GB579255A - Process for the esterification of wood - Google Patents

Abstract

The electrical insulating properties and resistance to moisture of wood are improved by treating the wood with an esterifying mixture containing an organic carboxylic acid, an organic carboxylic anhydride and a polyvalent metal halide under conditions such that the original form and fibrous structure are retained. The wood may be treated in thin sheets or veneer or in disintegrated condition such as wood meal. The esterifying mixture appears to react with the lignin and pentosan content of the wood as well as with the cellulose since after the esterification little or no staining is effected when the wood is subjected to the phloroglucinol test. The esterification may be carried out to an extent corresponding to an increase of the combined acetic acid content of 15-55 per cent by weight of the unacetylated wood. Sheets of natural wood veneer may be formed into bundles, the individual leaves being separated by a suitable material and supported in a closed vessel through which the esterifying medium is circulated. Wood meal may be packed into bags or containers before being placed in the esterifying medium. The esterification treatment renders the wood resistant to substantive cotton dyestuffs such as Chloramine Sky Blue. The moisture regain of air-conditioned material is reduced. The electrical properties such as dielectric constant and power factor are improved. The resistance to fungi and bacteria is increased. In examples, small pieces of oak or birch wood veneer are soaked in glacial acetic acid and then treated in a warm bath comprising 90-75 per cent acetic acid, 7-20 per cent acetic anhydride, and 3-5 per cent zinc chloride. A higher degree of esterification may be effected by subjecting the already esterified wood to a further treatment, using a bath containing a higher proportion of anhydride and using an inert solvent, e.g. benzol as diluent. The acetylated wood may be used in plastic moulding powders, and laminated plywood boards. If the esterification is carried out on laminated plywood board or bonded veneer, the resin glue or other bonding material must be chosen to be of such a nature that it is resistant to the esterifying agent. The process may be applied to resin-moulded wood meal mouldings in the form of moulded sheets or to moulded articles. Esterified wood veneer may be used in the manufacture of plywood with or without other sheet materials, e.g. cellulose acetate fabric or sheet or esterified paper sheet. Specifications 269,530 and 336,969, [both in Class 2 (ii)], are referred to.