Recent Advances in Synthetic Turf and Infill Materials

In today’s society, sport is something that is reported on a minute-to-minute basis, with full coverage of the latest sporting events at all times. As sports have become an even more central part of the world, the science behind every aspect of a sport is looked at under an intense microscope as advancements are made everyday to make sports safer, cheaper, and an overall better experience for everyone involved.

The playing surfaces used by athletes have become an even greater interest in recent years as new technologies have made it so that fields are now cheaper, safer and easier to maintain. Synthetic turf has quickly become the standard field for organizations that are planning on installing a new field. Synthetic turf has two main components that allow for it to be as realistic as possible: synthetic turf blades and infill materials. Rubber has always been the infill material of choice for the past decades, but new research proves that it may not actually be the best infill material available.

High levels of harmful pollutants and the inability for rubber to stay cool on exceptionally hot days have lead companies to try to find other alternatives to rubber hat have all the same characteristics, yet are more environmentally friendly and cool down quick. Due to the high interest of sports, the advancements of synthetic turf technologies have been researched in all sports realms from the soccer pitches of England horse tracks of California where safety is always the biggest concern.

Synthetic turf is a product that has advancements made frequently because all turf must be custom made for a specific sport that requires specific regulations. This paper documents the ongoing changes and research into synthetic turf and the science behind these major advancements. Today, most synthetic turf systems installed include three separate layers: a drainage layer, a multi-layered backing system, and resilient “grass” blades that are unfilled with a granular filler to resemble natural turf, as shown in Figure 1 . 1) There are two types of “infill” grass: an acrylic coated, green colored sand with antimicrobial properties and black crumb particles. When grass blades are “unfilled” it means that the man-made grass blades are interspersed with a top soil created with sand and/or granulated recycled tire rubber that provide the necessary stability, uniformity, and saliency for the turf to be strong enough to withstand intense use. By combining the grass blades with natural elements, it ensures that the grass has a realistic feel similar to natural grass.

The main objective when making synthetic turf is to ensure that it has a much of a natural feeling as possible. In order to give this natural feeling, the grass goes through a texturing process that curls the fibers of the grass to give a normal look that looks Just like real grass. The blades are usually not combined with the soil, but rather each blade customarily stands above the infill trial. Yarn filament companies that make the synthetic grass blades are always looking for an advantage over one another by continuing to look at their products to see how they can improve.

The three main components in producing these yarns are shape, polymer and process. All are tweaked based upon the application of the turf. Customized. The different shapes of yarn have been a constant variable that has seen many changes from the initial rectangle shape of traditional yarn. Companies have tried dozens of different shapes to see which ones will last the longest from basic haves such as diamonds and triangles to more obscure shapes like a dog bone or horseshoe. The shape that is chosen is always dependent on the application that the synthetic turf will be used.

For instance, if the grass is used in a children’s park, it will be much higher than the infield of a baseball field to add a cushion making the park a safer place to play. Along with shape, the polymer that a company chooses to use is extremely important in determining what will prove to have the best results. Polyethylene has typically been the choice to make turf blades and in a 2008 study by he DOD Chemical Company, octane-based polyethylene resin proved to be twice as resilient as butane-based polyethylene. 2) Overall, the goal of these companies is to produce a product that is reliable, but most important safe for athletes to play on. As more people become interested in sports, the safety of the athletes has become an even bigger concern. Currently, over 60 NCAA universities, 21 National Football League organizations, and two Major League Baseball clubs, use turf fields for athletes to compete on and those numbers are only increasing. Following a 3- ear prospective study in January 2010, it was concluded that turf fields are in fact safer than natural grass for athletes to compete on.

In this study, 24 universities were evaluated to see if there is any sort of correlation between not only how many injuries occurred, but also if the severity of the injuries were affected by changing the turf that was played on. The study showed that games played on turf produced 7% less injures, but more specifically, there was a 22% drop in severe injuries where severe injuries are considered to be those that leave a player out of competition for ore than three weeks. (3) Several different factors contribute to the fact that the turf is safer because it’s softer, easier to grip and reduces torsion.

These are the three factors that are attributed to the most common injuries in sports like leg sprains, concussions, and knee injuries. By making field conditions that allow players to have a safer experience, fewer injuries occur, which in turn makes the sport itself a better experience for players and spectators alike. Although it has been deemed that these fields are in fact safer to play on as far as injuries go, heat related injuries are still ajar drawback for synthetic turf.

