Sulfur-Based Copolymeric Polyamidoamines as Efficient Flame-Retardants for Cotton

The polyamidoamine derived from N,N′-methylenebisacrylamide (M) and glycine (G), M-G, has been shown to be an effective flame-retardant (FR) for cotton in horizontal flame spread tests (HFST), extinguishing the flame at 5% add-on. Its activity was attributed to its intrinsic intumescence. In vertical flame spread tests (VFST), M-G failed to extinguish the flame even at 30% add-on. Conversely, in VFST, the polyamidoamine derived from M and cystine (C), M-C, inhibited cotton combustion at 16% add-on, but in HFST failed to extinguish the flame below 12% add-on. Its activity was ascribed to the release of sulfur-containing volatiles acting as radical scavengers. In this work, the FR effectiveness of M–Gm–Cn copolymers with different G/C ratio was compared with that of the M–G and M–C homopolymers and of M–G/M–C blends of the same compositions. In HFST, both copolymers and blends extinguished the flame. In particular, M–G50–C50 and (M–G/M–C)50/50 extinguished the flame, even at 7% add-on. In VFST, the copolymers with ≥50% M–C units, similar to M–C, inhibited cotton combustion at 16% add-on. At the same add-on, the M–G/M–C blends failed to extinguish the flame. It may be concluded that, in contrast to blends, copolymers combined the merits of both homopolymers in all tests.