Shipwrecks, ranging from the RMS Titanic to the SS Endurance, provide significant — albeit quickly fading — insights into history. Conservators gradually dry out marine wooden artifacts to maintain them, but this process can cause damage.
To enhance the preservation of fragile marine objects, researchers in ACS Sustainable Chemistry & Engineering created a new hydrogel that swiftly neutralizes harmful acids and stabilizes waterlogged timber from a shipwreck that is 800 years old.
Wooden relics from shipwrecks are saturated with seawater, creating an environment where acid-producing bacteria and wood-decomposing fungi can flourish. To mitigate damage from acids and microbes, conservators typically eliminate water from these artifacts through freeze-drying or a method that substitutes water with highly pressurized carbon dioxide or a thick polymer.
However, these methods can extend for months and may increase brittleness or distort the objects. A more recent approach involves applying a gel over the moist, historical wood like a face mask, delivering acid-neutralizing or antimicrobial agents to the wood. However, removing the mask afterward can potentially harm the object’s surface.
Therefore, Xiaohang Sun and Qiang Chen aimed to create a hydrogel that would distribute acid- and microbe-fighting substances throughout the wood and gradually dissolve over time to prevent surface damage.
The researchers initiated their study by combining two types of polymers with potassium bicarbonate, a compound that neutralizes acids, and silver nitrate, which produces antimicrobial nanoparticles that bond the polymers to create a gel.
By adjusting the quantity of silver nitrate, the team successfully engineered hydrogels with varying durability; those with less silver dissolved within 3-5 days, while those with higher concentrations remained gooey solids.
In a compelling proof-of-concept demonstration, the researchers applied these hydrogels to 800-year-old wood from the Nanhai One shipwreck, found off China’s southern coast. They discovered that the gels neutralized acid up to 1 centimeter deep over 10 days, with the less silver-rich gels acting more rapidly, neutralizing acid within just 1 day.
Additionally, the team observed that artifacts treated with the dissolving gels better preserved their cellular integrity and were less fragile in comparison to those treated with the solid gels. The researchers believe that their innovative hydrogel could aid in the preservation and fortification of shipwreck wood without causing harm, significantly enhancing our ability to unravel the mysteries of the past.
Journal reference:
- Junjie Chen, Lifang Yang, Xuanwei Zhang, Yuelin Gu, Boya Su, Xiaohang Sun, Qiang Chen. Alginate–Nanosilver Hydrogels: A Self-Dissolving System for Comprehensive Preservation of Waterlogged Wooden Artifacts. ACS Sustainable Chemistry & Engineering, 2024; DOI: 10.1021/acssuschemeng.4c06707
