Cure kinetics of aqueous phenol-formaldehyde resins used for oriented strandboard manufacturing: Effect of zinc borate

The effect of zinc borate (ZB) on the cure kinetics of commercial phenol-formaldehyde oriented strand-board adhesives was studied using differential scanning calorimetry. ZB caused a separation of the addition and condensation reactions for both face and core resin (CR) systems with lowered cure temperature for the addition reaction. For the face resin, ZB did not change its nth-order curing mechanism, but retarded the whole cure reactions, and increased the reaction order and the activation energy. Compared with neat CR, the addition reaction of the CR/ZB mixture, which occurred at temperatures lower than 60 degrees C, also followed an nth-order reaction mechanism. The condensation reaction of the mixture was changed from an autocatalytic reaction to an nth-order one with the reaction order of about 1. The proposed models fitted the experimental data well. Relationships among cure reaction conversion (i.e., cure degree), cure temperature, and cure time were predicted for various resin/ZB systems. (c) 2006 Wiley Periodicals, Inc.