Zinc oxide with dominant (100) facets boosts vulcanization activity

The effect of zinc oxide (ZnO) with different crystal facets on the vulcanization activity efficiency was studied via experiments and theoretical calculation. Two types of ZnO particle with the similar size and specific surface, one with more (0 0 1) facets (table-like ZnO) and the other with more (1 0 0) facets (rod-like ZnO), were used to investigate the effects of different facets on the vulcanization activity. The results of curing rate index (CRI) suggested that rod-like ZnO has a faster cure rate than table-like ZnO and rod-like ZnO has a higher vulcanization activity efficiency than table-like ZnO because of higher cross-link density in the styrene butadiene rubber (SBR) composites cured by rod-like ZnO crystal. The DFT calculation results showed that the value of Zn-O binding energy on the crystal face of rod-like ZnO was lower than that of table-like ZnO, which indicated that more Zn2+ would be released into the rubber matrix during the process of vulcanization and it would efficiently promote the curing process. It was proposed that the vulcanization activity of ZnO was highly relative with the ZnO exposed facets, which is in the order of (1 0 0)(1) > (0 01) > (1 0 0)(2) > (0 0 (1) over bar), which was consistent with the experiment results.