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        # Stearic Acid in PVC Processing: External Lubrication, Internal Lubrication, and the Metal Release Mechanism

        

**Topic:** Explainer

        

Stearic acid is the primary external lubricant used in rigid PVC pipe and cable compounding in India and developing markets. By providing metal release and preventing plate-out on extruder dies, polymer-grade [NBT Stearic Acid](/products/additives/stearic-acid) ensures continuous production runs and high surface gloss.

        
        
        
        
        
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          ## Frequently Asked Questions

          
### Is stearic acid a stabilizer or a lubricant in PVC?

Primarily a lubricant (external), but it also contributes to stabilization indirectly  -  stearic acid reacts with metal components in Ca-Zn stabilizers to form calcium stearate, which provides internal lubrication and mild HCl scavenging.

### Why does my die get a yellow/brown build-up even with stearic acid in the formulation?

Plate-out is usually caused by either insufficient stearic acid loading (below 0.4 PHR for rigid PVC), the wrong grade (high iodine value = unsaturated fatty acids that polymerize on hot metal surfaces), or inadequate stabilizer loading causing localized thermal degradation that overwhelms the lubrication system.

### Can I use oleic acid instead of stearic acid as a lubricant in PVC?

No. Oleic acid (C18:1, unsaturated) polymerizes at PVC processing temperatures (160-200°C), forming a hard, dark resinous deposit on die surfaces rather than a lubricating monolayer. Always use saturated stearic/palmitic acid for PVC lubrication.

### What is the difference between stearic acid and zinc stearate in PVC?

Stearic acid (free fatty acid) provides external lubrication. Zinc stearate (metal salt of stearic acid) is an internal lubricant and stabilizer  -  it provides melt lubrication and HCl scavenging. In many formulations, both are used together for combined external and internal lubrication effect.

        
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By NBT Technical Desk · Updated 2026-07-04

        

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