Resistance of birch wood modified with sorbitol-citric acid to white-rot decay and weathering

Abstract The increasing interest in sustainable and bio-based wood modification strategies has led to growing attention toward improving the performance of low-durability wood species for exterior applications. Sorbitol-citric acid (SorCA) modification has previously been reported as an effective approach for improving wood properties. However, despite these studies, the biological durability of SorCA-modified silver birch ( Betula pendula ), particularly its resistance to mold and fungal decay, has not been systematically investigated. Moreover, its performance under natural outdoor exposure conditions remains largely unexplored. Thus, this study evaluates the decay and outdoor weathering resistance of birch wood modified with a SorCA system. Birch wood samples were vacuum-pressure impregnated with aqueous solutions of SorCA at 20% and 40% w/w and cured at 140 °C. The distribution of the modifying agent within the wood structure was examined using X-ray microtomography, which confirmed effective penetration with partial or complete filling of the wood lumina by the in-situ formed polyester network. The modified samples were subjected to ten months of natural weathering, mold exposure under high humidity conditions, and also to white-rot fungi ( Trametes versicolor ). Outdoor weathering results indicated improved resistance to surface deterioration in modified wood, although increased color change (ΔE) was observed due to the formation of chromophoric groups during curing and subsequent photodegradation. Under the conditions investigated, SorCA modification enhanced biological durability and weathering resistance, especially at higher concentrations. In general, SorCA modification showed great potential to improve the durability of birch wood with enhancing biological durability and weathering resistance.