Submitted to: Carbohydrate Polymers
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/20/2005
Publication Date: 4/1/2006
Citation: Shogren, R.L., Biswas, A. 2006. Preparation of water-soluble and water-swellable starch acetates using microwave heating. Carbohydrate Polymers. 64:16-21. Interpretive Summary: Starch acetates made by current commercial procedures result in much byproduct and are generally poorly soluble in water or precipitate from solution over time. Microwave processing was used to prepare starch acetates quickly and without added catalyst or solvent. These starch acetates were very soluble in cold water over long periods of time and had low viscosities, making them useful as coatings and adhesives. Thus, starch acetates produced by microwave processing have new functionality which should be useful for companies making coatings for paper, textiles, etc. and also should be economical.
Technical Abstract: Starch acetates of degree of substitution 0.1-1.5 were prepared by heating corn starch, acetic acid and acetic anhydride in sealed, stirred, Teflon vessels in a microwave reactor. Reaction efficiencies were typically >90% at reaction temperatures of 150-160 deg C for 4-7 minutes. Starch acetates were >90% soluble in cold water at DS values of 0.4-0.9 and reaction temperatures of 160 deg C. Acetylation rates and water solubilities decreased in the order waxy>normal>high amylose starch. Significant reduction in molecular weights of the starches occurred during microwave reactions. Acetylation occurred preferentially at the C6 position (70%) based on C13 NMR results. Acetylation at lower temperatures (120 deg C) gave starches of DS 0.2-0.3 which were water insoluble but highly swellable. These starches retained their native crystallinity, implying that acetate substitution was a block pattern.