Combined effects of the treatment of wood with formaldehyde
M Stevens, J Schalck
Treatment of fibrous materials with reagents in a vapor phase is neither new nor unique. Numerous examples exist in literature of vapor phase experiments on cellulose fibers and fabrics, and on wood. For many years the textile research and industry have used vapor phase processes for the treatment of textiles. The chemical modification of cellulose is based on different types of reactions e.g. esterification, alkylation, resin formation or polymerization, monomer grafting and crosslinking. Vapor phase treatment of wood offers certain potential advantages over the conventional liquid phase wood impregnation. The higher mobility of low molecular weight compounds in the gaseous state ensures a rapid, uniform and homogeneous distribution throughout the wood structure. The vapor phase treatment of wood is also a better approach from the standpoint of cell wall penetration. Bulking, which takes place in the cell wall only, means that less chemicals are required and that the final weight of the composite is limited. Furthermore, due to the low viscosity of a gas, the application of a lower pressure differential remains possible. Within the framework of a wood improvement programme carried out at the Laboratory of Wood Biology and Wood Technology (University of Ghent, Belgium) the treatments were based on the impregnation of wood with liquid synthetic monomers and with gaseous formaldehyde. The results of the hygroscopic and dimensional behaviour of the wood-plastic-combinations have been published previously. Other papers deal with the physical and chemical interactions between the synthetic products and the natural polymers of the cell wall. This contribution will be restricted to the treatment of wood with formaldehyde in the gaseous state.