Phosphorus nitrogen synergism

In most cases, a given fire retardant operates by several of these mechanisms, and much research has been done to determine the magnitude and role of each of these mechanisms in fire retardancy. The influence of the combining effect of several of these mechanisms is illustrated by phosphorus-nitrogen synergism. The theories involved in this synergistic system are discussed to demonstrate this interaction between mechanisms. Some mechanisms apply only to... 

Phosphorus—Nitrogen Synergism Theories. As mentioned previously, one role of phosphoric acid and phosphate compounds is to catalyze the dehydration reaction of wood to produce more char. 

This phosphonate polyol is very resistant to hydrolysis and has in its structure both phosphorus and nitrogen. A synergism between phosphorus - nitrogen has previously been mentioned in this chapter [1, 4, 5, 11]. 

The formulation of more recent APP-based systems also seems to be based on phosphorus-nitrogen synergism. Co-additives are polymeric in nature such as poly(triazine-piperazine) materials, essentially substituted melamine rings linked by piperazine groups, and poly(ethylene-urea-formaldehyde) condensates. The sequence of reactions leading to char formation in these systems is poorly understood. It is likely that both water and ammonia are evolved at certain stages, some phosphorus and probably some nitrogen remain incorporated in the char structure, and some phosphorus ends up as polyphosphoric acid. 

Phosphorus compounds, e.g. ammonium polyphosphate or encapsulated red phosphorus particles were also mentioned as efficient fire retardants [105,106]. As an additive, which combines the fire retardant function of nitrogen and phosphorus and exhibits synergism of nitrogen and phosphorus, melamine diphosphate was described [107]. Bromine compounds are synergistic fire retardants, if used jointly with antimony oxide [108]. 

Major Chemicals. Phosphorus. Combination salts of the phosphates have been used for retarding wood since the time of Gay-Lussac. Monoammonium and diammonium phosphates have been the most effective. The efficiency of phosphorus compounds can be increased by the presence of certain nitrogen compounds that produce a synergistic effect. The advantage of such synergism is that increased flame-spread resistance can be achieved with lower chemical loading levels. The amino-resin systems are based on this synergistic effect. 

Synergism between phosphorus and nitrogen is exploited in the flame-proof finishing of textiles. Synergism is reasonably supposed to occur between halogens and free-radical precursors such as organic peroxides and disulphides. 

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