Polyurethane (PU) is a versatile material that finds extensive use in various industries due to its durability, flexibility, and insulation properties. However, one significant drawback of PU is its flammability. To mitigate this risk, flame retardants are commonly added to polyurethane to enhance its fire-resistant properties.
The application of flame retardants in polyurethane is particularly crucial in the construction industry. PU foam is commonly used as insulation in walls, roofs, and doors. Fire incidents in buildings can have catastrophic consequences, making flame retardancy an essential aspect of building safety. Flame retardants enable PU insulation to meet rigorous fire safety standards and limit the spread and intensity of fires. This helps provide occupants with more time to evacuate and enhances the overall fire resistance of a structure.
Additionally, flame retardants play a vital role in the transportation industry. Polyurethane is used extensively in automotive interiors, including seats, headrests, and dashboards. With the high risk of ignition sources such as cigarettes or electrical malfunctions, flame retardancy is crucial to prevent rapid flame propagation and limit the generation of toxic gases. Flame retardants in polyurethane ensure that the material meets stringent automotive safety regulations.
Halo-phosphate compounds are a large class of additive organic flame retardants that are widely used in polyurethane foam plastics and have remarkable effects. There are many varieties of halo-phosphate flame retardants, just to name a few:
Tris(2-chloroethyl) phosphate (TCEP) is an additive flame retardant, which can be used in the production of polyurethane flexible foam and rigid foam. In comparison, TCEP has a better effect on rigid foam, because the closed cell rate of rigid foam is high, the air permeability is small, it is difficult for the flame retardant to volatilize, and the flame retardant effect can be maintained for a long time. When TCEP is used in flexible polyurethane foam, such as flame-retardant modified high-resilience foam, TCEP can be used in combination with melamine.
Tris (2-chloropropyl) phosphate (TCPP) is an additive flame retardant with good plasticizing effect and is mainly used as a flame retardant for polyurethane foam. Because the molecule contains phosphorus and chlorine at the same time, it has remarkable flame retardant properties, and also has plasticizing, moisture-proof, and anti-static effects. Because the content of phosphorus and chlorine is lower than that of TCEP, its flame retardant effect is relatively weakened.
As a flame retardant, phosphate ester also has a plasticizing effect. When the amount is too large, it will soften polyurethane and reduce its strength. Common phosphate ester flame retardants used in polyurethanes include:
Dimethyl methyl phosphate (DMMP) is a halogen-free low-viscosity liquid additive flame retardant. It is characterized by high phosphorus content, excellent flame retardant performance, less addition, low price, easy to use, and has dual functions of reducing viscosity and flame retardancy. In addition, the decomposition temperature of DMMP is higher than 187°C, so the thermal stability is better than that of halogen-containing flame retardants. It can be used in flexible and rigid polyurethane foams, especially for transparent or light-colored products and spray applications.
Diethyl ethyl phosphate (DEEP) is a new type of high-efficiency organophosphorus flame retardant, which can be widely added to various rigid polyurethane foams, including rigid foam formulations of various foaming systems. DEEP has low viscosity, does not contain halogen, and its chemical stability makes it very stable in the two-component system of polyether polyol and isocyanate. Its flame retardant efficiency is 1.5~2 times that of TCPP.