INFLUENCE OF THE ACIDITY AND SIZE OF BEECH PARTICLES ON THE HARDENING OF THE UREA–FORMALDEHYDE ADHESIVE
Sergej Medved and Jože Resnik
Presented work deals with the influence of acidity of beech particles of different size on the hardening of the urea–formaldehyde adhesive. The pH value and the milliequivalents of soluble and total acids were determined upon the method published by Subramanian et. al. in 1983. The method is based on the reaction between acids in wood and the aqueous solution of sodium acetate, where the equivalent quantity of acetic acid is generated. The quantity of the generated acetic acid was determined by the titration and presents the total acids in wood. The acetate solution helps to extract the acids soluble and insoluble in water. We determined that the particle size does not influence the pH value of particles and the quantity of the extracted soluble acids, but does have the influence on the quantity of the extracted insoluble acids. We furthermore determined that the particle size influences the gel time of the urea–formaldehyde (UF) adhesive. The shortest gel time was determined at the finer particles.
Key words: beech particles, soluble wood acids, insoluble wood acids, adhesive gel time