Expandable Graphite

Due to the expandability and high temperature resistance, expandable graphite (EG) is an excellent flame retardant material. Expandable graphite and expanded graphite have unique pore structure and excellent physical and chemical properties. Alfa Chemistry provides customers with EG products to help you advance the research and development of innovative flame retardant materials.

Advantages

As a new type of material, expandable graphite has a simple and easy-to-operate preparation process. It is non-toxic, low-smoke, and drip-free when heated, and can adapt to various environments, which is a new type of environment-friendly flame retardant material.

Flame Retardant Mechanism

The volume of EG expands hundreds of times as the temperature increases, and a carbon layer is formed on the surface of the polymer to isolate the heat source. During the expansion process, EG absorbs a lot of heat and releases acid ions in the interlayer to promote dehydration and carbonization. At the same time, it can also combine with free radicals produced by combustion and inhibit chain reactions.

In addition, EG can be used in combination with phosphorus compounds and metal oxides to produce a synergistic effect, and a small amount can be added to achieve the purpose of flame retardant.

Preparation

• Chemical intercalation
• Electrochemical method
• Ultrasonic oxidation
• Vapor diffusion
• Molten salt method

Applications

• Flame Retardant Coating

The EG is added as a synergistic component to ordinary coatings. In the fire, the EG expands to form a non-combustible carbon layer, which can effectively block the radiation of heat to the substrate, prevent secondary combustion, and improve the high temperature resistance and fire resistance performance of material.

• Flame Retardant Sealing Material

EG can be used to prepare expanded sealant strips. In addition, the use of adhesive to bond the EG to the glass fiber tape carrier can also play a sealing role.

• Flame Retardant Plastic

At present, there have been a lot of reports on the application of EG to polyurethane foam, flame retardant polyurethane, flame retardant polyolefin, flame retardant styrene plastic, flame retardant rubber, etc.

• Fireproof Board

Due to its low density and high and low temperature resistance, EG can be added to fireproof sheets to enhance its fire resistance and heat insulation performance, and it can reduce the density of the sheet at the same time.

Research Information

Synergistic flame retardancy of EG and aluminum hypophosphite (AHP)

Hongyu Yang et al. explored the synergistic effect of EG and AHP on the flame retardancy of rigid polyurethane foam (RPUF). The results show that an excellent flame retardant synergistic effect between EG and AHP was observed in RPUF due to the combined effect of the physical barrier of EG and the catalytic AHP carbonization formation. The flame retardant mechanism of EG and AHP in RPUF is shown in figure below. [2]

Illustration of flame retardant mechanism of RPUF/EG10/AHP5 [2]

References

1. Bartłomiej Mazela, et al. (2020). "Expandable Graphite as a Fire Retardant for Cellulosic Materials—A Review," Forests 2020, 11(7), 755.
2. Hongyu Yang, et al. (2014). "Aluminum hypophosphite in combination with expandable graphite as a novel flame retardant system for rigid polyurethane foams," Polym. Adv. Technol. 25, 1034–1043.