EFFECT OF OVERDRYING OF YELLOW-POPLAR VENEER ON PHYSICAL-PROPERTIES AND BONDING

The intent of this study was to follow the changes of various wood physical properties as the wood was overdried at high temperature and to determine if these changes correlated with the ability of the wood to bond with phenolic resins. Yellow-poplar (Liriodendron tulipifera L.) was dried from a water-soaked state at 170-degrees-C, 195-degrees-C, and 220-degrees-C for various lengths of time. Light reflectance, wettability, equilibrium moisture content (EMC), loss of wood substance, and compression shear bond strength were measured. Wettability was severely affected over time and was very quickly affected at high temperatures. The bulk properties, EMC and loss of wood substance, were slightly affected by drying for 224 min at 170-degrees-C but were more affected at the higher temperatures with time. The results for these bulk properties correlated well with light reflectance measurements regardless of temperature level. However, compression shear bond strength remained high and was unresponsive to either drying time or drying temperature. After these laboratory samples were analyzed, yellow-poplar plywood samples produced by an industrial manufacturer were tested for bond quality. One sample was composed of regularly dried veneer, and one sample was overdried.