Chlorinated Paraffins: Flame Retardants, Plasticizers, and Lubricant Additives

Why Chlorinated Paraffins Matter

Chlorinated paraffins (CPs) represent one of the most versatile and widely used classes of industrial additives in modern polymer processing and metalworking. Their unique combination of flame retardancy, plasticizing efficiency, and extreme-pressure lubrication properties makes them indispensable across a diverse range of industries, including plastics, rubber, paints and coatings, adhesives, sealants, textiles, and metalworking fluids. As cost-effective alternatives to more expensive specialty additives, chlorinated paraffins continue to play a critical role in enabling high-performance, fire-safe materials for construction, automotive, electrical, and consumer applications.

What distinguishes chlorinated paraffins is their remarkable multifunctionality. The same chemical backbone that provides flame retardancy through gas-phase radical scavenging also delivers plasticization by reducing intermolecular forces in polymer matrices, and imparts extreme-pressure lubrication through the formation of boundary films on metal surfaces. This versatility, combined with their relatively low cost and broad compatibility with various polymer systems, has established chlorinated paraffins as foundational additives in modern industrial chemistry.

Types of Chlorinated Paraffins

• Chlorinated paraffins (CPs) — a class of organic compounds produced by the chlorination of n-paraffin feedstocks. The resulting products are complex mixtures of polychlorinated n-alkanes with varying chain lengths and degrees of chlorination. They are generally unreactive and stable during storage at normal temperatures.
• Short-chain chlorinated paraffins (SCCPs) — CPs with carbon chain lengths primarily in the C10 to C13 range. These are characterized by lower molecular weight, higher chlorine content relative to chain length, and lower viscosity. SCCPs are primarily used in metalworking applications and PVC processing.
• Medium-chain chlorinated paraffins (MCCPs) — CPs with carbon chain lengths in the C14 to C17 range. MCCPs offer a balance between volatility and compatibility, making them suitable for a wide range of plasticizer and flame retardant applications in plastics, rubber, coatings, and adhesives.
• Long-chain chlorinated paraffins (LCCPs) — CPs with carbon chain lengths in the C18 to C30 range. LCCPs exhibit higher molecular weight, lower volatility, and greater thermal stability compared to shorter-chain variants. They are particularly valued in high-temperature processing environments and applications requiring low migration.

Short Profiles of Chlorinated Paraffins from Alfa Chemistry

Selecting the Right Chlorinated Paraffin

Mechanism of Action: Flame Retardancy

Chlorinated paraffins achieve flame retardancy through two primary mechanisms:

• Gas-phase free radical scavenging — During thermal decomposition, chlorinated paraffins release hydrogen chloride (HCl), which acts as a free radical scavenger in the gas phase. HCl interferes with the radical chain reactions that sustain combustion, effectively suppressing flame propagation. The main volatile degradation product is HCl, which is eliminated in two distinct steps during thermal degradation.
• Condensed-phase char promotion — The thermal degradation of chlorinated paraffins generates reactive species that can modify the thermal degradation mechanism of the polymer, promoting cross-linking and char formation that creates a protective barrier against heat and oxygen. In mixtures with polymers, the volatilization of the polymer is initially increased during dehydrochlorination, but in the resulting residue, volatilization occurs at a lower rate.

Mechanism of Action: Plasticization

As secondary plasticizers, chlorinated paraffins function by intercalating between polymer chains, reducing intermolecular forces and increasing free volume. This results in improved flexibility, processability, and low-temperature properties. Their compatibility with PVC and other polar polymers makes them particularly valuable in flexible PVC formulations, where they can partially replace more expensive primary plasticizers while also contributing flame retardancy.

Mechanism of Action: Extreme-Pressure Lubrication

In metalworking fluids and lubricants, chlorinated paraffins function as extreme-pressure (EP) additives. Under the high temperatures and pressures generated during metal cutting and forming operations, chlorinated paraffins react with metal surfaces to form a protective boundary film that reduces friction, prevents welding, and extends tool life. Recommended treat rates in metalworking fluids typically range between 2 and 40% depending on the intended machining operation.

Chain Length Selection: SCCP vs. MCCP vs. LCCP

• SCCPs (C10-C13) — Offer the lowest viscosity and highest chlorine content per unit mass. Preferred for applications requiring rapid dispersion, low-temperature performance, and maximum flame retardant efficiency. Commonly used in metalworking fluids, PVC processing, paints, adhesives, sealants, leather fat liquors, plastics, rubber, and textiles.
• MCCPs (C14-C17) — Provide a balanced combination of compatibility, thermal stability, and flame retardancy. Available in multiple viscosity grades (40 liquid, 45 liquid, 52 liquid, 135, 137) to suit different processing requirements. Widely used in PVC, rubber, coatings, sealants, and adhesives.
• LCCPs (C18-C30) — Exhibit the highest molecular weight, lowest volatility, and greatest thermal stability. Preferred for high-temperature processing applications and formulations requiring minimal migration. Used in flame retardant coatings, rubber conveyor belts, cable materials, epoxy resins, and polyester systems.

