Polyelectrolyte complex for flame retardant silk

Silk fabric, a common component of household decor and apparel for its strength and luster, presents a fire hazard due to its high burn rate and release of toxic fumes during combustion. To combat this danger, a two-step polyelectrolyte complex (PEC), comprised of polyethylenimine (PEI) and poly(sodium phosphate) (PSP), was deposited to imbue silk with flame retardant behavior. Additionally, sonication was applied during various steps of the PEC process to improve coating penetration and reduce fiber bridging. With sonication during deposition, this unique treatment is shown to have higher weight gains through a more uniform dispersion of phosphorus and increased fiber separation within the fiber bundle. With the addition of less than 6 wt.% of this PEI + PSP PEC, silk is rendered self-extinguishing in vertical flame testing, with more than 90% residue remaining for all coated samples. Gas and condensed phase analysis suggests an intumescent flame retardant mechanism. The efficient deposition of this low-concentration flame retardant PEC on silk allows for improved scalability with no significant alteration of the mechanical behavior.