How to use OI to quickly assess the flame retardancy of PVC materials ?

Why is Oxygen Index (OI) the "Gold Standard" for Evaluating PVC Flame Retardancy?

In industries such as wire and cable, electrical plugs, and construction materials, the flame retardancy of PVC directly impacts product safety. The Oxygen Index (OI), an internationally recognized metric, scientifically measures a material’s combustion behavior in fire scenarios. This article combines lab data + industry case studies to explain the relationship between OI and PVC flame retardancy.

1. What is Oxygen Index (OI)?

① Definition & Testing Standards

Oxygen Index (OI): The minimum oxygen concentration (%) required for a material to sustain combustion in a nitrogen-oxygen mixture.

Testing Standards: ASTM D2863 or ISO 4589 (sample size: 80mm×10mm×4mm).

② OI Classification & Flame Retardancy Levels

OI Range	Flame Retardancy Level	Combustion Behavior	Typical Applications
<22%	Flammable	Sustained burning, no self-extinguishing	General packaging
22%-27%	Slow-burning (Self-extinguishing)	Extinguishes slowly after flame removal	Standard PVC pipes
28%-35%	Flame-retardant (UL94 V-0)	Self-extinguishes within 10 seconds	Wires, cables, plugs
>35%	Highly flame-retardant	Extremely difficult to ignite, slow burn rate	Aerospace, automotive parts

2. How to Use OI to Assess PVC Flame Retardancy?

① Basic Evaluation Criteria

OI <26%: Fails UL94 V-0, high flammability risk (requires flame retardant additives).

OI 28%-32%: Typically meets UL94 V-0 (suitable for most electrical products).

OI ≥35%: High flame-retardant grade (for extreme environments like high-temperature or high-voltage applications).

② Real-World Test Data Comparison

PVC Type	OI Value	UL94 Rating	Combustion Behavior
Standard PVC (no additives)	23%	Not rated	Sustained burning, dripping
Flame-retardant PVC (Sb₂O₃)	30%	V-0	Self-extinguishes in ≤3 sec, no dripping
Halogen-free PVC	36%	V-0	Extremely difficult to ignite

Key Takeaway: PVC with OI ≥28% usually meets UL94 V-0, but additional tests (e.g., glow-wire ignition) may be required. 

3. Key Factors Affecting PVC’s Oxygen Index

① Material Formulation Impact

Factor	Effect on OI	Optimization Method
Chlorine Content	PVC inherently contains chlorine (OI≈23%)	Use high-chlorine PVC (e.g., CPVC)
Flame Retardant Type	Antimony trioxide (Sb₂O₃) +5-8% OI	Sb/P-N composite flame retardants
Fillers	Aluminum hydroxide (Al(OH)₃) +3-5% OI	Add 40-60% Al(OH)₃
Plasticizers	DOP reduces OI (-2-4%)	Switch to phosphate-based flame-retardant plasticizers

② Production Process Impact

Mixing uniformity: Poor dispersion of flame retardants may cause OI fluctuations (±2%).

Processing temperature: Excessive heat (>210°C) may degrade additives, lowering OI.

4. How to Choose the Right Flame-Retardant PVC Granules?

① Select OI Range Based on Application

Household plugs: OI ≥28% (UL94 V-0) 

Automotive wiring: OI ≥32% (heat-resistant, anti-aging)

Aerospace electronics: OI ≥35% (halogen-free, low smoke/toxicity)

② 3-Step Verification Process

Check certifications: UL card, SGS reports (confirm OI & UL94 rating). 

Conduct burn test: Use a lighter (compliant PVC should self-extinguish).

Inspect cross-section: High-quality flame-retardant PVC should be uniform in color and free of impurities.

Safety First—Material Matters!

Oxygen Index (OI) is a critical metric for evaluating PVC flame retardancy. Choosing high-OI PVC granules ensures product safety and compliance. INPVC has specialized in flame-retardant PVC R&D for 30+ years, providing reliable solutions !

Oxygen Index (OI) serves as a critical metric for evaluating PVC flame retardancy, where choosing high-OI PVC granules directly translates to enhanced product safety and regulatory compliance. INPVC combine decade-long expertise in flame-retardant PVC R&D with cutting-edge in-house laboratory facilities to deliver superior material solutions.

Backed by stringent quality control protocols, we guarantee:

✓ Batch-to-batch consistency

✓ Full traceability from raw materials to finished granules

✓ Compliance with international standards (UL, REACH, RoHS)

Trusted by leading electrical manufacturers across 30+ countries, INPVC continues to pioneer safer, smarter flame-retardant solutions for global applications.