Wood and fire retardants

These great advantages of fire retarding agents are coupled to several drawbacks due to the incorporation of hydrated salt molecules into the wood cell walls the treated wood looses mechanical strength and increases hygroscopicity. 

As shown above, flame retardants change the thermal decomposition of cellulose (fibres) to a more intensive char-formation which may be further increased by addition of intumescents [57], These substances not only lead to a thicker char barrier which is well-known as fire protection but also to char-bonded structures. They are resistant to air oxidation at elevated temperatures and thus form a second flame and heat barrier. As the thickness of the char layer has a strong influence on the thermal gradient between the surface and the fibre it improves the thermal protection of the material. TG, TMA and DSC were applied to four samples of cotton fabrics treated with different commercial flame retardants and two commercially available intumescents. The results show the interaction between flame-retardant cotton fibres and the intumescents, an enhanced char formation and the expected char-bonded structures [57]. 

Finally, the already mentioned investigations on the Mediterranean pine Pinus halepensis shall be cited again in which commercial cellulose as a model compound for studies of forest fuel pyrolysis, pine needles, pine needle lignin and extractives were analyzed with and without two ammonium salts as fire retardants [46]. Both salts provoked a lowered pyrolysis temperature of cellulose and a significant increase in char formation for cellulose (up to 2.4 times) and intact needles (up to 1.7 times), but they had negligible effects on lignin and extractives. 

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NFPA 701 Standard Methods of Fire Tests for Flame Propagation of Textiles and Films NFPA 703 Standard for Fire Retardant Impregnated Wood and Fire Retardant Coatings for Building Materials... 

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