Chlorine Content and Performance

The chlorine content of chlorinated paraffins typically ranges from 27% to 70% by weight. Higher chlorine content generally provides enhanced flame retardancy, increased density, and higher viscosity, while lower chlorine content offers better compatibility with non-polar polymers and lower viscosity for easier handling. Common grades include:

• 27-29% Chlorine — Low-chlorine, low-viscosity liquids (e.g., Chlorinated Paraffin 30 liquid: 1.000-1.040 g/cm³, dynamic viscosity 90-150 mPa·s at 20°C). Used where minimal flame retardancy is required and plasticization is the primary function.
• 35-42% Chlorine — Mid-range chlorine content liquids (e.g., Chlorinated Paraffin 35 liquid: 1.040-1.110 g/cm³; Chlorinated Paraffin 40 liquid: 1.110-1.160 g/cm³). Provide a balance of plasticization and flame retardancy for general-purpose applications.
• 50-63% Chlorine — High-chlorine content liquids and highly viscous products (e.g., Chlorinated Paraffin 50 liquid: 1.15-1.25 g/cm³, dynamic viscosity 3700-6200 mPa·s at 20°C; MCCPs 135: 59-63% Cl, 1.390-1.440 g/cm³). Deliver maximum flame retardant performance with excellent chemical resistance and heat stability.
• 70% Chlorine — The highest chlorine content grade, available as a white/off-white powder. Provides maximum flame retardancy with minimal plasticization. Used in demanding flame retardant applications such as FR coatings, cable materials, and rubber conveyor belts.

Practical Usage & Dosage

The effective dosage of chlorinated paraffins depends strongly on the polymer system, desired properties, chlorine content, and the presence of other additives. The following ranges serve as starting points; always validate with small-scale compounding and performance testing.

Typical Ranges by Application

• PVC Plasticization and Flame Retardancy: 5-30 phr — Chlorinated paraffins are used as secondary plasticizers in PVC formulations, typically replacing 10-30% of primary plasticizers. Higher loadings (15-30 phr) provide enhanced flame retardancy while maintaining flexibility and processability.
• Rubber and Elastomers: 10-40 phr — In rubber compounding, chlorinated paraffins function as both plasticizers and flame retardants. Used in chlorinated rubber paints, rubber conveyor belts, cable materials, and industrial rubber products.
• Coatings and Paints: 5-20 wt% — Incorporated into fire-retardant coatings, traffic paints, and industrial coatings to improve flame resistance and film flexibility.
• Metalworking Fluids: 2-40 wt% — Used as extreme-pressure additives in straight oils, soluble oils, and other metalworking fluid formulations. The recommended treat rate depends on the severity of the machining operation.
• Adhesives and Sealants: 5-25 wt% — Added to improve flexibility, tackiness, and flame resistance in various adhesive and sealant formulations.

Documented Examples

• Chlorinated Paraffin 70% in Rubber Conveyor Belts: Provides excellent flame retardancy and chemical stability for conveyor belt applications requiring fire safety compliance.
• MCCPs in PVC Formulations: Medium-chain chlorinated paraffins (40-52% chlorine) offer good compatibility, improved flexibility, and enhanced fire performance in PVC compounds, supporting applications requiring controlled viscosity and long-term stability.
• Chlorinated Paraffins (C23, 43% Chlorine) in Fire-Retardant Canvas: Functions as a flame retardant for fire-retardant and waterproof canvas materials, demonstrating the effectiveness of long-chain CPs in textile applications.
• Microencapsulated Long-chain Chlorinated Paraffin (MCP): Flame-retardant rigid polyurethane foam (MCP/RPUF) prepared with 20% MCP as a flame retardant can pass the UL-94 V-0 flame retardancy test. [1]

Synergy & Hybrid Approaches

Chlorinated paraffins are often used in combination with other additives to achieve enhanced performance:

• Chlorinated Paraffins + Metal Compounds — The combination of chlorinated paraffins with metal compounds generates reactive species that modify the thermal degradation mechanism of the polymer, providing enhanced flame retardancy.
• Chlorinated Paraffins + Antimony Trioxide — A well-established synergistic combination in halogenated flame retardant systems, where antimony trioxide enhances the flame retardant efficiency of the chlorine-containing additive. [2]
• Chlorinated Paraffins + Phosphorus-Based FRs — Combining chlorinated paraffins with phosphorus-containing flame retardants can provide complementary gas-phase and condensed-phase mechanisms for enhanced fire performance.

Related Resources

• Chlorinated Flame Retardants Overview

References

1. Yang, Zhitong, et al. ChemNanoMat 9.2 (2023): e202200473.
2. Zhang, Ping, et al. Energy Conversion and Management 51.12 (2010): 2733-2737.