Development of ENR-based compounds for green tyre tread applications with improved performance, processing characteristics and sustainability
2019-10-17T10:28:03Z (GMT) by
Silica filler is a renewable and environmentally friendly resource. The precipitated silica is the most commonly used as filler in rubber compounds especially in tyre rubbers compounds. Since the introduction of “Green Tyres” in the early 90’s, the use of silica as a reinforcing filler in a polar variant of natural rubber, epoxidized natural rubber (ENR) has grown. The greatest advantage of using silica over carbon black as a reinforcing filler in a tyre tread compound is that a lower rolling resistance is achieved, while maintaining good wet and dry traction. However, a previous study has shown that high silica loading in ENR without any coupling agent results in lack adhesion to the rubber matrix, which in turn affects the processability and physical properties of the rubber compound. In addition, the wear resistance of a silica filled ENR compound also was not as high as those of conventional Oil Extended Styrene Butadiene rubber (OESBR) and NR/BR compounds used in passenger car and truck tyre treads even with the presence of silane.
In this work, with the aim of improving silica filled ENR compound properties, the effect of X50S silane coupling agent concentration, water addition to silica during mixing a silica filled ENR compound and blending butadiene rubber (BR) into a silica filled ENR compound were studied. While, the recovered silica fillers from pyrolysis and geothermal sources, referred to as ‘rSilica’ and ‘geoSilica’ respectively have been used in place of conventional silica in ENR compound in order to determine whether they can be used to improve the sustainability of ‘green’ tyre tread compounds. All silica filled ENR compounds or blends for lab scale mixes were prepared in a Polylab Haake internal mixer and for the extrusion performance evaluation, a medium scale mixer was used to prepare the silica filled ENR compounds. The rheological properties of the compound were measured using a Mooney viscometer and Oscillating Disc Rheometer. The physical properties such as hardness, tensile strength, heat build-up and DIN and Akron abrasion resistance were also measured. The results showed that the ENR/silica compound properties such as tensile strength and hardness were as good as those of the conventional NR/BR compounds used in tyre tread. However, the most important finding was that the heat build–up property and Mooney viscosity decreased significantly with addition of X50S silane coupling agent and water. While the DIN abrasion resistance index increased significantly with BR content, exceeding that of the conventional compound at BR:ENR ratios of greater than 20:80. The rSilica which is recovered silica from pyrolysis of tyres did show reasonably good physical properties such as tensile strength, hardness and abrasion resistance as well as good processing characteristics compared to the commercial grade silica (Zeosil) may have potential to replace Zeosil silica in tyre compounds.