Using Dynamic Mechanical Analysis (DMA) to Develop Sustainable Tires

Written by Travis Parkman, Product Specialist Mechanical EIT

KEYWORDS: cellulose, natural rubber, plant-based, green tire, dynamic properties

You may not be able to reinvent the wheel, but companies are reinventing the tire, in terms of its materials. Natural rubber, an essential material in tire manufacturing, is extracted from rubber yielding plants as a form of sap. However, natural rubber is hardly used as is; instead, it is blended with a variety of fillers, vulcanizing agents, plasticizers, etc., to improve its performance for specific applications [1].  Tire companies are putting a focus on replacing these harmful fillers and chemicals with sustainable materials that are more environmentally friendly. These alternatives include plant-based and recycled materials [2].

For instance, Michelin debuted its ‘Démonstrateur 46’ racing tire earlier this year. The racing tire contained 46% of sustainable and recycled material. These materials included citrus rinds, sunflower oil, and pine resin, along with recycled steel, aluminum, and tires [2].

GREEN SOLUTIONS

Fillers are used for improving the properties of rubber, which includes strength, wear resistance, traction, and rolling resistance. Bio-based fillers are lightweight and sustainable options that are gaining traction in the tire market. Goodyear, for example, is shifting their focus from using sand silica as a filler to using rice husk silica ash [2].

Figure 1. Rice husk is a waste product of the rice industry and is rich in silica.

 Bio-based fillers can also be sourced from pineapple leaves, bamboo, kraft pulp, wheat straw, and banana fibres [1]. 

Goodyear is also making strides in using natural oils, such as soybean oils, as a green alternative for plasticizers [2].  Plasticizers are used in tire manufacturing to enhance the dispersion of other compounding ingredients and optimize the tire’s performance.  Historically, these come in the form of harsh petroleum products. Due to the environmental impact of these products, more manufacturers are focussing on using more sustainable plant-based oils, soybean, rice, castor, rice bran, palm, and soya bean oils [1].

MAINTAINING HIGH-QUALITY TIRE TREAD PERFORMANCE

To test the performance of these new innovative rubber compounds, the Metravib DMA+ series is a useful tool that can be employed. If you are not familiar with DMA, I recommend looking at a previous post talking about its basic principles.

A research group in Brazil conducted a study using two different soybean oils (OEST and OEPX) as green alternatives for tire tread compound plasticizers.  They compared the soybean oils’ performances to a common petroleum plasticizer, naphthenic oil (ONAF) [3].

Figure 2. tan(δ) versus temperature for the different rubber compounds compared to the blend without fillers or plasticizers (E-SBR/BR/blank) [3].

The group used a Metravib DMA to evaluate tan(δ) at different temperatures, as is shown in Figure 2. Their results show the addition of plant-based and petroleum plasticizers have a relatively large effect on the tan(δ), which is commonly used as an indicator for tire performance.  A higher tan(δ) at 0°C is related to better-wet traction while a lower tan(δ) at 60°C is associated with lower rolling resistance.

Table 1. tan(δ) values for the different rubber compounds [3].

The use of OEST and OEPX soybean oils maintained and improved the wet grip performance of the rubber compounds, respectively.  However, both soybean blends increased the rolling resistance of the compounds.  The group evaluated the tire tread performance using other instruments as well and found that the soybean oils exhibited faster-curing speed and abrasive wear resistance.  From this research and the use of a Metravib DMA, they were able to effectively describe the tire tread performance and demonstrate that soybean oil is a viable green alternative to petroleum products [3].  Other tire tread performance indicators that could have been studied by using Metravib DMA include but are not limited to crack growth behaviour [4], and heat build-up [5].

Figure 3. The Metravib DMA+Series provides accurate high force and frequency measurements with its one-piece test frame and has valuable hardware upgrades, including the crack growth module.

If you found the use of plant-based materials interesting, I recommend an article from Ed Park, titled Improving the Thermal Insulation of Bio-Based Materials with Pineapples Waste Aerogels, or if you want to learn more about whether Metravib DMA products can help you, contact us directly at sales@ctherm.com.

Works Referenced