Wash-Durable Polyelectrolyte Complex Flame Retardant for Polyester Fabric

Polyelectrolyte complexes (PECs) have emerged as a benign alternative to traditional, halogenated flame retardants. Despite their success, PEC electrostatic interactions are susceptible to degradation in variable pH environments or in the presence of ionic species, such as laundry detergent (typically both alkaline and anionic). Wash durability on cellulosic fibers has largely been overcome by covalently binding the PEC to reactive groups along the cellulose backbone, but synthetic fibers lack the same functionalization sites. Other approaches, such as crosslinking, must be developed for durable PEC flame-retardant finishing of polyester, of which there are few preexisting studies, especially those that accurately simulate laundering conditions. Crosslinking a poly(allylamine hydrochloride) (PAH) / poly(sodium phosphate) (PSP) coating, using a blocked isocyanate, results in flame-retardant polyester that extinguishes during vertical flame testing, even after 12 machine washes with an anionic detergent. The isocyanate reacts with free amines on the PAH to form urea linkages, as confirmed with FTIR, improving the coating’s resistance to laundering by forming a covalent network around each fiber. Thermal curing further strengthens the coating and mitigates mechanical damage, but it worsens flame retardance. The blocked isocyanate also decreases the contact angle of the coated polyester by 60 degrees, ultimately improving the hand of the textile. These crosslinked coatings open the door toward the commercial feasibility of durable PEC flame retardants for synthetic fibers.