Approach to fire retardation

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. 

The aromatic structure of these materials is of major importance in their thermal response and in their inherent fire resistance according to established criteria. Approaches to fire retardants that have been studied for this class of polymers are reviewed, and illustrative data on performance are presented. 

The environmentally friendly intumescence approach to fire retardancy is of paramount interest in the case of polyethylene (PE), polypropylene (PP) and polystyrene (PS) which together account for about 60% of all synthetic polymeric materials used today. These polymers decompose quantitatively on heating, to give volatile products, leaving a negligible residue. 

Ecological considerations and investigations of fire hazards such as CO and smoke production target the inert filler characteristics of nanocomposites. The rather physical mechanisms proposed for nanocomposites are advantageous for such considerations. Nanocomposites appear to be a promising eco-friendly approach to fire retardancy in polymers. 

Certain commercial formulations approach or exceed the Navy s standard paint in regard to fire-retardancy. 

Brady, G., Moberly, C.W., Norell J.R., and Walters, H.C. 1977. Intumescence A novel effective approach to flame retarding polypropylene. J. Fire Retardant Chem. 4 150-164. 

Fire suppression is accomplished by means that affect one or more of the legs of the fire triangle. Additives that liberate water of hydration upon heating cool the substrate and dilute the combustible gases. Although these additives are inexpensive, this is a relatively inefficient approach to flame retardation because high load levels, —30 wt%, are required. 

Specific aspects of barrier formation were discussed above. A silicate or sihcate-char surface layer acting as a barrier for heat and mass transport is probably the main general fire retardancy mechanism of all layered-silicate nanocomposites. Most sources claim that this mechanism is responsible for the strongly improved performance in a cone calorimeter test. In particular, the strong reduction in PHRR is used to propose that layered silicates are the most promising approach for fire retardancy of polymers. However, the barrier effects and their influences on cone calorimeter results are not described in detail, so that the specific characteristics of these mechanisms are unclear. 

The self-extinguishing characteristics of the chlorine-containing resins are improved by incorporation of antimony oxide but this approach is not possible where translucent sheet is required. As an alternative to chlorine-based systems a number of bromine-containing resins have been prepared and, whilst claimed to be more effective, are not currently widely used. It is probably true to say that fire-retarding additives are used more commonly than polymers containing halogen groupings. 

Many of these approaches have been employed to contribute to fire or flame retardency ... 

The ceramic approach which appears the best to date because of versatility of composition as well as fire-retardancy is illustrated by the formulation which follows. In future modifications of the recipe, the sodium silicate will be replaced by an insoluble constituent, such as a silicone. 

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