Flame Retardant Requirements for Rubber Materials Explained: The Standard Behind Safety

Flame Retardant Requirements for Rubber Materials Explained: The Standard Behind Safety

Rubber materials are widely used in modern industry and life, from car tires and seals to cable sheathing and household equipment. However, the flammability of rubber is also an important safety issue, especially in areas such as electrical equipment and building materials. To ensure safety in use, the flame retardancy of rubber materials often needs to be rigorously evaluated and graded. In this paper, we will introduce in detail the classification, testing standards, influencing factors of rubber flame retardant grade and its importance in practical applications.

I. Overview of Flame Retardancy of Rubber

The flame retardancy of rubber refers to the combustion behavior of rubber materials under the action of an ignition source, including the ease of ignition of the material, the flame 

propagation speed, the residue after burning and its contribution to the spread of fire. The flame retardancy of rubber is important for electrical insulation, building fire prevention, and automobile safety. In order to assess the flame retardancy of rubber materials, a series of test methods and standards are usually used, which are graded according to the burning characteristics of rubber materials under different conditions.

Ⅱ.The common rubber flame retardant grade and test standards

1. UL94 standard (Underwriters Laboratories)

UL94 standard is one of the widely used flame retardancy test standards worldwide, especially in the field of plastic and rubber materials.UL94 mainly classifies materials into several flame retardancy grades by testing their burning characteristics in vertical and horizontal directions. The main ratings include:

- V-0: When the material is ignited, the flame is extinguished within 10 seconds without dripping combustibles. v-0 is the highest flame retardancy rating, indicating that the material will self-extinguish quickly at high temperatures and will not ignite a secondary source of ignition.

- V-1: When the material is ignited, the flame is extinguished within 30 seconds and the dripping should not ignite the cotton. v-1 is slightly lower than v-0, but still has good flame retardancy.

- V-2: After the material is ignited, the flame is extinguished within 30 seconds and drips may ignite the cotton. v-2 is a lower level than v-1 and is suitable for applications where flame retardancy is not too demanding.

- HB (Horizontal Burning): When materials are placed horizontally, the flame expands more slowly before burning. the HB rating is usually applied to rubber materials with lower requirements for flame retardancy.

The V-0, V-1 and V-2 levels of the UL94 test are commonly used to evaluate the performance of materials under vertical burning conditions, while the HB level is used to evaluate horizontal burning. The test results of different levels have important reference value for the selection of materials in practical applications.

2. Oxygen Index (OI) method

Oxygen Index (OI) method is a common method to evaluate the flame retardancy of materials, mainly by measuring the minimum concentration of oxygen required to maintain the combustion of the material to evaluate its flame retardancy. The higher the Oxygen Index, the more difficult it is for the material to sustain combustion in air, and therefore the better the flame retardancy. Based on the oxygen index value, materials can be categorized as follows:

- Below 21%: Flammable materials. These materials are extremely flammable in air (21% oxygen concentration) and are not suitable for use in applications where fire protection is required.

- 21% to 28%: Non-combustible materials. This type of material is difficult to burn in air, has a certain degree of flame retardant properties, and is suitable for use in occasions with moderate fire protection requirements.

- Higher than 28%: flame retardant materials. These materials are almost impossible to sustain combustion in air and are suitable for applications with high fire resistance requirements.

Due to its simplicity and intuition, the oxygen index method is widely used in the flame retardancy test of rubber, plastic and other materials, especially in the occasions where quantitative evaluation of the burning behavior of materials is required.

3. DIN 4102 standard (Germany)

DIN 4102 is a German standard for flame retardancy testing of building materials, which is widely used in European countries. The standard categorizes materials into a number of classes based on their behavior in a fire, mainly including:

- Class B1 (flame-retardant materials): materials that show good flame-retardant properties in a fire, are difficult to ignite and have a slow flame propagation rate, and are usually used for highly demanding building materials.

- Class B2 (ordinary combustible materials): the material can burn under certain conditions, the flame propagation speed is fast, suitable for medium requirements of the application.

- Class B3 (highly combustible materials): the material is extremely flammable, the flame propagation speed is fast and it is usually not suitable for applications requiring fire protection.

The DIN 4102 standard is widely used in the construction industry, especially when evaluating fireproofing materials for the interior and exterior of buildings.

4. EN 13501-1 standard (Europe)

EN 13501-1 is the European standard for the fire performance of building materials and covers classes of fire resistance from class A1 (non-combustible materials) to class F (flammable materials). This standard is widely used to assess the performance of building materials in fire. The specific definitions of each class are as follows:

- Class A1: Non-combustible materials. They do not produce any significant flames, smoke or burning material in a fire.

- Class A2: Virtually non-combustible material that exhibits minor burning but does not produce toxic fumes or significant flames.

- Class B: Lower combustion performance with some flame retardancy. Suitable for building materials requiring moderate fire resistance.

- Class C-F: From refractory to flammable, the combustion performance of the material gradually increases as the class decreases, suitable for applications with different fire protection requirements.

