Reactive fire retardants, development

The first fire retardant polyester containing a reactive fire retardant monomer was introduced by the Hooker Electrochemical Corporation in the early 1950 s containing chlorendic acid as the reactive monomer (6). This pioneering development rapidly led to the introduction of variety of reactive halogen and phosphorus containing monomers, such as tetrabromophthalic anhydride, chlorostyrene and tetrabromobisphenol A, which found application in a wide variety of condensation polymer systems. 

FIRE RETARDANT FILLERS. The next major fire retardant development resulted from the need for an acceptable fire retardant system for such new thermoplastics as polyethylene, polypropylene and nylon. The plasticizer approach of CP or the use of a reactive monomer were not applicable to these polymers because the crystallinity upon which their desirable properties were dependent were reduced or destroyed in the process of adding the fire retardant. Additionally, most halogen additives, such as CP, were thermally unstable at the high molding temperatures required. The introduction of inert fire retardant fillers in 1965 defined two novel approaches to fire retardant polymers. 

Most circuit boards are FR-4 boards that meet standards for fire safety by the use of brominated epoxy resins in which the reactive flame-retardant tetrabromobisphenol A (TBBPA) forms part of the polymeric backbone of the resin. Alternative flame-retardant materials are used in only 3-5 per cent of the FR-4 boards, but additional alternative flame-retardant materials are also imder development. Little information exists concerning the potential environmental and human health impacts of the materials which are being developed as alternatives to those used today that are based on brominated epoxy resins. 

Further important ccranercial flame retardants, developed by associates of Dr. Toy are Fyrol 99 (non-reactive for soft polyurethane foams) as well as halogen-free compounds like Fyrol 51 e.g. for polyurethanes or Fyrol HMP for the fire-protection of automotive air filters (29). In the application for polymer films, in addition to flame protection, Fyrol HMP was (new Victastab HMP) found to enhance the tensile strength of Mylar polyester films considerably. 

It is clearly a truism that for reducing the fire risk in the applications of plastics, their flammability should be diminished. This is achieved either by reactive flame-retardants incorporated during the preparation (polymerization, polyaddition, polycondensation) of the polymer or by additive flame-retardants admixed in the course of plastics processing. The flammability of plastics is sometimes reduced by surface protection. The most recent methods of reducing flammability are the modification of the macromolecular structure and the development of thermally resistant polymers (high-temperature plastics). 

A low reactivity, low viscosity, white pigmented resin offering superior fire retardancy (Class 1, BS 476 Part 7) and low smoke development for non-transparent laminates, b. 72.5% c. 680-980... 

Another route to flame-retardant rigid foams is the use of flame-retardant polyether polyols which contain phosphorous and halogen (reactive type). In recent years, due to the fire-gas toxicity caused by halogen-, phosphorous- or nitrogen-containing flame retardants, other types of flame-retardants which do not produce toxic gases are being developed. 

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