Influence of polyethylene glycol and various carboxylic acids on the biological durability of beech wood (Fagus sylvatica) and Scots pine sapwood (Pinus sylvestris)

Abstract

The goal of this study was to investigate the impact of wood modification with polyethylene glycol (PEG) 400 and various carboxylic acids (citric acid (CA), malic acid (MA) and 1,2,3,4-butanetetracarboxylic acid (BTCA)) on the biological durability of beech wood (Fagus sylvatica) and Scots pine sapwood (Pinus sylvestris). For the brown, white and soft rot experiments, mass losses (ML) were calculated according to the respective standards. Weight percent gain, bulking and anti-swelling efficiency were determined to determine the quality of the modifications. Modifying agents, fixed inside the wood, demonstrated anti-swelling efficiency after leaching cycles (beech wood: 9–46 %). The decay resistance against brown and white rot fungi was considerably improved, with PEG/CA and PEG/BTCA being more effective than PEG/MA. Beech wood modified with PEG/CA achieved durability class (DC) 1–2, PEG/BTCA reached DC 1 and PEG/MA fell into DC 2–4. For Scots pine sapwood, PEG/CA and PEG/BTCA reached DC 1, while PEG/MA only achieved DC 4. The biological durability against soft rot fungi was less affected, and curing alone did not enhance the resistance to soft rot fungi. PEG/BTCA achieved DC 1, while PEG/MA and PEG/CA ranged between DC 1 and DC 3. The variants with different CA to PEG ratios as well as CA without PEG showed no major differences in terms of ML due to soft rot fungi. In conclusion, the modifications resulted in significantly lower mass losses.