Surface free energy, wettability and bonding of plywood after fire-retardant treatment with various chemicals

Abstract

Plywood usage has been increasing recently in the building and furniture industry due to its outstanding surface and resistance properties. Although it has many advantages, the flammability of plywood needs to be improved with fire-retardant chemicals. However, these chemicals which improve panels against burning can be differently influenced many properties of panels. This study aimed to investigate the surface roughness, wettability, and surface free energy of the veneers treated with some fire-retardant chemicals and to determine the changes in the mechanical properties of plywood. The beech, poplar, alder, and pine veneers were used as wood species whilst zinc borate, borax, monoammonium phosphate, and ammonium sulfate were used as fire-retardant chemicals in this study. The surface roughness and contact angle measurements were performed to determine the surface properties of veneers, and then the surface free energy values were calculated. The bonding and bending strength of the plywood panels produced from these veneers were determined according to the relevant standards. As a result of the study, the surface free energy values of veneers with lower contact angles and smoother surfaces were found to be higher. It was also determined that the bonding strength values of plywood panels produced from veneers with high surface energies were also high. Generally, the untreated veneers had higher surface free energy values than the treated veneers. Among the fire-retardant chemicals, zinc borate caused the highest surface free energy values in the beech and alder veneers while borax exhibited the highest values in the poplar and pine veneers.