Mechanism analysis of Eucommia ulmoides gum reducing the rolling resistance and the application study in green tires

Abstract Eucommia ulmoides (EU) gum is a natural polymer material extracted from Eucommia ulmoides (EU) oliver, which can be applied in the tire industry to reduce the rolling resistance of the tread compound and save the energy. However, the mechanism is not explicit, which limits EU gum to be applied widely. Therefore, the crystallization characteristics and mechanical properties of EU gum with different cross-linking densities are studied systematically to reveal the mechanism. It is found that the “forced crystallization”, namely the crystallization of EU gum is hindered by the internal stress caused by numerous cross-linking points, is the main reason to reduce the rolling resistance. When the temperature reaches the melting point (about 60 °C), the EU gum converts into the random elastic network state immediately under the internal stress without the viscous sliding existed in the traditional molten polymer material, which greatly decreases the tanδ value at 60 °C, an index can evaluate the rolling resistance of tread material. Compared with the pure EU gum, the tanδ value at 60 °C decreases with a maximum drop of 45.2% under the forced crystallization caused by vulcanizing. However, EU gum cannot be made into tire directly for its crystallization at ambient temperature, which damages the high elastic property of tire. So EU gum is blended into natural rubber (NR) and reinforced by the carbon black. As a result, the comprehensive properties are improved when the content of EU gum is controlled lower than 30phr. Compared with NR nanocomposite, the NR/EU gum nanocomposite with 10phr EU gum can reduce the rolling resistance by 25.6% and improve the abrasion resistance by 9.5%.