lnvestigation into the changes of wood surface layer by measurement of pH-value

Wood pH has been studied with regard to its affecting some change on wood surface. The change on wood surface was analyzed after the following: - chemical treatment; - aging in room climate;- exposure to the sun, rain and surrounding atmosphere; - exposure to ultraviolet radation. Each treatment was followed by measurements of the pH and the adhesion of the NC varnish. The procedure of pH measurement on the wood surface with a combined surface electrode was devised. A 25 mm circle was drawn on the wood surface with NC varnish to prevent water spreading along the fibers. Into the circle 0,75 ml of water was applied, the electrode plunged in. After 5 minutes, the pH was measured. Within this time, no negative effects of carbon dioxide on the water pH were established. The research was done on fir, beech, oak and poplar. After chemical treatment, the pH on the wood surface varied depending on the chemical used but some general conclusions about the effects of pH on the followmg adhesion may be drawn. Summer sunlight quickly reduces the adhesion of varnish on beechwood, increasing the pH of the wood surface. Sunlight, and in combination with the rain in February, lasting 10 days, does not affect adhesion significantly. Instead, the surrounding atmosphere seems to have a greater influence in this time period. Varnish adhesion may be enhanced with a certain dose of UV-light. It is likely that maximum adhesion is achieved by the highest pH. Wood pH should be regarded as an indicator of chemical changes rather than cause of change.