Influence of size and filler system on the pyrolysis behavior of styrene-butadiene rubber in tire wear particles

Abstract

Tire wear particles (TWPs) are generated by driving vehicles and found in the environment. Model TWPs of styrene-butadiene rubber (SBR) vulcanizates with different filler systems, namely, carbon black (SBR-C), carbon black/silica (SBR-M), and silica (SBR-S), were prepared using an indoor abrasion tester, and their pyrolysis behavior was investigated in terms of particle size and filler system. Abundances of the major pyrolysis products, namely, butadiene, 4-vinylcyclohexene (4-VCH), styrene, 2-phenylpropene (2-PP), and 3-phenylcyclopentene (3-PCP), were compared. The 4-VCH/butadiene and 4-VCH/styrene ratios of vulcanized SBR were lower than those of raw SBR, whereas the 2-PP/styrene and 3-PCP/styrene ratios of vulcanizates were higher than those of raw SBR. The abundance ratios of major pyrolysis products of the vulcanized samples showed different trends, although the three vulcanizates had the same compound formulation except for the filler system. The abundance ratio decreased in the order of SBR-C > SBR-M > SBR-S, which can be explained by the sulfur crosslinks and states of the bound rubber. The 4-VCH/styrene, 2-PP/styrene, and 3-PCP/styrene ratios of TWPs increased notably with increasing the TWP size up to 200 μm and then increased slightly or almost remained constant. The pyrolysis behavior of TWPs was influenced by the filler system and particle size. Our study suggests that the differences in the pyrolysis behavior depending on the filler system and particle size should be considered for the quantification of TWPs in environmental samples.