding interface.