Earth’s second most abundant natural material is the best natural replacement for single use plastics
In 1823, a scientist named Antoine Odier created a hornlike material after treating a beetle with potassium hydroxide. This was one of the earliest discoveries of chitin, a polysaacharide found in many animal, plant, and insects. It is the second most abundant natural polymer on earth.
Chitosan, a derivative of chitin, is one of the most exciting biomaterials now out on the market. While some biomaterials require additional land to be brought under cultivation, chitin does not need to be grown at all since it is so abundant in the natural world. This gives it immense potential as a land-efficient, circular, and low-carbon biomaterial. Seafood waste is a particularly high-yielding, sustainable source of chitin: crustacean shells and fish scales are full of it.
From niche to novel industrial biomaterial
Industrial chitin and chitosan production began in 1971 in Japan. Now, market interest in sustainable petrochemicals alternatives is boosting the fortunes of a material once regarded by a chemical curiosity. One of chitosan’s most promising aspects is that it can be worked into different physical properties and has wide-ranging applications, just like the petrochemical polymers they are set to replace.
One of the most formidable biomaterials startups to emerge in recent years has been Shellworks. Founded in 2019, this London-based company specialises in compostable chitosan-based packaging from seafood waste. Shellworks’ products are an exemplar of why chitosan should become a keystone decarbonisation technology: their feedstock valorises materials that would otherwise have gone to waste and their product is naturally compostable. Shellworks is now embarking on scaling and is poised to become among the first to produce chitosan industrially for packaging applications.
While Shellworks produces hard packaging for cosmetics, the US company Cruz Foam has been working on softer variants of this natural material. Ever since arriving on the sustainable packaging scene in 2017, it has been making a fully compostable “guilt-free” packaging foam out of shrimp waste from the seafood industry. The chitosan is mixed with starches and low-grade fibres, all of which are also bio-based.
The largest consumer product chitosan producer in the world is Icelandic marine biotech company Primex, already a world leader in pure chitosan powder for cosmetics, nutraceutical markets, and clean tech markets. These industries have been drawn to the material for its antimicrobial and antioxidant properties, particularly as consumers become sensitised to the ecological impacts of synthetic chemical pollution. Primex’s products include Lipsan, a weigh loss supplement, SeaKlear, a biodegradable and non-toxic water clarifier for pools, and Chitocare, a skincare ingredient with skin reparing properties.
Chitosan’s environmental benefits do not end at avoiding carbon emissions from consumer plastics. It is an effective and eco-friendly wastewater treatment material, or flocculant. The material’s highly reactive hydroxyl (-OH) and amines (-NH2) attract a wide range of pollutant particles including metal ions, phenol, antibiotics, and pesticides. Tidal Visions is a company that specialises in chitosan for wastewater treatments. Unlike conventional flocculants like polyacrylamides or alumnium sulfate, their chitosan alternative is biodegradable, posing less environmental harm.
Chitin in textiles
The Fraunhofer Institute for Interfacial Engineering and Biotechnology is investigating ways to turn waste insect product from animal feed production into biobased chemicals for textiles. The animal feed industry utilises insects as a cheap, fecund, and low-energy source of protein, lot of waste in the form of insect skins and shells. These substances are up to forty percent chitin.
The researchers at IGB have partnered with the Dutch manufacturer of insect protein Protix to obtain their experimental insect skins. They are trying to find a purification process to isolate chitin found inside the proteins and minerals that make up insect body parts using enzymes. From there, they can extract the chitin and, in the process, turn it into chitosan.
The chitosan could have a wide market as a bio-based sizing agent, a usually synthetic product that reduces friction in weaving machines and prevents warn breaking during weaving. It could also be useful for finishing textiles, for example in a water-repellent coating. This would be a massive step towards textile sustainability as fluorocarbons are currently widely used in waterproofing outdoor clothing.
Seafood waste is not the only source of chitin. Lignocellulose, the substance in tree bark that keeps plants upright, can be converted into the material. Researcher Stéphanie Baumberger has been leading InDIRECT, an industry-academic project looking at how insects could be used for this very purpose.
