The chemistry of THPC–urea polymers and relationship to flame retardance on wool and wool–polyester blends. II. Relative flame-retardant efficiency on wool,polyester, and wool-polyester blends

Optimum flame retardance in THPC-urea-type formulations was achieved by approximately 1—0.9 THPC-urea mole ratio and slow urea addition. A phosphonium salt structure is more efficient in flame retarding 100% wool and wool-polyester blends than a phosphine oxide structure. Both structures are equivalent in flame retarding 100% polyester. It is considered probable that a vapor-phase mechanism is predominant in the phosphorus-based flame retardancy of wool, whereas a mixed solid-vapor phase mechanism operates for 100% polyester.