Microencapsulated Red Phosphorus: A Multi-Material Application Atlas of an Efficient Halogen-Free Flame Retardant

Red phosphorus itself is an efficient flame retardant, with high phosphorus content, low addition levels, and outstanding flame-retardant efficiency. However, ordinary red phosphorus is prone to moisture absorption and oxidation, releasing highly toxic phosphine (PH₃) gas, showing poor compatibility with polymer materials, and having deep color and easy migration. These problems severely restrict its practical application. Microencapsulation technology forms a continuous, dense protective film on the surface of red phosphorus particles, greatly reducing its moisture absorption rate, effectively inhibiting phosphine release, and raising the ignition point from about 240°C to above 300°C. The encapsulated red phosphorus exhibits significantly improved compatibility and does not generate toxic gases during processing. It is precisely this technological breakthrough that enables microencapsulated red phosphorus to be widely used in numerous polymer material fields.
Thermoplastic resins are the most extensive application field for microencapsulated red phosphorus. In nylon (PA), an addition of only 7%-8% enables the material to meet the UL94 V-0 (1.6 mm) flame-retardant rating. It is also widely used in polyester (PET, PBT), polycarbonate (PC), polyolefins (PP, PE), EVA, and other materials. In addition, microencapsulated red phosphorus can be used for flame-retardant modification of polyoxymethylene (POM).
In thermosetting resin systems, microencapsulated red phosphorus is widely used in materials such as epoxy resin, phenolic resin, and unsaturated polyester. In these systems, encapsulated red phosphorus not only provides efficient flame retardancy but also maintains good processing and mechanical properties.
In the rubber and elastomer field, microencapsulated red phosphorus is applicable to butadiene rubber, ethylene-propylene rubber, silicone rubber, and others. In polyurethane (PU) foam, encapsulated red phosphorus can improve foaming performance and thermal insulation. In PC/ABS alloys, microencapsulated red phosphorus can also be compounded with other flame retardants to form a synergistic flame-retardant system. In addition, it is widely used in end-use scenarios such as wire and cable materials, conveyor belts, electronic and electrical appliances, automotive interiors, and fiber textiles.
Hongtaiji Company adopts a multi-layer microencapsulation process. Its microencapsulated red phosphorus products have an effective red phosphorus content of ≥80%, an ignition point of ≥300°C, phosphine release below 1 ppm, and moisture absorption of ≤1.2%. The products are widely used for flame-retardant modification of thermoplastic resins such as PET, PA, PE, and EVA, as well as thermosetting resins such as epoxy, phenolic, and unsaturated polyester, and rubber products.