Biodegradable Mulch Films and Geotextiles
Developed for Agriculture and Waterways Engineering
Biodegradable mulch films have been available at the market for some time now. Just as conventional polyethylene films, agriculturists use them to grow vegetables and strawberries, mainly, in order to keep the soil free from weed. The biobased variant includes a great benefit: It is supposed to decay right on the field, saving the farmer the tedious task of recollecting it. However, in fact, decomposition is rarely completed within the desired period of time, which is why the farmer will have to manually collect the film, nevertheless. This is the reason why biodegradable mulch films are hardly used at present, the more so as they are roughly three times as expensive as conventional products.
In two projects, teams composed of partners from research and business are undertaking investigations to develop new mulch films and geotextiles out of biobased polymers and natural fibers, due to start degradation at exactly the right point in time. The mulch films will be interesting for agricultural applications, while the geotextiles may be an alternative in waterways applications. A third project, already in progress, is looking into sprayable mulch films to deter vermin by optical effects. All projects are funded by the Federal Ministry for Food and Agriculture (BMEL) via the central coordinating agency in the area of renewable resources (Fachagentur Nachwachsende Rohstoffe e. V., FNR) acting as project manager.
Together with its three partners, Hof University of Applied Sciences, Hof, Germany, is currently working on the task of developing biobased and degradable mulch films that will reliably decay at defined points in time – corresponding to the cultivation periods of the respective crop. For example, investigations are aimed at developing a strawberry film that will start degrading after 1.5 years. Intense contact with soil as a result of ploughing is due to trigger decay. For the new types of compounds, the scientists tested biobased polymers such as starch, polylactide (PLA), polycaprolactone (PCL), polyhydroxyalkanoates (PHA), polybutylenadipat-terephthalat (PBAT) und polybutylensuccinate (PBS). The period of degradation they will define by combining fast to slowly degrading materials.
Geotextiles Serving as Filter
Together with four partners, a team of scientist at the Fraunhofer Umsicht Institute is actively engaged in developing geotextiles on the basis of plants, due to serve as filters to reinforce the banks of waterways. In the area of geotextiles, the term filter describes a cover that allows water to pass, while, at the same time, preventing erosion, i.e. sliding of soils down the banks. With this product, too, degradation within the right period of time plays a major role. The background of the investigations is the EU Water Framework Directive 2000/60/EG, which requires ecological improvement to be carried out in in the area of waterways, among others. One way to achieve this target is to reinforce riverbanks by plants rather than by stones in loose rip-rap revetments.
Geotextiles are used to protect the respective area from erosion during the critical initial period, when plants and especially their roots are only just developing. The different components of the textile are supposed to decompose at different speeds: The fast decaying natural fibers make way for roots to grow. Slowly degrading biobased polymer fibers are due to secure the soil over a period of at least three years, until vegetation completely takes over the task of riverbank reinforcement.
The new geotextiles are supposed to replace the current materials, which fall short of meeting requirements. For example, biobased reinforcements used at present are not stable enough, decomposing too fast. As opposed to this, nets and meshes of plastics or metals last for centuries. They represent a potential danger for humans and animals and removing them in case of renaturation is a costly and complex task.
The Future is Biobased
In a third project that was started last year, Hanover University, together with Heinrich Glaeser Nachf. GmbH, is developing a sprayable biobased mulch film with optical features to deter vermin. For this purpose, the film changes its color and reflected light spectrum. The BMEL also supports this project, via FNR.
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