Tert-butyldimethylsilyl chitosan synthesis and characterization by analytical ultracentrifugation, for archaeological wo
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ORIGINAL ARTICLE
Tert‑butyldimethylsilyl chitosan synthesis and characterization by analytical ultracentrifugation, for archaeological wood conservation Jennifer M. K. Wakefield1,2 · Susan Braovac3 · Hartmut Kutzke3 · Robert A. Stockman2 · Stephen E. Harding1,3 Received: 2 March 2020 / Revised: 10 July 2020 / Accepted: 17 July 2020 © The Author(s) 2020
Abstract The Oseberg ship is one of the most important archaeological testimonies of the Vikings. After excavation in 1904, the wooden gravegoods were conserved using alum salts. This resulted in extreme degradation of a number of the objects a hundred years later through acid depolymerisation of cellulose and lignin. The fragile condition of the artefacts requires a reconsolidation which has to be done avoiding water as solvent. We synthesized tert-butyldimethylsilyl (TBDMS) chitosan which is soluble in a 50:50 solution of ethyl acetate and toluene. Measurement of its molecular weight, to anticipate its penetration, provided a challenge as the density difference of the polymer and solvent was too small to provide adequate solute redistribution under a centrifugal field, so a two-stage process was implemented (i) determination of the weight-average molar mass of the aqueous soluble activated precursor, chitosan mesylate, Mw,mc using sedimentation equilibrium with the SEDFIT-MSTAR algorithm, and determination of the degree of polymerisation DP; (ii) measurement of the average degree of substitution DSTBDMS of the TBDMS group on each chitosan monosaccharide monomer unit using NMR, to augment the Mw,mc value to give the molar mass of the TBDMS-chitosan. For the preparation, we find Mw = 9.8 kg·mol−1, which is within the acceptable limit for penetration and consolidation of degraded wood. Future work will test this on archaeological wood from different sources. Keywords Analytical ultracentrifuge · NMR · Combined molar mass method
Introduction The Oseberg collection is in dire need of re-conservation. The Oseberg Viking ship burial was discovered in 1903 and excavated in 1904 (see for example Braovac et al. 2018). The grave mound contained a rich collection of different Special Issue: Analytical Ultracentrifugation 2019. * Jennifer M. K. Wakefield [email protected] * Stephen E. Harding [email protected] 1
National Centre for Macromolecular Hydrodynamics (NCMH), School of Biosciences, University of Nottingham, Sutton Bonington, Nottingham LE12 5RD, UK
2
School of Chemistry, University of Nottingham, University Park Nottingham, Nottingham NG7 2RD, UK
3
Museum of Cultural History, University of Oslo, St. Olavs plass, Postboks 6762, 0130 Oslo, Norway
artefacts; amongst them, many wooden objects which are today displayed at the Viking Ship Museum in Oslo, Norway (www.khm.no). The most degraded wooden artefacts were treated in 1905 with concentrated solutions of alum salts [KAl(SO4)2.12H2O and N H4Al(SO4)2.12.H2O] heated to 90 ℃. Although this treatment allowed the objects to retain their shape upon drying, it has caused de
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