[← Back to Knowledge Hub](/knowledge-hub)

        # Zinc Oxide (ZnO) in Rubber: Chemistry of the Vulcanization Activation Mechanism

        

**Topic:** Explainer

        

Zinc Oxide (ZnO) is the primary activator for sulfur vulcanization in the rubber industry, essential for tires, hoses, and footwear soles. ZnO reacts with stearic acid to form zinc stearate, which coordinates with accelerators to build stable, highly elastic cross-linked networks.

        
        
        
        
        
---

          ## 

          

        
---

        
---

          ## 

          

        
---

        
---

          ## 

          

        
---

        
---

          ## 

          

        
---

        
---

          ## 

          

        
---

        
---

          ## 

          

        
---

        
---

          ## 

          

        
---

        
---

          ## 

          

        
---

        
---

          ## 

          

        
---

        
---

          ## 

          

        
---

        
---

          ## 

          

        
---

        
        
---

          ## Frequently Asked Questions

          
### Why is stearic acid required alongside ZnO?

ZnO is insoluble in rubber and cannot interact with accelerators. Stearic acid reacts with ZnO to form zinc stearate, which is soluble and mobilizes the zinc ions to form active complexes.

### What is the difference between French process and direct process ZnO?

French process ZnO is produced from purified zinc metal vapor, yielding high purity (≥99.5%) and fine particle size. Direct process is produced directly from zinc ore, containing higher lead/cadmium impurities and coarser particles.

### Does ZnO prevent rubber aging?

Yes. ZnO exhibits excellent UV absorption and thermal conductivity. By absorbing UV light and dissipating heat during dynamic flexing (in tires), it protects the rubber from photo-thermal degradation.

### What is the CAS number for Zinc Oxide?

The CAS registry number for Zinc Oxide is 1314-13-2.

        
---

        

By NBT Technical Desk · Updated 2026-07-04

        

[Run a related diagnosis](/defect-doctor) · [Review standards](/standards) · [Browse materials](/products)

        

[Technical Editorial & Evidence Policy](/editorial-policy)