Regenerated cellulose fibers functionalized with lignin-derived boron-containing phenolic networks for durable flame retardancy and UV protection

The inherent flammability and insufficient ultraviolet (UV) protection of regenerated cellulose fibers limit their functional applications. Inspired by the natural polyphenol–polysaccharide synergy in plants, a lignin-derived boron-containing phenolic network (Lig-BPF) was incorporated into a cellulose spinning system and then coordinated with Zn 2+ to fabricate Cellulose/Lig-BPF@Zn fibers. Compared with pristine cellulose fibers, Cellulose/Lig-BPF@Zn increased the char residue at 800 °C from 13.72% to 30.35% under N 2 atmosphere, and reduced the peak heat release rate by 43.03%. The limiting oxygen index increased from 17.2% to 31.5%, and still remained 29.1% after 20 laundering cycles. TG-FTIR analysis showed an 88.56% reduction in total volatile release intensity, while Raman analysis confirmed an increased degree of graphitization, as evidenced by a decreased I D /I G value from 3.59 to 2.55. Furthermore, the UV protection factor increased from 11.42 to 128.82, and remained 109.74 after durability testing. Mechanistic analyses demonstrate that lignin-derived aromatic domains, boron-containing structures and Zn-coordinated species regulate cellulose pyrolysis and promote the char formation. This work develops a sustainable strategy for converting natural lignin into a bio-based flame retardant that simultaneously improves the flame retardancy and UV protection performance of regenerated cellulose fibers, providing a phosphorus-free and eco-friendly approach for preparing multifunctional carbohydrate-based fibers.