Sulfonation-modified Artemisia sphaerocephala gum films: Fabrication strategies and characterization

To enhance the bioactivity and expand the application scope of Artemisia sphaerocephala Krasch polysaccharide gum (ASKG), it was sulfonated to yield sulfonated ASKG (S-ASKG). Using ASKG as a control, comparative analyses of the physicochemical properties and functional characteristics were performed. Films fabricated from S-ASKG and ASKG were comparatively analyzed for their structural, mechanical, and barrier properties. Structural characterization by Fourier Transform Infrared (FTIR) spectroscopy and Hydrogen Nuclear Magnetic Resonance (¹HNMR) spectroscopy confirmed the successful grafting of sulfonic acid groups (-SO₃H) onto the polysaccharide backbone. Scanning electron microscopy (SEM) analysis showed that S-ASKG had a rougher surface morphology than ASKG. Four S-ASKG derivatives with varying degrees of substitution (DS) were systematically characterized. At a concentration of 5 mg/mL, S-ASKG4 exhibited superior antioxidant performance, with ABTS radical scavenging activity of 79.75 %, hydroxyl radical scavenging activity of 58.49 %, DPPH radical scavenging activity of 34.14 %, and superoxide radical scavenging activity of 47.97 %, outperforming unmodified ASKG. The S-ASKG films and ASKG films were prepared using the solvent casting method. The S-ASKG film exhibited a more uniform surface morphology with enhanced water molecule binding capacity and fewer structural defects. Compared with ASKG films, S-ASKG films exhibited higher crystallinity. The tensile strength increased from 8.46 MPa to 9.33 MPa, and the elongation at break increased from 30.37 % to 76.01 %. The water vapor permeability decreased from 2.583 × 10^-11 g·m^-1·s^-1·Pa^-1 to 1.267 × 10^-11 g·m^-1·s^-1·Pa^-1, and the oxygen permeability decreased from 0.0192cm³·mm/(m²·d·atm) to 0.0149 cm³·mm/(m²·d·atm). Both mechanical and barrier properties were enhanced. Furthermore, at a film concentration of 75 mg/mL, the S-ASKG film displayed significantly stronger antioxidant capacity, showing ABTS radical scavenging activity of 63.83 %, hydroxyl radical scavenging rate of 52.49 %, DPPH radical scavenging rate of 33.55 %, and superoxide radical scavenging rate of 43.37 %. Sulfonated polysaccharides showed significant potential for functional films.