Phosphorus content, char

Thermal gravimetric analysis shows that the increase in phosphorus content results in char yield increases which are correlatable with the self-extinguishment time decreases. This led to the conclusion of phosphorus "rich" barrier shielding the surfaces as a mechanism of the flammability decrease. 

Cotton with flame-retardant property was made by grafting with acrylamide and his-(heta-chloroethyl) vinylphosphonate, and subsequent treatment with stannic chloride. Thermal decomposition behaviors of unmodified and modified samples were studied under nitrogen atmosphere at 500 C. It was found that carbamoylethyl- and carboxyethylation, grafting and stannic chloride treatment increased the yield of char residue and water, but decreased that of tar. In flame-retardant cotton, the temperature of thermal decomposition onset and completion were lower than those in unmodified cotton. And the rate of thermal decomposition was slower than that in unmodified cotton. Phosphorus content in char residue did not change by thermal decomposition. But chlorine content introduced by grafting decreased by thermal decomposition. 

Phosphorus and Chlorine Contents. Phosphorus and chlorine contents of the samples in char residue at kOO C are shown in Table IV. Phosphorus content did not change by thermal decomposition in all samples. But chlorine content decreased by pyrolysis. Chlorine introduced by stannic chloride treatment hardly decreased, but that by grafting decreased easily by pyrolysis. Stannic chloride is not introduced in cotton in the form of stannic chloride, because the chlorine content of stannic chloride treated cellulose is very lower than that calculated from weight increase. X-ray diffraction trace of burned sample... 

Modified polymer Maximum phosphorus content (wt%) Phosphorus group Thermal stability Charring increase Ref ... 

Figure 12.1 Increase in char yield (calculated as the difference between the char yield of the phosphorus-containing polymer and those of the phosphorus-free polymer) versus the phosphorus content, from various...

According to the results of Ebdon et al. obtained from two series of MMA and styrene copolymers, char promotion could not be easily anticipated only from the phosphorus content. This means that a range of parameters modifies the efficiency of phosphorus as a flame retardant not only the phosphorus content, but also its chemical environment, its position in the macromolecule, and the host polymer. In this short chapter it is not possible to list in detail the influence of all these parameters. Therefore, only the main conclusions will be discussed in the following, from a narrow set of selected articles. 

A number of other compounds which have found use in niche applications show structural similarities in that they contain one or more cyclic 1,3,2-phosphorinane structures. This cyclic structure affords higher melting points (up to around 200°C) and lower volatility than comparable open chain compounds of similar phosphorus content and molecular weight [3]. The idea is that, on exposure to heat, the additive will not boil off but remain in the polymer to exert some char-forming action when it decomposes in the 300-400°C range. 

Epoxy JResin/ Curing Agent Temperature of Weight Loss (°C) Temperature of Rapid Weight Loss in (°C) Char Yield (%) Phosphorus Content (%) LOI (%)... 

The TG curves in Figure 6 indicate that the phosphorus presence in the grafted fabrics increase the thermal decomposition rate (curves 2,3,4 and 5 have different slopes in comparison with curve 1) facilitating the char formation (curve 4) and decreases the flammable volatile content. 

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