Effect of addition of polyvinyl acetate to melamine-formaldehyde resin on the adhesion and formaldehyde emission in engineered flooring

The objective of this research was to investigate the effect of adding polyvinyl acetate (PVAc), for reducing the formaldehyde emission level, on the adhesion properties of melamine-formaldehyde (MF) resin for fancy veneer and plywood in engineered flooring. We controlled the hot-press temperature, time and pressure to determine the bonding strength and formaldehyde emission. Blends of various MF resin/PVAc compositions were prepared. To determine and compare the effect of PVAc content, 0, 30, 50, 70 and 100% PVAc floorings, by weight of MF resin, were used. Wheat flour, 25% by weight of adhesive, was added as material to increase the quantity. To determine the level of formaldehyde emission, we used the desiccator method. The formaldehyde emission level decreased with increased additions of PVAc. At a PVAc replacement ratio of only 30%, the formaldehyde emission level of the coated sample by UV-curable coat was under E1 grade. Curing of the high MF resin content in this adhesive system (MF resin with PVAc) was well processed indicating that the bonding strength was increased. In the case of PVAc only, the bonding strength was much lower due to the already high temperature of 120 °C. The adhesion layer was broken by high temperature and pressure. The sample with 30% PVAc added to MF resin (MF resin: PVAc=70:30) showed good bonding strength compared with MF resin only in all cases, hot-press temperature, time, pressure and boiling test.