Tannin-caprolactam and Tannin-PEG formulations as outdoor wood preservatives: biological properties

oKey Message This article presents the enhancement in boron fixation as well as the improved biological resistance against fungi and termites for wood samples treated with tannin-caprolactam and tannin-PEG formulations. oContext Although the recently developed tannin-boron wood preservatives have shown high biological protection, they presented also average resistance against weathering. The tannin-caprolactam formulations have shown improved weathering resistances and dimensional stability. oAims For this reason, more detailed biological tests were performed to evaluate the influence of the caprolactam and PEG on the biological resistance. oMethods In this paper, the boron leaching of the tannin- caprolactam and tannin-PEG impregnated Scots pine speci- mens was observed and the biocidal effect against fungi. (Antrodia spp. and Coniophora puteana) and insects (Reticulitermes flavipes and Hylotrupes bajulus) were determined according to the guidelines of EN 113, EN 117, and EN 47. oResults The advanced formulations containing PEG have shown interesting resistance against fungal decay, but very low penetration and weak resistance against larvae while the tannin-caprolactam preservatives have shown overall im- proved biological performances and higher boron fixations. oConclusion The biocidal activity of the caprolactam-added formulations was overall enhanced and therefore these formu- lations are confirmed to be an interesting alternative for the wood preservation in outdoor environment.