Padauk (Pterocarpus soyauxii Taub.) extracts: An ecological solution for improving the natural water durability of welded wood

This study evaluates the effect of Padauk extracts on the natural cold water durability of welded beech wood. Wood specimens of 70 × 50 × 25 mm3 with initial moisture content of 12% were treated with Padauk extracts by capillary action for 7 days and further welded by high-speed dowel rotation wood welding. Water resistance test was performed by consecutive soaking (2 and 4 h) of treated and untreated specimens in two separate soaking tanks containing distilled water from 10 °C to 20 °C, then linear tensile and tensile shear tests were performed. Non-water leachable oligomers were determined using matrix-assisted laser desorption ionization time of flight (MALDI-TOF/MS) analysis. Internal adhesion level of the weld line was assessed through vertical density profiles of treated and untreated specimens. The results showed that the use of Padauk extracts improve the beech wood water resistance and the natural water durability of its welded joints. The respective tensile strengths obtained for the specimens treated at 0, 2 and 4 h of immersion in cold water were 2.34 KN, 1.56 KN and 0.86 KN. MALDI-TOF/MS analysis shows an abundance of molecules with aromatic methoxy groups (OCH3) which leach slowly in cold water, such as santalin B at 596 Da and santalin A at 583 Da which has an additional -CH3 group. X-ray densitometry confirmed a high densification (776.45 kg/m3) of the weld lines of the treated specimens and a peripheral densification of 762.74 kg/m3 compared to the 754.60 kg/m3 of the untreated specimens. These differences could be due to the chemical composition of the natural Padauk extracts, which justifies their water repellent potential on the treated beech wood.