Researchers in China have reported what they believe is a major breakthrough in shipwreck conservation, after developing a hydrogel that can quickly neutralise harmful acids and stabilise waterlogged timber – even when sampled from a submerged mediaeval vessel.
Wooden artefacts on shipwrecks are steeped in sea water, which enables acid-producing bacteria and wood-eating fungi to thrive. To prevent acid and microbial damage, conservators usually extract the water by freeze-drying, or replacing it with highly pressurised carbon dioxide or a viscous polymer.
These processes can however take months and increase the brittleness of the wood or warp the artefacts, say the scientists. With the new alternative, wet, historic wood is plastered with a gel that acts like a face-mask, infusing it with acid-neutralising or anti-microbial compounds.
Removing the mask
There remained one problem with this approach: peeling away the mask afterwards could damage the item’s surface.
So Xiaohang Sun and Qiang Chen of the School of Chemical Engineering & Technology at Sun Yat-Sen University in Guangdong set out to develop a hydrogel that would overcome the risk of surface damage by dispersing the compounds through the timber and then dissolving gradually over time.
The scientists mixed two polymers with potassium bicarbonate, an acid-neutralising compound, and silver nitrate, which forms anti-microbial nanoparticles that link the polymers to form a gel.
They were able to create hydrogels with different levels of staying power simply by adjusting the amount of silver nitrate. Gels with less silver liquified after 3-5 days, while those with more silver remained a “gooey solid”.
Less silver is more
The team then pasted hydrogels with varying amounts of silver onto pieces of wood taken from the 800-year-old Nanhai One shipwreck, which was discovered off China’s south coast.
They found that each gel neutralised acid up to 1cm deep after 10 days, but the dissolving gels that contained less silver did did the job more quickly – after as little as a single day.
They also found that artefacts treated with the liquifying gels better maintained their cellular structure and were less brittle than those treated with the solid gels.
The new hydrogel could, they say, be used to preserve and strengthen wood from shipwrecks without causing additional damage, enhancing the ability to untangle the mysteries of the past.
Funding was provided by the National Natural Science Foundation of China and the Guangdong Basic & Applied Basic Research Foundation, and the study can be found in American Chemical Society (ACS) Sustainable Chemistry & Engineering 2024.
Also on Divernet: 750-year-old wreck found off Dorset – timbers and all, 16th-century ship found – in Kent quarry lake, Timber-dating breakthrough re-ages Kyrenia shipwreck
