What are Halophosphate Additive Flame Retardants?

What Are Flame Retardants?

Like most other polymeric materials, polyurethane is not flame-resistant and produces toxic gases when burned, posing a threat to personal safety and property. In particular, polyurethane foam has low density and a large specific surface area. Furthermore, open-cell polyurethane foam has a high open-cell ratio and contains a large proportion of combustible components. During combustion, the high air permeability ensures a continuous supply of oxygen, making it highly flammable and resistant to self-extinguishing. Therefore, various methods are employed to impart a certain degree of flame retardancy to polyurethane products, particularly polyurethane foam. The addition of flame retardants is the most common and general method; flame retardants are essential additives for polyurethane foam materials.
There are many types of flame retardants. By form, they include solid powder and liquid flame retardants; by chemical nature, they include inorganic and organic flame retardants; and by chemical composition, they include halophosphates, phosphates, halogenated organics, melamine, ammonium polyphosphate, and aluminum hydroxide, among others.

Halophosphate Additive Flame Retardants

Tris(2-chloroethyl) Phosphate(TCEP) CAS 115-96-8

Tris(1-Chloro-2-Propyl) Phosphate(TCPP) CAS 13674-84-5

Tris(1,3-dichloro-2-propyl)phosphate(TDCPP) CAS 13674-87-8

Halogenated alkyl phosphate esters are a widely used and highly effective class of additive-type organic flame retardants in polyurethane foam. Most halogenated phosphate esters are liquid at room temperature, making them convenient to use. They exhibit good compatibility with polyols and are reasonably priced. The phosphides generated by these flame retardants at high temperatures consume the combustible gases released during the combustion of foam plastics, converting them into non-combustible carbides; halogens act as chain terminators in the combustion reaction of foam plastics, generating hydrogen halides to inhibit the combustion process. However, excessive use can cause charring in the center of the foam, leading to a significant decline in performance.
Common halogenated phosphate flame retardants include low-molecular-weight halogenated monophosphates and high-molecular-weight diphosphates.

Three Types of Low-Molecular-Weight Halophosphates

Tris(2-chloroethyl) Phosphate

Tris(2-chloroethyl) phosphate, abbreviated as TCEP, is a chlorinated and phosphorus-containing organophosphate compound. It is a colorless to pale yellow transparent liquid with CAS number 115-96-8, a molecular weight of 285.5, a density of 1.420–1.431 g/cm³, and a boiling point of 194°C (1.33 kPa). It is soluble in water and various organic solvents, has a faint creamy odor, and exhibits hydrolytic stability. It contains 10.8% phosphorus and approximately 37.2% chlorine.

Properties:

Applications

Tris(2-chloroethyl) phosphate is used as an additive flame retardant in adhesives. It offers excellent flame retardancy, low-temperature performance, and UV resistance, with a recommended dosage of 5–10 parts. It is suitable for phenolic resins, polyvinyl chloride (PVC), polyacrylates, polyurethanes, and other materials and can improve water resistance, acid resistance, cold resistance, and antistatic properties. It can also be used as a flame-retardant plasticizer.

Tris(1-Chloro-2-Propyl) Phosphate

Tris(1-chloro-2-propyl) phosphate, abbreviated as TCPP, is a flame retardant that belongs to the isomers of tris(chloropropyl) phosphate (TMCPP). Its molecular weight is 327.6. The theoretical phosphorus content is approximately 9.5%, and the chlorine content is approximately 32.5%.
TCPP has four isomers, one of which is tris(2-chloroisopropyl) phosphate, with CAS number 13674-84-5. It is the most widely available isomer of tris(monochloroisopropyl) phosphate, and the commonly referred to flame retardant tris(2-chloroisopropyl) phosphate (TCPP) refers to a mixture primarily composed of this compound.

Properties

Applications

Tris(2-chloropropyl) phosphate is an additive flame retardant characterized by low viscosity and good thermal and hydrolytic stability. Because its molecule contains both phosphorus and chlorine, it exhibits significant flame-retardant properties, as well as plasticizing and antistatic effects. However, since its phosphorus and chlorine content is lower than that of TCEP, its flame-retardant performance is slightly inferior to that of tris(chloroethyl) phosphate.
TCPP is primarily used as a flame retardant in polyurethane foam plastics. It is commonly used in polyurethane (PU) rigid foam and polyisocyanurate (PIR) rigid foam, as well as in polyurethane flexible foam. When used in polyurethane flexible foam, its durability is poor, but it does not cause scorching (core burning) of the foam. In addition to polyurethane foams, it can also be used as a flame retardant in polyvinyl chloride (PVC), polystyrene, unsaturated resins, phenolic resins, and cycloaliphatic resins, as well as in rubber, textiles, and coatings.

Tris(1,3-dichloro-2-propyl)phosphate (TDCPP)

Tris(1,3-dichloro-2-propyl)phosphate, abbreviated as TDCPP or TDCP, is a colorless to yellow, transparent, viscous liquid with CAS number 13674-87-8, a molecular weight of 430.9, and a theoretical chlorine content of 49.4% and phosphorus content of 7.2%.

Properties

Applications

TDCP is an additive flame retardant. It exhibits excellent hydrolytic stability and low volatility. Due to its high chlorine content, TDCP provides effective flame retardancy with long-lasting performance and has minimal impact on the physical properties of the foam. In polyurethane materials, it is primarily used in polyether and polyester-based PU flexible foams that require core burn resistance, low volatility, low smoke generation, and resistance to moisture aging; it can also be used in flame-retardant composite foams. It can also be used in other PU foam plastics, such as rigid foam, as well as for flame retardancy in polyvinyl chloride (PVC) resins, epoxy resins, phenolic resins, rubber, and fiber materials. It can be formulated into an emulsion for use in carpets, raincoats, and fabric finishing, and can also serve as an additive in fire-retardant coatings.