Synthesis, Characterization, and Performance of Urea–Formaldehyde Fibers

A series of urea–formaldehyde (UF) fibers with different urea-to-formaldehyde ratios were synthesized using the dry spinning technique at room temperature. Subsequently, they were cured at various temperatures, achieving diverse cross-linking structures. Structural and property analyses of the fibers were conducted using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS),¹³C nuclear magnetic spectrum analysis (¹³C NMR), thermogravimetric analysis (TGA), and fiber elongation strength testing. The results showed that during heat curing of the UF fibers, mainly hydroxymethyl and amino groups underwent dehydration to generate methylene, and finally the fiber formed a three-dimensional crosslinked structure. When the urea/formaldehyde molar ratio was 1:2 and the curing temperature was 180 °C, the breaking strength of the UF fibers was 202 MPa, elongation at break was 3.6%, and char yield at 700 °C was 26.28%.