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        # How CPW Works as a Flame Retardant in PVC: The Complete Combustion Science

        

**Topic:** Explainer

        

Flexible PVC cable compounds must meet strict vertical flammability tests to comply with national standards such as **IS 694** in India or SABS in Africa. To achieve self-extinguishing behavior cost-effectively, cable compounders rely on the gas-phase flame retardant mechanism of chlorinated paraffins. Combining [NBT Diamond Grade NP CPW](/products/plasticizers/cpw-diamond) with antimony trioxide creates a synergistic flame-quenching barrier, allowing local wire manufacturers to pass flammability tests while optimizing production costs in a highly competitive B2B market.

        
        
        
        
        
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          ## Frequently Asked Questions

          
### What is the minimum CPW loading required to pass IS 694 flame tests?

Typically 10-15 PHR of NBT Diamond Grade CPW (52% Cl) in a standard DOP or DOTP-based flexible PVC formulation achieves LOI ≥ 28%, sufficient for IS 694 compliance. Adding 2-4 PHR Sb₂O₃ reduces the CPW requirement to 8-10 PHR.

### Does higher chlorine content CPW always give better flame retardancy?

Yes, for a given loading level - but higher chlorine grades also increase viscosity. This creates a practical ceiling at around 52% Cl for PVC compounding. Beyond 52%, processing difficulties outweigh the flame retardancy gain for most compounders.

### Can I use CPW alone for flame retardancy, without antimony trioxide?

Yes, but at significantly higher loading (20-25 PHR). The Sb₂O₃ synergist amplifies CPW efficiency roughly 2.5x. Using both together at lower loadings is more cost-effective and has less negative impact on mechanical properties.

### Does CPW affect electrical insulation properties of the PVC compound?

At recommended loadings (10-15 PHR), the impact is negligible. Volume resistivity typically remains above 10¹² Ω·cm. Excessive CPW loading (above 20 PHR) can reduce electrical resistance, which is a concern for high-voltage cable applications.

        
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By NBT Technical Desk · Updated 2026-07-04

        

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