There is no doubt that artificial turf is becoming more widely popular as the surface covering of choice for football fields. The technology surrounding artificial turf and synthetic grass development has been advancing in all areas including the fiber technology, tuft technology and system installation. One of the crucial parts of an artificial turf system is the rubber infill.
Why Does Synthetic Turf Grass Need Infill?
Synthetic turf surfaces have traditionally been cushioned by the use of rubber granules. These rubber granules are known as synthetic grass infill and they serve a couple of purposes. The first is that the rubber infill allows the blades of synthetic grass to stand upright giving the grass a natural appearance.
The aesthetic aspect, and in particular the chromatic appearance of synthetic-grass cover, may be influenced also by the nature and by the characteristics of the infill, essentially, it is considered extremely important that synthetic turf at least looks like real grass.
The next requirement that had to be satisfied when choosing the material for artificial turf infill was that it would provide a cushioned surface to play on similar to that of natural grass.
Another consideration that had to be factored in when choosing rubber granules as the infill for synthetic turf surfaces was the fact that these particular surfaces were going to have to be capable of withstanding higher than normal stresses. The sports that are played on synthetic turf include soccer, American football, tennis, hockey and, more recently, baseball.
When you install synthetic grass you are putting in a product that does not grow as real grass does and so, an aim in manufacturing the grass is to prevent the surface from wearing out in a non-uniform way and a big contributor to the degradation of the surface has to do with the infill. You can imagine that on a soccer field the area in the goal box at either end as well as the midfield area would come under much greater stress than the areas near the corners or the sidelines. A material such as rubber granules provides a covering that will stand up to the constant traffic without becoming noticeably different to the rest of the field over a reasonable period of time.
Similarly, those playing on the synthetic grass surface usually wear specialist sporting shoes with some kind of spikes or cleats to maximise the ability to stop and change direction without slipping. It’s inevitable that using this kind of footwear on artificial turf will cause the infill to shift and get knocked out of place. Rubber granules were found to move less than other types of infill such as infill that had a high proportion of sand in its content.
It should be noted that the rubber granule particulate infill that is discussed here is the kind of infill that was intended to be restricted to synthetic turf that is manufactured for sporting surfaces. The fears and concerns that have been raised in recent times over the health risks associated with coming in contact with the granulated rubber has prompted alternative materials to be sought.
Original Recycled Tire Rubber Granule Infill
The original material that was used for synthetic turf infill was largely rubber granules made from recycled tires. This rubber material was also known as styrene-butadiene rubber (SBR) and it was often bulked up with carbon-black fillers and provided the stability, durability and cushioning that was required for such a surface. Because the material was available in large quantities and there had been problems disposing of the used tires, it was able to be made at a price that was low enough to make it attractive.
It has since become known that the rubber granules sourced from recycled tires contains all sorts of impurities with justified concerns over its toxicity.
Further arguments against the particulate recycled-tire material as infill for synthetic grass cover includes the preponderant black color of the infill due to the high content of carbon it contains. This coloring results in high absorption of solar radiation making the surface get extremely hot and prone to overheating.
This infill was also prone to crumbling as it aged which resulted in the formation of dust that could either become airborne or would be washed away resulting in environmental concerns.
It should also be noted that the rubber granules used as infill for synthetic turf was originally manufactured for a completely different purpose, i.e. as car or truck tires. The properties of the material are characterized by its low density and high degree of resilience. This means that not only is the infill more prone to being displaced by traffic but it is extremely elastic or overly bouncy.
So for all of these reasons an alternative material has been sought to replace the SBR infill in synthetic turf.
Alternative Synthetic Turf Infill
To that end I have listed a few of the synthetic grass infill options that are either in use or in development around the world. This article is not exhaustive nor is it intended to be perceived as a recommendation to use or discard any one type of infill, but rather as a record of the choices available.
There are a number of alternatives to rubber infill for synthetic grass, most of them completely discard the rubber granules that have either wholly or partially comprised the infill of synthetic turf surfaces. The aim is to make synthetic grass as near to natural grass in both look and feel while still providing a safe, cushioned surface that won’t heighten the possibility of injury
Geo Safe Play
The first product we will look at is called Geo Safe Play which is manufactured by Limonta Sport. The main notable point to be made about Geo Safe Play is that it is made with infill materials that are 100% environmentally friendly and provides a “natural” solution for synthetic turf infill. It is made with a combination of natural plant fibers and cork and the literature assures us that it provides the highest level of sports performance.
A soccer field, infilled with Geo Safe Play is similar to the highest quality natural grass fields, and it guarantees the possibility to use the field intensively, even under bad weather conditions.
Geo Safe Play by Limonta Sport in Italy is the proven and patented solution for infilling synthetic turf with materials that are 100% environmentally safe.
The Product is produced with carefully selected, specially-treated organic and blended fibers, and retains moisture for perfect drainage and low temperatures compatible with natural soil. Geo Sport infill is also said to make the synthetic turf surface up to 70% less abrasive than other synthetic turf fields.
Another feature of using Geo Sport infill is that it retains moisture thanks to the natural fibers and as a consequence won’t get as hot as other synthetic turf surfaces. Geo Sport has been tested by Limonta Sport in Italy for almost a decade.
The product is marketed under the name InfillPro Geo and is guaranteed to last for 8 years regardless of the weather conditions under which it is subjected.
