In this study, antifungal properties of an organoclay additive were investigated. Two types of organoclay (red and white) were tested in Petri dishes to determine their toxicity against the brown rot fungus Coniophora puteana and the white rot fungus Trametes versicolor. Red organoclay was more efficient than the white one and, depending on the fungus, inhibited or stopped the fungal growth. Red organoclay was chosen as an additive to produce a new type of plywood product. Biological durability of this plywood product was determined according to the methods: NF B 51-295 (bending strength test) and LVS ENV 12038:2002 (mass loss test). The loss in bending strength exceeded 81% and 65% after exposure to brown and white rot fungi, respectively. The mass loss of the plywood product after the decay test was higher than 3%, which defined the material as not fully resistant against decay fungi. According to CEN/TS 15083-1:2005, the plywood product corresponded to the durability class 3 (moderately durable) to 5 (not durable) depending on the fungus.

Scots pine (Pinus sylvestris L.) is the most common wood species in Latvia. It is classified as not durable, therefore additional protection against microorganisms is needed prior its use outdoors. Presently Cu-containing wood preservatives are commonly used, but the biggest drawback is the poor Cu fixation, therefore raising concerns about the impact on the environment. Three types of specimens were used to carry out the experiments – untreated, Latvian originated Scots pine; Scots pine commercially treated with preservatives that belong to a group of Cu-boron-triazole (CBA) products; and Scots pine, impregnated with micronized-Cu solution using a standard full cell process. In order to make sure that all of the specimens are equal in their components, elemental analysis was performed and content of nitrogen (1.2 – 2.5 g kgE-1), carbon (485.5 g kgE-1), oxygen (456.0 g kgE-1) and hydrogen (55.6 g kgE-1) was determined. The treated specimens were leached according to the European standard EN 84. For micronized-Cu impregnated Scots pine the total Cu content in leachates obtained by atomic absorption spectroscopy was 0.15 mg gE-1 of wood, and 0.06 mg gE-1 of absolute dry matter with CBA preservative impregnated Scots pine wood. Subsequently, according to the European standard EN 113, treated Scots pine blocks were exposed to brown-rot fungus Coniophora puteana and to white-rot fungus Trametes versicolor for 16 weeks. Mass loss for wood treated with micro-Cu was 48.4% (484 g kgE-1) and 1.5% (15 g kgE-1) respectively, but for CBA – 49.5 % (495 g kgE-1) and 1.2% (12 g kgE-1). Both samples proved to be inappropriate for outdoor use (use class 3).