Experimental Study on the Wear Particles Features Induced by the Rubber-Carbon Nanotube Composites

Rubber-carbon nanotubes (CNTs) composites, with its good anti-wear ability, good thermal conductivity, and high tear resistance ability, has great potential for future applications in tire industry. However, due to the uncertainty of the toxicity of the CNTs, there are raising eyebrows on the safety of this kind of tire material, especially the secondary hazard such as released particles induced by the tire wear. Therefore, it is significant to investigate the related topics to the rubber-CNTs material and its derivative.　This paper conducted experiments on the rubber-CNTs composites to explore the relationship among the parameters closely related to tire wear (CNTs content, load, velocity, and slip ratio), TWPs (tire wear particles) features (quantity and size) and surface wear mechanism from the perspective of tribology. The test tires made by styrene butadiene rubber (SBR) compositing with content variation of CNTs as reinforcing fillers were prepared. Then, utilizing the self-developed abrasion tester, the influence of the mentioned parameters on the TWPs were studied. Furthermore, the morphology of the worn composites tread was explored to build the relationship among the wear mechanism, TWPs’ features, and the mentioned parameters. Handheld laser particle counter CLJ-3016H and non-contact infrared thermometers Fluke 59 Pro were employed to measure the particle quantity and tread temperature, respectively. The tribological performance of SBR without CNTs was also investigated as comparison.　As the CNTs’ content increased, the anti-wear ability of the SBR-CNTs composites was improved greatly and the quantity of TWPs showed a considerable decrease. The quantity of TWPs varied wildly without and with reinforcement of 1% CNTs. The TWPs quantity with a particle size of 3 μm decreased by 50%, and the quantity of TWPs with particle sizes of 5 and 10 μm decreased by 79% and 68% respectively, indicating that CNTs effectively reduced the fine wear particles generation. However, the tire tread temperature was independent on the content of CNTs. The abrasive wear was the dominant mechanism on the tread and gradually became milder with the increase of the CNTs content.　As the load increased, the quantity of TWPs from SBR-CNTs was reduced by about 50% compared with that by SBR. The abrasive wear were the governing wear mechanism on the both tread of the SBR-CNTs composite and SBR. However, due to the high load and temperature, the tread adhesion of the raw SBR was much severer, leading to more TWPs adhere to the interface and lighten the release of the TWPs.　As the velocity increased, the quantity of the TWPs generated by SBR-CNTs composites was reduced about 50% than that generated by SBR. The growth rate of TWPs induced by velocity variation was much more than that induced by load at the same variation rate of the both independent variables. The fatigue wear accompanied by abrasive wear was the dominant wear mechanism on the both tread of the SBR-CNTs composite and SBR, which led to the thermal ageing and stickiness of the rubber tread, especially to the SBR without reinforced by CNTs. The stickiness of the SBR tread was much severer at higher velocity, leading to more TWPs stick to the interface and reduce the TWPs’ release.　As the slip ratio increased, although the TWPs generated by SBR-CNTs were less than that generated by SBR, the production rate of TWPs of 3 μm in size from the SBR-CNTs was much higher than that of SBR. The reason was probably due to the higher stiffness of the SBR-CNTs composite, leading to produce much fine TWPs. On the contrary, the fine TWPs of the SBR tended to agglomerate on the tread to form greater debris, resulting in reducing the fine TWPs released into the air.　The results provided scientific guideline to evaluate the TWPs hazard to the environment and living organisms caused by rubber-CNTs composite. Meanwhile, the study was also helpful for the automobile industry, tire manufacturers, and decision-making departments to make related development strategy and environment-friendly policy.