Turf producers use underground nets to support grass growth. Removing the nets from fully-grown turf is difficult, so the material often remains in the soil, causing pollution. Wageningen Food & Biobased Research and their industrial partners came up with a solution in a TKI project: a net made of biobased plastic that retains full functionality for the needed period before it starts to biodegrade.
The use of plastic nets is common in the grass industry. The big advantage for producers is that turf can be harvested faster this way. "The nets facilitate transport and reduce the risk of damaging the turf. It can also be harvested earlier," explains Wouter Post, project manager at Wageningen Food & Biobased Research. "Because the nets cause soil pollution, producers are looking for biodegradable alternatives. Existing alternatives marketed under this label are never fully biodegradable. Net fragments or microplastics, whether visible or invisible, are always left behind in the environment."
Degrading too quickly
In the TKI project “Biobased biodegradable nets for horti- and agriculture”, Post and his colleagues are working with the industrial partners on a fully biodegradable solution. One of these partners is Hendriks Graszoden, a major international player who for a number of years now has supplied the turf used in the European and World Cup football competitions. Biodegradable polymers that break down in soil are already available to be used in the production of nets, but the problem, according to Post, is that they degrade too quickly: "The challenge: how do you make a net that retains its function for 12 to 14 months, but then breaks down completely as quickly as possible, i.e. without leaving any microplastics in the soil?"
BioPBS as base material
With this mission in mind, the researchers started working with BioPBS in their lab. BioPBS is a bio-based polymer made from succinic acid by the chemical company PTTMCC. Untreated, the polymer appeared to break down too quickly in the soil. Subsequently, about twenty new formulations were developed and tested; partly mixtures of different polymers, partly bioPBS to which natural stabilisers were added. "It became evident that we had to supplement the mixtures with these additives, because the biodegradation rate would be too fast otherwise. We selected the best formulations, which were used by the Italian manufacturer Tenax to produce trial nets. One of them, a 7,000 square metre net, was successfully installed in Hendriks' fields in September 2020, where grass has now started to grow."
Although only time will tell whether the trial is successful – the turf needs about a year to mature before it can be harvested – measurements so far look promising. Post emphasizes that many factors influence a net’s biodegradation rate: "We used soil from Hendriks for the lab tests. But in the lab, you are working under stable conditions, while conditions outside in the field vary greatly. We already know that the net breaks down more slowly on location than in the lab. And to complicate matters even more, each location has different conditions."
Gerdien Vloet of Hendriks Graszoden looks back on the project optimistically: "The parties involved worked well together towards this final goal, with a tangible result: a net that eventually loses its function and is biodegraded completely."
If the trial proves successful, Post believes things can move quickly: "Hendriks has already indicated that it wants to initially use the nets for the cultivation of grass for the sports industry."
In the meantime, he is already thinking about other applications for bioplastics that degrade slowly but completely: "Agricultural and horticultural businesses are eager to use this technology. For example, we are now investigating the possibility of using this technology to produce plant plugs used for cuttings. This material requires a much shorter biodegration rate, which can vary from plant to plant."
Champions league final
The net on Hendriks' fields marks an important step towards zero soil pollution. Post would be delighted if the final of the Champions League 2022 was played on grass grown with Wageningen technology: "That’s one way for the Netherlands to finally be part of a Champions League final."
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Wageningen University & Research