All tyres on the market today include a fossil fuel component, and numerous attempts have been made to minimise the use of such non-renewable resources. In March Sumitomo Rubber releases its Enasave 97 tyre, in which the use of fossil fuels is limited to 3 per cent – a major advance on previous attempts. However for Sumitomo Rubber a 97 per cent renewable ingredient content is not enough. On February 14 company president Tetsuji Mino unveiled Sumitomo’s vision of and work towards a 100 per cent natural resources.
“Relying on 3 per cent fossil fuels is a major hurdle,” Mino said. “I don’t think we can make it in one or two years, but I’m determined to put the tyre on the market even if it takes five to ten years.” The residual 3 per cent in the Enasave 97 is required for the antioxidant and the rubber accelerator used in the vulcanisation process, and previous attempts to eliminate it have drawn a blank. According to senior executive officer Takaki Nakano, “With the current technology, they cannot be replaced by natural resources.”
The proportion of petroleum materials used in the Enasave 97 was cut to residual levels by eliminating the use of synthetic rubber in the tyre’s sidewall and airtight inner liner. Owing to the molecular structure of natural rubber, creating an airtight skin using this product is more difficult than with synthetic rubber, therefore a change in its structural composition was required to make it suitable for use. Similarly, before non-petroleum derived rubber could be utilised in the tyre’s bend-resistant sidewall the company needed to create a blend of natural and modified rubber to replace the synthetic component. As these two rubbers did not blend easily a mixing method using vegetable oil was devised.
Sumitomo Rubber is also working towards reducing tyre rolling resistance by 50 per cent, although it has not set a date for the commercial release of any such product. This tyre under development can reportedly improve vehicle fuel efficiency by about 10 per cent. “Some part of the rolling resistance is caused by the friction between tyres and the road required for deceleration, but the rest is generated by the thermal energy induced by other factors,” said Nakano. “So, we are trying to minimise any unnecessary energy.”