Extrusion of starch-based loose-fill packaging foams: Effects of temperature, moisture and talc on physical properties

Starch-based loose-fill packaging foams were made in a single-screw laboratory-scale extruder. Corn starch was blended with polystyrene in the ratio of 70: 30 and extruded into foams using talc and polycarbonate as additives. Extrusions were carried out at moisture contents of 16, 18 and 20% (dry basis), and at barrel temperatures of 140 and 160 degrees C. The influences of extrusion temperature, moisture content of starch, talc and polycarbonate on the radial expansion and other selected physical properties of starch foams were investigated. The effects of moisture and talc contents on the radial expansion of foams were found to be critical, while the role of temperature was close to significant. The expansion ratio increased when the moisture content was increased from 16 to 18%, and then decreased when moisture content was increased to 20%. In general, the expansion ratios of foams were higher at 160 degrees C as compared to 140 degrees C. Although polycarbonate mixed well with the starch-polystyrene melt, it was not effective as a structural and anti-shrinking agent, and it did not contribute to the radial expansion. In general, the bulk densities and unit densities of the starch foams decreased as the moisture content and extrusion temperature increased. Scanning electron microscope images showed that the addition of talc yielded foams with smaller-sized cells, with less expansion of the foam melt, and thus a higher density. X-ray diffractograms revealed that the crystallinity of starch foams increased post-extrusion, and there was adequate dispersion of the starch and polystyrene polymers to make the foam water-resistant. Copyright (c) 2008 John Wiley & Sons, Ltd.