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The closure of Group I refineries will inevitably limit the availability of the high-viscosity mineral oils commonly used in tyre tread formulations. Nynas’ new tyre oil offers an alternative with excellent performance. To address the decline of high-viscosity oils and rebalance the heavy tyre oil market, Nynas has developed a new highviscosity tyre oil.
Although only some Group I oil is used in tyre formulations, the very heavy residual aromatic extracts (RAE) are commonly used components that stem from the bottom fraction of the Group I refinery process. “Having first established that hydrocarbon resins can be used to steer the tyre performance, we decided to investigate if a plasticising oil of high molecular weight could have a similar effect,” says Anna Eriksson, Technical Coordinator, Technical Development and Market Support, Naphthenics.
In a study focusing on the molecular weight influence on wet grip, lab-scale samples of a range of plasticising oils of varying molecular weight were evaluated in a tyre tread formulation based on a functionalised SSBR/BR system. “The results showed a strong correlation between the molecular weight and higher ‘wet out’ ability at 0°C (wet grip).” The study lead to the development of heavy naphthenic black oil (Heavy NBO) that was evaluated further in other tyre tread formulations with RAE as the benchmark reference, and the results validated a very good performance. “Our results also suggest a 25 percent improvement of the curing time when NBO is used instead of RAE or treated distillate aromatic extract (TDAE),” Eriksson adds.
As the rolling resistance and wet grip of tyres display an anti-correlating relationship, the challenge is to find the best possible balance between these two properties for an overall optimised tyre performance. Rolling resistance and wet grip properties are usually measured using dynamic mechanical analysis (DMA), where the relation between flow and storage characteristics are presented in Tan Delta values at different temperatures. A low “tan d” at 60°C indicates low rolling resistance, whereas a high “tan d” at 0°C indicates high wet grip. The tailor-made naphthenic black oil Nytex 4700 has proven to have a very positive effect on rolling resistance, which affects the fuel economy of tyres.
Text: Gittan Cedervall
The graphs show the wet grip (tan d @ 0°C) and the rolling resistance (tan d @ 60°C) for rubber formulations made with oils of vaying molecular weight (Mw), as well as treated distillate aromatic extracts (TDAE) and residual aromatic extracts (RAE).
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