Halogen-Free Flame-Retardant TPE: UL 94 & Selection
Halogen-Free Flame-Retardant TPE Guide
TPE combines the soft elasticity of rubber with the processing efficiency of thermoplastics, making it widely used in wire and cable, electronic connectors, household appliance components, automotive parts, and industrial equipment. However, when products are used in power transmission, electronic devices, or environments exposed to high temperatures or open flames, flame-retardant performance becomes an essential material selection criterion in addition to softness, mechanical properties, and processability.
Conventional TPE is an organic polymer material that can burn when exposed to sufficient heat or flame. Therefore, flame-retardant performance is achieved through polymer selection, flame-retardant systems, and overall formulation design to reduce ignition potential and slow flame propagation.
As the electronics and electrical industries continue to place greater emphasis on safety, environmental protection, and regulatory compliance, Halogen-Free Flame-Retardant TPE has become an increasingly important material choice.
This article explains the fundamentals of halogen-free flame-retardant TPE, common flame-retardant mechanisms, UL 94 flammability classifications, and the key considerations for product design and material selection.
Learn how halogen-free flame-retardant TPE suppresses combustion and slows flame spread.
What Is Flame-Retardant TPE?
Flame-retardant TPE is a thermoplastic elastomer engineered through material structure or formulation design to exhibit lower flammability when exposed to fire, reduce flame propagation, and extinguish more quickly after the ignition source is removed.
Flame-retardant does not mean the material is completely non-combustible. Instead, it is designed to achieve the following:
● Delay ignition
● Reduce flame spread
● Shorten afterflame time after the ignition source is removed
● Minimize the risk of secondary ignition caused by molten dripping
● Reduce heat release during combustion
● Improve the safety of electrical and electronic products
The actual level of flame-retardant performance depends on factors such as product thickness, formulation, test method, and service conditions.
Therefore, selecting a material based solely on the term “flame-retardant TPE” is not sufficient. The applicable test standard, specimen thickness, and flame-retardant classification should also be verified.
What Is Halogen-Free Flame-Retardant TPE?
“Halogen-free” generally means that the flame-retardant system does not rely primarily on halogen-based flame retardants such as bromine or chlorine.
Conventional halogen-containing flame retardants provide excellent flame-retardant efficiency, but under certain combustion conditions they may generate corrosive gases and higher levels of smoke. As a result, halogen-free materials are often preferred for electronics, electrical equipment, communication devices, and products with higher environmental requirements.
Halogen-free flame-retardant TPE typically requires balancing the following properties:
● Flame-retardant performance
● Softness
● Tensile strength
● Elongation
● Heat resistance
● Surface quality
● Flowability
● Stable extrusion or injection molding performance
Excessive flame-retardant loading may increase hardness, reduce toughness, or alter processing flow characteristics, while insufficient loading may fail to achieve the required flame-retardant rating. Therefore, developing halogen-free flame-retardant TPE involves comprehensive formulation design that considers the polymer, flame-retardant system, compatibility, and processing conditions rather than simply adding flame retardants.
Common Flame-Retardant Mechanisms in TPE
Flame-retardant formulations typically rely on multiple mechanisms working together, including gas-phase and condensed-phase actions, rather than a single mode of protection.
Thermal and Oxygen Barrier
Some flame-retardant systems form a protective layer on the material surface when exposed to heat, reducing heat transfer into the material while limiting contact between oxygen and combustible gases.
A stable and continuous protective layer helps delay further polymer decomposition and combustion.
Char Layer Formation
Certain flame-retardant systems promote surface charring, forming an insulating carbon layer.
The char layer helps to:
● Block external heat
● Reduce continued polymer degradation
● Minimize the release of combustible gases
● Slow flame penetration into the material
The integrity and stability of the char layer directly affect flame-retardant performance.
Heat Absorption and Release of Non-Combustible Gases
Some halogen-free flame-retardant additives absorb heat during thermal decomposition, lowering the material surface temperature while releasing water vapor or other non-combustible gases that dilute combustible gases and oxygen in the combustion zone.
However, these systems generally require relatively high loading levels, making it important to consider their impact on TPE softness, density, and mechanical properties.
Suppression of Combustion Chain Reactions
Combustion is a chain reaction involving free radicals. Some flame-retardant systems interrupt these reactions, reducing the material’s ability to sustain combustion.
In practical formulations, multiple flame-retardant mechanisms are often combined to achieve both effective flame retardancy and balanced material properties.
What Is UL 94?
UL 94 is one of the most widely used flammability test standards for plastic materials. It evaluates the burning behavior of materials under specified specimen dimensions and test conditions.
Common UL 94 vertical burning classifications for TPE include:
| UL 94 Rating | General Description |
|---|---|
| V-0 | Short afterflame time after removal of the ignition source, with stricter requirements for burning drips |
| V-1 | Self-extinguishes within the specified time, but allows a longer afterflame time than V-0 |
| V-2 | Self-extinguishes within the specified time, but burning drips capable of igniting cotton may occur |
Among V-0, V-1, and V-2, V-0 is generally the most stringent classification.
