by Max Greiner, Sophie Kikowatz & Lara Herrmann

What are the most important steps of the chitosan production? 

We use shells that are left over from peeling crabs and prawns. Often there are remains of meat (protein) and calcium carbonate, but the most interesting substance of such shells is chitin, which is the binding material in the shell. This is a strong, but also elastic material. Chitin is constructed like puff pastry, that is why you need different steps to extract it. The calcium carbonate is removed using low concentrated hydrochloric acid, the protein is removed with low concentrated caustic soda. Depending on the properties of the shells and the remaining proteins, these reactions can take longer or must be repeated. Between the steps, the shells are rinsed with plenty of water. The big amounts of shells are directly processed in Asia close to the peeling places. Part of our production technology is the neutralisation of used hydrochloric acid and caustic soda. The output is NaCl and H2O, salt and water. Separated proteins and chalk can be used as feed. That‘s why it‘s a waste free production. The chitin is processed to chitosan, because chitin is almost insoluble. By eliminating the acetyl groups from chitin you get chitosan. This process is called deacetylation and happens by cooking in 50% concentrated caustic soda. If more than 50% of the chitin are deacetylated we call it chitosan. We have a lot of different chitosans available that are mostly deacetylated around 90%. 

This resource is a natural material. Do you see fluctuations in the composition and how do you handle that? 

Of course, you have fluctuations. And this is actually the expertise of the chitosan producer: to supply the client always the same quality once he has found the right chitosan, which fits in his technology and application. We must adapt the recipe to the quality of the shells (e.g. change of the chemical concentration, reaction time, etc.) From which animals are the shells (crabs or prawns or shrimps), which part of the shell is used (legs, claws, head or tail)? We always should pay attention to that. 

This means you can achieve different properties using different concentrations? 

Exactly. If you have long chain molecules (e.g. 100 or 1000 viscosity) it’s much better film-forming than one with 10 viscosity. We have special short chain molecules that can even enter plant cells to stimulate their immune system.

You are talking about different ways to use chitosan. In which properties do you see a big potential, maybe even potentials that are not used yet? 

The biggest benefit is: chitosan comes from a natural and renewable source. It‘s non-toxic and biodegradable. And therefore, it can be used for example in water purification. We have our biggest application area in cosmetics and in wastewater treatment or water purification of rivers and lakes. There it is of special interest using chitosan, because it is not dangerous for aquatic life, environment and health. One example is the Spreewald area. The rivers there are polluted with iron from open-cast mines. The iron sludge is flocculated with chitosan and can be easier. The result is clear water. Chitosan is currently used in disinfection, as it prolongs the normally short effect of alcohol-based agents. It is also used in hair styling products to increase the ability of the hair to keep the moisture. In floor cleaners it can create a lotus effect on the surface and has an antistatic effect. A lot of water can be saved in the textile industry using chitosan as a sizing agent. The fibres are sized before weaving, e.g. a coating is applied onto the fibers to prevent them from breaking. This is usually done with starch, which must be washed out afterwards. Using chitosan has the same effect but does not require washing out. This is already commercially applied in Italy. Chitosan is one of the few naturally occurring positively charged substances, while all the others are negatively charged. That is why it acts like a magnet and can also bind bacteria or fungi. Different lengths of molecules and charge densities allow various modifications as well as grafting and cross-linking of additives.

Do you have an example for that? 

You can cross-link starch to chitosan and create a very nice bioplastic. 

Do you already have experience with material recycling? 

We didn’t achieve that with our recipe. Our strong cross-linked material had no thermoplastic properties. Chop it into small particles and stick back together with chitosan, maybe this would work. But that was not in our focus. And honestly speaking, chitosan is already recycled material, because it is made of food waste.

We visited madebymade in the south of Leipzig, which produces protein flour from maggots. Insect skin and pupa shells are by-products. Could you use those? 

The pupa is black and we couldn’t process it to white or at least light yellowish chitosan. The cosmetic industry demands white chitosan. But the main problem was, the chitosan was not completely soluble. That’s why we don’t see a big potential in using such raw material. The crab shells are much better suitable for producing chitosan. It also depends on the yield, if you want work productively a good raw material is very important. Of course, you could also make chitosan from cockroaches or bees or mushrooms. But the yields are not as good and the production technology with the crab shells is already established that even different varieties can be produced. Not everyone is able to do that. Many chitosan producers only see at the end of the process, which quality they have produced. With our technology we can define the quality and with the chosen recipe and by controlling the reaction parameters we get what we want.

One disadvantage is that the crabs are harvested and peeled in Asia. This creates a long transport route. 

That is true. That really is a problem. But the big crab and shrimp processing factories are not in Europe, because peeling by hand is too expensive here. We are currently in contact with a company in Spain that processes crayfish there. The crayfish were released in rice fields some years ago and the number of these species has increased rapidly because they have no natural enemies. Instead of trying to reduce the species a real industry has developed to market the crayfish as a local delicacy. Now there are many shells left and it is worth thinking about the setup of a chitosan production. In order to achieve high prices and to compensate for the higher production costs, they want to sell mainly to the pharmaceutical industry. But they don‘t need such large quantities. 

But maybe the plastics industry…

Yes, the other industries need a lot, too. But they need to meet a certain price. The conventional plastics industry is a huge competition. The consumer is willing to pay 20-30% more for organic (bioplastics), but not three times more of the price. 

Anke Wunder is an employee at BioLog Heppe GmbH. The company, based in Landsberg near Halle, develops and researches applications and technologies for the biopolymers chitin and chitosan and their derivatives.

BioLog Heppe