Fabricating flame retardant polyacrylonitrile fibers modified by sodium lignosulfonate and copper ions

A facile and eco-friendly approach was developed to endow polyacrylonitrile fibers (PAN) with excellent flame retardancy and char-forming capability. First, aminated PAN (A-PAN) was prepared via ethylenediamine treatment. Next, sodium lignosulfonate (SLS) was adsorbed on the surface and interior of A-PAN through strong ionic bonds to obtain the SLS modified A-PAN, i.e., SLS/A-PAN. Afterwards, copper ions (Cu2+) were chelated with SLS/A-PAN to construct Cu/SLS/A-PAN. The modified PAN samples were characterized by solid-state 13C NMR, FTIR, XPS and SEM. TGA demonstrated that the preferential degradation of Cu/SLS/A-PAN was prone to forming much char residue whether in N2 or air atmosphere, which acted as an effective barrier to hinder the decomposition of PAN matrix so as to exhibit excellent flame retardancy. Additionally, the char residue of Cu/SLS/A-PAN showed numerous intumescent vesicles with continuous wavy-like char layer and its ID/IG value was 1.28, exhibiting superior degree of graphitization. Particularly, compared to the pristine sample, the peak of heat release rate of Cu/SLS/A-PAN decreased significantly. In addition, TG-IR indicated the volatile products of Cu/SLS/A-PAN were significantly reduced. SLS and Cu2+ were cooperative in endowing Cu/SLS/A-PAN with excellent flame retardancy and superior char-forming capability.