Effect of Synthesis Variables on Tack in Urea-Formaldehyde Resin

Abstract The degree of tack-the ability of resin to adhere to another surface under light pressure and over short time-in urea-formaldehyde resin varies throughout the particleboard manufacturing process and affects mill maintenance and board quality. A three-part study was conducted to evaluate the effects of certain synthesis variables-molar formaldehyde:urea ratio, ingredient concentration, reaction pH, and reaction catalyst-on tack of urea-formaldehyde resin in particleboard manufacturing. Southern pine particleboard mats were formed and prepressed in the laboratory, and tack was evaluated with the push-off method. Reaction pH significantly affected tack and viscosity, which were highly related. On the average, reducing formaldehyde:urea ratio and ingredient concentration increased tack; these two variables may be significant to tack development and resin morphology. Reaction catalyst did not affect tack or other resin morphology. Reaction catalyst did not affect tack or other resin characteristics, but resin surface tension contributed significantly to tack development. Further study should better define optimum manufacturing time and make tack development in particleboard manufacturing more predictable.