Amylose triacetate, films

Typical stress-strain curves for this unplasticized amylose triacetate film and for film containing 20% dibutyl phthalate plasticizer are shown... 

Fig. 1. Stress-atrain relationship of amylose triacetate film containing...

In general, the properties of these amylose triacetate films are very similar to those of cellulose triacetate films. A comparison of some of their properties is given in Table II. 

Amylose triacetate prepared from butanol-precipitated starch may be plasticized with almost any of the common plasticizers which are applicable to the plasticization of cellulose triacetate. For example, some suitable plasticizers are dimethyl or diethyl tartrate, tributyl citrate, tributyl phosphate, tricresyl phosphate, polyethylene glycol, and pentaerythritol tetraacetate. Addition of only 10-20% plasticizer is sufficient to give amylose triacetate films a useful and lasting degree of... 

Marchessault, Sarko etal. [10, 11] have investigated the chiroptical properties of amylose xanthates extensively. The CD of amylose triacetate in trifluoroethanol shows, apart from the expected acetyl z -> tt transition at about 230 nm, an additional shortwave peak. This is again explained by assuming a helical conformation of the amylose chain. Dextran acetates and mycodextran acetates, on the other hand, do not show conformational effects. The considerable changes in the CD spectra of amylose triacetate films when the temperature increases from 30 to 190°C are particularly remarkable. As X-ray diffraction analysis shows, these effects are connected with crystallisation processes and transformation during annealing. 

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. 

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. 

Starch acetates normally contain 2 to 3% moisture. They have a strong binding power for water as is indicated by the observation that an unplasticized amylose (fraction A) triacetate film soaked in water will lose about one-third of its tensile strength. 

Compariton <4 Propetiiet cj UnplatUlicited Films of Amylose TriacetaU and Cdhdose Triacetate... 

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. 

Other than the early studies on the determination of unit-cell parameters, little work has been done on the determination of structure of the different crystal forms of amylose. The major reason for this is the nature of the material itself namely, its powdery character. Following additional developments in the preparation of amylose, the discovery of its film-forming ability, and the synthesis of film-forming derivatives of amylose (such as the triacetate), some new structural studies were attempted, on which some comments will now be made. 

Conner is caused by the shift of the potential curve acting on a dipole in oystaliine molecuies. The latter is caused by the rotation of dipoles due to the stress-induced change of the potential curve. The direction crystalline phase and mostly in the oriented amorphous phase. The local field acting on demies in such phases nuy be different from the perfectly crystalline phase. The reversal of the piezodectric constant with increasing temperature is aho known for the oriented films of cellulose triacetate (1S and amylose (20. ... 

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