Intumescence-based

The complete absence of cross-linking reactions prevents potential char-forming reactions being favored in the presence of conventional condensed-phase flame retardants, and hence, the most effective flame retardants for polyolefins are usually bromine-based so that flame inhibition in the vapor phase is effected or intumescent-based, where char-promotion arises from the flame retardant itself. 

Recently, some reports have explored the potential of synergistic effect between silica and other flame retardants.53-55 For example, silica showed synergistic effect with alumina in polypropylene (PP)/ammonium polyphosphate (APP)—pentaerythritol (PER) intumescent-based system. The data indicate that the HRR values improved by incorporating silica into the intumescent-based formulation and the improvement was much more pronounced by combining both silica and alumina in the formulation. 

Intumescents are said to have a key advantage over filler-type non-halogenated flame retardants in that they are effective at lower addition levels than traditional materials. For example, an intumescent based on ammonium polyphosphate will achieve the same level of protection at addition levels of 25 to 35 parts by weight (pbw) as atypical non-halogenated flame retardant, such as alumina trihydrate or magnesium hydroxide, at between 60 and 70 parts by polymer weight. 

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-... 

Intumescent materials, which are water-based systems, cure by evaporation. If applied during periods of high humidity, the areas of application may experience blistering when the humidity drops and the evaporative curing continues. In such environments, solvent-based materials are recommended. 

Fire Retardent Paints. Fire retardant paints are based on chlorinated rubber and chlorinated plasticizers with added SbO. These reduce the rate of spread of flames. Addn of NH4H2PO4, PE, or dicyandiamide produces an intumescent or swelling paint that forms a thick insulating layer over the surface to which it is applied when exposed to flames Fire retardant paints do not control fires and are no substitute for an automatic sprinkler system. They are best used where the only hazard is exposed, combustible, interior finish materials or in isolated buildings where sprinklers will not be installed. The paint must be applied at the rate specified on the container if spread thinner the proper... 

Fire-retardant paints for wood have been developed using urea-formaldehyde resins and ammonium phosphate. Heat causes this compound to intumesce and develop an insulating layer for the surface upon which it is applied. Oil-based fire-retardant paints usually contain organic materials such as resins, paraffins, or chlorinated rubbers combined with inorganic vehicles, or they may be compounded of inorganics such as ammonium compounds. 

All the above formulations have been investigated and evaluated on perforated and unperforated Celotex fiberboard. Results demonstrate that a satisfactorily formulated intumescent water- or oil-base paint is the best type of paint to apply to acoustical fiber board to secure optimum fire or flame resistance. These paints, by their intumescent nature, tend to close the openings in the acoustical fiber board and insulate the basic fiber under the coating. 

A series of compounded flame retardants, based on finally divided insoluble ammonium phosphate together with char-forming nitrogenous resins, has been developed for thermoplastics.23 These compounds are particularly useful as intumescent flame-retardant additives for polyolefins, ethylene-vinyl acetate, and urethane elastomers. The char-forming resin can be, for example, an ethyle-neurea-formaldehyde condensation polymer, a hydroxyethyl isocyanurate, or a piperazine-triazine resin. Commercial leach-resistant flame-retardant treatments for wood have also been developed based on a reaction product of phosphoric acid with urea-formaldehyde and dicyandiamide resins. 

Ammonium polyphosphate AP420 series Clariant (Germany) Intumescent gelcoats (epoxy, UP, or PUR based)... 

As the polyol-based char formers needs to be substituted, Li and Xu40 reported the synthesis of a novel char former for intumescent system based on triazines and their derivatives. It is a macromo-lecular triazine derivative containing hydroxyethylamino, triazine rings and ethylenediamino groups (Figure 6.7). They showed that the new char former in an intumescent formulation containing APP... 

In this part, we will distinguish between natural and synthetic fibers because different methods are usually involved to provide flame retardancy by intumescence for the two classes. A few papers report recent development and performance of intumescent textiles. Very often the authors describe the mechanism of action of their materials as mechanism via charring enhancement or something similar. Nevertheless based on the chemical nature of the flame retardant used and by the described... 

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