Fenton-induced degradation of polyethylene glycol and oak holocellulose. A model experiment in comparison to changes observed in conserved waterlogged wood

Abstract

Degradation of polysaccharides and polyethylene glycol have recently been observed in the wood of the Swedish war-ship Vasa. The signs of degradation are highly correlated to the presence of iron compounds, indicating iron initiated reactions of Fenton type. In order to test this hypothesis pure polyethylene glycol (PEG, M_w =1500 u) and prepared oak holocellulose were oxidized by hyddroxyl radicals induced by Fenton's reagent [Fe(II)/H₂O₂] in aqueous solution. The changes in molar weight distribution (MWD) were analysed by MALDI-TOF mass spectrometry and size exclusion chromatography. The changes in MWD were consistent to random scission of the polymers according to statistical simulations. By NMR analysis the main PEG degradation products formed were identified as PEG molecules with different end groups: alcohols, aldehydes and formate esters; the latter hydrolyse to formic acid. The all over results show close similarities to the situation observed in the Vasa wood and strengthen the hypothesis of oxidative degradation initiated by iron compounds in the wood.