Linear polyamidoamines as novel biocompatible phosphorus-free surface-confined intumescent flame retardants for cotton fabrics

Eight linear polyamidoamines (PAAs) prepared by polyaddition of amines to bisacrylamides are investigated as intumescent surface-confined flame retardants for cotton textiles. The structure of the amine-derived subunits governs their performances. In ignitability tests, aminoacid-deriving PAAs exposed to direct flame for 10 s do not burn, but produce carbonaceous crusts sheltering the underneath sample apparently intact. PAAs carrying guanidine pendants partially volatilize without burning. 2-Methylpiperazine-derived PAAs burn completely. Thermogravimetric analyses show that in air at ≥400 °C all PAAs leave substantial char residues that oxidize at >500 °C. Horizontal flame spread tests on PAA-impregnated cotton stripes show flame extinction for add-ons ranging from 4 to 20%, apart from 2-methylpiperazine-deriving PAAs that never extinguish flame but slow down flame propagation leaving a substantial residue. In vertical flame spread tests, no PAA induces flame extinguishment at add-ons up to 20%, but all PAA-treated fabrics leave significant residues. In cone calorimetry tests, all PAAs increase the time to ignition and decrease the peak of heat release rate and the effective heat of combustion. Most PAAs remarkably reduce the release of CO and CO2. After the above tests the combustion residues of PAA-treated cotton fabrics present intumescent bubbles. All results indicate that PAAs warrant potential as effective surface-confined intumescent flame retardants.