###### Abstract
[32] found out that the strength of glued joints in the specimens from pinewood impregnated with the fungicide alkaline copper quaternary (ACQ) decreased by more than 16% when 0.1% ACQ was used. However, a further decrease in the strength of glued joints when the concentration of ACQ increased to 1% was only slight. [PERSON] et al. [33] dealt with the effect of impregnation of pinewood with a micronized copper azide-type C (MCA-C) biocide in the amount of 1.0 kg/m\({}^{3}\) and 2.4 kg/m\({}^{3}\) to manufacture cross-laminated timber (CLT). In contrast, following the experiments, the strength of the glued joints was, in the case of the specimens, with lower MCA-C (1.0 kg/m\({}^{3}\)) significantly lower compared to the specimens with higher MCA-C (2.4 kg/m\({}^{3}\)). [PERSON] and [PERSON] [34; 35] did not confirm a significant negative effect of the biocides copper arsenate (CA), ACQ and MCA on the strength of glued joints in LVL beams made from pine and mple wood veneers using PF or polyvinyl-acetate (PVAc) glues. Nowadays, the attention of practice is focused on the issue of wood waste recycling and its reuse to manufacture wood-based panels [36; 37]. However, many recycled wood materials can contain various chemical components providing high durability and thus, the adhesion strength of glued joints in the manufacturing of wood-based panels can be affected in a negative way [38; 39; 40]. [PERSON] et al. [41], when investigating the presence of the preservative, chromatated copper arsenate (CCA), in removed beams made from pine wood, found that there was a decrease in the CCA content in wood beams from the surfaces to the central part as a result of partial leaching by water during long term exposure to outdoor conditions. Subsequently, the studies of [PERSON] et al. [42; 43] dealt with using the mentioned wood material to manufacture bonded beams. The strength of glued joints prepared from wood specimens with CCA was lower compared to untreated ones. Theoretically, the strength of glued joints or adhesion strength \"wood--glue\" depends on many factors related to the presence of wood preservatives or other chemical additives in wood: (1) the presence of the specific type and the amount of a preservative in recycled wood; (2) technological parameters related to applying the preservative to wood in the past, e.g., impregnation pressure, time, and temperatures; (3) exposure history of recycled wood, e.g., leaching, evaporating, and changes to the chemical structure of a preservative, as these factors affected the preservative distribution across the wood. The studies of [PERSON] et al. [44], [PERSON] et al. [45] dealt with the effect of an extended time of impregnation of various wood species--coniferous as well as broad-leaved--with the preservative Imersol-Aqua on the change in the strength of glued joints when using the PVAc and PUR glues. The extended time of impregnation resulted in a decrease in the strength of glued joints because of the higher preservative quantity rate in wood. In general, it can be stated that several chemical substances--usually wood preservatives--have a negative effect on the strength of glued joints made from new and/or recycled wood. An increase in their concentration and the extended time of impregnation of wood results in noticeable negative effects, especially when linked with a specific type of wood and amount of glue. A decrease in the strength of glued joints prepared from impregnated wood is associated with a decrease in the adhesive bonding on wood surfaces owing to (1) the presence of improper, especially hydrophobic substances on wood surfaces; (2) the lower or higher penetration rate of cell lumens filed with a chemical substance used [21; 46; 47; 48]. Gluing quality of recycled wood depends also on its aging history--connected either with changes in its molecular, anatomy and geometry structure [14] and for chemically treated woods as well as with changes in the amount, distribution and composition of preservatives, coatings and other additives present in the wood.