|Zhou, Genwen - FORMER USDA/ARS|
|Wu, Ying Victor|
Submitted to: Polymers and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 4, 2002
Publication Date: N/A
Interpretive Summary: Starch is a low cost, annually renewable resource which can be used as a filler to lower the cost of biodegradable materials. When starch in its native granular form is added to biodegradable plastics, it alters flow properties and mechanical strength. In order to properly design process- ing methods for starch-filled materials, it is necessary to characterize the viscosity, or resistance to flow. In this work, the effect of starch particle size on viscosity was characterized. By separating potato starch into fractions with different granule sizes, it was found that granule size had no significant effect on viscosity. However, when granule size was varied by using different types of starch, it was observed that smaller granule starches had higher viscosities. This effect was related to the bulk density of the starch. The bulk density is a measure of how well the granules of a given starch pack together. These results, which demonstrate ethe role of starch granule properties on viscosity, are of interest to researchers in the fields of biodegradable materials and processing.
Technical Abstract: The effect of starch granule size on the viscosity of starch-filled poly (hydroxy ester ether)(PHEE) composites was investigated with different sizes of potato starch and different starches (rice, corn, wheat, and potato). Potato starch was separated using an air classifier into different particle size fractions: <18 microns, 18-24 microns, 24-30 microns, and >30 microns. The starch was dried to a moisture content of 0.5 percent to minimize moisture effect on composite rheology. PHEE and potato starch were extruded with starch volume fractions of 0.46 and 0.66. Stress relaxation, frequency and strain sweep, and temperature dependence measurements were carried out. Although small variations in viscosity were seen with the different potato starch fractions, differences were not significant at a volume fraction of 0.46. Viscosity differences between the different particle size fractions were more pronounced at a volume fraction of 0.66. The temperature dependence could be described by an Arrhenius relation, with an apparent activation energy of 84 kJ/mole. At a volume fraction of 0.46, the starch/PHEE viscosities increased in the order potato starch <wheat starch = corn starch <rice starch.