Due to the way most synthetic turf fields are designed, the infill materials, which conduct heat typically, have a tendency to actually change the temperature of the field, making it unsafe for athletes to compete on. In a 2012 experiment by Penn State University, researchers examined ten different types of turf that varied in many different ways. They varied in color as well as the types of infill used to see how well or how poor they conduct heat, and to see how the different elements of the turf affect the turfs ability to heat up or cool down.

The test results proved that there was not a sample used in the experiment that could be found to significantly reduce the temperature. Even when there were reductions of five to ten degrees, they proved to be insignificant when the turf heated up to around 150 degrees. (4) When the sun heats up the turf that much, there needs to be a drastic change in temperature on field in order for the turf to truly be effective. One of the ways to reduce these that can easily and quickly cool a field down when necessary.

Penn State created another experiment to test the affects of an irrigation system to see how the enrapture of the field would change due to the field being cooled down intentionally by water. The results of the experiment showed that an irrigation system is not nearly as effective as thought. The efficiency of the irrigation system is based upon how quickly the temperature of the turf changes following the irrigation and also how quickly the turf returns to its original temperature.

As shown in Figure 2, the temperature of the turf initially decreases by 20 – 30 degrees Celsius, but within two hours, the turf heats back to nearly 50% of its initial temperature. (5) The experiment shows that an irrigation system is not only ineffective, but also not cost efficient to use because it makes little to no improvement on the temperature of the field. Since this possible solution to cool down turf did not work, it is obvious that there needs to be some change in either the fibers used to make the turf or perhaps a change in the infill used.

In 2013, Fielder, the leading synthetic turf company, unveiled its new product, Fielder Revolution Colonial. This is a turf that has been proven to be not only cooler to play on, but also cheaper to maintain because it makes irrigation systems obsolete. This new field was designed after researchers looked at all common infill materials used in synthetic turf today and found cork to be a material that absorbed little heat, while also having the shock absorbent characteristics that all infill materials, such as crumb rubber, need to still be effective.

Following independent studies, the Colonial field was 35 degrees Fahrenheit cooler than the traditional turf fields that are sand based. (6) This innovation shows how issues are directly confronted with technology that can help solve some things like the inability to keep field temperatures low. By looking at the three layers of turf, scientists can look into specific aspects that change the performance of the turf, which in turns affects the performance of those who play on the turf. Another aspect of synthetic turf that is continually under watch is the environmental hazards that could possibly stem from crumb rubber.

Rubber is a complex mixture that is made of several different components that can be both toxic and carcinogenic. There has been a recent worry by the public about the safety of the infill materials and if it can affect those who have continual exposure to the field. When looking at the environmental hazards of synthetic turf, both indoor and outdoor turf must be taken into account because in a indoor setting, these chemicals will have a much higher tendency to collect and become more harmful. Due to the presence of dust, it creates the opportunity for any potentially harmful chemicals in the turf to be picked up by the air and then inhaled.

Because of the instance of dust, indoor turf facilities will naturally have a higher tendency to be dangerous as compared to outdoor turf facilities. Following the testing of all kinds of synthetic turf, OTOH indoor and outdoor, experimentation proves that synthetic turf proves to have no sort of elevated health risk both indoor and outdoor, although the direction of airflow must be taken into account when creating indoor fields so that toxins properly flow in order to decrease the build up of these toxic chemicals. 7) While this shows that turf does in fact not prove to have any health risks involved, it does not take into account the time the fields were installed. This is an important factor to look into (PAP), in rubber granulates that are used to make the infill that can potentially become harmful. When a synthetic turf field is first set and it consists of rubber granulate that contain this pollutant, PAP levels are higher than the health-based soil standards.

As time goes on, infill rubber is removed by players so PAP levels quickly decrease, but often times in order to ensure field quality, more rubber is added to the field, which only increases these levels once again. (8) Along with increased PAP levels, the amount of lead in crumb rubber infill has also raised some questions. In 2008, Thomas Jefferson Park in Manhattan closed down because it was found that there was an elevated lead level in the crumb rubber.

Despite the fact that out of the 113 parks in New York City that use infill crumb rubber, Thomas Jefferson was the only one that showed an increase above the EPA standard, the city has decided to no longer use rubber because of the potential hazards it could pose to citizens, especially children. (9) In 2007, a similar situation occurred in a Newark, New Jersey field, so experts looked closer into the issue by evaluating lead levels in commonly occupied areas by children like recreational fields and child care centers.

Researchers concluded that when the turf deteriorates, dust with high lead levels is rated. In this case, the dust is once again a threat because it carries lead that could harm those who play in those commonly occupied areas. They also concluded that due to the fact that there still is no standardized way to annually check lead levels, it is important to continually sample synthetic turf samples to check for any elevated levels of lead. (10) Crumb rubber does pose some harmful threats, but it can also be very useful even with fields that consist of real grass.

