Char Formation in Polyamides (Nylons 6 and 6.6) and Wool Keratin Phosphorylated by Polyol Phosphoryl Chlorides

Polyamides (nylon 6 and 6.6) phosphorylated by spirocyclic pentaerythritol phosphoryl chloride (SPDPC), cyclic 1,3-propanediol phosphoryl chloride (CPPC), and cyclic 2,2- diethyl-1,3-propanediol phosphoryl chloride (CDPPC) can yield phosphorus levels up to 0.7% (w/w). Calculations suggest that only primary amine groups at the end of the molecular chain are the possible phosphorylation sites. The presence of substituted 1,3-propanediol phosphonate moieties significantly increases polyamide char formation above 500°C, and scanning electron microscopy indicates that the residual char has an intumescent structure. SPDPC-phosphorylated wool keratin yields higher phosphorus levels up to 2.06%. For nylons 6 and 6.6, the presence of a methylolated triazine (as the commercial agent Lyofix MLF NEW, Ciba) in the pad-cured treatment can increase the phosphorus level further to significantly enhance char formation. SEM images suggest that the reacted substrates yield char volume expansions in wool of up to 336% compared to the control sample chars.