The potential of improving wood preservative penetration into glued wood products bonded with one-component polyurethane by discontinuous adhesive bondline design

As a vast majority of glued wood products are intended for outdoor use or for building construction, impregnation with different agents is important for ensuring proper performance. It has been shown that the impregnation prior to gluing has several disadvantages, therefore the possibility of carrying out impregnation after gluing is analysed in the present research. Impregnation efficiency as well as the effect on the bond quality is evaluated for the one-component polyurethane glued wood specimens. The results showed that the impregnation with Cu preservative after gluing did not affect the shear strength of the glued wood specimens, but did significantly restrict Cu preservative penetration due to the adhesive bondlines. Considering the results, the possibility of improving the impregnation efficiency was also investigated. By using specific adhesive application designs, which cover the bondline only partially, it was possible to improve the impregnation efficiency. However, the Cu distribution was inhomogeneous and the improvement was noticeable only up to the second bondline. The partial adhesive application design also affected the bond strength of glued wood specimens, which resulted in a decrease both in dry and wet state. However, the reduction was not so sever as to cause delamination during three consecutive wetting and drying cycles.