Evaluation of Microplastic Generation from Novel Composite Graphene Nanoplatelets-Rubber Tires

With the increased uptake of electric vehicles, which have a higher mass than conventional internal combustion engine vehicles, minimizing microplastic generation from tires as they wear down against the road is of growing importance. Rubber tires are also ubiquitous, as they are used in personal vehicles, commercial trucks, and braking mechanisms on trains. Existing rubber tires wear down quickly and are known to produce large amounts of microplastics which are released throughout the environment. Our study investigates the ability of several new rubber matrices augmented with graphene nanoplatelets (GNP) to reduce wear emissions from tires. The evaluation of abrasion resistance was conducted following ISO 4649 standards. Abrasion resistance testing consisted of placing a rubber sample in direct contact (sliding across) with a rotating drum wrapped in an abrasive sheet, rotating rotations per minute resulting in a test run equivalent to rolling a tire along the road for 40 meters. Assessment of particle emissions was also conducted by collecting the air from the abrasion resistance testing within an environmental enclosure using a vacuum pump and the TSI DRX DustTrak 8533 connected with the TSI P-Trak Ultrafine Particle Counter 8525. Physical characteristics of the composite rubber material were also evaluated, including material hardness and the water contact angle. The results showed functionalized carboxylic GNP (COOH-GNP) at low concentrations improved wear resistance and decreased emissions compared to the control conventional rubber tire matrix. The rubber samples composed of COOH-GNP 2% showed an improvement in mass loss of 43.94% less mass loss compared to the control conventional rubber tire matrix, and the COOH-GNP 4% samples showed an improvement in mass loss of 31.05 % less mass loss compared to the control conventional rubber tire matrix. Ecotoxicological studies were also performed. Future work will investigate the fundamental mechanism of how COOH-GNP additives enhance wear resistance and reduce harmful sub-micron microplastic emissions, a broader range of rubber composite compositions, and improved methods for the assessment of aerosolized microplastics from the tire wear studies.