Impregnation of Wood

the introduction of chemical substances into wood in order to improve its characteristics and impart new properties. Impregnation stabilizes dimensions, increases strength and resistance to water, moisture, and chemicals, and reduces cracking. The most common methods of impregnation employ antiseptics, which ensure protection against wood rot and other forms of biological deterioration, and fire retardants, which prevent wood from catching fire and burning. Impregnation is used in the railroad industry, power engineering, the manufacture of railroad cars, shipbuilding, and construction.

Impregnation of wood is classified as diffusive, capillary, or hydrostatic (pressure treatment), depending on the physical phenomena involved in the process. Diffusive impregnation is based on the diffusive migration of impregnants through the moisture-filled capillaries (seeDIFFUSION); only water-soluble impregnants are suitable for this method. In capillary impregnation, the impregnating fluid migrates through the capillaries in the wood under capillary pressure (seeCAPILLARY PHENOMENA). For example, in capillary impregnation using crown suction, the aqueous impregnating solution passes through openings in the lower section of the trunk or through the butt end into the sapwood of living or freshly felled tree by means of the suction force exerted by the crown. In pressure treatment, the impregnants migrate through the capillaries in the wood under artificially induced pressure. Liquid and gaseous substances are suitable for impregnation, as are melts of solid substances whose melting point does not exceed 200°-230°C.

In industry, impregnation of wood is primarily done with an autoclave under a pressure of up to 1.4 meganewtons/m² (14 kilograms = force/cm²). The pressure treatment of unseasoned wood includes butt treatment, autoclave-diffusive methods, and successive drying and impregnation. In butt treatment, aqueous solutions are introduced under a pressure of up to 1 meganewton/m² (10 kilograms = force/cm²) through one of the butt surfaces; in successive drying and impregnation, the wood is placed in an autoclave, where it is first dried, then impregnated. Impregnation technology requires that the wood be processed before impregnation; the processing methods include barking, mechanical working, drying, and slitting—the creation of slit-shaped openings that stimulate impregnation.