An extensive investigation of plywood dryout and delamination was conducted in this study. It included laboratory tests of key variables for urea formaldehyde (UF) bonded plywood. A statistical equation was developed to quantify the effect of veneer moisture content, temperature, assembly time, glue spread rate, and amount of catalyst on wood failure percentage. The following are the main findings:
Veneer with a low moisture content (MC) level is more likely to create glueline dryout than high MC sheets when UF resin is utilized. Although veneer with a high MC level could minimize the occurrence of dryout, maximum allowable veneer MC (peak MC) is limited by other factors. UF gluing systems can employ a maximum MC range of 10 to 12%, which is much higher than the one that applies to PF resin (6 to 8%).
Sheets having temperatures over 100°F are strongly correlated with dryout problems.
An excessively long assembly time could significantly affect bonding, especially when veneer or ambient temperatures are high.
Increasing glue spread rate can be used to minimize dryout caused by high veneer temperature and low veneer MC.
In UF gluing systems, catalyst level heavily influences bonding and the extent to which dryout occurs.