Preparation of high-strength, high-modulus PVA fiber by synthesis of syndiotacticity-rich high molecular weight PVA polymers with VAc and VBz via emulsifier-free emulsion polymerization

Different vinyl acetate (VAc) and vinyl benzoate (VBz) monomer ratios have been chosen as monomers to create high polymerization degree ( P n ) and high syndiotacticity-diad content ( S-diad ) poly(vinyl alcohol) (PVA) polymers via emulsifier-free polymerization in order to address the problem of limited mechanical capabilities of PVA fibers prepared with low P n and low S-diad polymer. The variations in hydrogen bonding, P n , S-diad , and viscosity of different PVA polymers were investigated and evaluated using Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, gel permeation chromatography, and a viscosity tester. Moreover, various PVA fibers with high strength and modulus have been manufactured using a synthetic polymer as the raw material for dry-wet spinning. The effect of P n and S-diad on the mechanical and thermal characteristics of PVA fibers is evaluated using a variety of characterization techniques, such as the scanning electron microscope, differential scanning calorimetry, thermogravimetric analyzer, X-ray diffraction, and tensile tester. As the ratio of VBz monomer increased, the results suggested that VBz may have a considerable impact on the P n and S-diad of PVA polymers, the  OH vibration absorption peak reduced from 3491 to 3442 cm −1 ; the P n increased from 2112 to 17,704; and the S-diad rose from 51.2% to 60.1%. In addition to the fact that P n and S-diad significantly increased the fibers' strength and modulus, the crystallinity increased from 41.8% to 51.7%, and the orientation degree rose from 87.5% to 91.7%, as P n and S-diad increased; the tensile strength and highest elastic modulus increased from 9.71 ± 0.3 cN/dtex to 12.74 ± 0.5 cN/dtex (increased of 31.2%) and 264.52 ± 9.3 cN/dtex to 338.41 ± 8.6 cN/dtex (increased of 27.9%); the elongation at break decreased from 5.63 ± 0.3% to 2.92 ± 0.2%.