Zn2+-DTPMPA chelated cellulose nanocrystal hybrid: synergistic flame-retardant, antibacterial and mechanical reinforcement mechanisms for PA66 composites

The inherent flammability, lack of antibacterial function, and “performance-sustainability trade-off” caused by traditional additives of polyamide 66 (PA66) severely restrict its application in safety-critical fields like aerospace and medical devices. Thus, this study prepared a green bio-nanohybrid (DCZ) by constructing interfacial chelation between Zn 2+ and diethylene triamine penta(methylene phosphonic acid) (DTPMPA) on the surface of cellulose nanocrystals (CNC). When compounded with PA66, DCZ exhibits excellent properties: limiting oxygen index (LOI) reaches 31.3 %, peak heat release rate (pHRR) decreases by 65.3 %, total heat release (THR) decreases by 26.8 %, and no melt dripping as well as good antibacterial performance. Notably, the chelation-induced cross-linked interphase also improves the material's tensile strength by 61.9 %. After 30 days of UV irradiation or immersion in pH 3–11 solutions, the LOI loss remains less than 4 %, breaking the bottleneck of poor weather resistance of traditional flame-retardant PA66 under harsh environments. This strategy upgrades PA66 into a multifunctional “safety material” platform, which can be processed into films, fibers and complex profiles. It provides a green and feasible technical path for the development of high-end safety materials for aerospace interiors, medical devices and other fields.