18 Dr Fenton and Mr Berry, Studies on Cellulose Acetate 



however, worthy of note that there appears to be some relation 

 (with undoubted exceptions) between the dielectric constant and 

 solvent action. 



Influence of methods of preparation upon the properties 

 of cellulose acetate. 



The materials obtained by acetylating cellulose with acetic 

 anhydride diluted with acetic acid in presence of various catalysts 

 such as concentrated sulphuric acid, ferric sulphate, ortho tolui- 

 dine bisulphate, may show considerable variations in properties 

 depending upon the temperature, length of time of acetylation, 

 and numerous other factors. When cellulose is acetylated and 

 the product at once precipitated by water, it is nearly insoluble in 

 acetone. Various methods have been adopted in order to convert 

 the product so obtained into an acetone-soluble modification. The 

 most widely used of these methods is that of Miles. This consists in 

 heating the acetic acid solution of the cellulose acetate with water 

 in rather greater quantity than that required to combine with the 

 residual acetic anhydride. Sodium acetate may also be added to 

 react with the catalyst if still present. The results are usually 

 supposed to be due to chemical hydration. 



In our experiments, cellulose was acetylated under the influence 

 of various catalysts, and the effect of treatment, by the Miles 

 process was subjected to a critical examination. The most marked 

 effects of this process are the changes in solubility in acetone and 

 chloroform, most cellulose acetates being soluble in chloroform 

 and insoluble in acetone before the treatment. This change in 

 physico-chemical properties was found to be accompanied by a 

 fall in the acetyl number. In one case the untreated cellulose 

 acetate with an acetyl number of 60-9, yielded a product after the 

 Miles process carried out at 100° for 48 hours with an acetyl 

 number of 46-7. In another case when the treatment was carried 

 out at the same temperature for 23 hours, the acetyl number fell 

 from 60-5 to 50-4. The specific gravity of the cellulose acetate is 

 also greatly reduced after the treatment. The influence on the 

 heat test is not well marked but the decomposition point appears 

 to be lowered somewhat. 



In our view these results are to be ascribed to partial hydrolysis 

 of the cellulose esters, not to hydration as is commonly supposed*. 

 Apart from the diminution of the acetyl number already mentioned, 

 we have carried out a series of experiments which have demon- 

 strated that cellulose acetate does not form a hydrate. These 



* Oux view that the effect of the Miles process is essentially hydrolytic and not 

 due to chemical hydration has been expressed subsequently by Ost {Zeifsch. 

 angeic. Chem. 1919, xxxii, 66, 76, and 82). 



