Abstract
Key MessageThis 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.ContextAlthough 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.AimsFor this reason, more detailed biological tests were performed to evaluate the influence of the caprolactam and PEG on the biological resistance.MethodsIn this paper, the boron leaching of the tannin-caprolactam and tannin-PEG impregnated Scots pine specimens 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.ResultsThe 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 improved biological performances and higher boron fixations.ConclusionThe biocidal activity of the caprolactam-added formulations was overall enhanced and therefore these formulations are confirmed to be an interesting alternative for the wood preservation in outdoor environment.
Highlights
Most of the European temperate wood species are low to moderately durable when exposed outdoor and susceptible to degradation, including biological attacks and weathering
Using boron compounds means facing some problems: (i) from a technical viewpoint, boron compounds remain leachable from treated timber due to their high solubility, and (ii) despite a favorable environmental profile, boron compounds have seen their use restricted by the European Commission (98/8/EC 2008)
Mimosa (Acacia mearnsii) tannin extract was supplied by Silva Chimica (Cuneo, Italy), and hexamethylentetramine, boric acid, sodium hydroxide, caprolactam, and polyethylene glycol (PEG) were provided by Sigma-Aldrich
Summary
Most of the European temperate wood species are low to moderately durable when exposed outdoor and susceptible to degradation, including biological attacks and weathering. Non-metallic water-borne boron formulations have a long history as wood preservatives, as well as a broad range of activity against decay fungi and insects in protected above ground contact situations (Williams and Amburgey 1985; Drysdale 1994; Thevenon et al 1997). Boron compounds for wood protection are highly effective for stand-alone formulations as well as associated to other active ingredients for more complex formulations where they act as a co-biocide (Freeman et al 2009). The key issue to extend boron preservatives’ use for wood protection appears to be their fixation at low levels into the wood (Obanda et al 2008)
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