Studying physical state of films based on casava starch and/or chitosan by dielectric and thermal properties and effects of pitanga leaf hydroethanolic extract

Cassava starch (CS) and chitosan (CH) are biopolymers used alone or blended (CS/CH) to produce films, thanks to their excellent film-forming properties. Their main physical properties have been characterized, but their physical and water state have not yet been studied. The objective of this research was to study the water and macromolecular physical state of CS, CH and CS/CH films by DSC and dielectric properties, after sorption isotherms determinations. Biopolymers and obtained films were also analyzed by SEM, FTIR, X-ray diffraction and gas permeability. Dielectric properties of active films containing pitanga leaves hydroethanolic extract were also analyzed. All films presented type II sorption isotherms. Glass transition temperature of films decreased with the increase of moisture content (Xw) following the Gordon and Taylor model. The dielectric constant behaves depending of the monolayer moisture content (Xm): increased linearly as a function of Xw when Xw > Xm. For Xw ≤ Xm, the dielectric constant remained constant. An exponential relationship between α-relaxation and Tg was calculated. •Cassava starch and chitosan produces homogenous and high gas barrier films.•Films moisture content (Xw) varied with water activity according to the GAB model.•Films glass transition temperature varied with Xw following the Gordon & Taylor model.•Dielectric constant increased linearly with Xw for above the water monolayer.•α-relaxation reduced exponentially as a function of glass transition temperature.