There is an estimated 5,000 fields across the United States that use synthetic turf, but the majority of fields are dad from grasses such as Bermuda grass and Kentucky bluegrass. These are the two most commonly used grasses due to their high resiliency to wear and can extend the amount of time that the grass can withstand constant use. One of the biggest issues that field managers run into with these grasses, is when the cold temperatures of the winter start, the grass has a difficult time retaining its color because it no longer has its regular growth pattern.

In order to keep the grass growing properly over the winter, managers will over seed during this winter dormancy phase, which is a major financial burden when parks are paying for grass o grow, yet nobody is using them. Associate professor at the University of Tennessee, Dry. John Coronas, conducted an experiment to see how placing crumb rubber on these grasses could lengthen the life of the grass by reducing wear tolerance. His project had positive results as it was shown that adding crumb rubber to grass fields made the grass last longer by decreasing the amount of wear tolerance.

By increasing the longevity of the grass fields, it also makes them safer to play on. (11) Crumb rubber is the most commonly used infill because of its easy accessibility which makes it a cheaper product too, but there are other options to use s infill for synthetic turf. Hole TYPE Infill Solutions uses the same format to create synthetic turf, but the difference in their product is that they have an innovative infill that has the exact same role as rubber, but lacks the environmental hazards that come with crumb rubber.

One of the biggest flaws that also come with crumb rubber, which is a thermoses mixture, is that it is unable to be recycled. So Hole recycled and transformed numerous times. Since the infill is created by first-use lassoers, the infill granulates are guaranteed to posses none of the harmful Heimlich that are in rubber such as Pass. As shown in Figure 3, these infill granulates are cylindrical and hollow to ensure proper shock absorption. (12) Shock absorption can be adequately calculated by the G-Max value of granulates.

The G- Max value is the highest ratio of deceleration to acceleration by gravity. This value is important in ensuring that the synthetic turf has a feel that is very similar, if not identical to the feel of a grass field. Not only does the G-Max value show how realistic synthetic turf is, but it is also a gauge of the safety of the turf. When a player collides tit the turf, there is no force lost so it either goes into the turf or returns to the player thus the harder a surface is, the higher the likelihood of injury.

This is a product that has been tested and now approved by FIFE as a valid option for those who are deciding to create a turf field. FIFE makes sure that year after year, the quality of their fields are in optimal conditions for their athletes to play. By continuing to look for new and innovative options for their synthetic turf, such as some clubs using Hole Infill, it shows that in a sport that over a billion people play relied, synthetic turf is now the standard for soccer pitches. 13) Since this option is in its infancy, the product is still very expensive and used mostly in Europe for soccer fields, there has been little interest about it in North America, although it is very plausible that this innovative infill could make its way to North America in years to come. Another infill that has recently gained popularity, especially in the equestrian world, is Tappet Footings. The difference with this infill as compared to Hole, is that it is not placed in synthetic turf, but laid out across the width of a horse rack, so it must have much stronger properties on its own.

This revolutionary synthetic surface has gained fame because of its ability to persist through every kind of weather condition that could possibly affect a horseradish track. The mix has stood through hurricanes, floods and temperatures ranging from -17 to 110 degrees Fahrenheit. When creating this virgin infill, inventor Michael Dickinson made sure that it had all the properties to withstand the test of time. As shown in Figure 4, the Tappet system is set up like synthetic infill turf in that there is a layering system that ensures that the Tappet mix has a strong base that can withstand constant use.

This virgin polymer has the similar advantages of synthetic turf. For instance, Tappet has proven to be safer for both Jockeys and horses alike since it decreases the amount of falls as well as increasing the amount of times a horse can run. The seven-inch cushion provides a sturdy, yet comfortable base for horses to gallop across the finish line. (14) The largest full-scale study comparing the benefits of synthetic turf to its possible flaws was conducted in 2009 by the US Environmental Protection Agency.

Following the report, the government agency determined that there is no substantial safety issues that should prevent anyone from using synthetic turf and that it is indeed the most cost efficient way for parks to maintain fields. (15) Whether infill is used as an environmentally friendly option or a way to prevent any further damage to grass fields, synthetic turf infill is now the leader in sport fields. One way to attest that synthetic turf is indeed the best surface to play on, is that in 2014 when the Super Bowl plays in the Meadowland in New York, it will be the fourth consecutive who knows how far synthetic turf innovations can go.