Effect of hardening parameters of wood preservatives based on tannin copolymers

Amongst polyphenols, tannins belong to the most effective chemical protection systems against biological attack on trees. Tannins are water-soluble and are thus leached out easily when used for wood protection. In situ polymerized tannin-hexamine wood preservatives have better leaching resistance (LR), but they do not resist weathering. In this study, tannin copolymer formulations were prepared with hexamine, formaldehyde, furfural, glyoxal, furfuryl alcohol and maleic anhydride, impregnated in wood, and cured at higher temperatures. The wood samples treated with these formulations were tested for their anti-swelling efficiency (ASE), leaching behavior, mechanical properties, and their resistance against fire, weathering and biological attack. Several tannin-treated specimens showed improved hardness and enhanced leaching and fire resistance. Some formulations also responded well to artificial weathering cycles, but natural weathering cycles deteriorated their performance. Samples treated with maleic anhydride showed improved leachability and high biological resistances, even without the addition of inorganic biocides. These organic and biofriendly products can be considered as promising alternatives to heavy metal-based wood preservatives.