Acrylic: Flammable or Flame-Resistant? An Authoritative Guide to Acrylic vs. Modacrylic Flammability

Acrylic is an extremely common synthetic fiber, widely used in apparel, home textiles, and industrial fields due to its lightweight, warm, and wool-like feel. However, the “flammability” of regular acrylic fabric remains a critical industry focus, especially as global markets impose increasingly strict fire safety standards, presenting significant challenges for exporters. Many are confused about the difference between acrylic and its “modified” version, Modacrylic. This guide will thoroughly clarify the fundamental differences from a technical perspective to help you make compliant and safe choices.

Core Conclusion: Acrylic is Flammable, Modacrylic is Flame-Resistant

The conclusion regarding the flammability difference between Acrylic and Modacrylic is unequivocal: regular acrylic is a flammable fiber, while modacrylic is a flame-resistant fiber. Although their names are similar, they have fundamental differences in chemical structure, burning behavior, and safety applications.

What is Acrylic?

Acrylic Fiber is a synthetic fiber polymerized from acrylonitrile monomers. According to the authoritative definition from the U.S. Environmental Protection Agency (EPA), the weight percentage of acrylonitrile units in acrylic fiber is at least 85%. It is a common textile raw material, but it is highly flammable, burns rapidly, and has a low Limiting Oxygen Index (LOI), classifying it as a flammable material.

What is Modacrylic?

Modacrylic Fiber is a chemically modified acrylic fiber. Also according to the EPA‘s definition, the weight percentage of acrylonitrile units in modacrylic fiber is less than 85%, but at least 35%. During polymerization, they are co-polymerized with a significant amount of flame-retardant comonomers (such as chlorine or phosphorus-containing monomers). This structure gives them natural, permanent flame resistance, classifying them as “Inherent FR” (Flame-Resistant) fibers with self-extinguishing properties.

Official Applications and Production Regulation

According to official U.S. EPA documentation, both fibers are synthetic polymer fibers with acrylonitrile as the main monomer. They have a wide range of uses, such as in the production of carbon fiber, apparel, home furnishings, carpets, and other industrial and consumer products (like paint roller covers). Because the production process involves acrylonitrile, the EPA has established National Emission Standards (NESHAP) to regulate hazardous air pollutant emissions during production. This reflects the industrial importance of these materials and the seriousness of their regulation.

Key Metric Comparison: Why the Huge Difference?

The vast difference in flammability between acrylic and modacrylic is primarily determined by their Limiting Oxygen Index (LOI), which in turn stems from their different chemical structures.

The Decisive Difference: Limiting Oxygen Index (LOI)

The Limiting Oxygen Index (LOI) is a critical metric for measuring a material’s fire performance, indicating the minimum oxygen concentration required to sustain combustion. The higher the LOI value, the more flame-resistant the material. Typically, fabrics with an LOI below 20% are considered flammable.

• Regular Acrylic: The typical LOI range is 17–20. This value is far below the approximate 21% oxygen concentration in the air, meaning it ignites easily and can sustain combustion in the air.
• Modacrylic: The typical LOI range is 26–33 (commonly ≥ 28). This value is significantly higher than the air’s oxygen concentration, meaning it is difficult to ignite in normal air, and even if ignited, it will self-extinguish immediately upon removal of the flame source.

Chemical Structure: The Root of the Difference

The LOI difference between the two is determined by their molecular chain structure:

• Regular Acrylic: Its main chain is polyacrylonitrile (≥85%) and contains no flame-retardant groups. When heated, it decomposes easily and produces flammable gases, fueling combustion.
• Modacrylic: It incorporates chlorine (Vinyl chloride) or phosphorus-containing comonomers during polymerization. These flame-retardant groups release flame-inhibiting free radicals during combustion and promote charring on the fiber surface, forming a heat and oxygen barrier that stops the flame from spreading.

Burning Behavior Comparison: Dangerous Flammability vs. Safe Self-Extinguishing

Under actual fire conditions, regular acrylic will accelerate a fire, while modacrylic effectively stops flame spread. Their behaviors are completely different.

The Burning Hazards of Acrylic

Regular acrylic is a highly flammable material. Its chemical structure makes it extremely dangerous when exposed to a flame source. When it makes contact with fire, it burns rapidly and will continue to burn even after the flame source is removed.

Its primary hazards are:

• Melting & Dripping: During combustion, acrylic fibers melt and form hot drips. If these molten drips stick to the skin, they can cause severe secondary burns.
• Toxic Gas Release: When acrylic burns at high temperatures, it releases highly toxic gases such as cyanide, posing a severe threat to the health and life of anyone trapped.

The Safety Features of Modacrylic

Modacrylic is a flame-resistant material. When exposed to a flame source, it will soften and shrink but does not melt and drip. It chars slowly, forming a barrier. Its most critical feature is that it is Self-extinguishing; as soon as the flame source is removed, combustion stops immediately, effectively preventing the fire from spreading and not producing toxic gases on the same level as regular acrylic.

