Problems related to bonding of impregnated timber and insufficient protection of glued wood with surface treatment were the main reasons for adding biocides to adhesives before bonding. To protect lamellas biocide diffused from the glue line into the wood structure: at the same time the glue lines should have preserved their mechanical properties. Tested samples were glued with MUF and PU adhesives with addition of 0.5 or 0.1 % of boron or copper in form of boric acid and copper hydroxide carbonate. The shear test (SIST EN 392) and delamination test (SIST EN 291) were used to test the mechanical properties of glue lines and dielectric analysis was used to measure glue hardening, while the rheometer to test the rheological properties. Boron and copper diffusion was measured visually and by ICP ablasion. Fungal decay was tested according to SIST EN 113 standard. Results show that glue line hardening was more efficient when using adhesive with added biocidesč the rheological properties of the glues with addition of boric acid did not significantly differ from the glues without biocides. Shear strength prepared with the glues with biocides did not decrease, in contrary, in some cases it even increased. Similar influences of added biocides were observed at the delamination test of glue lines as well. Furthermore, there is a significant correlation between sample moisture content and boron diffusion. The quickest and most intensive diffusion of boron compounds was measured from glue lines with boron concentration of 0.5 %. Unfortunately, it turned out that the amount of added compounds was too low to protect glued timber against fungal decay.
|
