Dimensional stability and bending properties of silver birch ( <i>Betula pendula</i> Roth.) modified wood with sorbitol and different types of polycarboxylic acids

Wood modification with bio-based chemicals such as sorbitol–citric acid (SorCA) system is a low-cost and effective approach, while the low pH of the modifying agent reduces the mechanical properties of modified wood. Thus, this study was conducted to find alternative polycarboxylic acids with comparable functional groups, reactivity, and processing conditions. Silver beech wood (Betula pendula Roth.) was modified through in situ esterification approach using sorbitol in combination with citric acid (CA), tartaric acid (TA) or malic acid (MA). Wood samples were modified at 20% w/w of sorbitol–CA, –TA, and –MA at 1:3 molar ratio and cured at 140°C for 24 h. The SorCA modified samples showed the highest leaching resistance followed by SorMA and SorTA. The samples modified with SorTA and SorMA illustrated superior dimensional stability compared with SorCA. The modulus of elasticity (MOE) was slightly improved in all modified samples in comparison with unmodified birch. However, the modulus of rupture (MOR) was marginally decreased, particularly in the samples modified with SorCA and SorTA.