Dynamics property recovery of archaeological-wood fibers treated with polyethylene glycol demonstrated by high-resolution solid-state NMR

We used high-resolution Solid-State ¹³C NMR to better understand and optimize the conservation process of archaeological waterlogged woods by polyethylene glycol (PEG) impregnation via the study of the molecular interactions between PEG and residual celluloses. By both deconvoluting NMR spectra and analyzing the behavior of ¹³C magnetization build-up under proton to carbon cross-polarization conditions, we were able to quantify PEG penetration and extract parameters sensitive to molecular dynamics such as proton spin lattice-relaxation-time constants in the rotating frame T_1ρH and the cross-relaxation time constant T_CH. By exploring a large range of PEG concentrations for the impregnating solutions we show that the PEG penetrates inside the fibers and interacts at a molecular level with the cellulose fibrils thus restoring the dynamics properties of the damaged molecular cell wall network. At high PEG concentration, the polymer accumulates in the remaining free volume with more and looser molecular interactions with the residual wood components. This feature explains the facility for these hydroscopic materials to exude from the wood and led to deleterious consequences for the restored artefacts.