This is an extract of a paper presented by leading composites scientist Dr Floreana Coman to a 2013 Synthetic Turf Technology Clinic initiated by TTNA.
Australia produces a very high quality modern synthetic turf. It evolved from “Generation 1” in 1962, when the US Government commissioned Monsanto Corporation to carry out research. The first version was physically very hard on users. The second generation came in 1980 using a textile technology tufting machine for polypropylene. In 1993, “Generation 3” renounced polypropylene and introduced ‘polyethylene’, to be followed with “Generation 4” offering much softer blades for users.
The basic terms used to describe components of synthetic turf are the:
Dr Coman likened synthetic turf to a composite, describing it as a polymer loose matrix composite. Composite refers to a product made up of a mix of materials with particular qualities, made more consistent when a supporting matrix material is added and an intimate-to-perfect bonding between the elements is created. In the traditional Polymer Matrix Composite (PMC) the reinforcement, in the form of fibres or fabrics, plays the key role as it provides key properties such as strength, stiffness and fatigue resistance.
Synthetic turf is made up of similar layers of reinforcement and supporting matrix, but more loosely connected (when compared to traditional composite products). In the case of Polymer Loose Matrix Composites the blades play the role of reinforcement, providing strength, stiffness and fatigue resistance as traditional reinforcement does. Dr Coman said the “mechanical, physical and thermal properties are anisotropic - or dependent on fibre direction, as well as dependent on the type and amount of the fibres/reinforcement and the type and amount of matrix/backing material."
The blades are made of polyethylene (PE). Polyethylene plastic is an inert material up until 120 degrees Celsius. It will not change form. At the molecular level it is quite simple, made up of six basic atoms of two carbon and four hydrogen (C2H4) which link in long chains by polymerisation.
Polyethylene is a safe recyclable plastic that is also used in food handling and for medical applications/storage.
Dr Coman said “chains make it very difficult to conduct heat. Lower density PE conducts very little heat, and higher density conducts more. Polyethylene was created in a laboratory ‘accident’ in 1933 when two chemicals were placed together under pressure. Because it is a poor conductor of heat it was first used as an insulator in 1942. It also has good chemical resistance against basic acids and bases, and is resistant to gentle oxidants and reducing agents. It does not give off any types of gas. These blades are an “inert” substance.
To protect the blades from UV rays an additive is included during extrusion, along with colour pigment. Australia produces and purchases high-grade encapsulated colour pigment, which contains no heavy metals.
The proliferation of the blades improves the product, and is measured in Denier (or Tex) for yarn linear density. (Denier is grams/9,000m of the yarn, and Tex is grams/1,000m of the yarn.)
Blade extruders understand the scientific properties of molecular weight; melt rheological characterisation; thermal analysis (shape change); density determination, cross-linking analysis and mechanical properties.
Polypropylene is currently used for the backing (matrix), as the density, or weight, is slightly lower, and it has a higher melting point. The polypropylene backing is not exposed to UV rays. Polypropylene exhibits good strength and no water absorption directly into the material. “No emissions can come out of these atoms,” Dr Coman said.
"In the past, certain overseas manufacturers provided no UV additives, and extruded at temperatures in excess of 200 degrees Celsius, ensuring the product would rapidly perish," she said.
“In over 40 years there has never been an instance of human illness or environmental damage caused by synthetic turf. Although it is an inert substance, as a precautionary measure very cheap imported turf should be tested to check for any trace of metals,” Dr Coman said. "Where parts of the backing might contain recycled rubber tyres this is unlikely to give off any emissions, due to the late stage in its life-cycle. This is often coated a lighter colour, which is simply to reduce heat absorption. No public health concerns have been confirmed in any international research, she said.