Tough and swelling-resistant gellan gum-based biofilms with excellent transparency, surface hydrophobicity and barrier capability.

The rising energy and environmental crisis brought by extensive usage of disposable synthetic plastic packaging necessitates the pursuit of ecofriendly packaging materials. Herein, a novel type of biofilms from exopolysaccharide gellan gum (GG) were developed through successive sol-gel transition, hydroalcoholic pretreatment and ionic anchoring before air-drying. Universal electronic testing machine, gravimetry, contact angle meter and UV-visible spectrophotometer were employed to investigate the mechanics, swelling-resistance, surface hydrophobicity and barrier property. The results indicate hydroalcoholic pretreatment ameliorates the toughness of GG films, with the breakage elongation and tensile toughness reaching ~17 % and 9.44 MJ/m. Metal-ion anchoring bestows swelling-resistance and surface hydrophobicity to GG films. The equilibrium swelling ratio after Fe-anchoring dropped to ~150 % in water, in stark contrast with the measurable swelling ratio of those unanchored beyond 2700 % which were followed by loss of dimensional integrity. The surface hydrophobicity is improved significantly with the water contact angle enlarged from 48° to 77° after Fe-anchoring. Metal-ion anchoring also improves the water vapor barrier performance, and notably Cu/Fe-anchoring endows UV light-shielding ability to GG films. The prominent performance along with the environmental friendliness of GG is conducive for future application in single-use packaging materials.