Effect of nitrogen additives on thermal decomposition of cotton

As a part of investigation of phosphorus–nitrogen synergistic flame retardancy of cotton fabrics, functions of three nitrogen compounds, urea (UR), guanidine carbonate (GC), and melamine formaldehyde (MF), were studied. The cotton fabrics treated by three compounds exhibited different thermal degradation patterns but similar limiting oxygen indexes, proven nitrogen compounds alone have no significant flame retardant effect on cellulose. The thermal decompositions of the nitrogen compounds were different during the pyrolysis and combustion. UR decomposed quickly and releases large amount of ammonia and other non-flammable gases, while MF promoted char formation with cellulose. GC exhibited both gas releasing and char formation on cotton under heat. Activation energy of decomposition of GC and MF treated cotton was more than the untreated cotton and lower for UR treated cotton. UR and GC treated cotton showed decrease in heat of combustion values and that of MF treated cotton showed an increase in values as compared to untreated cotton. Fourier transform infrared spectra (FTIR) analysis of chars obtained after thermal gravimetric analyses (TGA) treatment showed presence of nitrogen in the char bonded chemically as heterocyclic. Chars of MF and GC treated fabrics contain more C–N bond as compared to UR treated fabrics indicating greater interaction of GC and MF with cellulose during thermal decomposition.