Combustion forming hollow nanospheres as a ceramic fortress for flame-retardant fiber

Simple, effective and safe flame retardants are required to improve flame retardant properties of polymer fibers.However, traditional additive flame retardants, such as halogen-flame retardants and intumescent flame retardants, are likely to cause phase separation of functional phases due to their poor dispersibility and compatibility, or are difficult to be suitable for the high temperature processing conditions of melt-spun fibers. Here, in an effort to develop a practical flame retardant system in which zinc diphosphinate(DEPZn) and D-glucose(DG)were selectively incorporated into polyethylene terephthalate(PET) fiber was developed. As a result, the dense nano-scale zinc phosphate microspheres were formed on the surface and inside the residual carbon during combustion. Thus, PET fibers were endowed with excellent flame retardancy through a thermal barrier and enhancement of physical strength for the carbon layer. Moreover, a synergistic flame-retardant effect was found between DEPZn and DG. DG reduced the size of the zinc phosphate nanosphere from 200 nm to 50 nm, making the carbon layer denser and smoother. As a result, the peak heat release of the resultant PET composite fiber decreased to 410 k W/m~2 compared 1276 k W/m~2 for neat PET fiber. Moreover, the total smoke release also dropped from 71 MJ/kg of neat PET fiber to 64 MJ/kg for PET composite fibers. These results provide a promising strategy for the production of industrialized PET flame retardant fibers.