Optimizing Flame Retardant Performance in PVC Cable Compounds

In the production of PVC cable compounds, balancing superior flame retardancy with physical, mechanical, and electrical integrity is essential. Flame retardancy is primarily measured by the Limiting Oxygen Index (LOI)—the minimum oxygen concentration required to support combustion. For high-safety applications, a material is generally considered high-performing when the LOI exceeds 30%.

1. The Role of Plasticizers

Plasticizers such as Dioctyl Terephthalate (DOTP), Trioctyl Trimellitate (TOTM), and Tricresyl Phosphate (TCP) significantly impact smoke emission and flame resistance:

• Oxygen Index Impact: Research shows that as the proportion of plasticizer increases, the LOI typically decreases across most plasticizer types.
• Smoke Suppression: While most plasticizers increase smoke density, phosphate-containing plasticizers and TOTM provide a synergistic benefit by enhancing smoke suppression in the PVC matrix.

2. Synergistic Effects of Flame Retardants

The addition of inorganic flame retardants is the most effective way to boost the LOI. While Antimony Trioxide (Sb₂O₃) is a standard additive, it has limitations when used alone.

• Synergy is Key: To achieve ultra-high LOI, a composite system is required. For example, combining Sb₂O₃ with Zinc Borate (ZB) and Magnesium Hydroxide (Mg(OH)₂) yields a significantly higher flame retardant effect than Sb₂O₃ alone.

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