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Not a disposable product: biodegradable films for agriculture

If one’s gaze wanders over the many harvested stubble fields in the fall, the sight of silage bales is often part of it. Packaged in mostly green or white film, the round bales are used to produce feed for cattle and cows through lactic acid fermentation.

Researcher Isabell Kleiber in front of the objects of her research: silage films are to be produced sustainably in the future; Image: Hof University of Applied Sciences;

But the bales, which are often used by walkers and children as photo motifs or climbing objects, are not as close to nature as one might think. The reason: Until now, the films used for them have been disposed of after use – recycling is simply not common and also only possible with great effort. A feasibility study at the Institute for Applied Biopolymer Research (ibp) at Hof University of Applied Sciences, headed by Prof. Dr. Michael Nase, is now to lay the foundations for permanently changing precisely that. This study strengthens the profile of the young institute with regard to the development of films for agriculture.

Due to the increasing demand for feed, silage production in German agriculture has increased significantly in recent decades. “As a consequence, more and more films are also needed. Until now, these have been produced conventionally and are therefore usually based on petroleum. In the soil, they therefore also leave behind detectable microplastics. In addition – and this is particularly regrettable – they have so far unfortunately been purely disposable and therefore bad for the eco-balance,” explains Isabell Kleiber. The 24-year-old holds a Master of Engineering and is a research associate at the Institute for Applied Biopolymer Research (ibp) at Hof University of Applied Sciences. There she is in charge of the “Agri-Stretch” research project.

Away from disposable articles

As part of a feasibility study, she wants to investigate by April 2022 to what extent and under what conditions conventional silage films can be replaced by ecologically sustainable films made from biopolymers. “Our goal is for films in the future to be made of 100 percent renewable raw materials. So we want to develop them from a disposable item to a product that is compostable or recyclable and can therefore be perfectly integrated into the agricultural production cycle,” says Isabell Kleiber.

Bio-plastics for compostability

To achieve this, the young researcher from the district of Hof is experimenting with different biopolymers and their composition. On the “Compounder”, a device for mixing the substances, she prefers to mix PLA and PBAT – two plastics that are produced on the basis of renewable raw materials and are therefore considered “bio-plastics”.

Offsetting higher price

The challenge in her work, however, is by no means limited to finding a bio-based stretch film

Our task is to ensure that the ecological film actually has better properties than the conventional film – because ultimately it will also cost a little more

Isabell Kleiber, Project Manager

Up to now, bio-plastics have cost EUR 4 to 6 more per kilo – a difference that will also be reflected in the price per meter for the finished film.

High requirements

And further: “First and foremost, the film must demonstrate a 400% elongation at break. This means that it must be possible to stretch it very strongly without it tearing. It also has to be very UV-resistant, since it will usually be outdoors for a whole year. And, of course, impermeability to water and oxygen is also part of it, because otherwise the fermentation process in the silage won’t work.”

So far, he said, initial investigations have been positive, so one is hopeful that the goal of the project can be achieved. So far, for example, it has been assumed that the compatibility of ecology and the necessary film function can best be achieved using a three-layer film, with each layer covering a different requirement. If this is confirmed, the company is aiming for a follow-up project involving an industrial partner starting in 2022, which will then look in detail at the technical feasibility of an ecological agricultural stretch film.

Image: Hof University of Applied Sciences

The ongoing feasibility study is funded by the Agency for Renewable Resources (FNR).

So far, several projects for films with application fields in the agricultural sector have been and are being implemented at the institute. Examples are the projects BioMulch, BioSiFo and Vinofol. In the BioMulch project, a degradable mulch film was developed, which is now to be modified in a follow-up project so that it releases nutrients when it decomposes in the soil. The development of a biobased and biodegradable silage film is being addressed in the BioSiFo project. The Vinofol project aims to contribute to the yield and sugar increase of grapes through the use of reflective films.

Rainer Krauß

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