Freedom from the ‘Black Gold’

By 2013 Sumitomo Rubber plans to be selling tyres containing absolutely no petrochemical materials. This news was printed in the company’s 2008 – 2011 environmental statement, which was published in Japanese only on November 17. It appears likely the oil free tyres will initially be sold on the Japanese market only.

The company’s ambition to produce an oil-free tyre is not new; Sumitomo Rubber president Tetsuji Mino first stated this goal on February 14, shortly before the launch of the three per cent oil content Enasave 97 tyre. “Relying on three 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.” At the time, company senior executive officer Takaki Nakano said that the residual three per cent fossil fuels, required for the antioxidant and the rubber accelerator used in the vulcanisation process, could not be replaced by natural resources using current technology.

Sumitomo reports that, in a typical 195/65R15 91S size passenger car tyre it produces, 66 per cent of the raw materials used, in weight, are petroleum sourced. The ultra low proportion of petroleum materials used in the Enasave 97 was made possible by eliminating the use of synthetic rubber in the tyre’s sidewall and airtight inner liner. Instead the company utilised an epoxidised natural rubber that it calls ENR – Evolutional Natural Rubber. Silica was used as a filler instead of carbon black, vegetable oils instead of petroleum-based processing oils and in the casing synthetic fibre was replaced by vegetable fibre.

Owing to the molecular structure of natural rubber, creating an airtight skin using ENR 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.

The Sumitomo environmental report does not make clear exactly how the remaining three per cent petroleum product, described by Tetsuji Mino as a ‘major hurdle’ earlier in the year, can be dispensed with altogether. Company spokesman Ryota Senshu answers this question only by stating that “oil is now under development.”

The company planned to sell 20,000 units of the Enasave 97 tyre in the 12 months from June 2008 through its Dunlop, Goodyear and Falken brands, with four different sizes on offer. According to Mr. Senshu, tyre sales have so far been in line with Sumitomo’s expectations.