Surface, mechanical and barrier properties of bio-based composite films based on chitosan and whey protein

• Self-standing chitosan, whey protein, composite bilayer and blend films are produced.
• In the dry state, blend films are excellent barrier to oxygen.
• Bilayer films have significantly lower WVP in comparison to both pure and blend films.
• Water vapour plasticized the whey protein and chitosan films.
• Good adhesion and integrity of the chitosan and the whey protein layer are observed.

Mono-component and composite bilayer and blend films composed of chitosan and whey protein were made. Colour, microstructure, water contact angles, swelling, water vapour sorption, barrier properties (oxygen, water vapour), water vapour diffusion coefficients and mechanical properties were determined. The influence of water vapour on barrier properties was studied in relation to the surface and structural properties. Mono-component and bilayer films were transparent with a homogeneous surface. Contrarily, blend films were translucent. Bilayer films had significantly lower water vapour permeability in comparison to mono-component and blend films. In all bilayer films, the air side (chitosan) was characterized by swelling, while the support side (whey protein) swelled after initial absorption. At low relative humidities, blend films were excellent barrier to oxygen and they completely lost their gas barrier performance in a humid environment. Bilayer films had enhanced mechanical resistance. The films with higher chitosan content showed higher capacity for elongation. Lamination and blending of chitosan and whey protein is a useful method to obtain new materials with desired functional properties.

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