Electron beam pretreatment to enhance Schiff base of watermelon seed shell nanocellulose with tannic acid-decylamine: The complex's universality for various emulsion systems

Nanocellulose has shown great potential and practical applicability across numerous fields, but its inherent hydrophilicity is a major limitation for its use in non-aqueous environments. In this work, electron beam irradiation pretreatment at 40, 80, and 120 kGy accelerated the Schiff base reaction of watermelon seed shell nanocellulose (WNC) with tannic acid and decylamine. Consequently, hydrophobic WNC with a DS of 0.42–0.72 was synthesized, up to 40%–140% higher than untreated WNC (0.30). A decreased hydrophilic-lipophilic balance and contact angle confirmed the improved lipophilicity. FTIR confirmed the successful formation of imine (-C=N-) linkages, indicating effective Schiff base grafting. Morphological observations revealed that a transformation of WNC from elongated ribbons into aggregated granules with more crystal defects formed after modification. Hydrophobic WNC exhibited enhanced oil-holding capacity and radical-scavenging activity. A cascade strategy was developed to fabricate stable low-oil emulsions and high internal phase emulsion (HIPE) gels using the hydrophobic WNC. Notably, the HIPE gels showed strong oil entrapment and effectively retarded lipid oxidation. This work unlocks the value of agricultural byproducts as a source of nanocellulose and offers a streamlined and sustainable strategy for producing highly functional nanocellulose. • EBI altered the aggregate structure of watermelon seed shell nanocellulose (WNC). • Crystal defects and hydroxyl exposure promoted WNC hydrophobic modification. • Hydrophobized WNC exhibited enhanced oil-holding capacity and antioxidant activity. • WNC improved the thermodynamic and gravitational stability of low-oil emulsions. • HIPE gels stabilized by WNC effectively retarded lipid oxidation during storage.