Author
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Carriere, Craig |
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Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/18/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Starch is a commodity polymer that is utilized today in a wide variety of commercial applications ranging from foods and adhesives to blends and composites. Increasingly, starch is being used in applications previously regarded as the realm of synthetic polymers due to the low cost and potential biodegradability of the material. In order to compete on a cost-effective basis a better understanding of the factors that govern the flow properties of starch needs to be developed. In this study the molecular weight between entanglement points for waxy and normal maize starches was determined for the first time. This parameter is of importance in determining the flow properties of materials. The entanglement molecular weight for starch was found to be much higher than literature values for typical commercial polymers. This finding indicates that molecular weight of over one million are required to produce starch-based materials with consistent physical properties. Starch is a renewable resource, and its potential to replace non-renewable petrochemical-based polymers offers manufacturers a low-cost alternative to the increasing price structure of many commercial synthetic polymeric materials. Technical Abstract: The entanglement molecular weights of waxy maize (WM) and normal maize (NM) starches were calculated from solution rheological data. Small-amplitude oscillatory shear experiments were conducted on both WM and NM starch solutions dissolved in 90/10 DMSO/water. The viscoelastic properties of the solutions at several different concentrations were measured and then shifted to produce a master curve for each of the materials. The theory of Doi and Edwards was used to calculate the plateau moduli from which values for the entanglement molecular weights for WM and NM starches were calculated using rubber elasticity theory. The entanglement molecular weight for WM starch is 100 +/ 15 kg/mol. For NM starch the value for the entanglement molecular weight is 96 +/ 8 kg/mol. These two values are within experimental error of one another and represent the entanglement molecular weight of amylopectin, the major component of WM and NM starches. This value is markedly higher than typical commercial polymers. |
