Abstract
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 give phosphorus levels up to 0.7%(w/w). Calculation suggests 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 500oC 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 trazine (as the commercial agent Lyofix MLF new, Ciba) in the pad-cured treatment can increase the phosphorus level further to give significantly enhanced 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.