MARY ROSE TRUST
SCIENCE & TECHNOLOGY
Natl. Acad. Sci. USA 2014, DOI: 10.1073/ pnas.1406037111). It was designed by Zarah Walsh and Oren A. Scherman of England’s University of Cambridge and coworkers in collaboration with Mark Jones, head conservator at the Mary Rose Trust, in Portsmouth, England. SHIP OUT OF WATER
A new polymeric material could help with the conservation of large archaeological wood artifacts, like the Mary Rose, a salvaged 16thcentury English warship.
SUPRAMOLECULAR POLYMER NETWORK attacks multiple
sources of damage to waterlogged archaeological wood
CONSERVATORS trying to preserve his-
hard to avoid wood degradation after excatoric sunken ships have their work cut out vation,” says Lars Berglund, a polymer scifor them. entist at the Royal Institute of Technology Not only have the vessels been damaged who has been involved with conservation of by water, but marine organisms—mithe Vasa. “With the Vasa, iron present in the crobes, fungi, and other critters—have wood leads to significant and continuing chowed down on the wood. Oftentimes, chemical degradation as the ship is standing iron trapped in the wood has also catalyzed in the museum,” Berglund says. “At present, the formation of acid that’s eaten at the there are no practical preservation methods ship from the inside. that can solve the problem.” But help might be on the way: A new preA new preservative could be the material servative material fights all those types of conservators have been looking for (Proc. damage simultaneously. One historic ship that’s O gotten a lot of attention N N CH2 from conservators is the = H H Mary Rose, an English warN N CH2 ship that sank in battle in 8 O 1545. It was discovered in 1971 – – BF BF 4 4 and raised from the + + N CH3 seafloor in 1982. =R N The conservaOH R tion process for the Mary = Rose has been similar to that OH used for other historic OH R wooden vessels, such = O as the Vasa in Stock= Fe3+ holm. For nearly 20 years, the R = polymer chain = Mary Rose was sprayed with solutions of polyethylene glycol containing a broadTIGHT NETWORK A four-component spectrum biocide. And it’s been treated system made of functionalized chitosan separately with chelating agents to remove and guar, a macrocyclic host molecule, iron. and iron forms a supramolecular polymer “The main problem with archaeological network that treats multiple types of ships like the Vasa and the Mary Rose is it’s damage sustained by waterlogged wood. CEN.ACS.ORG
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THE NEW MATERIAL is a supramolecular
polymer network made from four components, each of which has a specific job to perform. The biopolymer chitosan, which has antibacterial properties, is functionalized with both naphthol and catechol. A second biopolymer, guar, is decorated with a viologen derivative, which also has antibacterial properties. A macrocyclic host molecule, cucurbit[8]uril, links the polymer chains together. The fourth component—iron—comes from the wood itself and also helps connect the network. To form the network, the viologen moiety acts as the first guest in a ternary hostguest complex with cucurbituril. Naphthol or catechol can act as the second guest. If iron is present in its +3 oxidation state, catechol lets go of the cucurbituril and binds iron instead. “We made a two-tier system,” Walsh says. “We add enough naphthol that the structural stability of the material will always be at a certain minimum level. But it can get stronger if iron is present.” That extra strength is important because iron often signals the presence of acid, which weakens the wood. So far, the material has been tested as a surface treatment with small pieces of wood from the Mary Rose. “The next stage is to scale up and use these new polymers on large ship timbers,” Jones says. One hoped-for benefit is that it will speed up conservation, “so it won’t take 20-plus years, like it’s taken to conserve the Mary Rose,” he says. “It will speed things up, and it will solve a number of problems, all with one form of treatment.”—CELIA ARNAUD
ADAPTED FROM PROC. NATL. ACAD. SCI. USA
NEW TREATMENT FOR OLD WOOD
