Influence of polyethylene glycol and various carboxylic acids on the physical and mechanical properties of beech wood (Fagus sylvatica) and Scots pine wood (Pinus sylvestris)

The goal of this study was to investigate the influence on physical and mechanical properties of beech wood (Fagus sylvatica) and Scots pine wood (Pinus sylvestris) modified with polyethylene glycol (PEG) 400 as an alcohol and various carboxylic acids (citric acid, malic acid and 1,2,3,4-butanetetracarboxylic acid). PEG 400, chosen for its large and flexible structure, was expected to minimize the negative effects on mechanical properties. However, contrary to expectations, tensile and impact bending strength decreased - similar to other modifications. Tensile strength decreased (beech: 36.0% to 46.3%), while the modulus of rupture did not show a strong decrease (beech: 2.4% to 15.2%). The modulus of elasticity (beech: 1.6% to 14.7%), compression strength (beech: 11.7% to 40.6%) and hardness (beech: 6.0% to 17.1%) increased. Impact bending strength was reduced (beech: 43.0% to 69.3%). Modifying agents, fixed inside the wood, demonstrated high anti-swelling efficiency during leaching cycles (beech: 27.1% to 45.9%). Equilibrium moisture content was reduced between 20.8% and 39.1% for beech at a relative humidity of 65%.