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, 2(3), 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 (∼ 15 MPa) was obtained at 140°C, 20 min and 176 kN. Selected films, including the optimal, showed similar water sorption profiles and close values of water vapor permeability (∼ 2.5-3.7 × 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.
REQUIMTE/LAQV, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal; Dairy and Functional Foods Research Unit, United States Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA. Electronic address: ana.sousa@ars.usda.gov.
Ana M M
AM
Sousa
REQUIMTE/LAQV, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal. Electronic address: hileiak@yahoo.com.
Hiléia K S
HK
Souza
Dairy and Functional Foods Research Unit, United States Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA. Electronic address: LinShu.Liu@ars.usda.gov.
LinShu
L
Liu
REQUIMTE/LAQV, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal. Electronic address: pilarg@fe.up.pt.
Maria P
MP
Gonçalves
D000362:Agar / Q000737:chemistry*; D055595:Mechanical Phenomena; D010968:Plasticizers / Q000737:chemistry*; D013227:Steam; D013696:Temperature; D014867:Water
D010968:Plasticizers; D013227:Steam; D014867:Water; D000362:Agar
Agar; Central composite rotatable design; Choline chloride; Mechanical properties; Response surface methodology; Urea