How to Achieve Flame Resistance in Acrylic: Two Technical Paths

To obtain “acrylic-like” products with flame-resistant properties, there are two distinct technical paths in the market:

Path 1: Inherent FR – Choosing Modacrylic

This is the safest and most stable method. Instead of using regular acrylic, one directly chooses the Modacrylic fiber mentioned above. Its flame resistance comes from the fiber’s chemical structure, making it permanent. It will not degrade or disappear with washing or wear.

Path 2: FR Treatment – Processing Regular Acrylic

Regular acrylic fabric can also have its fire performance significantly improved through FR treatment technology. This method involves chemically adding flame retardants at the finished fabric stage.

• Implementation: By adding flame retardants or coatings (like organophosphorus or nitrogen-based flame retardants), a protective layer is formed on the acrylic fabric surface to reduce its burning speed.
• Durability Issues: The flame resistance from this treatment may not be permanent. Exporters must pay attention to its wash durability. Only fabrics using specific durable FR treatments (like the Proban process) can ensure good fire performance is maintained after multiple washes (e.g., after 50 washes).

Acrylic vs. Modacrylic: A Full Performance Comparison

Although the two are very similar in appearance and feel—both are soft, lofty, warm, and easy to dye—they differ vastly in safety performance, technical specifications, and cost.

Core Technical and FR Differences

Performance Item	Regular Acrylic	Modacrylic
Chemical Structure (EPA Standard)	≥85% Acrylonitrile	35–85% Acrylonitrile + FR Comonomers
Fiber Property	Regular Chemical Fiber	Inherent FR Fiber
Flammability Rating	Flammable	Flame-Resistant / Self-Extinguishing
LOI (Limiting Oxygen Index)	17–20 (Flammable)	26–33 (Flame-Resistant)
Behavior After Flame Removal	Continues to burn	Self-extinguishes
Melting & Dripping	Will drip (Hazardous)	Minimal/No Drip / Chars
Smoke Volume	Heavy black smoke	Low to medium smoke
Source of FR Property	Requires FR Treatment	Natural (Inherent)

Feel and Cost Differences

• Feel and Appearance: The two are very similar, both being soft, lofty, and warm. Modacrylic typically offers better dimensional stability and is less prone to shrinkage.
• Cost Difference: The price of Modacrylic is significantly higher than regular Acrylic. This is because its flame-retardant comonomers are more costly, and the production process is more complex.

Flammability Comparison: Acrylic vs. Other Common Fibers

The table below compares the fire performance of untreated regular acrylic with other common fibers:

Material	Burning Speed	Melting/Dripping	Toxic Gas Release	Fire-Resistance Rating
Acrylic	Fast	High	Cyanide, etc.	★★
Cotton	Medium	None	None	★★★
Polyester	Slow	Slight	Low	★★★★
Nomex (Aramid)	Does not burn	None	None	★★★★★
Kevlar (Aramid)	Does not burn	None	None	★★★★★

Note: Fire-Resistance Rating is a relative comparison.

Application Scenarios and Advice for Exporters

Due to the fundamental difference in flammability, exporters must be extremely cautious when selecting fabrics to ensure products comply with target market safety regulations.

Application Comparison: When to Choose Acrylic vs. Modacrylic

The application areas for these two fibers have almost no overlap. The wrong choice will lead to severe safety risks and compliance issues.

Use Category	Regular Acrylic	Modacrylic
Apparel & Knitwear	✔ Common	✔ Usable (Higher safety)
Industrial Protective Wear (FR)	✘ Absolutely Prohibited	✔ Core Material (FR Workwear)
FR Curtains / Stage Drapes	✘ Unsuitable	✔ Standard Material (NFPA 701)
Home Textiles	✔ Common	✔ Recommended (Safer)
Transportation Interiors (Aviation/Rail)	✘ Unsuitable	✔ Standard Material

Exporter Compliance Advice

For textile exporters, selecting acrylic fabrics that meet international fire standards is crucial.

1. Ensure Compliance Standards: You must select fabrics that meet target market fire standards (e.g., NFPA 701 or ASTM F1506).
2. Prioritize Inherent FR: In high-risk applications, Modacrylic should be prioritized over FR-treated acrylic because its flame resistance is permanent and reliable.
3. Review FR Treatment Technology: If choosing FR-treated regular acrylic, you must use a durable FR treatment and request wash durability test reports (e.g., proving it still meets standards after 50 washes).

For exporters needing high-standard FR solutions, ensuring supply chain professionalism is critical. For example, Begoodtex’s line of inherent FR Modacrylic fabrics is designed specifically to meet these stringent international standards, helping clients easily meet global market compliance demands.

FAQ (Frequently Asked Questions)