Intumescent

Ablative materials are classified according to dominant ablation mechanism. There are three groups subliming or melting ablators, charring ablators, and intumescent ablators. Figure 4 shows the physical zones of each. Because of the basic thermal and physical differences, the classes of ablative materials are used in different types of appHcations. 

C. Paone, Preventing Cook-Off with Intumescent Materials, Army RD A Bulletin, Jan.—Feb. 1990. 

Protective Coatings. Some flame retardants function by forming a protective Hquid or char barrier. These minimize transpiration of polymer degradation products to the flame front and/or act as an insulating layer to reduce the heat transfer from the flame to the polymer. Phosphoms compounds that decompose to give phosphoric acid and intumescent systems are examples of this category (see Flame retardants, phosphorus flame retardants). 

A newer self-intumescent phosphoric acid salt has been introduced by Albright WHson as Amgard EDAP, mainly as an additive for polyolefins. It is a finely divided soHd, mp 250°C, having a reported phosphoms content of 63 wt % as H PO. It appears to be the ethylenediamine salt of phosphoric acid (1 1). Unlike ammonium polyphosphate, it does not require a char-forming synergist (62). 

E. Termine and K. G. Taylor, "A New Intumescent Flame Retardant Additive for Thermoplastics and Thermosets," n Additive Approaches to PolymerModification, SPE RETEC Conference Papers, Toronto, Ontario, Canada, Sept. 1989. 

Steel stmctures should be protected by approved fireproofing treatment, eg, concrete or insulating, ie, intumescent or ablative materials untreated steel should be protected by some method of cooling, eg, a water-spray system. 

Some of the chemicals mentioned above and others, such as chlorinated mbber or paraffin, antimony trioxide, calcium carbonate, calcium borate, pentaerythrithol, alumina trihydrate, titanium dioxide, and urea—melamine—formaldehyde resin, may be used to formulate fire retardant coatings. Many of these coatings are formulated in such a way that the films intumesce (expand) when exposed to fire, thus insulating the wood surface from further thermal exposure. Fire retardant coatings are mostly used for existing constmction. 

One possible solution to the problem is to make greater use of intumescent materials which when heated swell up and screen the combustible material from fire and oxygen. Another approach is to try to develop polymers like the phenolic resins that on burning yield a hard ablative char which also functions by shielding the underlying combustible material. 

Intumescents (up to 2 hours this can be the most expensive, depending upon the application)... 

Intumescents are thin films or mastics, which swell under heat to many times their original thickness. Their major use is in circumstances where the architectural statement of steel is to be preserved. As such, their costs vary considerably. Their application is fast and can be either by spray or bmsh. They are generally used internally, but external intumescents are available. 

Fire Smoke detectors, intumescent coatings/seals... 

These intumescent coatings, when subjected to fire, form a char between the substrate and the fire source. The basic product coated becomes flameproof (36,159). 

These coatings provide the most effective fire-resistant system available but originally were deficient in paint color properties. Since, historically, the intumescence producing chemicals were quite water-soluble, coatings based thereon did not meet the shipping can stability, ease of application, environmental resistance, or aesthetic appeal required of a good protective coating. 

More recently there have been developed water- resistant phosphorus-based intumescence catalyst. This commercially available product, as an example Phos-Chek P/30 tradename from Monsanto, can be incorporated (with other water insoluble reagents) into water-resistant intumescent coatings of either the alkyd or latex-emulsion type. These intumescent coatings, formulated ac-... 

Specimens of NR ABS/(Octa -I- AO) heat-treated at 350°-400°C developed brittleness of connected pores, whereas VO ABS (Octa -1- AO -I- EPDM), similarly treated, was tougher with large elongated pores about twice the size of the non-treated specimen. Such behavior suggests an intumescent effect of EPDM, i.e. the development of a thick porous surface layer, inhibiting the diffusion of flammable products of plastic degradation towards the gas phase and heat transfer into the plactic mass. 

Intumescent additives. React with the polymer substrate to produce a char layer which forms an effective barrier between heat source and oxygen and... 

Melamine and melamine salts (e.g., borates, phosphates) act in a similar manner promoting char formation and intumescence. 

Antimony trioxide and chlorinated paraffinic derivatives are common materials used as fire retardants, as are intumescent zinc (or calcium) borate, aluminium hydroxide and magnesium hydroxide. These inorganic materials, used as bulk fillers, act to reduce the fire hazard. Halogenated materials release chlorine, which then combines with the antimony trioxide to form the trichloride, which is a flame suppressant. 

The history of polymer fire retardance is reviewed from its inception with the early Egyptians to the most recent developments in intumescent fire retardants and inherently fire retardant polymers. 

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