Protective bacteria: Biopolymer coating for textiles

It defies wind and weather and protects us from a wide range of environmental influences: Functional clothing. Special coatings are responsible for this. Polyacrylates or polyurethanes, which are based on crude oil and therefore a finite resource, are often used for this purpose. The German Institutes of Textile and Fibre Research Denkendorf (DITF) are therefore researching alternatives from renewable sources – including polymers from bacteria.

In an interview with K-Mag, Dr Thomas Stegmaier and Dr Thomas Hettich talk about textile coatings made from bacteria, their production and advantages.

How did you come up with the idea of using biopolymers from bacteria for textile coatings?

Dr Thomas Stegmaier and Dr Thomas Hettich: One of our research focuses is on replacing fossil-based polymers with renewable raw materials that can be used to produce more sustainable polymers for textiles. This includes both fibres and coatings. We are keeping a very close eye on developments in biotechnology and the agricultural sector, which are very dynamic when it comes to finding suitable raw materials. Some bacteria have the particular advantage that they consist of a suitable meltable biopolymer with a high weight proportion of up to 50%. The task in the harvest is then to separate this polymer from the remaining biomass. Here we work closely with our partner, the Fraunhofer IGB, which cultivates highly efficient bacterial cultures.

Can you describe the process of how PHA is produced and which factors influence the properties of the end product?

Stegmaier & Hettich: Some bacterial strains store PHA as energy reserves – a comparison can be made with humans who store fat deposits. The decisive factor for the creation of these reserves is that they are not adequately supplied with all nutrients, but are, for example, undersupplied with nitrogen and oversupplied with sugar or fatty acids. The resulting surplus of carbon and hydrogen from sugar or fatty acids is converted into PHA by the bacteria. Depending on the bacterial strain, PHA differs in its repeating unit, molecular weight, polydispersity, viscosity and melting point.

How do the properties and applications of polyhydroxyalkanoates (PHA) differ from traditional petroleum-based coating materials?

Stegmaier & Hettich: Petroleum-based coatings for textiles have a long history of development and have excellent properties. A high level of waterproofness for clothing, for example, can only be achieved with a coating. The PHAs available to date have good basic characteristics, which we utilise to our advantage. However, many properties still need to be developed so that the coated textiles can fulfil their function.

What technical and ecological advantages do textiles coated with PHA offer, particularly in terms of wind and water resistance?

Stegmaier & Hettich: The advantages lie in the pronounced sustainability. Until now, windproof and waterproof textiles have been made from petroleum-based raw materials or partly from recycled materials. The high barrier effect of PHA against wind and water has already been demonstrated in films made from it.

What challenges had to be overcome in the development of PHA-based coatings for technical textiles?

Stegmaier & Hettich: Conventional coating systems are produced with polymers where the synthesis is already designed with a view to the properties required later in the product. This is not easily possible with the biosynthesis of PHA.

What other research and development goals are the DITF pursuing in the field of bio-based textile coatings?

Stegmaier & Hettich: In the long term, we would like to identify technical possibilities for replacing coating systems that are currently based on fossil resources with bio-based systems. These polymer systems are generally also biodegradable, so that the problem of microplastics in our environment can be tackled.