A more environmentally friendly path to the family of the flame-resistant semi-ladder “Lola” fibers

High strength flame-resistant semi-ladder fibers of the “Lola” family (PNBI) have been obtained by an acid-free and more environmentally friendly method with controlled heating of precursor fibers in an inert atmosphere. The suggested two-step method consists in preparation of a prepolymer (PANI-O) in N-methylpyrrolidone. The prepared PANI-O dopes were additionally modified by introducing a certain part of a non-solvent (ethanol) to smooth the interdiffusion mass-transfer and prepare defectless precursor fibers. A detailed study of the thermal behavior of the PANI-O fibers by DSC and TGA shows that the maximum exothermic effect is observed at 320–370 °C, associated with formation of a ladder structure, i.e., transformation of the PANI-O into the PNBI-O. As a result, after the heat treatment, the flame-resistant PNBI “Lola” family fibers were obtained with an oxygen index of up to 83, tensile strength of ∼500 MPa, relative elongation of ∼5% and elastic modulus of ∼12 GPa. Flame-resistant semi-ladder PNBI fibers were obtained by acid-free environmentally friendly way through PANI-O prepolymer stage. • PNBI fibers were obtained by an environmentally friendly way. • PNBI fibers were obtained through a PANI-O prepolymer stage. • Ethanol addition leads to defectless pre-polymer fibers by dry-wet spinning. • LOI of 83 for the H 3 PO 4 impregnated PNBI fibers was obtained. • Outstanding mechanical properties were recorded for the obtained PNBI fibers.