Potential release of nano-carbon black from tire-wear particles through the weathering effect

Abstract

Carbon black (CB) is commercially produced by the partial combustion of hydrocarbons, mainly used as a reinforcing material in tires. Generally, driving cars emit a considerable amount of particulate matter (PM), and this acts as a major source of PM in urban areas. While exhaust PM emissions are strictly regulated and controlled by the government, non-exhaust PM emissions from tire-wear and break-wear have been overlooked. Additionally, as CB is tightly bound in the rubber matrix of tire-wear particles (TWP), the possibility of nanoparticle exposure from TWP has also been ruled out. However, TWP could be fragmented through the weathering effect, continuous abrasion on the road, and resuspension. Therefore, in this study, we investigated the potential release of nano-CB from TWP through the weathering effect using a ball milling process. With increasing milling time, countless free-bound nanoparticles were detached from the parent TWP samples. Based on several analyses of elemental composition, morphological change, and crystallinity, it is possible to define the free-bound nanoparticles as nano-CB. Additionally, nanosized carbon-based materials were found in real-time field tests on highways. Therefore, it has been confirmed that nanosized carbon particles can be released from TWP or exhaust PM.