Phase Behavior of Ionic Liquids/Melamine-Formaldehyde Prepolymer/Coagulator System and Its Influence on Fiber Formation Performance

The melamine-formaldehyde (MF) fiber is recognized as a high-performance flame-retardant material. In this study, the phase separation behavior of MF prepolymer (pre-MF) was investigated using ionic liquids (ILs) as solvents, with the aim of establishing a process for MF fiber spinning. The cloud point titration method, in conjunction with a turbidity correlation equation, was employed to construct the ternary phase diagram of the IL/pre-MF/coagulator system across the entire compositional range. The effects of IL type (molecular weight of pre-MF), coagulator species, and regeneration temperature on the phase separation behavior during MF fiber fabrication were systematically examined. Furthermore, MF fibers were prepared to evaluate the influence of coagulation bath conditions on fiber formation, curing behavior, and properties. The structure and morphology of the MF fibers were characterized by scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface area; the results show that the type of coagulation bath leads to significant differences in the structure and properties of the fibers. Fibers coagulated in water exhibit a dense architecture; the resulting fibers possess favorable mechanical properties, including a tensile strength of 150 MPa and a limiting oxygen index of 37.5%. This study is expected to promote the development of MF fibers.