Submitted to: Biomacromolecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 2, 2007
Publication Date: April 4, 2007
Citation: Glenn, G.M., Klamczynski, A., Chiou, B., Wood, D.F., Orts, W.J., Imam, S.H. 2007. Heat expanded starch-based compositions. Biomacromolecules. 55(10):3936-3943 doi url:http://dx.doi.org/10.1021/jf0630163. Interpretive Summary: Many starch-based foam materials are made by pressurizing starch and water mixtures and then explosively releasing the pressure to make a foam product. It is very difficult to use these technologies to make molded articles. This paper describes a technology for making starch foam at ambient pressures. The technology has potential for making molded starch foam products that could be used for biodegradable packaging.
Technical Abstract: A heat expansion process similar to that used for expanded bead polystyrene was used to expand starch-based compositions. Foam beads made by solvent extraction had the appearance of polystyrene beads but their open-cell structure precluded them from expanding further when heated. Non-porous beads, pellets or particles were made by extrusion or by drying and milling cooked starch slurries. The samples expanded into a low density foam by heating 190°C to 220°C for more than 20 s at ambient pressures. Formulations containing starch (50-85%), sorbitol (5-15%), glycerol (4-12%) ethylene vinyl alcohol (EVAL, 5-15%) and water (10-20%) were studied. Bulk density was negatively correlated to sorbitol, glycerol and water content. Increasing the EVAL content increased bulk density, especially at concentrations higher than 15%. Poly(vinyl alcohol) (PVAL) increased bulk density more than EVAL. Bulk density was lowest in samples made of wheat and potato starch compared to corn starch. The expansion temperature for the starch pellets decreased more than 20°C as the moisture content was increased from ten to twenty five percent. The addition of EVAL in the formulations decreased the equilibrium moisture content of the foam and reduced water absorption during a 1 hr soaking period.