Polyethylene glycol (PEG) is used to treat wood as a consolidation method. The effect of PEG on the shear strength during pull-out of crystalline cellulose (CC) fiber out of an amorphous cellulose matrix is simulated with molecular dynamics. The interfacial shear force shows a stick-slip behavior and is weakened with increasing moisture content. The shear strength increases at low moisture content, manifesting a slight strengthening of interfacial mechanical property due to cohesive forces exerted by the water molecules. At higher moisture content the shear strength reduces due to breakage of the hydrogen bonds between CC and matrix by water molecules. When adding PEG, amorphous cellulose around the crystalline fiber is replaced by PEG, forming a mixture with the amorphous cellulose. It is found that PEG-treated CC-AC composite maintains its shear strength and does not deteriorate the dependence of the shear strength on moisture content. A shear strength model based on the number of hydrogen bonds between the fiber and the matrix is developed and validated. The model reveals that, although the shear strength per hydrogen bond between the fiber and PEG is lower than the shear strength per hydrogen bond between the fiber and amorphous cellulose, the final shear strength is partly compensated by an increase in the total number of hydrogen bonds with increasing PEG ratio.

Since PEG reduces the moisture content in the composite at low relative humidity, PEG treated wood in museum conditions (RH<40%) will show enhanced shear strength. The framework is a basis for further investigation of realistic archeological wood with PEG-treatment.