Adhesives are almost always based on fossil raw materials such as crude oil. Fraunhofer researchers have now developed a process for using the bio-based raw material keratin. This powerful protein compound is found, for example, in chicken feathers. Different adhesives for different application areas are possible.
Adhesives are almost everywhere: in sports shoes, smartphones, carpets, furniture, textiles and packaging. Even car windscreens are glued. Experts know of more than 1,000 different types of glue. These glue together almost every material imaginable. Glue does not weigh much and is therefore suitable for lightweight constructions. Moreover, glued surfaces do not warp because pressure is evenly distributed, unlike screw joints. Glue does not rust and seals against moisture. In addition, surfaces joined with glue are less sensitive to vibrations. And adhesives are cheap and relatively easy to work with.
Feathers from poultry meat production
Until now, adhesives were almost always produced from fossil raw materials such as crude oil. The Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB is now taking a different approach. The researchers use feathers as a starting material instead of crude oil. Feathers accumulate as waste during poultry meat production. They are destroyed or mixed into animal feed. However, feathers are far too good for waste because feathers contain the structural protein keratin. This biopolymer is formed by animals for claws, hooves and feathers. Its fibrous structure provides high strength.
Keratin for the production of adhesives
Keratin is an eco-friendly substance because it is biodegradable. Due to its structure, it also has properties that make it particularly suitable for the production of adhesives. The polymer structure combined with the property of crosslinking reactions via functional groups makes keratin predestined for the production of all kinds of adhesives. "The properties required for adhesives are to some extent already present in the starting material. They just need to be uncovered, modified and formulated," explains project manager Dr Michael Richter.
KERAbond
In the KERAbond project "Speciality chemicals from tailor-made functional keratin proteins", Kera stands for keratin and the English word bond for bond . In this project, Fraunhofer IGB has collaborated for the past three years with Henkel AG & Co. KGaA, specialising in the adhesives sector.
The project partners developed and optimised a new process. In the first step, the feathers supplied by the slaughterhouse are sterilised, washed and mechanically shredded. This is followed by an enzymatic process in which the long-chain polymers or protein chains are broken down into short-chain polymers via hydrolysis.
Adhesives, hardeners, coatings and primers
The result? Short-chain polymers can serve as starting materials for further development of specially formulated adhesives. "We use the process and chemicals as a toolbox with which we can produce the desired properties of the final product," says Richter. In this way, parameters such as curing time, elasticity, temperature behaviour or strength of the desired special adhesive can be defined. Moreover, it is possible to produce not only simple adhesives, but also related substances such as hardeners, coatings or primers.
Next step
The next step is scale-up. This scale-up took place at the Fraunhofer Centre for Chemical-Biotechnological Processes CBP in Leuna. The aim was to prove that the production of keratin-based chemicals can also be realised cost-effectively on an industrial scale. Several kilos of chicken feathers were processed and the material produced was used for the first promising material tests at the Fraunhofer IGB and at Henkel.
Building block for a bio-inspired economy
The Fraunhofer IGB has been working on all aspects of the bioeconomy for years and has built up a lot of expertise in areas such as keratin. That is why the chemical company Henkel approached the Fraunhofer IGB for this project. Economically, the project carries weight. According to Statista, around one million tonnes of adhesives were produced in Germany alone in 2019. Their total value is around €1.87 billion.
Patent application
And the scientific output is also impressive: A patent application has been filed for the new process and a publication has appeared in a scientific journal. Two PhD students, who conducted intensive research on the project at Henkel and Fraunhofer, are expected to complete their dissertations in the first quarter of 2024. The new keratin-based technology will enable the sustainable and bio-inspired production of many chemicals.
Opening photo: Feathers contain keratin, a water-insoluble structural protein from which components of adhesives can be made (photo: Fraunhofer IGB)
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