Process for the acetylation of wood elements

A composite wood product containing acetylated wood elements characterised by retaining an average value of at least 90% of its modulus of elasticity after subjection to 25 wet-dry/freeze-thaw cycles measured according to DIN EN 12467/12, wherein one wet-dry cycle consists of storage of the test samples with dimensions 500 mm×500 mm×12 mm in water at a temperature of 20° C. for 18 hrs, followed by drying of the test samples in an oven for 6 hrs at a temperature of 60° C. and a relative humidity of 20% and wherein one freeze-thaw cycle consists of storage of the test samples with dimensions 500 mm×500 mm×12 mm in water at a temperature of 20° C. for 3 hrs, followed by freezing of the test samples at a temperature of −20° C. for 3 hrs.

A composite wood product containing acetylated wood elements characterised by retaining an average value of at least 90% of its bending strength after subjection to 25 wet-dry/freeze-dry cycles measured according to DIN EN 12467/12, wherein one wet-dry cycle consists of storage of the test samples with dimensions 500 mm×500 mm×12 mm in water at a temperature of 20° C. for 18 hrs, followed by drying of the test samples in an oven for 6 hrs at a temperature of 60° C. and a relative humidity of 20% and wherein one freeze-thaw cycle consists of storage of the test samples with dimensions 500 mm×500 mm×12 mm in water at a temperature of 20° C. for 3 hrs, followed by freezing of the test samples at a temperature of −20° C. for 3 hrs.

A composite wood product containing acetylated wood elements characterised by retaining at least 70% of its modulus of rupture after soaking for 48 hours in water at ambient temperature.

A composite wood product containing acetylated wood elements characterised by two or more of an average value in thickness swelling not exceeding 5% after subjection to 25 wet-dry/freeze-thaw cycles as described in Table II, retaining an average value of at least 90% of its modulus of elasticity after subjection to 25 wet-dry/freeze-thaw cycles measured according to DIN EN 12467/12, wherein one wet-dry cycle consists of storage of the test samples with dimensions 500 mm×500 mm×12 mm in water at a temperature of 20° C. for 18 hrs, followed by drying of the test samples in an oven for 6 hrs at a temperature of 60° C. and a relative humidity of 20% and wherein one freeze-thaw cycle consists of storage of the test samples with dimensions 500 mm×500 mm×12 mm in water at a temperature of 20° C. for 3 hrs, followed by freezing of the test samples at a temperature of −20° C. for 3 hrs, retaining an average value of at least 90% of its bending strength after subjection to 25 wet-dry/freeze-dry cycles or retaining at least 70% of its modulus of rupture after soaking for 48 hours in water at ambient temperature.

A process for the manufacture of a composite wood product from wood elements, comprising treating the wood elements

• with acetic anhydride at a temperature of 30° C. to 190° C. at a pressure of atmospheric to 15 barg for up to 80 minutes and thereafter heating with an inert gas which may be mixed with acetic anhydride or a mixture of acetic anhydride and acetic acid to a temperature of 150° C. to 190° C. at a pressure of 1 to 5 barg for a period of 5 to 300 minutes to make acetylated wood elements, and
• forming the acetylated wood elements into the composite wood product.