Process for the acetylation of wood and acetylated wood

A process for the acetylation of wood comprising the steps:

• (a) in a reaction pressure vessel submerging wood having a moisture content from 1 to 4% by weight and an oven dry density of above 500 kg/m3 in an acetylation fluid comprising acetic anhydride and/or acetic acid at a temperature of 10° C. to 120° C.,
• (b) increasing the pressure in the vessel to 2 to 20 bar for a period of 1 to 300 minutes,
• (c) removing excess acetylation fluid from the vessel,
• (d) introducing into the vessel an inert fluid, circulating and heating the fluid until the internal temperature of the wood begins to show a first exothermic reaction, controlling the supply of heat to the wood until the first exothermic reaction is complete and maintaining the internal temperature of the wood below 180° C.,
• (e) heating the circulating fluid to a temperature of 85° C. to 160° C. for a time of 10 to 120 minutes to initiate a second exothermic reaction, controlling the supply of heat to the wood until the second exothermic reaction is complete and maintaining the internal temperature of the wood below 180° C., such that the acetylation fluid contains reaction products of an acetylation reaction,
• (f) removing the acetylation fluid containing the reaction products of acetylation by evaporation under vacuum,
• wherein the wood is in the form of a wood beam or board having a width of from 2 cm to 30 cm, a thickness of from 2 cm to 16 cm, and a length of from 1.5 m to 6.0 m, wherein the wood is acetylated to an acetyl content of at least 20% by weight at its geometrical centre in one impregnation and acetylation cycle.