1C-PUR-bonded hardwoods for engineered wood products: influence of selected processing parameters

European hardwood species such as beech, oak and ash present a potential alternative to commonly used softwoods in glued engineered wood products. To date, mainly amino- and phenoplast adhesives are used for bonding these hardwoods, but some one-component polyurethane (1C-PUR) adhesives prove to offer an alternative when combined with a primer pretreatment. Therefore, a study was conducted to examine the influences of primer treatment and other parameters, such as surface machining and press time on the bondability of ash, beech, oak and—as a reference—Norway spruce. Delamination and block shear tests were conducted according to current European standards. Furthermore, information about bonding quality was gathered by means of microscopic glue line thickness measurements. The results suggest that the primer treatment is able to significantly enhance the bonding quality of hardwoods. The choice of the surfacing method causes some significant changes in the primer effectiveness. However, not all species were equally affected. The influence of the primer treatment on shear tests in a dry state was rather low throughout the series and only little significance was found. similar results were found after variations of the press time.