Factors affecting water resistance of alginate/gellan blend films on paper cups for hot drinks

Enhanced film water resistance of paper cups was achieved by physically blending sodium alginate (NaAlg) and gellan gum with crosslinking treatment. Pure and blended films were prepared and characterized via Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and positron annihilation lifetime spectroscopy (PALS). Results demonstrated excellent compatibility between the two polysaccharides. Total mixed solution concentration, component ratio, glycerol content, Ca²⁺ concentration, crosslinking time, and dry temperature affected water resistance. Water permeability (WP) and swelling degree (SD) were tested. Optimal conditions were as follows: total mixed solution concentration, 2.4% (m/v); component ratio, 2:1; glycerol content, 0.5% (m/v); Ca²⁺ concentration, 5% (m/v); crosslinking time, 5min; and dry temperature, 50°C. WP and SD values were 78.1×10^-8g/msPa and 66.3%, respectively. Properties of the films showed the synergistic effect between NaAlg and gellan, which can be used for water-resistant film coating on paper cups for hot drinks.