One of the questions I get asked most frequently is “what polymer should I use to make synthetic turf” and the answer is …It’s not that simple annoyingly!

There is not one polymer that fits all, and not even one polymer that suits all extrusion equipment.

Firstly, you need to decide on its purpose and what type of grass fibre you want to make, and then what do you want to achieve? For example, I would not use the same polymer for a landscape product that I would use for high-performance sports yarn. “Why?”, I hear you shout.

Well, for starters, generally speaking the price of landscape yarn is significantly lower than for a high-performance sports yarn as the latter is expected to handle a much intenser and larger footfall and is expected to the safety and quality of the game where a landscaping product is mainly to answer an optical desire. So, using a high-end super-duper polymer for a landscaping product would not make financial sense.

Secondly, currently there are no mandatory performance standards for landscape yarn – though this might change with the industry focus on environmental care, secondary microplastics and end-of-life solutions. Until such standards are adopted, a landscaping yarn is not expected to have a technical performance.

Your selection of a polymer also depends on the extrusion equipment you have. It might be possible that your equipment is not capable of running some of the new generation polymers. This can force you to make a compromise in materials. Perhaps using additives and tweaks to the process to achieve your end goals.

Purpose driven

Even looking within the sports bracket, it is likely you will need a different polymer for a hockey product than for a MUGA, or a non-filled sports surface for football. Ideally, if you want to be a full-service supplier you will need multiple polymer grades and types.

With the rise in non-filled surfaces, dry hockey turf as well as other industry challenges, the industry is increasingly looking to combine and blend materials in order to meet sport requirements. Trying to get all your performance from one polymer is a big ask, and when you factor in that the majority of polymer producers are not producing grades specifically for the requirements of synthetic turf, it becomes a bigger task.

Other materials can be used as enhancing additives, such as plastomers which have the elastomeric benefits of a rubber and the polyolefin benefits of a plastic. This helps to improve the splitting behaviour in the machine direction as well has a positive benefit for resilience.

Different qualities

Another question that pops up regularly is “do you use C4, C6 or C8? isn’t C8 the best?” I usually reply with “Why do you want to know, and why do you think that?” Frankly speaking, what you should be more concerned with is “does the yarn meet all your performance requirements?” irrespective of the monomer you have selected. The truth is there is good C4 and there is bad C8 and vice versa, making the question much bigger than that. For example, the selection of the density and the melt flow index play a huge part. Then there is how will you process the polymer you’ve selected. You could take a very expensive bespoke C8 but if you select the wrong extrusion conditions then you may as well have used a bargain basement C4 for all the performance that you will eventually be handed!

Finding the right density

Higher density polymers are stiffer and be more resilient, but they are brittle and wll split and break down a lot faster than a lower density material. But lower density materials have little body and tend to collapse in a carpet, causing issues with ball roll, traction, and maintenance problems.

You can temper a materials density with the melt index (also known as MFI, MFR). The MI is affected by the chain length, as it is this that determines the flow characteristics. The MI is an indicator of the molecular weight, whereby the higher the molecular weight the lower the MI, it is inversely proportional to viscosity.

So, if the chains are long the MI will be low, the material will have higher melt viscosity and greater melt strength. The resulting yarns will have superior impact performance when compared with yarn produced with comparable density that is made of shorter chains thus higher MI.

It’s a matter of balance

A higher density polymer can have better performance with higher MI, but a lower density polymer will have improved performance with a lower MI. Of the two options a lower density material, with a lower MI is the better pick. The lower density has a higher degree of entanglement, so the more elastic type of material – so better resilience and softness, but the lower MI, so higher molecular weight of the chains, improve its durability.

As I already pointed out, it is impossible to answer the question of what polymer you should use for a turf product. Having that said, I hope I have opened your eyes to the complexity of making that “green stuff, better known as plastic grass”, and made it clear why your yarn supplier might be asking you so many questions!

Jacki Stephen is an independent consultant with close to 30 years’ experience in producing synthetic turf. She writes in her own capacity. The views or information shared in this article are not necessarily the views of the publisher.