ARS | Publication request: Preparation and Physical Properties of Starch Stearates of Low to High Degree of Substitution

Submitted to: Starch
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 20, 2010
Publication Date: May 1, 2010
Citation: Shogren, R.L., Biswas, A., Willett, J.L. 2010. Preparation and Physical Properties of Starch Stearates of Low to High Degree of Substitution. Starch. v. 62(1):333-340.

Interpretive Summary: This research found that corn starch with fatty acids attached (starch stearates) could be made in a simple manner and that these have potential use in coatings, adsorbents and liquid crystalline devices. Biobased polymers are needed to replace polymers made from imported petroleum. Biopolymers such as starch need to be chemically modified in new ways, however, to confer desired properties. We have now found that starch stearate molecules can self-assemble into ordered structures which reflect only certain wavelengths of light (blue). Starch stearates also form very water resistant coatings and can absorb hydrocarbons found in gas and oil. This information will benefit scientists in academia and industries who are involved in making new biobased materials for applications such as oil absorbents, water resistant and selectively reflective coatings, liquid crystalline devices and smart responsive materials.

Technical Abstract: Starch stearates of degree of substitution (DS) 0.07-2.40 were prepared by heating dry starch and vinyl stearate in the ionic liquid BMIM dca at 75 Degrees C. Starch stearate of low DS (0.07) was insoluble in water but formed a gel and absorbed over seven times its weight of water. Starch stearate with high DS (2.4) was soluble in chloroform or toluene and had a high degree of swelling in hydrocarbons such as hexane. Films cast from starch stearates had water contact angles of 84-93 Degrees, indicating a very hydrophobic surface. X-ray diffraction and DSC of DS > 0.6 indicated some short-range crystallization of the stearate side chains. Optical birefringence was noted at moderate to high DS, suggesting liquid crystal formation. Starch stearates of DS ~0.6 showed intense birefringence resembling starch granules in DMSO while cholesteric liquid crystalline behavior was observed in toluene (reflected blue light). Blue light reflection disappeared on heating to >60-80 oC then reformed on cooling. These results suggest that starch stearates have some interesting structural ordering and have potential applications as water absorbents, hydrocarbon/oil absorbents, water resistant coatings and liquid crystalline materials.