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Experiments on the degradation of tributyltin oxide: A progress report
1984 - IRG/WP 3287
A variety of experiments designed to assess the chemical and physical factors affecting the degradation of tributyltin oxide in treated timber are described. Simple procedures in which temperature and oxygen availability were increased in the presence of wood and water suggest that the wood itself was of prime importance. Attempts to decrease degradation with antioxidants were unsuccessful but led to the idea that free radicals may be instrumental in the degradative mechanism. Subsequent work in which a range of antioxidants and free radical producing systems were used confirmed the susceptibility of tributyltin oxide to the action of free radicals. It is suggested that the presence of free radicals in the painted and treated wood system may be an important factor in the eventual degradation of tributyltin oxide.
R J Orsler, G E Holland

Environmentally benign wood preservatives based on organic biocide antioxidant combinations: A brief review of laboratory and field exposure results and discussion of a proposed mechanism
2004 - IRG/WP 04-30335
The combination of various organic biocides with commercial antioxidants generally increased the biocides’ efficacy 2-3 fold against wood-destroying fungi in short-term laboratory decay tests, and some positive results have been obtained after 2-4 years of outdoor exposure. The two antioxidants principally examined, propyl gallate and butylated hydroxytoluene, are low cost and, since both are food additives, benign. The biocides studied have either been examined as potential wood preservatives or are used in commercial wood preservative systems. The purpose of this paper is to: 1) briefly summarize our prior laboratory decay results; 2) briefly discuss results obtained so far from outdoor exposure tests, both above-ground and ground-contact exposure; 3) discuss differences in results between laboratory decay tests and the outdoor exposure data; and 4) propose a mechanism by which antioxidants could protect wood.
T Schultz, D D Nicholas, W Henry, C Pittman, D Wipf, B Goodell

Antifungal activity and synergistic effect of cinnamaldehyde combined with antioxidants against wood decay fungi
2007 - IRG/WP 07-30445
The objective of this study was to investigate the antifungal activity and synergistic effect of cinnamaldehyde combined with antioxidants against wood decay fungi. Five antioxidants, propyl gallate, octyl gallate, quercetin, eugenol and catechin were tested against various wood decay fungi. Octyl gallate and eugenol were found to be the only two antioxidants processed antifungal activities. IC50 values of octyl gallate were 0.47 and 0.04 mM against L. betulina and L. sulphureus, respectively. The IC50 values of eugenol were 0.37 and 0.25 mM against L. betulina and L. sulphureus, respectively. The synergistic effects were also found on the combinations of octyl gallate-cinnamaldehyde and eugenol-cinnamaldehyde. The combination of either using octyl gallate with cinnamaldehyde or eugenol with cinnamaldehyde greatly reduced the concentrations to achieve the inhibitory effect that a higher concentration was needed by octyl gallate, eugenol or cinnamaldehyde alone. The antifungal action of octyl gallate could be attributed to its pyrogallol group functioning as an attached moiety to the hydrophilic portion of the membrane surface and the octyl moiety interfering with the hydrophobic interior surfaces of the membrane. Meanwhile, the synergism of cinnamaldehyde with octyl gallate or eugenol could be due to the interference of fungal cell wall synthesis and destruction on cell wall and membrane plus the additional radical scavenging effect. Results also suggested that antioxidant with fungicidal effect might be a better candidate than pure antioxidant for the system of fungicide/antioxidant.
Fu-Lan Hsu, Tsair-Bor Yen, Hui- Ting Chang, Shang-Tzen Chang

Impregnation of wood with antifungal compounds from low-quality tree biomass
2022 - IRG/WP 22-30763
In this paper we have reviewed recent research on the development of bio-based preservative formulations for wood done at the Department of wood science and technology, Ljubljana. Preservative formulations used in this investigation were prepared using plant polyphenols as biocidal agents. These nonstructural components of wood were stilbenes and flavonoids, and were extracted from wood of broken and less-utilized trees, respectively. Woody biomass of the lowest quality was selected as a row material for extraction. Pine knotwood (Pinus sylvestris and Pinus nigra) and black locust heartwood (Robinia pseudoacacia) were extracted with acetone. Obtained extracts were examined with gravimetrically, spectrophotometrically and with chromatographic analysis. Further on, purified stilbenes and flavonoids were prepared for the antifungal assay. The extracts were colorimetrically analyzed on antioxidant properties by measuring free radical scavenging activity. The resistance of with extractives impregnated wood was measured with a so-called mini-block test (modified EN 113). Wood of less durable conifers and deciduous tree species was impregnated in a vacuum-pressure chamber, whereat water solutions of the hydrophilic extracts were used. After impregnation, the retention of extracts in the wood matrix was examined gravimetrically and with microscopy (CLSM and SEM). Antifungal properties of wood extractives of pine and black locust were determined by in vitro measuring the inhibition of fungal growth, and with measuring the resistance of the impregnated wood against fungal decay. The results of the fungal tests clearly show that hydrophilic extractives of less-quality wood of pines and black locust inhibit both fungal growth and reduced fungal decay of wood. It was found that the wood extracts of pines and black locust can be referred as to natural antioxidants since they inhibited the activity of free DPPH radicals. The results of our investigation show that low-quality wood of broken and less-utilized trees can be explained as a relevant source of natural compounds with antifungal and antioxidant properties. Wood polyphenols could be used as natural biocidal agents in bio-based preservative solutions.
V Vek, I Poljanšek, A Balzano, M Humar, P Oven