The municipality of Amsterdam, Senbis Polymer Innovations, GrassMax and Fitco Grass will jointly investigate whether biodegradable synthetic yarn fibres can be used to reinforce a natural turf surface.
Hybrid surfaces significantly increase the hours a natural turf can be used: from about 250 hours on a 100% natural turf field to about 800 hours for a hybrid field. More importantly, the field always looks green and remains flat and stable, irrespective of the usage intensity. Hybrid fields come in both lay-and-play and stitched options. The latter is preferred, thanks to their almost 30-year-old track record, proven contribution and their longer life-span. Some stitched solutions have been in use for over 25 years. Turf surfaces that have been reinforced with synthetic yarn are used at the very highest level of football and rugby, but they do have a downside. “The Environmental Agency for Amsterdam municipality doesn’t allow it because you introduce plastic into the soil. Despite the claim that the soil and plastic fibres can be separated when the field is removed, the Environment Agency wants to prevent any chance of pollution,” Bert Klein of the municipality of Amsterdam explains. He regards hybrid fields as the ideal solution for a variety of situations and at many clubs. However, as the presence of microplastic particles smaller than 2000th of a millimetre can be detected in wastewater, it is understandable that municipalities go to great lengths to prevent any discussion about adding plastic to the soil or the environment.
Klein has now challenged Senbis Polymer Innovation, GrassMax and Fitco Grass to combine their strengths and to develop a solution. “We want a solution whereby we do not have to remove and replace the top soil or the fibres when we renovate a hybrid surface, but where we can simply mill or plough the field and the biodegradable synthetic yarns used to reinforce the surface will simply dissolve in a natural way. That will save us a lot of transport movements, with all the associated problems of traffic issues and the CO2 emissions from the vehicles.” At present, the sieved topsoil of a hybrid surface is still viewed as a contaminated soil. That is why both the topsoil and the recovered synthetic yarn fibres must be processed by a recognised processor. “The fibres must dissolve naturally in the soil without leaving a residue. This also applies to yarn wear fragments that have left the field,” he adds.
René van Bremen of Senbis Polymer Innovations believes this should be possible. Senbis has already developed a biodegradable infill and is currently testing a biodegradable synthetic turf carpet. “Based on their knowledge and expertise, our R&D colleagues can accurately estimate which ingredients should be added to the compound and to what extent, to either speed up or slow down the process of biological decomposition.” However, he points out that Amsterdam municipality has upped the challenge. “The city of Amsterdam wants to reinforce an existing natural turf field. The soil life present here could accelerate the biological decomposition of the fibres. The challenge we face is to manage that process properly.” Usually, the topsoil of a hybrid surface is very poor, almost similar to the subbase of a synthetic turf surface. This is why van Bremen refers to the project as a trial instead of a test. “There is a chance that we will come to the conclusion that we need to adjust the compound. But these kinds of trials are necessary to collect data and experiences in the process to develop the final product.”
Largest yarn producer
Together with Europe’s largest independent synthetic turf yarn producer Fitco Grass, Senbis will now develop a biodegradable yarn that should offer a sustainable alternative to the polyethylene and polypropylene used currently for reinforcing a natural turf surface. Luc Decraemer from Fitco Grass is looking forward to the challenge. “We have already developed bio-based synthetic yarns, so I expect that we will also be successful in extruding biodegradable yarns,” he says enthusiastically. “With bio-based yarns, the availability of raw materials was the biggest problem. That is not the issue with the raw material from Senbis. The challenge we’ll face here, in particular, is to ensure that the yarn will last as long as it is needed before quickly dissolving naturally once the field is renovated.” To be sure this will happen, Senbis will also be explicitly involved in the extrusion process. “Like all other suppliers of raw materials for synthetic yarns, Senbis only supplies the compound. In this trial, it will be important to establish what effect the compound has on the product stability during the period of use and on the biodegradability after renovation of the field,” van Bremen explains. “For the time being, we assume that this yarn will have to last for at least 10 years in soil. The required lifespan is, of course, directly related to the ultimate business case.”
