Effects of Hot-Pressing Parameters on Shear Strength of Plywood Bonded with Modified Soy Protein Adhesives

The heating rate of the core layer of plywood during hot-pressing is of great importance to the final quality of the plywood and is affected by many factors, such as the hot-pressing temperature (THP), hot-pressing pressure (PHP), hot-pressing time (tHP), veneer layers, and moisture content. In this study, multi-plywood using modified soy protein (MSP) adhesives prepared to investigate the effects of THP, tHP, and veneer layers on the core layer temperature during hot-pressing. The results indicated that all the core layer temperature curves were divided into four stages. The first constant temperature stage and the slow warming stage were decisive with respect to the time needed for the core layer to reach the THP. The time of moisture vaporization was approximately 400 s in the 3-layer plywood and approximately 900 s in the 5-layer plywood. In order to get an ideal strength the tHP should greater than the time of moisture vaporization; therefore in theory, the optimum parameters of the 3-layer plywood production were tHP of 600 to 720 s and THP of 120 to 125 °C. The research provides a theoretical basis for optimizing the hot-pressing of plywood