Waterlogged archaeological wood of shipwrecks, like Varsa and Mary Rose, has been treated with polyethylene glycol (PEG) for its consolidation and stabilization. Archaeological wood after being submersed for hundreds of years in sea, shows a reduced strength and density, increased porosity, permeability, and hygroscopicity. During drying to museum conditions, a high risk exists of drastic shrinkage, distortion and possible collapse of the wood causing irreversible damage to the artifact. During decades-long PEG treatment, PEG molecules diffuse into the wood structure and replace the water molecules stabilizing the wood structure, making wood less susceptible to changes in humidity and able to sustain mechanical load. To better understand the consolidation mechanism, Molecular Dynamics is combined with Grand Canonical Monte Carlo simulations [1] to model sorption and sorption-induced deformation and determine the mechanical properties of mixtures of amorphous cellulose (AC) and PEG at molecular scale. The results show that pure AC is a hygroscopic material, showing a substantial swelling-induced sorption and a mechanical weakening upon sorption. Pure PEG remarkedly shows much higher moisture contents and swelling strains at high relative humidity (RH) compared to AC, what opens the question how PEG can reduce AC’s sorption behaviour. Our results confirm that adding PEG reduces the sorption and swelling behaviour of AC. This counterintuitive observation can be explained by: (1) PEG fills a large part of the existing porosity in AC, as such preventing additional sorption; (2) PEG molecules are constrained by the existing AC structure, hindering swelling and additional swelling-induced sorption. Simulations for mixtures at different PEG content indicate an optimal PEG mass fraction of 15%, whereafter sorption and swelling start to increase again. We also introduce a new simple hygromechanical model based on the coupling between sorption and swelling, mechanical weakening and the filling of the porosity of AC by PEG [2]. Finally, we analyse the data with a poromechanical model proposing an approach to optimize the treatment of AC with PEG. REFERENCES [1] M. Chen, B. Coasne, R. Guyer, D. Derome, J. Carmeliet, Role of hydrogen bonding in hysteresis observed in sorption-induced swelling of soft nanoporous polymers, Nat Com., 2018 29;9(1):3507. doi: 10.1038/s41467-018-05897-9 [2] A. Shomali, C. Zhang, B. Coasne, D. Derome, J. Carmeliet, Molecular mechanism