Structural, thermal, optical, and mechanical properties of composite films developed from the button mushroom (Agaricus bisporus)-sourced high molecular weight chitosan and potato starch

Films were fabricated using the button mushroom (Agaricus bisporus) sourced high molecular weight chitosan with or without potato starch using the casting method. Glycerol was used as the plasticizer. Chitosan content in the film-forming solution (FFS) was varied (0.5, 0.75 and 1.0% w/v of FFS) while potato starch (1.0% of FFS) and glycerol (25% of the total solid content in the solution) contents were not varied. The control sample contained only chitosan (1.0% of the FFS) and glycerol. The effect of increasing the content of chitosan on the rheological properties of FFS and the properties of the films were investigated. The FFS's shear viscosity and shear modulus (elastic and viscous components) increased with increasing chitosan content. Morphological examination revealed that the films exhibited a compact structure devoid of large pores and cracks. Surface roughness captured with an atomic force microscope was reduced (19-6 nm) with increasing content of chitosan in the film. The films exhibited two hydrated crystalline phases at 9 and 20^o. Light transmittance and glossiness of the films were enhanced with increasing chitosan content. FTIR analysis indicated the increasing availability of reactive sites with the increasing content of chitosan leading to an enhanced hydrogen bonds network and increased cohesion of the film structure. This may be the reason for improved mechanical properties and reduced water vapour permeability of the films with increasing chitosan content.