Flame retardant effect of lignin/carbon nanotubes/potassium carbonate composite coatings on cotton roving

A new composite flame retardant coating for cotton roving has been investigated. The proposed coating comprises natural lignin, pure carbon allotrope carbon nanotubes (CNTs) and non-toxic potassium carbonate (K2CO3). The series of complementary experiments, including thermogravimetric analysis, vertical burning in fire tube, limiting oxygen index (LOI) measurement and combustion in mass loss calorimeter enabled the formulation of an optimum composition including aqueous suspension with 1 wt% of CNTs, 1 wt% lignin (L) as well as 1 wt% of K2CO3. Applying L/CNT/K2CO3 on cotton roving increased LOI from 17.1 to 38.5%, decreased final mass loss and temperature during vertical burning from 100 to 78% and 457 to 190 °C, respectively. Moreover, peak heat release rate and total heat released dropped from 97.5 to 70.4 kW/m2 and from 4.2 to 1.6 MJ/m2, respectively . The above experiments supported by scanning electron microscopy and Raman spectroscopy allowed also the explanation of the complementary mechanisms responsible for the overall fire retardant effect.