Alternative plasticizers for the production of thermo-compressed agar films

Agar films were produced by thermo-compression using choline chloride (ChCl) as a plasticizer with urea. The three solid components were mixed together with the salt and urea (minor components) added to agar (main component) according to a fixed mass ratio of, respectively, 1.16:1:5. A central composite rotatable design (CCRD) with three parameters, 2³, was used to evaluate the effects of temperature (X₁; °C), time (X₂; min) and applied load (X₃; kN) of heat-pressing on the maximum tensile strength (TS) of the films (Y; MPa). Mixtures of urea and agar prepared at a mass ratio of 1:5 did not form homogeneous films suggesting the important plasticizing role of the salt. Heat-pressing the mixtures at more draconian conditions led to much darker and opaque films, with better mechanical resistance (higher values of TS). The most resistant film (~15MPa) was obtained at 140°C, 20min and 176kN. Selected films, including the optimal, showed similar water sorption profiles and close values of water vapor permeability (~2.5-3.7×10^-9gm^-1s^-1Pa^-1). The fracture behavior and mechanical properties of the films were greatly affected by additional water plasticization when the films were stored at different conditions of relative humidity.