Lignin Modification of Wood Veneers

Pine, birch, and ash wood veneer with thickness of 1.5 mm were purchased from Glimakra of Sweden AB. Balsa wood (Ochroma pyramidale) was purchased from Wentzels Co. Ltd, Sweden with dimensions of 100 mm×100 mm×1.5 mm. The lignin modification solution was prepared by mixing chemicals in the following order: deionized water, sodium silicate (Fisher Scientific UK, 3.0 wt %), sodium hydroxide solution (Sigma–Aldrich, 3.0 wt %), magnesium sulfate (Scharlau, 0.1 wt %), DTPA (Acros Organics, 0.1 wt %), and then H₂O₂ (Sigma–Aldrich, 4.0 wt %). The wood substrates were submerged in the lignin modification solution at 70 °C until the wood became white. The samples were then thoroughly washed with deionized water and kept in water until use.