Most flexible injector
Of the various installers of hybrid fields, GrassMax was the most enthusiastic to participate in the trial. Fitco Grass will therefore use the Senbis raw material to copy the polyethylene yarn that it developed specifically for GrassMax. Marc Vercammen of GrassMax says: “We usually inject a combination fibre that consists of three straight and three textured yarns.” Decraemer explains that a copy of the current fibre provides the best comparison material. “If we manage to copy that fibre and inject it in a regular configuration, we can compare the two yarns one-on-one and get a good idea of how biodegradable yarns will perform compared to yarns from polyethylene.”
Decraemer expects that the Senbis material is also suitable for producing other shaped yarns. “Ultimately, we should be able to use it to make any type of yarn,” says the man who once pioneered the monofilament fibre. However, Vercammen does not expect that this will be necessary with regard to application in a hybrid surface. “There has been too much focus on the yarn shape for years, especially for a full synthetic turf field. In a hybrid field, only the yarn thickness is relevant, as this determines how the yarn will wear over time.”
Two test sites
The pilot will be carried out on two different fields to obtain a better picture of the possible influences of different environments. “It is our intention to stitch the yarns 18 centimetres deep in a grid of two by two centimetres,” Vercammen continues. Because these are existing fields, it is possible the soil is contaminated with stones. “If that is the case, then we will have to vary the stitching height a little bit.” GrassMax has that flexibility. It prides itself on the fact that its machines have been engineered in Germany. “They are very accurate. At the same time, we also have the flexibility to adjust the density of the grid or the stitching depth.” This allowed GrassMax to reinforce the field for the FIFA World Cup final in Qatar with 18cm long fibres, while the field in the Stade Vélodrome in France was reinforced with 15cm long fibres for the Rugby World Cup. “The various stadium applications simply have different expectations,” he explains. Vercammen too expects few major issues in Amsterdam. “For us, it is especially important that the yarn comes off the spool well and can be cut well,” says the person who has been selling stitched reinforced hybrid fields for over 15 years.
Large group of winners
Once the installation is finished, the field will be closely monitored. “Exactly how we are going to do that and for how long is something we are still discussing,” says Klein. According to van Bremen, one of the things they are trying to establish is what requirements the European Commission wants to impose on secondary microplastics and what method the synthetic turf industry should use to predict how a synthetic turf surface will wear over time. “This is currently being discussed within the European Committee for Standardization [CEN], but it will take some time before this will become clear. That is precisely why this is an opportunity for the synthetic turf industry to come up with its own proposals, partly based on these types of practical trials.”
The monitoring is also used to gain knowledge about how such a field should be maintained in the future. “We will have to find a balance between an easily playable playing field and an approach that honours the fibre as long as it is not expected to decompose,” explains Vercammen. The fact that many of the intended parameters are still unclear does not bother him. “There are various parties already looking at these types of solutions, but one of the things that appeals to me about this collaboration are the agreements that have been worked out by the partners. It is an important and serious project for everyone. That is precisely why we were happy to be involved.” Klein agrees that the stakes are high. “Amsterdam municipality has approximately 400 hectares of sports surfaces. As far as the synthetic turf fields are concerned, we are currently looking at how we can make those fields as future-proof as possible. If this trial with Senbis, Fitco Grass and GrassMax succeeds, we may be able to take an even bigger step in terms of making our sports surfaces more sustainable, while also respecting the positive sentiment people feel for natural turf.”
Van Bremen notes that the entire synthetic turf industry stands to win if the trial succeeds. “The European Commission is certainly open to self-regulation. If we succeed in achieving the objectives set in Amsterdam, we will have an example of how the synthetic turf industry itself can develop solutions that support the ambitions of the policymakers. That is precisely why it is important that we emphasise these types of projects as much as possible. Hopefully, this will make policymakers realise that the synthetic turf industry is serious about dealing with the issues and that the industry can be a partner in resolving these.”