The company lists the advantages of InfillPro Geo as:
- It is a natural infill that is 100% environment-friendly and non-toxic;
- It eliminates the unpleasant odours that are typical of traditional rubber granules infills;
- It maintains a constant degree of humidity that prevents the playing surface from overheating;
- It will not rot and will not permit mold growth;
- Provides excellent resistance to UV rays;
- It gives high resistance to wear and ageing;
- It is identical in appearance to the highest quality natural grass fields;
- There is a reduction of risk of abrasion for players;
- Provides perfect drainage;
- elevated shock absorption and reduced energy restitution
- Allows you to make the most of players’ athletic activities in conditions of maximum safety;
- Provides perfect foot stability, even under extreme playing actions;
- 100% compatible with synthetic fibres.
Thermoplastic elastomer (TPE) infill is the latest preferred alternative to the recycled tyre rubber granules, also known as styrene-butadiene rubber (SBR) and is a stability and shock absorbent solution that has been developed for synthetic turf. Below a couple of companies producing thermoplastic products have been cited as examples. There are an increasing number of TPE manufacturers creating an expanding range of polymer technologies used for artificial turf.
One of the big selling points of thermoplastic infill is that it is said to be an environmentally friendly solution that can be recycled. Their properties allow them to remain durable while rebounding back to its original shape after compression.
Thermoplastic is a polyolefin elastomer material that uses prime raw materials in its production and give you a healthy balance of a product that is low cost while possessing the characteristics that gives the synthetic turf its more natural characteristics.
Dow Thermoplastic Infill
Dow produces three thermoplastic products that can be combined with other materials as part of a synthetic turf infill system depending on the performance is required.
Affinity Polyolefin Plastomers (POPs) are versatile polymers designed to provide superior levels of performance, ease of processing, and value to applications ranging from polymer modification to compounding. Exhibiting high flexibility and elasticity, the resin is utilized to improve resilience, softness, and toughness of the structure.
Engage Polyolefin Elastomers bridge the gap between rubber and plastic, inspiring new design possibilities. ENGAGE Polymers are the materials of choice for a wide variety of applications, offering an excellent combination of the flexibility and toughness of synthetic rubber with the processability of plastics. The combination yields properties such as low density, softness, and colorability. Moreover, the resin can be used to modify other materials such as polypropylene for impact resistance or improved low temperature performance.
Another producer of thermoplastic infill products is Airlastic which produces a similar range of synthetic turf infill products to Dow. The Airlastic products include: Airlastic LFR (low friction rubber) which is an environmentally friendly infill that is manufactured as a black product and the granule sizes range from 1 to 3 millimetres; Airlastic TPE Natural which is produced in a brown color in granules that are slightly smaller and is made to look like natural earth; and, Airlastic TPE LD, a low density thermoplastic infill that is available in green or brown and is said to be a high performance material that requires less weight per square meter to achieve specific sport characteristics.
Part of the appeal of thermoplastics such as the Airlastic system is that it allows the synthetic grass fibers to be woven more closely together which makes the synthetic grass even more natural looking. This means that not only can it be used for sporting fields and playgrounds but it becomes suitable as a landscaping synthetic grass material.
EPDM (Ethylene Propylene Diene Monomer) is a crosslinked rubber compound that you also hear referred to as virgin material. These infills are made of pure EPDM rubber and fillers whose composition varies. The crosslinked structure of EPDM is achieved with sulphur or peroxides. The size of the EPDM granules are similar to SBR and they are able to be colored so that it looks as natural as possible when laid down as part of the artificial turf.
Dow produces an EPDM product that is calls Nordel EPDM rubbers (ethylene propylene diene monomer) which utilizes its INSITE™ Technology to control molecular architecture and deliver improved performance, processability, and efficiencies that benefit compounders and processors alike, setting new and higher standards in EPDM performance.
The strong selling points of EPDM are that it is a durable product that results in a reliable surface that closely resembles a natural grass playing surface also, it is non-toxic and environmentally friendly. However it is a more expensive product and requires fillers due to its high density.
The product developed by MondoTurf is known as MondoTurf Ecofill Star and it is a polyolefin-based granule infill which possesses qualities that put it ahead of infill made from SBR granules as well as natural grass. Polyolefin is a thermoplastic polymer produced from a single monomer
The main features of the infill are that it is environmentally friendly in its composition and completely recyclable. The combination of post-consumer recycled resilient granules and sub-angular sand gives the synthetic grass turf outstanding durability.
The shock absorption provided by Ecofill is higher than both while the energy return is significantly lower than rubber granules. A problem described with rubber granules has been that it can be too springy causing greater stress on muscles and joints than would otherwise be experienced.
Ecofill is also more dense on the ground than rubber granules and so it is less likely to shift, making the ground more stable which will improve athletic performance and lower the instance of injury.
Tests have demonstrated that synthetic grass made with Ecofill infill results in a 50% reduction in overheating compared to rubber granules. Additionally, the odor that is typical of rubber granules is removed.
Mondoturf Ecofill Star has been installed in over 300 facilities worldwide and has been designed through extensive biomechanical research to reproduce the properties of natural grass while removing the problems of artificial grass fields made of rubber granules.
As mentioned above, this document is not exhaustive. It attempts to describe what is being done in the synthetic turf industry to overcome some of the problems, concerns and criticisms of earlier versions of artificial turf. The products and companies mentioned are representative of what is available.
There are also more products and materials that are being developed and used in production for landscaping synthetic grass infill. These products, such as SuperFill STF, are not covered as part of this document and will be discussed at a later time.