|Lawton jr, John|
Submitted to: Polymer Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/4/1999
Publication Date: N/A
Citation: Interpretive Summary: Increase in U.S. agricultural production has resulted in commodity abundance and lower prices. New value-added products must be found to give more profit to the farmer. Starch, particularly from corn, can be used to produce starch-based biodegradable plastics which would not only give value-added products but reduce the waste associated with petroleum-based plastics. Disposable plastic use in the U.S. is an 18 billion pounds per year industry. Better knowledge of the relationship between structure and properties in starch-poly(hydroxy ester ether) (PHEE) blends is needed to design products which can successfully meet the required properties. It was found that the viscosity of the blend during extrusion was significantly changed when the moisture content of starch was changed. Different internal structures were produced as a result of the changes in the melt flow behavior. These structures had different properties. Hence, ,an understanding was developed which would help determine the manner in which these blends should be processed to tailor the end properties. It was also found that the moisture or, consequently, the viscosity influenced the amount of PHEE at the surface of the product. Products with no or little starch on the surface are important since they are more water resistant, which is a desired property for these products.
Technical Abstract: The effect of moisture content and temperature on the melt flow behavior and the resulting morphology of thermoplastic starch(TPS)/poly(hydroxy ester ether)(PHEE) blends is studied. The critical role played by the ratio of the melt viscosities of the two polymers is examined. The viscosity ratio (lambda) was found to vary over two orders of magnitude (0.1-10) with changes in the TPS moisture content (15-30%) and temperature (120-160 deg C). This had a substantial effect on the level of mixing, nature of dispersion, and the onset and nature of co-continuity. Deformation (in the flow direction) of the dispersed starch phase was possible under high moisture conditions (higher lambda), leading to fibrillar and laminar types of morphologies at 50-80% starch level, whereas processing at a low moisture level (lower lambda) produced a more dispersed morphology. When the viscosities of the two phases were significantly different, the low viscosity polymer migrated to the surface. Surprisingl lambda increased with temperature at 20% moisture TPS but decreased with temperature at 30% moisture TPS. Hence, moisture content and temperature greatly affected the surface enrichment of the lower viscosity polymer. Water partitioning took place between TPS and PHEE during extrusion, dependent on the pre-extrusion moisture content of TPS but independent of the relative concentrations of the two polymers.