Phenolic Polymer Flammability

No discussion of polymer fire retardance would be complete without at least a brief mention of the highly aromatic polymers, all of which are very difficultly flammable if they burn at all (1 ). Although the low flammability of phenolic and furane resins are well known, these thermally... 

Auad, M.L. Zhao, L.H. Shen, H.B. Flammability properties and mechanical performance of epoxy modified phenolic foams. J. Appl. Polym. Sci. 2007,104, 1399-1407. 

The polymer eomponent, whieh is a thermosetting resin, forms eross-linked bonds between chains of molecules, whieh enhanees the eharacteristic of the produet. Unsaturated polyesters and vinyl esters are primarily used as resin systems. Epoxies are also used in some eases, but the eure eyele is longer. Phenolic resins have gained importanee these days because of their inherent properties, especially in applications that require lower flammability, reduced smoke generation, and higher thermal stability. New resin systems such as... 

Some polymers are easier to foam than others. Indeed, it was not until methods were found to circumvent the inclusion of cells in the early history of the phenol formaldehyde polymer that it gained any commercial significance. The development of foamed phenolic resins only became important much later when a specific need arose to produce rigid foam with reduced flammability. This consideration also led to the development of polyisocya-nurate foams and carbodiimide foams. On the other hand, the polypropylene family of polymers, although having a tonnage far exceeding that of phenol formaldehyde resins, is... 

The flammability behavior of some polymer blends is summarized in Table 6.7. Here one can also obtain some useful information thus, if the material burns readily while melting slowly and emits a deflnite paraffinic odor, these point to a polyolefin blend. Highly sooty flames are a deflnite indication that aromatic structures are present, while the odor of burnt horn indicates nitrogen-containing components. The identification of PVC in blends is relatively easy because generally a stinging smell of hydrochloric acid develops while the material usually burns very poorly. When polycarbonates are present in the blend, a typical odor of phenol is noticed in most cases. 

These observations also clearly indicate that in this flame-retardant system, brominated phenols are first evolved at slightly lower temperatures than those of the flammable product such as 1,3-butadiene and butylene terephtha-late evolved from the substrate polymer, PBT, to cause the initial flame-retarding effect. In addition, HBr would then be evolved over the whole degradation temperature range for PBT to cause free radical trap in volahle phase and char formation to decrease flammable products. 

Intrinsically non-flammable polymers are few, but phenolic resins have a good reputation both in Are and smoke performance, which has resulted in their becoming increasingly favoured for reinforced plastics structures, for example, underground transport, where such concerns are greatest. Polyether ether ketone (PEEK) is also a low fire and smoke polymer. Unsaturated polyesters, vinyl esters and epoxy resins bum readily, but modified versions are available with improved behaviour. For example, both bromine and chlorine are used extensively in the form of chlorendic (HET) acid, tetrachlorophthalic anhydride (TCPA) and tetrabromo-phthalic anhydride (TBPA) which can be reacted into the polyester in small quantities and can act as permanent (non-migrating) flame retardants. 

---