Interaction between wood and polyurethane‐alkyd lacquer resulting in a decrease in the glass transition temperature

The long‐term properties of paint and glue are of great interest to both manufacturers and users of these materials. If a good bond is achieved, the surface between the wood and the paint or glue will be less susceptible to degradation. Thus, the wood and polymer must be compatible and develop some kind of bonding force between them. A high degree of interaction between wood and commercial polyurethane‐alkyd lacquer was shown as a decrease by 10°C of the glass transition temperature (T_g) for the lacquer on wood compared to the pure lacquer. The lacquer also demonstrated good adhesion to wood at a microscale. The interaction was investigated with dynamic mechanical thermal analysis and scanning electron microscopy fractography. The reason for the decrease in Tg is probably because of the lacquer having a higher free volume when applied to the wood, most likely due to it being subjected to tensile forces developed during the drying of the lacquer. Results from investigations of wood impregnated with two different acrylates, a polymethylmethacrylate and a more hydrophilic acrylate, support the suggestion that a decrease in T_g will occur if the polymer adheres to wood, but that poor interaction with little or no adhesion will result in no decrease in T_g. This article also presents results of the dynamic mechanical behavior of Scots Pine in the tangential direction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 595–605, 2002