Hot-pressing process optimization by response surface methodology

For the development of three-layer medium density fiberboard (MDF) panels bonded with phenol-formaldehyde resole resin, response surface methodology (RSM) was employed to optimize the relationships between three hot-pressing variables (face-layer moisture content (MC), platen position, and creep closing time) and MDF panel performance. The time to reach 120 °C at the core linearly decreased and increased, respectively, with increasing MC and platen position. The maximum density of the face layers determined by vertical density profiles increased to a maximum and then decreased as both MC and platen position increased. All bending properties (modulus of rupture and modulus of elasticity) were well above the specified requirement by the American National Standards Institute (ANSI). The average internal bond (IB) strength was just below the ANSI requirement. IB strength did fit to a statistical model and was linearly related with MC and platen position. The response surfaces of all mechanical properties were found to be saddle shapes. The optimum conditions based on the IB strength were determined as follows: an MC of 13.4 percent, closing time of 3.8 minutes, and platen position of 111 percent of the target board thickness. The edge thickness swelling, water absorption after 24-hour soaking in/cold water, and linear expansion were about 3.2, 14.4, and 0.29 percent, respectively.