Phenolic adhesives based on eucalyptus pyrolytic oil: Effect of urea addition on synthesis and properties

The present work aimed to evaluate the effect of urea addition on the synthesis parameters and properties of phenolic adhesives produced with oil from the pyrolysis of eucalyptus wood. The adhesive formulations were synthesized according to an entirely randomized design involving two formaldehyde/demethylated oil (F/DO) molar ratios (1.4 and 1.7), three NaOH/DO molar ratios (0.9, 1.0 and 1.1) and five levels of urea (0, 5, 10, 15 and 20%), totalizing 30 formulations. The following parameters and properties were obtained: reaction time (min) and temperature (°C); solids content (%), gel time (s), viscosity (cP) and pH. Regression analysis was performed and quadratic models were adjusted for reaction conditions (time and temperature) and some adhesive properties. Synthesis reactions were more controllable in terms of reaction time in the following conditions: urea addition in levels from 5 to 15% with F/DO molar ratio of 1.7 and NaOH/DO molar ratio of 1.0.