Phosphorus-containing plastics additives

Additive flame-retardants, however, may also be suitable, for example ammonium polyphosphate, tris(2-chloroethyl) phosphate, or other phosphorus-containing plasticizers. 

In common with most thermoplastics, ABS polymers are not flame resistant. In principle, a flame-resistant ABS could be made by incorporating halogen- and/or phosphorus-containing structures either by (a) copolymerization of appropriate monomers or (b) addition of small molecules containing these structures as plasticizers. Recognizing that the second approach can involve a serious loss in heat deflection temperature, hardness, and occasionally impact strength (4), we have favored the copolymerization approach in the work described here. 

Among phosphorus-containing additive flame-retardants, phosphates are mostly applied as secondary plasticizers in formulations of flame-retarded plasticized PVC. Other additive agents are admixed with natural and synthetic rubbers, polyester and epoxy resins, polyurethane foams, polystyrenes and polyethylenes, etc. 

Organic peroxides can occur in small amounts in some types of polymers such as PS as a result of the fact that a peroxide has been used as a polymerisation catalyst in polymer manufacture. Also, stable organic peroxides such as dicumyl peroxide have been used as synergists, in conjunction with bromine and or phosphorus-containing additives, to impart fire resistance to cellular expanded PS and other types of plastics. 

Developed for PVC cable insulation compounds. Akcros has developed a special CaZn-based system under the Interlite name, especially for formulations containing flame-retardant additives, many of which are known to have detrimental effects on properties such as initial stability and ageing performance. Included is a grade for formulations containing phosphorus-based plasticizers, developed with Akzo Nobel s Phosflex range. 

Phosphate esters (alkyl or aryl, or mixed) of phosphoric acid constitute an important family of organophosphorus flame retardants.25 Triethylphosphate, a colorless liquid boiling between 209°C and 218°C, and containing 17 wt % phosphorus, has been used commercially as an additive for polyester resins/laminates and in cellulosics. In polyester resins, it functions as a viscosity depressant as well as a flame retardant. Trioctylphosphate is employed as a speciality flame-retardant plasticizer for vinyl composites where low temperature flexibility is critical. It can be also included in blends, along with general purpose plasticizers, such as phthalate esters, to improve low temperature flexibility. 

The volume leaders among fire retardants with 35 million pounds were the three phosphate plasticizers for PVC tricresyl phosphate, cresyl diphenyl phosphate and triphenyl phosphate. The remaining 6 million pounds were made up of octyl diphenyl phosphate, tributyl phosphate, tri(dibromopropyl) phosphate, tri(dichloropropyl) phosphate and tri-(chloroethyl) phosphate. Polymeric phosphorus and phosphorus halogen-containing additives are used in concentrations of 3-25 p.p.h. in polyesters, flexible and rigid polyurethane foam, and phenolics. 

Complex compounds of chlorine, phosphorus and bromine have been developed for flameproofing polyester resins, polyolefins and polyurethanes. Unfortunately such compounds are usually toxic and expensive, and many of them, especially those containing hi proportions of bromine, suffer from poor heat and light stability. Considerable research effort is being expended to develop a broad spectrum, highly efficient heat and light stable flame retardant additive for plastics materials which could be sold at an economic price, but none of the products currently on the market fully satisfy all the requirements of an ideal flame retardant. 

Flammability. Rigid polyurethane foams, along with other organic plastics, have been the subject of much work in the field of flame retardance. A variety of phosphorus and/or halogen containing additives (reactive and non-reactive) are now available which improve the flame resistance of polyurethane foams. The choice of additives and of test methods is however best decided upon in the light of the application envisaged. Table 7 shows some typical properties. 

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