Silk Fibroin Dispergation

By means of specially developed techniques for using the glass clectrode, the ninhydrin test and the method for the determination of amide nitrogen, several properties, including the isoelectric points, the acid-base titration curves, the amide nitrogen, amino nitrogen, and the specific rotations of a number of samples of regenerated fibroin were compared. The samples which had been dispersed in lithium bromide solution, resorcinol, hydrochloric acid or alkaline glycerol copper sulfate solution, representing the various types advocated in, practice, were compared with untreated samples under exactly the same conditions. The following conclusions were reached: 1. Regenerated fibroin, obtained from the solutions mentioned, had essentially the same chemical characteristics as undispergated fibroin. This result was in agreement with that of Abderhalden and Brackman. 23 These investigators reported no change in the particle size of fibroin exposed to lithium bromide solutions various lengths of time and at various temperatures. This conclusion also gave further credence to the work of von Weimarn in which, under proper spinning conditions, regenerated fibres were obtained having a tensile strength as high as that of the original fibres. 2. The exposure of silk fibres to the action of water at temperatures as high, as 130° had a deteriorating effect upon the protein when the action was prolonged. A portion of the fibroin was decomposed, the fibres were weakened and became more easily disintegrated mechanically and more readily dispergated. These effects would be of use in the dispergation of the more difficultly dispersed silks, provided the decomposition which was produced was not sufficient to affect materially the physical properties of the resulting regenerated fibres. 3. In the regeneration of fibroin containing small amounts of decomposition products of the protein, there was a tendency for the protein decomposition products to remain dispersed unless the coagulation was very thorough. This is desirable in the respinning of silk fibres. 4. The titration curve for silk fibroin showed a large base combining power compared to the acid combining power. This is due, possibly, to the large number of acidic tyrosine hydroxyl groups present in fibroin. 5. The electrometric titration curves indicated an isoelectric point of about pH 3.2 for the silk fibroin of Italian yellow silk.