Acrylic fibers [polyacrylonitrile (PAN) fibers] have excellent flame-retardant properties after they are modified by hydrazine hydrate and metal ions; however, their widespread applications are restricted because of poor mechanical properties. To improve the mechanical properties of these modified PAN fibers, poly(vinyl alcohol) (PVA) was added to the spinning solution of PAN as an effective reinforcing agent. The structure of the fibers before and after modification was studied by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy, and wide-angle X-ray diffraction. The mechanical properties and flame resistance of the fibers after treatment were also tested by a single-fiber tensile tester and a limiting oxygen index (LOI) analyzer, respectively. We found that the LOI of the modified fibers was reduced from 54.7 to 29.1 after the introduction of 50 wt % PVA; however, the tensile strength was dramatically improved from about 1.50 cN/dtex to more than 4.00 cN/dtex. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43006. Recently, we reported a convenient two-step method for obtaining flame-retardant acrylic fibers. 19 With shorter processing procedures, the tensile strength of the fiber was improved slightly. Empirically, to be used in woven form, the tensile strength of the fiber should be above 2.50 cN/dtex. Therefore, it is still necessary to improve the mechanical properties of these metalbased flame-retardant-modified PAN fibers. Because of the
