(419a) Mechanism for Nanoparticle Release from Automotive Tire Tread.

In the US, automotive tire wear generates nearly a million tons of tire wear particles (TWPs) annually, making up 40% of microplastic (MP) pollution, predominantly made of 100-micron cylindrical particles (MP-TWPs). This unregulated particulate emission from tires exceeds the regulated emission from exhaust by three orders of magnitude. With electric supplanting internal-combustion vehicles TWP emissions will increase due to higher torque and vehicle weight. Automotive tire tread is composed of 25-30% nanoparticles (NPs) of carbon black and/or silica. Our preliminary work shows for the first time that interfacial charged nanoscale tire wear particles (nano-TWPs) can be found adhering to the surface of in-use tires and can be collected from laboratory abraders as an aerosol and as electrostatic depositions. Partly based on this observation, a novel interfacial electrostatic mechanism is proposed which involves: 1) breakup of the filler network under cyclic load; 2) chemical-mechanical breakup of the elastomer network at the tread surface; 3) enhanced convective transport of the nano-aggregates under cyclic shear of the rubber; 4) newly recognized cyclic flexo-electric and more conventional tribo-electrostatic interfacial charge on the elastomer/nanoparticles which drive expulsion from the rubber matrix. We have used X-ray Photon Correlation Spectroscopy, voltage measurements under cyclic load, static X-ray scattering measurements, aerosol mobility and charge analysis, spectroscopy, dynamic mechanical testing as well as microscopy to verify a proposed mechanism that drives free nanoparticles from tire tread during tire wear. We have studied the impact of nano-filler surface treatment and various typical tread compounds to understand methods to prevent the release of nanoparticles during tread wear. The work is a collaboration between researchers at the University of Cincinnati, Akron Rubber Development Laboratory, the Health Effects Laboratory (HELD) of the National Institute of Occupational Safety and Health in Cincinnati and X-ray scientists at Argonne and Brookhaven National Laboratories.

The project is supported by NSF CBET - 2409292 Beaucage, the Centers for Disease Control, Argonne National Laboratory, and Brookhaven National Laboratory. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility at Argonne National Laboratory and is based on research supported by the U.S. DOE Office of Science-Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This research used beam line 11-ID CHX of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.