Amylopectin acetates

Diffusion measurements " have been made on starch acetates dissolved in such solvents as acetic acid and acetic anhydride, and molecular weight values up to 224,700 have been indicated. Unfortunately, diffusion constants of starch fractions have been investigated only to a very limited extent. Diffusion measurements probably would provide evidence of value in the determination of the physical shape of the molecules of the two starch fractions the rate of diffusion of the amylopectin acetate should conform most nearly to the normal hydrodynamic predictions for spherical macromolecules. 

Since amylopectin acetate produces only brittle films and plastics, its molecules probably have a non-linear structure which may be branched or coiled. A further striking difference between amylose triacetate and amylopectin triacetate is that the former can be obtained in the form of a highly fibrous mass, whereas the latter occurs only as a fine powder. 

As amylopectin predominates in all known starches, the poor film-forming properties of whole starch acetates become understandable. Artificial mixtures of amylose and amylopectin triacetates (acetylated fractions A and B) show increasingly poor film-forming properties as the proportion of amylopectin acetate in the mixture is increased. 

Esters from unsaturated fatty acid chlorides are usually viscous or limpid oils soluble in hydrocarbons and turpentine, and whose primary applications are as varnishes, films, artificial threads, aqueous emulsions, and rubber-like plastics.2067,2068 Heating them in an inert gas produced insoluble products formed by polymerization involving double bonds in the acyl moieites.2069 As mentioned in the section on nitrates, acetates of amylose are less compact than amylopectin acetate.1468 Esters of unsaturated acids have also been proposed as re-moistenable adhesives.1971 1972... 

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. 

Amylopectin is the polymeric component of starch and consists mainly of glucose units joined at the 1,4-positions. Relative molar mass tends to be very high, e.g. between 7 and 70 million. A variety of modified starches are used commercially which are produced by derivatisation to give materials such as ethanoates (acetates), phosphates, and hydroxyalkyl ethers. Modified and unmodified starches are used in approximately equal tonnages, mainly in papermaking, paper coatings, paper adhesives, textile sizes, and food thickeners. 

The acetylation of amylopectin with pyridine and acetic anhydride presents more difficulty, even when using freeze-dried material,26 and the most satisfactory method is that involving prior dispersion in formamide, after which esterification occurs readily at room temperature. 

Staudinger and Husemann determined the osmotic pressure of solutions of a potato starch acetate which had been fractionated into four parts by precipitation of its chloroform solution with ether. The molecular weights of the fractions ranged from 45,000 to 275,000. All of the fractions were soluble in chloroform, but fractions of low molecular weight were also soluble in acetone. For various concentrations of solute in either chloroform or acetone, the osmotic pressure did not increase in direct proportion to the solute concentration, but the deviation from van t Hoff s law was the smallest in the case of the acetone solutions. Osmotic pressure measurements on amylose and amylopectin tri-acetates dissolved in tetrachloroethane have been made by Meyer and co-workers, who have deduced molecular weights for these substances of approximately 78,000 and 300,000, respectively (see above discussion of the purity of these fractions). 

Paralleling their film-forming properties, these amylose triacetates can be molded into strong, tough plastics, but the amylopectin triacetates yield only very brittle products. Similarly, Mullen and Pacsu have shown that whole starch acetate produces clear, transparent, molded pieces which, however, are brittle. 

Common starch esters include the acetates. High d.s. starch acetates have been formed by using acetic anhydride with either sodium acetate or pyridine catalysts at 90-100 °C [158,159,160]. The major use of starch acetates have been in the study of the stmctures of amylose and amylopectin after acid hydrolysis. Acetylation of granular starch in aqueous suspension by acetic anhydride at pH 10-11 is used to produce low d.s. starch acetates that are primarily used for the stabilization of their viscosity and for their water-soluble clarity. The acetylation decreases the hydrophilic character and increases the hydrophobic character of starch. The major uses of starch acetates is in the paper industry for surface sizing to give improved print quality, uniform porosity, surface strength, and resistance to various solvents [161]. 

Acetic acid Activated attapulgite Aleuritic acid d-Alpha tocopherol d-Alpha tocopheryl acetate d/-Alpha tocopheryl acetate d-Alpha tocopheryl acid succinate d/-Alpha tocopheryl acid succinate Aluminum distearate Aluminum monostearate Amylopectin a-Amylose... 

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