However, UL 94 ratings must always be interpreted together with the tested specimen thickness. For example, the same material may achieve V-0 at a greater thickness but not necessarily at a thinner section.
When selecting materials, the following should be confirmed:
● Flame-retardant rating
● Tested specimen thickness
● Material color
● Actual product wall thickness
● Whether the result is based on formal certification or internal testing
● Whether the final product is subject to additional end-product safety regulations
A UL 94 material rating is not equivalent to a complete fire safety certification for the finished product. Additional testing may still be required depending on the intended application.
Applications of Halogen-Free Flame-Retardant TPE
Halogen-free flame-retardant TPE is commonly used in products requiring flexibility, electrical insulation, and flame-retardant performance, including:
● Wire and cable jacketing
● USB and Type-C cables
● Power cords and signal cables
● Electronic connector sleeves
● Cable bend protectors
● Plug and connector overmolding
● Soft components for household appliances
● Communication cables
● Automotive electronic wire harness components
● Charging equipment and accessories
● Industrial control cables
● Soft injection-molded parts requiring flame-retardant performance
Different applications require different levels of flame retardancy, softness, heat resistance, flex fatigue resistance, and processing methods. Materials should therefore be selected according to the specific product design requirements.
How to Select the Right Halogen-Free Flame-Retardant TPE
Material selection should not be based solely on the UL 94 rating. The overall application requirements should also be evaluated.
The following factors should be considered:
Regulatory Requirements
Different products may need to comply with different industry standards, including:
● UL 94
● RoHS
● REACH
● Halogen-Free requirements
● Customer-specific specifications
Regulatory requirements vary across markets and end-product brands, so applicable standards should be confirmed early in product development.
Processing Method
Different processing methods require different levels of material flow and thermal stability, such as:
● Injection molding
● Extrusion
● Co-extrusion
● Overmolding
Flame-retardant materials are generally more sensitive than standard TPE formulations and therefore require appropriate processing conditions.
Mechanical Properties
While improving flame-retardant performance, the material should also maintain:
● Softness
● Tensile strength
● Elongation
● Resilience
● Abrasion resistance
● Flex fatigue resistance
Avoid sacrificing required product performance solely to achieve a higher flame-retardant rating.
Service Environment
For products used in high-temperature or outdoor environments, the following should also be evaluated:
● Heat aging resistance
● Weather resistance
● UV resistance
● Damp heat resistance
● Chemical resistance
Considering the complete service environment helps improve product durability and long-term reliability.
DING JI POLYMER Halogen-Free Flame-Retardant Material Solutions
DING JI POLYMER offers a wide range of halogen-free flame-retardant TPS compounds for electronics, electrical products, wire and cable, industrial equipment, and consumer electronics applications.
Customized compounds are available with different flame-retardant ratings and processing characteristics to provide:
● Excellent processing flowability
● Stable injection molding and extrusion performance
● Soft touch
● Good mechanical properties
● Heat aging resistance
● Weather resistance
● Customized hardness options
Among them, the TOP-PELLET® CE Series is DING JI POLYMER’s halogen-free flame-retardant TPS compound series developed specifically for electronics, electrical products, and cable applications, providing tailored flame-retardant and processing solutions for different product requirements.
Conclusion
As the electronics, communication, and new energy industries continue to demand higher levels of product safety and environmental compliance, halogen-free flame-retardant TPE has become an increasingly important material choice.
An effective flame-retardant material should not only comply with relevant regulations but also provide excellent processing efficiency, mechanical performance, and long-term reliability. Through comprehensive material design, optimized flame-retardant systems, and application-specific evaluation, the optimal balance among safety, product performance, and manufacturing efficiency can be achieved.
- Frequently Asked Questions (FAQ)
-
Does Halogen-Free Flame-Retardant TPE Always Achieve UL 94 V-0?
Not necessarily.
Whether a material can achieve a V-0 rating depends on its formulation, specimen thickness, and test conditions. Different products may produce different test results.Does Halogen-Free Mean the Material Is Completely Non-Combustible?
No.
Flame-retardant materials are designed to reduce the risk of combustion, slow flame propagation, and shorten afterflame time—not to make the material completely non-combustible.Are Flame-Retardant Materials Always Harder?
Not necessarily.
Flame-retardant formulations may affect material hardness and mechanical properties. However, with appropriate polymer selection and formulation design, it is still possible to achieve a balance among softness, processability, and flame-retardant performance.Can Flame-Retardant TPE Be Used for Extrusion?
Yes.
Many flame-retardant TPE formulations are suitable for extrusion applications, including wire and cable jacketing, communication cables, and protective sleeves. However, the appropriate material should still be selected according to the product design and processing equipment.