The project explores the reuse of seafood waste, looking for possible applications in the interior design field. Seafood waste well describes a typical behaviour towards leftovers: it is something smelly to push away so as not to see it; but it hides a significant potential, unknown as the sea is. The aim is to value something that is currently discarded, by developing circular materials that can be applied in our homes.
After experimenting with fish skins and shrimp shells, further research looked at mussels’ waste (Mytilus galloprovincialis) as the main raw material to experiment with. It is estimated that over 7 million tonnes of mollusc shells are discarded by the seafood industry each year as unwanted waste. The vast majority of these shells are either thrown in landfills or dumped at sea near the coast. Both options generate a bad environmental impact and a huge waste of potentially useful biomaterials (Source: Science Daily | 5 July 2017).
In this perspective, the name of the project “Blue Shel(l)ter” reminds us of the sea and of the home seen as a safe shelter. As the shell protects the mussel while it is alive, the materials produced from its waste aim to be safe surfaces for the interiors, free from toxic chemicals.
The first step to start processing the shells has been understanding their functioning as well as their chemical composition. The process has been, therefore, differentiated depending on the different parts that compose the shell, putting emphasis on the variety within the nature of the mussel.
Ground shells have been used together with lime to make a decorative paint for the walls that imitates organic patterns from the marine world. Lime + seashells paint is an ancient material, used by past populations for its good antibacterial and moisture regulator natural properties. It is also a potential mono-material as shells can turn into lime if brought to high temperatures, thus acting both as aggregate and binder.
Sometimes not all the shell has been used to be ground, but the internal part, the nacre, has been processed separately to make an iridescent paint or to be mixed with a natural binder such as gelatine or alginate. Alginate, which comes from seaweeds, proved to be a good and versatile binder combined with the shells. Samples in the shape of pearls have also been made using alginate and a process called spherification, usually found in molecular cuisine.
Finally, the mussel’s byssus has also been processed by combining it with alginate, resulting in a compound that shows good resistance to weight. The byssus is the bundle of filaments that allow the mussel to attach to a solid surface and has to resist the force of the waves. Alginic acid is found in the cell walls of a wider variety of brown algae, as a hydrophilic substance that forms a viscous gum when in contact with water. Together the two ingredients form a compound that is easily moulded into a desired shape and can be machined once dried. The addition of a calcium salt provides more water resistance to alginate composites, by a chemical reaction called cross-linking: sodium alginate molecules float freely into a liquid until they are linked together by calcium ions. Calcium-linked alginate molecules form a more solid structure compared to non-crosslinked sodium alginate, thus gaining also in water resistance.
The first steps in processing the shells consist in cleaning them with water, letting them air-dry and, once dried, removing the organic remains of the mussel. Then they can be ground or cooked in a kitchen oven to make them more brittle. If kept longer in the oven they will start to turn colour and the inner part called the nacre will partially split. Once ground they are mixed with a binder such as lime to make paint with, or they are mixed with an alginate solution using different techniques to make different composites.
As for the byssus, after collecting it from fresh mussels and rinsing it in water, this is soaked in vinegar to remove any residual shells, as the low pH of the liquid will dissolve the calcium carbonate from which seashells are made. A second rinsing is necessary before mixing it with the sodium alginate solution. Tannic acid, from plants, can also be added at this stage as its antibacterial properties can prevent mould. The mix is then poured into the mould, protected with a gauze and let dry in the sun. A dehydrator can help in the winter season, to quicken the process. Once dry it is then sprayed with the calcium chloride bath and let it dry again.
Information submitted by the maker and edited by the Future Materials Bank.
Mussels' Byssus, Sodium alginate, Calcium chloride, Vinegar, Tannic acid, Lime, Gelatine