Influences of moisture content on the catalysis of sulfur dioxide and attainable properties in a vapor-phase treatment of wood with formaldehyde

Abstract

Influences of moisture content on the catalysis of sulfur dioxide and physical properties of reaction products were examined for a vapor-phase treatment of spruce wood with formaldehyde. The reaction rate was strongly dependent on the amounts of water and sulfur dioxide in the reaction system, and this was consistent with a proposal that the hydroxymethylsulfonic acid (HOCH₂SO₃H) formed from sulfur dioxide, water, and formaldehyde acts as a catalyst for the reaction. However, not all water molecules contributed to the formation of HOCH₂SO₃H, because some were adsorbed by the wood components. When the initial moisture content was high, polymeric cross-linking was likely because the ultimate weight gain was much greater than the value estimated based on monomeric cross-links. The lower values of antiswelling efficiency and higher equilibrium moisture content at a specific level of weight gain also suggested the existence of polymeric cross-links. However, the difference in the length of cross-links did not significantly influence the mechanical properties.