In-situ assembly of hyperbranched phosphonitrile networks and ZrP: Preparing durable flame retardant and high char-forming regenerated cellulose fibers

Addressing the dual challenges of diminishing fossil reserves and proliferating plastic waste accumulation, harnessing renewable cellulose resources offers a promising solution. Guided by the principles of intumescent flame retardant system, the eco-friendly hyperbranched phosphonitrile networks integrating acid, carbon and gas sources was prepared and covalently anchored onto Lyocell fabrics. Further, the hyperbranched phosphonitrile networks induced the interfacial assembly of zirconium phosphate (ZrP) to construct flame retardant Lyocell fabrics (Lyocell-TCHNs@ZrP) with low-temperature multiphase catalytic carbonization and high-temperature physical shielding effects. The char residue of Lyocell-TCHNs@ZrP under N 2 atmosphere was increased from 13.63 % of original sample to 39.12 % at 800 °C, while the thermo-oxidative behavior was also suppressed in air conditions. Meanwhile, the peak heat release rate (PHRR) and total heat release (THR) of Lyocell-TCHNs@ZrP were reduced by 66.10 % and 80.90 %, which showed great self-extinguishing ability in combustion test. In addition, the tensile strength of Lyocell-TCHNs@ZrP was slightly improved, while the hand feel and whiteness were well remained. This work provided fundamental insights into the molecular design of hyperbranched intumescent flame retardants and the synergistic interaction between solid catalysts, along with an effective strategy for the fire safety performance of cellulose derived textiles.