Structural properties of films and rheology of film-forming solutions based on chitosan and chitosan-starch blend enriched with murta leaf extract

Chitosan (CH) and chitosan-corn starch (CH-CS) film-forming solutions (FFS) and films, with or without polyphenol-rich aqueous extract from murta (Ugni molinae Turcz) leaves (PEML) were prepared. The impact of the FFS type and PEML, considering pH values of the FFS, on dynamic and steady-shear behavior of FFS, interaction mechanisms of PEML with polymer chains and changes on infrared spectra of films were investigated. Mechanical properties, thickness and color from films were also evaluated. Blending CH with PEML produced huge aggregates that were visible to the naked eye. Rheological parameters, K and n, were affected significantly by the FFS type and the PEML presence. Viscosity of both FFS increased with the addition of PEML, leading a gel-like structure and thixotropic behavior. Sol–gel transition occurred when PEML was added to FFS, increasing strongly their elasticity. The addition of PEML to CH-CS blend film leads to a reduction (p < 0.05) of elongation at break and tensile strength, increasing its thickness and yellow color. The PEML formed electrostatic interactions with chitosan. Ester linkages and hydrogen bonds were also formed between PEML and both chitosan and starch blends.