Understanding Polyurethane Flame Retardants in Three Minutes

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Why are flame retardants needed? Most polymer materials such as PE, PP, ABS, and PU are flammable; when they burn, they release large amounts of smoke and toxic gases that can cause poisoning and suffocation. Additionally, this poses challenges to fire fighting and rescue efforts. Therefore, it is necessary to use certain methods to make these polymers flame resistant, which has given rise to the market for flame retardants. Flame retardants are defined functionally as elements known for their flame-retardant properties. What are flame retardants? ★ Most flame retardants achieve their flame-retardant effect through the combined action of several mechanisms. Classification of flame retardants: • Different flame-retardant elements used: halogen-based, phosphorus-based, nitrogen-based, phosphorus-halogen based, phosphorus-nitrogen based. • Different components used: inorganic salts, organic substances, organic/inorganic mixtures. • Different methods of application: additive type, reactive type, synergistic type. Flame retardants suitable for different polymers: • Polyolefins PP/PE: magnesium hydroxide, aluminum hydroxide, TDCPP, ammonium polyphosphate, octabrominated ethers, triphenyl phosphate, hexabromocyclododecane, MPP, zinc borate, decabromodiphenylethane, coated red phosphorus, TBC. • Polystyrene PS: TCPP, TDCPP, HBCD, MCA, TBC, MPP, decabromodiphenylethane, decabromodiphenyl ether, zinc borate. • Polyesters PBT/PET: TDCPP, triphenyl phosphate, MPP, decabromodiphenylethane, decabromodiphenyl ether, coated red phosphorus. • Epoxy resins EP: TCPP, TDCPP, IPPP, decabromodiphenyl ether, DMMP, triphenyl phosphate, decabromodiphenylethane. • Acrylonitrile butadiene styrene ABS: octabrominated ethers, triphenyl phosphate, decabromodiphenylethane, decabromodiphenyl ether, TBC. • Unsaturated resins UPR: TCPP, TDCPP, DMMP, HBCD, TBC. • Nylons PA6/PA66: MCA, MPP, FB, decabromodiphenylethane, decabromodiphenyl ether, coated red phosphorus. • Polyvinyl chloride PVC: TCEP, TCPP, TDCPP, IPPP, MCA, octabrominated ethers, triphenyl phosphate. • Phenolic resins PF: TCEP, TCPP, TDCPP, triphenyl phosphate, zinc borate. • Polycarbonates PC: triphenyl phosphate, HBCD, MCA. • Polyurethanes PU: TCEP, TCPP, TDCPP, DMMP, triphenyl phosphate, MPP, FB. What are polyurethane flame retardants? PU flame retardants are additives used in the synthesis of polyurethane materials to endow them with flame-retardant properties. Introduction to commonly used polyurethane flame retardants: I. Halogenated phosphates 1. Tri(2-chloroethyl) phosphate (TCEP) Ø It is the earliest, most widely used, and cheapest additive-type flame retardant. Ø It can be used in both soft and rigid foams; it works better in rigid foams. Ø It has good resistance to hydrolysis and high flame-retardant efficiency. Ø It tends to volatilize easily, resulting in poor long-term flame-retardant performance. Ø If its usage exceeds 15%, the physical properties of the foam material deteriorate. 2. Tri(2-chloropropyl) phosphate (TCPP) Ø Is an additive-type flame retardant that also possesses good plasticizing properties; Ø It is commonly used in PU rigid foams and PIR rigid foams, as well as in PU soft foams; Ø Its molecule contains both phosphorus and chlorine, which contributes to its significant flame-retardant effects; Ø It offers benefits such as plasticization, moisture resistance, and antistatic properties; Ø However, its phosphorus and chlorine content is lower than that of TCEP, resulting in relatively weaker flame-retardant effects. II. Phosphate-based flame retardants 1. Dimethyl methylphosphate (DMMP) Ø It is a halogen-free, low-viscosity liquid additive flame retardant; Ø It has a high phosphorus content, excellent flame-retardant properties, requires a small amount to be effective, is inexpensive, and is easy to use. It serves both to reduce viscosity and to provide flame retardancy; Ø Its decomposition temperature is above 187°C, giving it good thermal stability; Ø It can be used in both soft and hard PU foams, and is particularly suitable for transparent or light-colored products as well as for spraying applications; Ø It is not suitable for being pre-mixed into composite materials, and it is recommended to add it before the foaming process begins. 2. Diethyl ethylphosphonate (DEEP) is a new type of highly effective organic phosphorus flame retardant; its flame retardancy is 1.5 to 2 times that of TCPP. It is widely used in the formulations of rigid foam systems across various applications. It contains no halogens, has low viscosity, and remains very stable in two-component AB systems. It functions as an efficient viscosity reducer, improving the workability of water-based rigid foam and polyester-based rigid foam systems. It is not suitable for use in isocyanate-based components such as prepolymers or single-component foams. Current status of the international flame retardant market: The four main markets are the United States, Europe, Japan, and other Asia-Pacific regions. As awareness of environmental protection, safety, and health grows among people around the world, countries have begun to focus on the research, development, and application of environmentally friendly flame retardants, and have achieved certain results in this regard. Relevant laws and regulations: RoHS Directive, Stockholm Convention, REACH Directive. In the United States and Europe, the proportion of brominated flame retardants used in total flame retardant usage is low, and this proportion is on the decline. Around 2012, the usage rate of brominated flame retardants in other parts of Asia (mainly in China) had dropped to around 40%.