Characterization of Blue Maize and White Sorghum Flour Films Made By Thermoplastic Extrusion

Abstract

The feasibility to produce flexible films from blue maize (BM) and white sorghum (WS) flours plasticized with sorbitol/glycerol through extrusion/compression was evaluated in this work. Screws speed rotation (50, 60, 70 rpm), extrusion temperature (100, 110, 120, 130 and 140°C), number of extrusion passes (1 or 2) and chemical modification of flour with maleic anhydride were the analyzed variables. Flexible films were obtained from all the treatments with tensile strength values in the range of 0.7-2.3 MPa and strain at break in the range of 0.08-0.74 mm/mm. Mechanical tests results showed that one extrusion cycle at 120°C and 60 rpm were the best tested. Extrusion temperature had effect weather in mechanical properties, microstructure and color of films; moreover FTIR analysis showed the induction of oxidized products at higher temperatures. Compared with native flours, films made with chemically modified flours increased tensile strength in a 29% for WS films, and strain at break in a 517% in BM films. Consistently, more uniform microstructure was observed by SEM in films made with chemically modified flours, and DMA indicates better matrix-plasticizer interaction than films made with native flours. BM and WS flours are suitable raw materials to produce thermoplastic films, although effective strategies to get materials with better performances have to be developed.