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ARS Home » Midwest Area » Peoria, Illinois » National Center for Agricultural Utilization Research » Plant Polymer Research » Research » Publications at this Location » Publication #114829

Title: MECHANICAL PROPERTIES OF THERMOPLASTIC STARCH/POLY(HYDROXY ESTER ETHER) BLENDS-EFFECT OF MOISTURE DURING AND AFTER PROCESSING

Author
item WALIA, PARVINDER - CHEM DEPT BRADLEY UNIV
item Lawton Jr, John
item Shogren, Randal

Submitted to: Journal of Applied Polymer Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Increase in U.S. agricultural production has resulted in commodity surpluses and lower prices. New value-added products are needed 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. In this work starch was blended with poly (hydroxy ester ether)(PHEE). Better knowledge of the relationship between structure and properties in these blends is needed to design products which can successfully meet the required properties. It is also important to understand how these properties change with the humidity and time. The blend structure was strongly dependent on the processing conditions, especially the moisture level. This led to different mechanical properties. The blends processed at high moisture levels possessed elongated starch structures (fiber and sheet-like) which improved the strength and stiffness of the blends. A model was used to predict the change in properties with the relative humidity and the aging time. Hence, and understanding was developed which would help determine the manner in which these blends should be processed to tailor the end properties.

Technical Abstract: The mechanical properties of thermoplastic starch (TPS) and poly (hydroxy ester ether)(PHEE) blends were studied as a function of starch concentration. The moisture level present during processing significantly affects the morphology. A completely dispersed droplet morphology was observed at low moisture levels. Conversely, the dispersed phase was significantly deformed under high moisture conditions, leading to fibrillar and laminar types of morphologies at high starch levels. The change in morphology has a significant effect on the mechanical properties. The presence of elongated starch domains improved the tensile strength and modulus of the blends with no loss in ductility. The blend modulus could be effectively represented by the particular morphology present at any given starch concentration range, using a generalized form of the Halpin-Tsai equation. The properties of the blends changed with conditioning time and relative humidity (RH), due to the change in the moisture content of each phase. An attempt was made to express the blend modulus as a function of the relative modulus of the two phases, calculated at any given RH or conditioning time. The data could be shifted fairly well from one RH to another under equilibrium conditions. However, a shift from one conditioning time to another was difficult, owing to the slower kinetics of moisture exchange at higher amounts of PHEE, which has to be accounted for.