New strategies towards the next generation of skin-friendly artificial turf surfaces

The issue of skin friction related injuries has been one of the problems challenging the artificial sports turf industry. It has been identified by users as a major factor impeding acceptance of artificial turf at the professional level. However, information explaining the mechanisms for skin-turf abrasion is limited and little progress has been made, it appears, to derive an appropriate testing method for product approval or in evidence of improvement of the skin-friendliness of these products in sport surface surfaces. This research project focused on exploring the potential for improving the skin-friendliness of artificial turfs through a multi-faceted approach: identifying the contribution of the abrasive-components in modern artificial turf surfaces through mechanical testing; while critically evaluating currently available skin friction standards , evaluating strategies for polymer material modifications to reduce the skin-surface friction; and the designing of an appropriate bench-top set-up for the lab-based assessment of material skin-friendliness. The lack of understanding of skin-turf interaction was addressed by identifying the turf-component that has the greatest influence on the skin-turf friction with the mechanical device used in the current industry standard. The skin -turf frictional profiles of a series of third generation (3G) turf surfaces were examined, in combination with independent measurements of the silicone skin surface roughness pre- and post-friction testing. Results indicated that turf carpets without any infill material exhibited the highest frictional values while surfaces completely filled with either sand or rubber displayed similarly low frictional values, independent of infill type. Morphological measurements also showed the largest decrease in surface roughness for skin samples tested on carpet-only surfaces, indicating a smoothening effect via abrasion. This abrading effect is alleviated with the addition of infill to the surface, with fully-filled surfaces having the least damage to the skin s. This unprecedented study suggests that the carpet may have the largest influence on the overall frictional behaviour of an artificial turf surface narrowing down the turf component to be targeted when applying product improvements to address skin-friendly properties. The strategy of material surface modification was then employed, to study the effect of polyzwitterionic brushes on improving the skin-friendliness of the identified polypropylene substrate. To address the intended application for artificial turfs, a bench-top test was developed to investigate the frictional properties of the hydrated samples outside of commonly used aqueous environments, where an excess of lubricating water molecules is absent. Photo-grafted poly(sulfobetaine methacrylate) (pSBMA) brushes of various irradiation durations were prepared and the improvement in frictional properties was studied. Frictional measurements using silicone skin tips, under both dry and hydrated surface conditions, showed that the applied modification was capable of forming a stable lubrication layer in the absence of excess water, significantly reducing the coefficient of friction by up to 78.8 %. The pSBMA brushes also provided the additional advantage of antifouling exhibiting resistance towards pathogenic Staphylococcus aureus with almost zero surface colonization for well-grafted samples. The low skin -sample friction under ambient conditions and desirable fouling-resistance highlights the potential of pSBMA brushes as a modification strategy for achieving skin-friendly surfaces targeted at reducing the risk of skin abrasions. The tribological implications of counter-surface selection were investigated. Frictional assessments of the pSBMA-modified samples were carried out using standard steel tribo-tips, in addition to the skin tips used. Measurements with the skin tips showed that the hydrated pSBMA brushes were successful in reducing initial skin -sample friction though the effect diminishes with extended testing, attributed to the drying of the interfacial water. The standard steel tribo-tips were unable to reciprocate these results, returning consistently low frictional values regardless of extent of surface modification or hydration. These observations draw attention to the importance of counter-surface selection in frictional assessments, highlighting how appropriate test materials can identify characteristic surface properties while providing an interaction that simulates that of the intended application. The simple experimental set-up used may potentially be enhanced as an intermediate product qualification method in the manufacturing of skin-friendly artificial turf yarns

Addressing skin abrasions on artificial turfs with zwitterionic polymer brushes

To address the skin-friendliness of synthetic surfaces intended for sports applications, the frictional properties of hydrated zwitterionic polymer brushes are investigated outside of the common aqueous environment where an excess of lubricating water molecules is absent. Photo-grafted poly(sulfobetaine methacrylate) (pSBMA) brushes of various irradiation durations are prepared on polypropylene substrates and the improvement in frictional properties of the pSBMA-modified surfaces against a silicone skin counter-surface is studied. Frictional measurements under both dry and hydrated surface conditions shows that the applied surface modification was capable of forming a stable lubrication layer in the absence of excess water, significantly reducing the coefficient of friction by up to 78.8%. The pSBMA brushes also provide the additional advantage of antifouling – exhibiting resistance towards pathogenic Staphylococcus aureus with almost zero surface colonization for samples irradiated for 1200 s. The low skin-sample friction under ambient conditions and desirable fouling-resistance highlights the potential of pSBMA brushes as a modification strategy for achieving skin-friendly surfaces targeted at reducing the risk of skin abrasions

Tribological investigation into achieving skin-friendly artificial turf surfaces

A main concern with artificial turfs is the increased incidences of skin abrasions compared to playing on natural grass. The proliferation of these surfaces draws attention to the skin-friendliness and related test methods of the products. This study focuses on the yarn component and explores the significance of tribopairs in identifying the skin-friendly property of hydrophilically-modified polypropylene. The frictional behaviour of poly(sulfobetaine methacrylate)-grafted substrates were studied under dry and hydrated conditions with standard steel tribotips, commonly used in frictional assessments. The measurements were repeated with tribotips made from silicone skin, used in large-scale artificial turf testing. Results showed that when hydrated, hydrophilic polymer brushes were successful in reducing silicone skin-sample friction by 75.8%. Interestingly, when extended trials were conducted, a step-jump in the frictional values of highly-modified samples was observed, attributed to the diminishing hydrated layer with prolonged testing. In contrast, the standard steel tribotips were unable to discern the effects of surface grafting or hydration, measuring consistently low frictional values across all samples. This study highlights the importance of tribotip selection and introduces a bench-top test method that can potentially be used for the quantification of skin-friendliness of artificial turf yarns during product development stages

Insights to skin-turf friction as investigated using the Securisport

© 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.The objective of this study was to investigate the effect of the infill and fibers of an artificial turf surface to the overall frictional behavior of the surface. The assessment was conducted using the Securisport test device in accordance to the FIFA Test Method so as to evaluate the effectiveness of the standard test in describing the frictional property of an artificial turf surface. Experiments showed that surfaces of varying infill depths and infill types produced characteristic features in their friction profiles that were a result of the fiber-infill interactions. The surface without infill exhibited the highest frictional values, with distinct peak and trough features. Surfaces completely filled with sand or rubber displayed similar profiles with relatively low frictional values. Test results showed that turf fibers influenced the frictional behaviour of partially-filled systems to a great extent. The results from the Securisport were useful in providing insights to how various turf components affect the skin-turf interaction and may be beneficial in the development of more skin-friendly turf products