Effects of plasma modification on adhesion properties of wood

The study investigated the use of dielectric barrier discharge for surface modification to improve adhesion properties of Shorea contorta (white lauan), Gmelina arborea (yemane) and Acacia mangium. Wood specimens were exposed to oxygen plasma at intensity levels ranging from 5.8 to 46.5 kW min/m2 to improve adhesion of phenol formaldehyde, urea formaldehyde resins and polyurethane coating. Work of adhesion was calculated based on contact angle measurements to determine thermodynamic changes on plasma modified wood. Surface characteristic was evaluated using atomic force microscopy (AFM). Results of the study showed that plasma modification resulted in significant improvement in work of adhesion for the three wood species investigated. Mechanical tests of plywood and wood laminates using plasma treated S. contorta glued with phenol or urea formaldehyde resins indicated improvement in shear strength of adhesive joints. No improvement or decrease in shear strengths were observed for plasma treated G. arborea and A. mangium. Pull off strengths of polyurethane coating on plasma treated S. contorta and A. mangium specimens showed slight improvement in strength of coated film. Effects of plasma treatment on adhesion properties of wood appear to be species specific and vary with process parameters.