The thermo-oxidative behavior of cotton coated with polyamidoamines: a solid-state NMR-EPR joint study

Cotton is not fire-resistant and therefore poses a serious hazard in the event of a fire when used in indoor furnishings. However, cotton can be made flame-retardant through treatments with additives. The development of bio- and eco-friendly treatments using different types of additives is currently a quite active research. Polyamidoamines (PAAs) derived from alpha-amino acids are both bio- and eco-friendly flame retardants (FRs) and do not release smoke during combustion. Aim of this study is to investigate the reactions that take place in cotton impregnated with PAAs during a fire. Given the rapidity of the process, it is difficult to follow the transformations occurring in the burning material. Thus, we adopted the strategy of thermal oxidizing the material under controlled conditions and characterizing the intermediate products. No evidence on the mechanism of thermal oxidation of cotton in the presence of the PAAs has been reported so far. We used 13C solid state NMR spectroscopy to study the products of partial combustion of cotton impregnated with different PAAs based on glycine and cystine. Figure 1 shows the 13C cross polarization magic angle spinning (CP-MAS) spectra of cotton impregnated with cystine charred at different temperatures as an example. EPR spectroscopy was also used to gain insight into the mechanism of thermal oxidation.