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 (Xi; degrees C), time (X-2; min) and applied load (X-3; 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 (similar to 15 MPa) was obtained at 140 degrees C, 20 min and 176 kN. Selected films, including the optimal, showed similar water sorption profiles and close values of water vapor permeability (similar to 2.5-3.7 x 10(-9) gm(-1) s(-1) Pa-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. (C) 2015 Elsevier B.V. All rights reserved.