100B-37 |
Zein-based biodegradable packaging films produced by extrusion |
Y. WANG, Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, 382-D, AESB, 1304 W. Pennsylvania Ave., Urbana, IL 61801 and G. W. Padua. Maximization of food safety and convenience will increase the demand for food packaging. However, new packaging materials should be of low environmental impact. Zein has been intensively studied for its film-forming ability and therefore its potential as biodegradable packaging. Zein has been processed into moldable resins but research is needed on improved methods for producing usable packaging films. In this study, we compared the structure and tensile properties of zein films produced by single-screw and twin-screw extrusion. Extruder feed was prepared by dissolving zein and oleic acid (70g oleic acid/ 100g zein) in 75% ethanol then pouring the solution into ice-water to form a dough. The dough was kneaded to form a cohesive mass, which was chopped into small pieces before extrusion. Both extruders, a single-screw (Model EPL-V501, C.W. Brabender) and a twin-screw (Model ZSK-30, Werner-Pfleiderer) were equipped with slit dies and operated at room temperature. The extruded sheet was pulled off by a set of rollers and allowed to dry at room conditions. Tensile properties were measured according to ASTM standard methods. Structure was observed by scanning electron microscopy on freeze-fracture surfaces of zein sheets. Tensile strength, % elongation, and modulus of single-screw extruded sheets were 3.1MPa, 115%, and 101Mpa, respectively. Corresponding data for twin-screw extruded sheets were 4.2Mpa, 96%, and 96.4Mpa, respectively. SEM on single-screw extruded sheets showed a large number of tiny holes, believed left over after moisture evaporated out; internal structure of twin-screw extruded sheets was smoother with lesser number of holes. Structural differences were attributed to the higher pressure and higher shearing force developed in the twin-screw extruder, which effectively squeezed out extrudate moisture and resulted in a more compact and uniform structure. Single-screw and twin-screw extrusion of zein-oleic acid resins produced continuous sheets of flexible plastic material potentially useful for food packaging.
Handout (.ppt format, 1743.5 kb)
Session 100B, Food Packaging
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