Novel nanocomposite material might prevent shipwrecks from rotting

Shipwrecks are coming — soon, to a museum near you. And it’s all thanks to nanotechnology.

A novel approach hopes to turn the damp, pitted wood of ancient shipwrecks into a showstopper. The team is currently using ‘smart’ nanocomposites to conserve the 16th-century British warship, the Mary Rose, and its artifacts. Should the process prove effective, museums will be able to display salvaged wrecks in all their glory without them rotting away.

The old that is strong does not wither

Thousands of shipwrecks have come to rest on ocean floors through the centuries. These drowned leviathans spark the passion of both researchers — who can learn a lot about past battles and ways of life from the wrecks — and public alike.

However, it’s very risky to go in and try to recover shipwrecks. Metal ships tend to weather the years underwater with some grace, but the wooden ones quickly rot away — after roughly a century, the only parts that remain are those that were buried in silt or sand soon after the sinking. Even worse, these timber skeletons quickly deteriorate once brought up to the surface.

While underwater, sulfur-reducing bacteria from the sea floor move into the wood and secrete hydrogen sulfide. This reacts with iron ions (rust) from items like nails or cannonballs, forming iron sulfide. This compound remains stable in environments that sport low levels of oxygen but binds with the gas to form acids that attack the wood.

In a paper being presented today at the 256th National Meeting & Exposition of the American Chemical Society (ACS), one team of researchers detail their efforts to keep wooden shipwrecks intact after recovery.

“This project began over a glass of wine with Eleanor Schofield, Ph.D., who is head of conservation at the Mary Rose Trust,” recalls Serena Corr, Ph.D., the project’s principal investigator.

“She was working on techniques to preserve the wood hull [of the Mary Rose] and assorted artifacts and needed a way to direct the treatment into the wood. We had been working with functional magnetic nanomaterials for applications in imaging, and we thought we might be able to apply this technology to the Mary Rose.”

The Mary Rose was one of the first sailing ships built for war. Work on the wooden carrack (three-masted ship) began in 1510, and she was set to sea in July 1511. She remained one of the largest ships in the English navy for over three decades, during which she fought against the French, Scottish, and Brythonic navies — a task at which the Mary Rose excelled. The ship bristled with heavy cannons that popped out from gun-ports (which were cutting-edge technology at the time), and one of the first ships in the world capable of firing a full broadside.

Still, for reasons not yet clear, the ship sank in 1545 off the south coast of England. It was re-discovered in 1971 and recovered in 1982 by the Mary Rose Trust, along with over 19,000 artifacts and pieces of timber. The wreck helped provide a unique snapshot of seafaring and daily life in the Tudor period. It was displayed in a museum in Portsmouth, England, alongside the recovered artifacts.

Only 40% of the initial wooden structure survived the centuries underwater, and even this was rapidly degrading on the surface. So the Trust set out to preserve their invaluable wreck.

Corr’s goal was to avoid acid production by removing free iron ions from the wreck. She and her team at the University of Glasgow started by spraying the wood with cold water to keep it from drying out, which prevented further microbial activity, they explain. Afterward, they applied different types of polyethylene glycol (PEG) — a common polymer —  to the wreck. The PEG replaced water in the wood’s cells, forming a more robust outer layer.

The team, alongside researchers from the University of Warwick, are also working on a new family of magnetic nanoparticles to help in the conservation effort. They analyzed the sulfur species in the wood before the PEG treatment was applied, and then periodically as the ship dried.

This process will help the team design new targeted treatments to scrub sulfur compounds from the wood of the Mary Rose.

The next step, Schofield says, will be to use a nanocomposite material — based on magnetic iron oxide nanoparticles coated in active chemical agents — to remove these sulfur and iron ions. The nanoparticles will be applied directly to the wood and later guided through its pores to any particular areas using external magnetic fields. Such an approach should allow the team to completely remove the ions from the wood, they say.

“Conservators will have, for the first time, a state-of-the-art quantitative and restorative method for the safe and rapid treatment of wooden artifacts,” Corr says. “We plan to then transfer this technology to other materials recovered from the Mary Rose, such as textiles and leather.”

The paper “Magnetic nanocomposite materials for the archeological waterlogged wood conservation” has been presented today, Tuesday 21th August, at the 256th National Meeting & Exposition of the American Chemical Society (ACS).