Red Phosphorus Flame Retardant

Cross-Linking And Grafting Technology

Red phosphorus is a purple-red or slightly brown amorphous powder. Alfa Chemistry provides red phosphorus flame retardants, which have the advantages of good flame retardant effect, high flame retardant efficiency, halogen-free and economical.

Flame Retardant Mechanism

On the one hand, red phosphorus and plastic materials undergo a series of changes in the process of burning together to form polymetaphosphoric acid, which forms a sticky and thin film wrapped around the surface of the polymer, thus reducing the contact with oxygen and inhibiting the process of oxidation.

On the other hand, phosphoric acid, metaphosphoric acid, polymetaphosphoric acid, etc. formed by red phosphorus act as dehydrating agents to promote the dehydration of polymers into carbon, which increases the effect of flame retardant.

Special Treatment Technology

Direct use of red phosphorus flame retardants has many problems, including easy absorption of moisture, poor compatibility with resins, easy coloring of products, and flammability. Therefore, in order to continue to use red phosphorus as a flame retardant, it is necessary to carry out proper treatment of red phosphorus, such as microencapsulation coating treatment and whitening treatment of red phosphorus.

Cross-Linking And Grafting Technology

  • Microencapsulation coating treatment
  • Microencapsulation is a special coating technology that coats red phosphorus. It usually seals and coats red phosphorus particles through a polymer film. The microencapsulated red phosphorus not only improves the compatibility with plastic polymers, but also improves the ignition point. At the same time, due to the coating of the polymer film, it is isolated from the air and is not easy to be oxidized.

  • Whitening treatment
  • In the process of making red phosphorus microcapsules, a layer of white aluminum hydroxide can be deposited on its surface, that is, whitening treatment, which can improve the color limitation and make it more widely used.


Mainly used in PE, PP, EVA, PC, PA, PBT, PET and epoxy, phenolic, unsaturated polyester, etc., especially suitable for products that can meet the requirements with a small amount of flame retardant.

Research Information

The research by Longchao Du et al. showed that microencapsulated red phosphorus (MRP) has a synergistic effect with hydrotalcite. Adding a certain amount of MRP clearly resulted in an increase in LOI value and a decrease in HRR and MLR as well as loading of hydrotalcite in the EVA blend, while maintaining a V-0 rating in the UL-94 test.[1]

Effects of MRP on HRR and MLR of EVA/hydrotalcite compositesEffects of MRP on HRR and MLR of EVA/hydrotalcite composites [1]

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  1. Longchao Du, et al. (2009). "Flammability characteristics and synergistic effect of hydrotalcite with microencapsulated red phosphorus in halogen-free flame retardant EVA composite," Polymer Degradation and Stability 91(5), 995-1001.
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