The impact of primers for wood bonding on beech wood’s Young’s modulus

When producing load-bearing timber products with one-component polyurethane adhesives and certain wood species, e.g., beech or larch, primers can be used to obtain stronger and more durable bonds. The active chemicals of three existing primer systems, hydroxymethylated resorcinol formaldehyde (HMR), polysorbate 20 (PS20), and poly(ethylene glycol) (PEG), were used to impregnate beech wood. Young’s modulus (E) in the radial direction was determined in tensile mode. A modified E can influence the deformation and stress distribution at the wood-glue interface. Compared to the untreated wood, the average E was reduced by 7% for the water-treated reference and the HMR treatment. With the PS20 treatment, the average E was reduced by 16%, compared to the untreated wood, and by 45% with the PEG treatment.