The Potential of Size-Exclusion Chromatography for Evaluating the Suitability of Hydrophilic Extracts in Wood Preservation

European beech wood has low natural resistance to microbial attacks especially when it is exposed outdoors. We looked at ways of improving this by applying three hydrophilic extracts from other species known for their ability to inhibit fungal growth. We prepared oak heartwood and black locust bark extracts by accelerated-solvent extraction with aqueous methanol and freeze-drying, and obtained black wattle bark hot-water extract commercially. The molecular size of the phenolic components and associated saccharides in the extracts were determined by size-exclusion chromatography (SEC). We found that two extracts improved beech wood durability even at low concentrations (5 wt.% solution); the most effective extract was black wattle extract. The worst performance, by black locust bark extract, was attributed to the presence of small-molecule phenolics. The total phenolic content was up to 9× lower than that reported for fresh extracts. Even though the extracts were not stored specifically to preserve the original phenolic content, we found that two were still effective as fungal inhibitors.