pH-responsive packaging films based on modified bacterial cellulose Pickering emulsions: Effect of emulsion concentration and droplet size

Active films have gained significant attention as an emerging technology, yet research on Pickering emulsion films with environment-responsive release performance remains limited. Bacterial cellulose (BC) was modified to obtain two solid particles (BC-COOH and BC-PEI), which were subsequently used to prepare corresponding emulsions (PE-COOH and PE-PEI). Characterization revealed differences between the emulsions: PE-COOH showed larger droplets (6.46 μm) with zeta potential of −45.16 mV, whereas PE-PEI exhibited smaller droplets (320.56 nm) with zeta potential of +54.96 mV. Two emulsion types with distinct droplet sizes were incorporated into sodium alginate (SA), prepared composite films (EC and EP). The influence of emulsion concentration (5–15 % v/v) and droplet size on film morphology and properties was investigated. SEM images showed that EP3 showed non-porous morphology, and the surface had good compatibility with SA. The EP3 films exhibited excellent UV–vis blocking efficiency (92.4 % at 280 nm), thermal stability and significant antioxidant properties. However, there were limitations in mechanical properties, with tensile strength and elongation at break decreasing by 15.72 % and 57.90 %, respectively. Based on the comprehensive performance evaluation, EP3 was selected for pH responsiveness testing. The cumulative release of EP3 film was 0.175 μL/mg at pH 7.2. When the pH increased to 8.5 and 10.0, the cumulative release increased by 53.14 % and 76.0 %, respectively. Under alkaline environment (pH 10), the particle size of PE-PEI increased to 6663.33 nm and the zeta potential changed to 37.43 mV, which further confirmed the pH-responsive property of the films loaded with emulsion.