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As a market and technology leader in the field of the polyurethane-based materials, BASF successfully combined its diverse range of products with its application-oriented R&D to develop a composite flooring material with excellent shock absorption and high rebound properties. This polyurethane-based flooring structure can be used in public spaces, indoor and outdoor tracks and children's playgrounds.
The active lifestyle and increased sport participation in Europe, North America and the Asia-Pacific region creates a demand for multifunctional and safe sports facilities, where high-efficiency absorbing materials can help athletes, casual users and children to achieve their best performance, while at the same time, lowering risks of exercise-related injuries.
BASF’s shock-absorbing flooring material combines properties previously thought incompatible, such as outstanding softness, cushioning and excellent resilience. To achieve this, the company used thermoplastic polyurethanes (TPU), which is one of the most versatile engineering thermoplastics.
Fundamental Research Leads to High-Performance Absorbing Materials
TPU is a block copolymer with a macromolecular chain composed of alternating soft and hard segments. Upon processing, due to the distinct polarity of the soft and hard segments, a partial phase-separation occurs in the bulk material, which leads to the formation of a microdomain structure. The hard domains act as physical cross-linkers and contribute to the mechanical strength, while the soft domains give the elastic properties of the material.
This fundamental knowledge allowed the scientists at BASF to tune the properties of TPU by changing the domain ratio. The result is a wide range of materials that vary from thermoplastic elastomers to rigid thermoset foams and adhesive compounds that can be reprocessed or recycled like any other thermoplastic material due to their lack of covalent cross-linking.
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The application of the new material as a shock-absorbing flooring surface requires the elasticity of an elastomer (rubber) to provide excellent impact absorption and rebound, ease of application (with varying thickness), highest possible wear resistance, low maintenance and resistance to diverse weather conditions, oil and water.
Thermoplastic Polyurethane Foams Offer Excellent Flexibility and Durability
At the core of the excellent shock absorption properties of the newly developed flooring material is the world’s first expanded thermoplastic polyurethane (E-TPU) commercialized by BASF in 2013 under the name Infinergy®.
Expanding (foaming) is particularly beneficial for TPU and helps to overcome its relatively high cost and high hardness. The foaming of the material leads to a reduction in material consumption (because of the volume expansion), and the hardness can be effectively reduced without the addition of any plasticizers.
The high demand for low-density TPU foams (more than 23 million tons in 2019) and their various applications as light-weight, highly flexible absorbing materials with a significant cushioning effect, and fast energy restoration after compression focused a great deal of academic and industrial research and development on polymer foaming technologies. Being one of the technology leaders in the field, BASF boasts a broad portfolio of particle foams, from rigid foam, such as expanded polystyrene (EPS), to soft and stretchy E-TPU.
Closed-Cell Foam Particles with Outstanding Elasticity and Shock Absorption
A special grade of BASF’s closed-cell elastic particle foam, produced by the expansion of the well-established TPU Elastollan® and branded Infinergy®SP, combines the properties of TPU with the advantages of foams, making it as elastic as rubber but much lighter.
The closed-cell structure of the foam particles prevents the water uptake, making it particularly suitable for all-weather sports flooring applications. The E-TPU boasts a significantly higher rebound height than EPS and expanded polypropylene (EPP).
In a high-frequency fatigue test (5 Hz at a maximum pressure of 250 kPa), Infinergy® retained 92.5% of its original thickness (still returning almost all the energy applied to it) after 40,000 cycles. At the same time, the counterpart particle foams remained permanently compressed.
Importantly for outdoor applications, even at temperatures of -20 °C, Infinergy® does not lose its elastic properties. Table 1 summarizes the fundamental physical features of Infinergy® and its counterparts.
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Table 1. Infinergy® E-TPU key physical properties at a glance
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Material
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Infinergy®
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EPP
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EPS
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Density [kg m-3]
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110 – 320
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20 – 200
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15 – 30
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Ultimate tensile strength [kPa]
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600
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270 – 1930
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80 – 900
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Water uptake (in 24 hrs) [% vol.]
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<2
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<2
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< 1.5
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Working temperature range [°C]
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-20 to +40
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-40 to +60
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-150 to +80
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Rebound (ball rebound test) [%]
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55
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30
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20
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Elongation at break [%]
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100 – 150
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<21
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<15
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The shock-absorbing flooring solutions from BASF are based on Elastan® and Elastocoat® series of TPU coatings and adhesives combined with Infinergy®SP particle E-TPU foam. This combination results in a variety of porous and non-permeable surfaces suitable for walkways, athletics tracks, school fields and playgrounds.
Durable Polyurethane-Based Flooring Structures
The polyurethane-based flooring structures offer superior tensile strength and durability, and consist of a layer of Elastocoat® in which Infinergy®SP is embedded (with Elastan® as a binder) for excellent shock absorption and rebound.
With the outstanding cushioning effect of the E-TPU particles, the flooring surface absorbs the kinetic energy generated as the runner’s feet land. It returns some of the energy to the runner, while at the same time cushioning the impact. In this way, it provides a safer sporting experience and a reduced risk of sports injuries.
When used in playgrounds, the high-performance surface softens falls very efficiently and provides a safe play environment.
Low Environmental Impact and High Sustainability
The absorbing material also scores highly in terms of sustainability. Its manufacturing is entirely based on ethylene diphenyl diisocyanate (MDI), which means that the production cycle does not require additional solvents, chlorinated paraffin (as plasticizer), heavy metal catalysts, or methylene orthochloroaniline (MOCA) as curing agents.
It is also free from polycyclic aromatic hydrocarbon (PAH), is fully recyclable, and can be applied with conventional tools. Thanks to its low weight, the material can be used in places where terrain restrictions apply. It is suitable for indoor and outdoor use, as it can be applied in water-permeable and waterproof formulations. All this makes the new polyurethane-based flooring structures a prime choice for modern, sustainable and safe sports grounds, playgrounds, gyms and running tracks.
References and Further Reading
Advanced Flooring Solutions. [Online] www.basf.com. Available at: https://www.basf.com/gb/en/who-we-are/core-topics/urban-living/advanced-flooring-solutions.html (Accessed on 02 April 2020).
Infinergy® ‒ Small Beads, Big Possibilities. [Online] www.basf.com. Available at: https://plastics-rubber.basf.com/global/en/performance_polymers/products/infinergy.html (Accessed on 02 April 2020).
Flooring structures for sports fields and playgrounds. [Online] www.basf.com. Available at: https://plastics-rubber.basf.com/global/en.html
Gama, N. V., et al. (2018) Polyurethane Foams: Past, Present, and Future. Materials, 11, 1841. Available at: https://doi.org/10.3390/ma11101841
Sun, X., et al. (2015) Fabrication of Highly Expanded Thermoplastic Polyurethane Foams Using Microcellular Injection Molding and Gas-Laden Pellets. Polymer Engineering and Science, 55, 2643-2652.
Somarathna, H. M. C. C., et al. (2018) The use of polyurethane for structural and infrastructural engineering applications: A state-of-the-art review. Construction and Building Materials, 190, 995-1014. Available at: https://doi.org/10.1016/j.conbuildmat.2018.09.166
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