Effects of wet treatment on bonding strength and electrothermal performance of electrothermal plywood bonded with emulsion polymer-isocyanate adhesive

To create a green, safe, and aldehyde-free indoor heating environment, an eco-friendly emulsion polymer-isocyanate (EPI) adhesive was applied to the preparation of electrothermal plywood with built-in carbon fiber paper. The optimized process parameters of electrothermal plywood were 0.9 MPa, 120?, 6 min, and 200 g/m(2) for hot-pressing pressure, temperature, time, and glue spread amount, respectively. After water immersion for 24 h, the bonding strength of wet-treated electrothermal plywood decreased to 0.89 MPa. The pull-out cracks of the carbon fiber paper were the main fracture form of the wet-treated electrothermal plywood, and the wood failure percentage was 0%-10% under the tensile load. Hydrolysis of the adhesive layer of the wet-treated electrothermal plywood occurred. The relative C and N contents in the wet-treated electrothermal plywood decreased by 6.1% and 25.3%, respectively. Moreover, the resistance of the wet-treated electrothermal plywood increased by 273.4% because the internal conductive path was interrupted during the intrusion of the water molecules. The highest electric-to-radiant transfer efficiency of the electrothermal plywood was 72.4%, with a power density of 200 W/m(2). In conclusion, wet treatment has a significant effect on the bonding strength and electrothermal performance of the electrothermal plywood bonded with EPI adhesive.