Laser ablation of machined wood surfaces. 2. Effect on end-grain gluing ofpine (Pinus silvestris L.)

The effect on glue joint strength of removing the layer of cells on end-gra in surfaces of wood damaged by machining - the mechanical weak boundary lay er (MWBL) - is presented. The wood surfaces have been laser ablated using d ifferent types of lasers of different wavelengths. The goal has been to det ermine whether or not the strength of end-grain glue joints is influenced b y the MWBL and to show how the laser wavelength affects the glue joint stre ngth. All tests were carried out with a PVAc-glue with hardener, and two di fferent glue pressures were used. The joints were tested by bending notched and fatigued specimens. The statistical evaluation of the results shows th at one laser gave a significantly higher glue joint strength than the other s. One main conclusion is that the glue joint strength could have been improve d with a stronger glue. An ESEM-analysis showed that fracture occurred prim arily in the glueline and not in the boundary layer.