Cotton, additives Flame retardants

Textile Flame Retardants. The first known commercial appHcation for phosphine derivatives was as a durable textile flame retardant for cotton and cotton—polyester blends. The compounds are tetrakis(hydroxymethyl)phosphonium salts (10) which are prepared by the acid-cataly2ed addition of phosphine to formaldehyde. The reaction proceeds ia two stages. Initially, the iatermediate tris(hydroxymethyl)phosphine [2767-80-8] is formed. 

A/-substituted, long-chain alkyl monomethylol cycHc ureas have also been used to waterproof cotton through etherification. Other water repellent finishes for cotton are produced by cross-linked siHcone films (56). In addition to the polymeri2ation of the phosphoms-containing polymers on cotton to impart flame retardancy and of siHcone to impart water repeUency, polyduorinated polymers have been successfuUy appHed to cotton to impart oil repeUency. Chemical attachment to the cotton is not necessary for durabUity oU repeUency occurs because of the low surface energy of the duorinated surface (57). 

Tetrakishydroxymethylphosphonium salts (THPC, THPS, etc.) are of major importance as raw material monomers in the flame-retardant treatment of cotton (industrial protective clothing, furnishing fabrics, etc.). Proban chemicals are produced from THPC or THPS with urea194. These compounds have been often patented as additives of natural and artificial fibres210,211, coatings 212,213 and in fire-proofing solution for wood214. 

Although in principle rayon can be flame retarded by the same processes developed for cotton, the majority of research efforts have focused on additives to the viscose spinning bath. One successful additive, based on an alkyl dioxaphosphorinane disnlfide (Fig. 8.15), is used at 20 % for effective flame retardancy. ... 

The burn results for polymers 15 and 19 show that the polymers are inherently flame retardant with low base flammability (Table 4). The polymer dripped but did not ignite the cotton when it was subjected to the UL-94 flame test, and with the addition of 1 wt% PTFE, it did not drip. The PCFC results show that these polymers have a high heat release capacity when compared with the BPC carbonates and aryl ethers, but it is still significantly less than that of the base commodity polymers, such as polyethylene or polystyrene (Table 5). 

In many cases, even normal textiles must be made fireproof. In principle, this objective can be achieved in three ways copolymerization with small amounts of a flame-retarding comonomer, addition of flame-retarding low-molar-mass substances to the spinning solution, or post-treatment of the textiles with flame retardants. The last method is indeed very flexible and economic but does not always yield completely technologically satisfactory results. Consequently, it is only used for the natural fibers wool and cotton. 

The chemical fibers rayon and cellulose acetate are made fireproof by adding flame-retardant additives to the spinning solution. The active substance in this case is distributed throughout the whole fiber and is not only on the surface, as in the case of wool and cotton. 

The Institute of Natural Fibres in Poznan, Poland has developed new barrier fabrics, both woven and non-woven. The first was a cotton weave containing a small addition of polyester. The latter was made of flame retardant flax and hemp fibres. The flame retardant and its application method were developed by the institute. The flame retardant, called FOBOS M2T, was based on urea polyborates and the sodium salt of alkyl-aryl sulfonic acid. The method of impregnation is cheap and simple. It can be carried out on typical finishing equipment and increase manufacturing costs by only 10-15%. 

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]. 

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