Lignin is notoriously difficult to decompose into intermediate products without a lot of energy-heavy processing. However, feeding insects that can metabolise the stuff opens the way for a low-impact technique to convert lignin refinery by-products into high value chitin. Once the insects have incorporated chitin into their exoskeleton, it is extracted using chemical processes. The exoskeleton is demineralised with hot mineral acids and then deproteinised with hot alkali treatment.
The InDirect project effectively uses insects as bioreactors, harnessing their metabolisms to create a high value material. Living organisms harbour complex chemical processing mechanisms that would be difficult and costly to replicate using synthetic technology. Added to the fact that insects grow and reproduce rapidly, this could offer a highly cost-effective way to valorise organic waste streams. By 2019, InDirect was demonstrating pilot scale of their insect chitin harvesting process.
Another EU consortium project on Chitosan started early in 2022. CHampITINE, located in Belgium, aims to valorise byproducts from the mushroom farms by obtaining chitosan from them. On the chemical side, chitin from mushrooms will be extracted and analysed. The project also aims to assess economic feasibility of this value chain by finding out how much chitin is contained in tehse waste byprdocuts, the amounts of waste biomass produced by mushroom growers in the Flanders area, logistical and storage requirements, and scoping potential sales markets and price points.
Experimenting with Chitosan
Chitin’s physical versatility expands when combined with other biomaterials. These composites offer better mechanical functionality for specific applications than any one of the individual components that make it up.
Combining chitin with other natural biomaterials improves its durability while retaining its ready biodegradability. One natural partner for chitin is lignocellulose, another abundant natural substance found in wood and which has a similar chemical makeup. A 2019 article in the Journal of Bioresources and Bioproducts reported a dense material that is strong, flexible, and thermally stable that combines crab shell and chitin with lignocellulose from poplar wood.
There are numerous other possibilities for chitosan biocomposites. In at least two studies, researchers developed biocomposites from chitosan and rice straw. The addition of rice straw to chitosan increased the material’s resistance. A chitosan and sunflower stalk blend yielded mechanical and thermal properties similar to insulating biobased materials already available on the market. Biocomposites have also been developed in the lab using barley, date palm, and sisal.
Chitosan has been tapped as a sustainable food packaging alternative due to its natural antimicrobial properties that defends against fungi, molds, yeasts, and bacteria. Some physical properties of chitosan make it ideal for food films: for example, it is easy to obtain bright, transparent sheets from the substance.
Nonetheless, pure chitosan’s other physical properties still limit its uptake in the food packaging. These include low mechanical and thermal stability as well as high sensitivity to humidity. Blending chitosan with other materials can overcome these drawbacks. For example, a lab demonstration showed that chitin isolated and purified with CC/malonic acid increased its thermal stability. Starch, pectin, alginate, and protein can make the material less permeable to water.
Before it can hold applications as a food film, chitosan’s elasticity would also need to be improved. Protein blends have proven suitable for this. Adding quinoa protein to a chitosan film gave the material a more flexible, elastic quality similar to that of oil-based plastic films. Protein-chitosan composite could also make for edible food packaging and films. To achieve a more water-repellent product, natural waxes, resins, fatty acids, beeswax and vegetable oils can be added.
Blending can also alter chitosan’s properties in ways that make it more amenable to working the material on an industrial scale. Chitosan on its own cannot be heat sealed or extruded like conventional packaging materials. Forming it into a sheet relies on a casting method where the chitosan is dissolved with a solvent (generally acetic acid) and poured into a surface to dry. Creating a biodegradable blend with thermoplastic starch can render the material more like conventional plastics in their workability, allowing for thermocompression, blown extrusion and melt extrusion. Adjusting the natural properties of pure chitosan with blends will be key to scaling production in chitosan food packaging.
Chitosan stands out among other natural materials as a highly sustainable, cheaply available, and versatile biocomposite base for almost all single-use plastic applications. Growth in chitosan packaging will depend on innovators who can draw out its functional potential by building on a wealth of research into its chemical interactions with other biodegradable materials.