Full definition
The essential vulcanization activator in sulfur-cured rubber compounds, used in combination with stearic acid to dramatically improve the efficiency of the sulfur-accelerator cure system. Without ZnO, sulfur vulcanization is impractically slow even with accelerators. Mechanism: ZnO + stearic acid form zinc stearate, which reacts with accelerator to create highly active zinc-accelerator complexes that catalyze sulfur cross-linking. Dosage: 3-5 phr (parts per hundred rubber) standard for most compounds. Also functions as: primary curing agent for chloroprene (CR/neoprene) rubber (5-10 phr ZnO provides cross-linking via the chlorine atom), mild reinforcing filler, white pigment, and UV absorber. Per ASTM D4295 for rubber-grade ZnO specifications: high surface area (active ZnO, 40-60 m²/g) is preferred for maximum activation efficiency. Environmental note: ZnO is classified as an environmental toxicant in some regulations, driving research into reduced-ZnO and ZnO-free cure systems. For white/colored FDA food-grade compounds, ZnO serves as both activator and white pigment. One of the few ingredients present in virtually every sulfur-cured rubber compound worldwide.