Complexes of starch polysaccharides and poly(ethylene co-acrylic acid): Structure and stability in solution

Authors

  • R. L. Shogren,

    Corresponding author
    1. U.S. Department of Agriculture, Agricultural Research Service, Northern Regional Research Center, 1815 N. University St., Peoria, Illinois 61604
    • U.S. Department of Agriculture, Agricultural Research Service, Northern Regional Research Center, 1815 N. University St., Peoria, Illinois 61604
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  • R. V. Greene,

    1. U.S. Department of Agriculture, Agricultural Research Service, Northern Regional Research Center, 1815 N. University St., Peoria, Illinois 61604
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  • Y. V. Wu

    1. U.S. Department of Agriculture, Agricultural Research Service, Northern Regional Research Center, 1815 N. University St., Peoria, Illinois 61604
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Abstract

Chiroptical methods have been used to study the conformation and interactions of amylose and amylopectin with poly(ethylene co-acrylic acid) (EAA) in aqueous solution. These studies, along with X-ray diffraction and solid-state NMR data, show that amylose and EAA, as well as amylopectin and EAA, form helical V-type inclusion complexes when mixed in aqueous suspension. This structure apparently accounts for the partial compatibility observed in films containing starch and EAA. About 2/3 by weight of EAA does not interact with amylose and probably represents the ethylene-rich central core of the EAA micelle. EAA/amylose complexes in 10 mM NaOH were stable to temperatures > 90°C, whereas EAA/amylopectin complexes in the same solvent were largely disrupted at this temperature. Urea, at a concentration of 8 M, further destabilized both EAA/amylopectin and EAA/amylose complexes. Solutions with an alkaline pH (> 9.5) dispersed EAA optimally and allowed maximum complexing with amylose. At pH values > 13, the EAA/amylose complexes were weaker, most likely due to electrostatic repulsion between ionized hydroxyl groups of amylose and carboxyl groups of EAA.

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