by Hannah Kannenberg & Theresa Voigt

Where do you see the advantages of PHB over conventional plastic? 

We do not pollute our environment with toxins at this point, if you do it right. The material is completely biodegradable no matter where. Whether it ends up in the ocean or the forest floor, at some point it will actually be completely degraded. 

Do you think that by changing the way society thinks, manufacturers will be willing to pay the high price for the material in the future in order to produce truly sustainable products?

I hope that we go more and more in this direction, that we say we want to become sustainable for certain things. Firstly, that it is not produced from fossil raw materials but from another biological source, e.g. as with starch, one works with plants or with PHB with microorganisms, but also that one does not compete with the food industry. It has also been tried to produce PHB with plants, but then it competes again with the food industry. Then you have a field with genetically modified plants that produce PHB, that’s not exactly acceptable either, so you have to be very careful there. Fermentation with microorganisms such as bacteria or yeasts would be quite conceivable and also feasible as an industrial mass product. The process is still relatively complicated at the moment, so the question is whether it can be simplified even further, perhaps with a different microorganism. Here, one could also use a genetically modified microorganism. Since the fermentation takes place in a closed bioreactor and the microorganisms are killed at the end of the process. 

How can a foil be produced from the granulate? 

The granules are dissolved with chloroform. This gives a clear viscous solution which can be spread on a glass plate and then the foil can be peeled off. One must now wait until the chloroform has evaporated. The material becomes opaque. Depending on which solvent is used, the material properties of the P3HB change. 

Could these foils also be made by melting down the material and then spreading it on a plate, or do you always need the chloroform for this?

Simply melting the granules and brushing them on, probably also works then you would have something similar, only not from a solution but from a melt. We have not done that now, but I could imagine that it also works. You just have to watch the temperature range very carefully, otherwise the material will decompose. But I could also imagine that PHB is melted in an extruder and a film is drawn, just as tapes and threads can be drawn.

In your opinion, is it possible to recycle the material?

I think it can be recycled, but the recyclability here is also limited because with each processing stage or the longer the material is in this recycling process, the shorter the chains become and then the material becomes more and more brittle at the end.

added not only from the top, but ideally from both sides so that the tapes melt evenly and are then pressed into the desired shape.

Dr. Gundela Peschel has been a research associate at the Biotechnikum of the Hans Knöll Institute (HKI), Jena, since 1992. Her research focuses on the development and optimisation of purification processes for natural substances and proteins and biotechnological processes for natural substances and proteins.

Hans Knöll Institute