The EN 13501-1 standard provides a comprehensive fire retardant rating system through comprehensive evaluation of the performance of materials under actual fire conditions, which is suitable for the selection of materials for different application scenarios in the construction industry.

Ⅲ.Factors affecting the flame retardancy of rubber

The flame retardancy of rubber materials is affected by a variety of factors, including chemical composition, additives, physical structure and so on. Understanding these factors is essential to improve the flame retardancy of rubber.

1. Chemical composition

The chemical composition of rubber directly affects its combustion characteristics. Natural rubber (NR) and most synthetic rubbers (e.g. SBR, BR) contain a large number of hydrocarbons in their structure, which makes them prone to decomposition and release of flammable gases at high temperatures, thus promoting combustion. In contrast, certain specialty rubbers, such as chloroprene rubber (CR) and fluoroelastomer (FKM), have high thermal stability and flame retardancy due to the presence of halogen elements in their molecular structure.

2. Application of flame retardants

The addition of flame retardants is a common method to improve the flame retardancy of rubber. Commonly used flame retardants include halogen compounds, phosphorus compounds, aluminum hydroxide, magnesium hydroxide and so on. These flame retardants inhibit the combustion of rubber through different mechanisms such as:

- Physical isolation: e.g. Aluminum hydroxide and magnesium hydroxide, which generate water vapor by heat absorption and decomposition during the combustion process, cooling the combustion zone and diluting the combustible gases.

- Chemical inhibition: e.g. halogenated flame retardants release hydrogen halide gas during the combustion process, inhibiting the combustion chain reaction.

- Carbon formation: e.g. phosphorus compounds form a stable carbon layer at high temperatures to isolate oxygen and protect the internal structure of the material.

The selection and dosage of flame retardants need to be adjusted according to the specific application requirements of the rubber, in order to improve the flame retardant properties while minimizing the adverse effects on the mechanical properties and processing performance of rubber materials.

3. Physical structure

The physical structure of rubber materials, such as molecular weight, cross-linking degree, crystallinity, etc., also has an impact on their flame retardancy. Higher cross-linking degree and crystallinity usually improve the thermal stability of the material, making it more difficult to decompose and burn at high temperatures. In addition, the introduction of nanomaterials, such as nanosilica and nano-alumina, can also improve the flame retardancy of materials by enhancing their thermal stability and physical strength.

Ⅳ.The practical application of rubber flame retardancy

In practical applications, the flame retardancy of rubber directly affects its safety and service life. In the following fields, the flame retardant property of rubber is especially important:

1. Cable sheathing

Cable sheathing materials need to have good insulation and flame retardancy to prevent the spread of fire in case of electrical equipment failure. Low Smoke and Halogen Free Flame Retardant Rubber (LSZH) is currently the preferred material for cable sheathing, which does not produce toxic fumes during combustion and is characterized by slow flame propagation.

2. Automobile industry

In the automotive industry, rubber materials are widely used in tires, seals, gaskets and other components. These parts work under high temperature, friction and other harsh conditions, so they need to have good flame retardant properties, especially for the battery pack seals of electric vehicles, flame retardant requirements are more stringent.

3. Construction materials

The application of rubber materials in the construction industry mainly includes flooring, sealing materials, waterproof layer and so on. The fire performance of building materials is directly related to the overall safety of the building, so the flame retardant requirements for rubber materials are high, especially in high-rise buildings and public facilities.

4. Aerospace

In the aerospace field, rubber materials are used for seals, insulating materials and so on. These materials work at high temperatures and high pressures, so they need to have excellent flame retardant properties to ensure the safety of aircraft and spacecraft.

The flame retardancy of rubber materials is one of the key factors determining their application in many fields. By studying various aspects of the chemical composition, additives, and physical structure of rubber materials, their flame retardancy can be significantly improved. For rubber materials in specific applications, they should be selected according to their flame retardancy level and actual needs, in order to ensure the safety and reliability of the use of materials. In the future, with the progress of science and technology, more efficient and environmentally friendly flame retardants and new rubber materials will continue to emerge, providing more comprehensive solutions for fire safety in various industries.

Ⅴ.Rubber Flame Retardants from YINSU Flame Retardant Corporation

YINSU Flame Retardant Company is committed to providing comprehensive rubber flame retardant solutions to meet the stringent safety and performance requirements of industrial applications. Our products include:

Red Phosphorus Masterbatch XJ-85M: This is a halogen-free flame retardant masterbatch designed specifically for rubber materials, which provides excellent flame retardancy during the vulcanization process while maintaining the physical properties of the material.

Red Phosphorus Compound Powder XJ-A2: This powdered non-halogenated flame retardant is suitable for a wide range of rubber formulations, effectively reducing the burning rate of the material and improving its safety under harsh conditions.

Our range of rubber flame retardants, including XJ-85M and XJ-A2, represent highly effective flame retardancy that ensures that rubber materials meet the necessary flame retardancy standards while taking into account environmental impact and ease of processing. YINSU Flame Retardant's rubber flame retardant products are the ideal choice when you are looking for reliable, high-performance flame retardant solutions.