As an efficient halogen-free and environmentally friendly flame retardant material, red phosphorus flame retardant has been widely used in the field of heat shrink tubing. Heat shrink tubing is widely applied in electronics, power, communications and other fields, with strict requirements for flame retardant performance. With its unique flame retardant mechanism and high efficiency, red phosphorus has become a key component in halogen-free flame retardant systems for heat shrink tubing.
Red phosphorus has extremely high flame retardant efficiency, with a phosphorus content of 100%, making it one of the most efficient flame retardants. At high temperatures of 400–500°C, red phosphorus depolymerizes into white phosphorus, which then oxidizes to form viscous phosphorus oxyacids. These acidic substances can both cover the material surface to form a protective film and accelerate polymer dehydration and carbonization to generate a dense carbon layer. This carbon layer effectively isolates external oxygen and combustible gases, interrupts the combustion chain reaction, and achieves condensed phase flame retardancy.
However, ordinary red phosphorus is prone to moisture absorption and has poor compatibility with polymer materials. To solve this problem, microencapsulation coating technology is commonly used in industry for surface treatment of red phosphorus. The coated red phosphorus not only has greatly improved stability and significantly reduced moisture absorption rate, but also does not bloom, migrate, or corrode molds during processing, and has little effect on the physical properties of the product.
In practical application of heat shrink tubing, microencapsulated red phosphorus is often used in combination with inorganic flame retardants such as magnesium hydroxide and aluminum hydroxide. For example, using EVA and LDPE as base resins, an environmentally friendly halogen-free flame retardant heat shrink tube prepared with microencapsulated red phosphorus and magnesium hydroxide fully meets the environmental requirements of the EU RoHS directive. In high-end application scenarios such as automotive wire harnesses and oil pipelines, heat shrink tubing using microencapsulated red phosphorus compounded with amino silane modified magnesium hydroxide has excellent flame retardancy, flexibility, and insulation performance.
The application value of red phosphorus flame retardant in heat shrink tubing is reflected in multiple advantages such as high-efficiency flame retardancy, low smoke and low toxicity, and environmental compliance. With increasingly stringent environmental regulations, microencapsulated red phosphorus and its compounding technology will continue to promote the development of heat shrink tubing towards high performance and greenization.
