Thermoplastic Coating Processes for Plywood

Plywoods were coated with maleate-modified polypropylene using different types of processing method than used for thermoplastics, such as extrusion, calendering, and compression molding. The aim of this project was to achieve adequate adhesion between the thermoplastic coating and the plywood. The adhesion between the modified polypropylene and plywood reached using the different coating processes was compared with a peel test and button pull test. Visual and microscopic observations were also made. The coating of plywood with modified polypropylene succeeded visually with all used coating methods, and adequate adhesion was achieved. Results of the adhesion tests indicated that during the coating process, a high melt temperature decreased viscosity and thereby improved penetration; low pressure in the contact area indicated the importance of the surface roughness of the top-ply smaller air gap because there is no oxidizing effect on the polypropylene copolymer and the air gap cools the melt, also the shorter coating time at high-temperature zones improved adhesion. The adhesion between polar plywood and nonpolar polypropylene was adequate with calendering and modified extrusion methods.