High DS starch acetates

Low DS starch acetates ate manufactured by treatment of native starch with acetic acid or acetic anhydride, either alone or in pyridine or aqueous alkaline solution. Dimethyl sulfoxide may be used as a cosolvent with acetic anhydride to make low DS starch acetates ketene or vinyl acetate have also been employed. Commercially, acetic anhydride-aqueous alkaU is employed at pH 7—11 and room temperature to give a DS of 0.5. High DS starch acetates ate prepared by the methods previously detailed for low DS acetates, but with longer reaction time. 

High DS starch acetates are used to create brittle films and molded products. These have had little application, due to the economic superiority of cellulose acetates. In general, specific gravity and melting temperature both decrease with an increase in acetylation (45). Highly acetylated starches above 15% acetyl content (DS approximately 0.7) are soluble in water at 50° to 100°C and insoluble in organic solvents. When the acetyl content reaches 40% (DS approximately 2.5), the derivatized starch is soluble in aromatic hydrocarbons, ketones, and glycol ethers. 

Low DS starch acetates have reduced gelatinization temperature ranges and reduced tendency to retrograde after pasting and cooling. Gelling may be completely inhibited if the DS is sufficiently high. Low DS starch acetate polymers also form films which are useful in textile and paper manufacture. 

Low DS starch acetates are susceptible to deacetylation at high pH. Considering the time effect of viscosity change, the starch has likely deacetylated into its original form. 

Starch acetates may have low or high DS. The industrial importance of low DS acetates results from their abiUty to stabilize aqueous polymer sols. Low DS acetates inhibit association of amylose polymers and reduce the association of the longer outer chains of amylopectin. These properties are important in food appHcations. Highly derivatized starches (DS 2—3) are useful because of their solubiHty in organic solvents and abiHty to form films and fibers. 

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