GB352445A - Improved treatment of artificial threads and films made from cellulose esters and ethers - Google Patents

Abstract

The tensile strength of artificial threads and films made from cellulose esters or ethers is improved by treatment of the finished threads &c. with a neutral organic swelling medium that is capable of producing a highly swollen condition of the thread &c. and a high degree of plasticity therein, and whilst maintaining contact with the swelling medium applying a gradual stretch to the thread or film until its length is increased to 200 per cent up to several 1000 per cent of its original length or even more. In addition to the increase of tensile strength which is evidenced by an improved X-ray structure, the threads &c. are simultaneously fined, and by reason of this it is possible to make fine strong threads from relatively coarse and cheap intermediate products. In the case of cellulose acetate silk, a suitable swelling medium is 50 per cent aqueous dioxane; and the treatment may be applied to such silk as prepared from spinning solutions containing dioxane. The improvement in the threads is assisted by the application of lateral pressure, as by rolling transversely of the direction of drawing to threads before, during or after the simultaneous swelling and stretching operations. The gloss and feel of the stitched threads depend to some extent upon the conditions of stretching and on the character of the after-treatment to which the threads are subjected, for example, according as they are washed with hot or cold water, or with methyl alcohol, or with sodium sulphate solution. The process may be applied to single threads or to twisted thread bundles, or to threads in the form of hanks, or even to fabrics, without any sticking together of the individual filaments taking place. In examples illustrating the stretching of cellulose acetate threads, the swelling medium consists of 50 per cent aqueous dioxane and acetone-carbon tetrachloride, the extent of the stretching varies from 2-3 up to 20 times the original length, and the duration of the stretching from 8-12 minutes. The treatment may be combined with other operations such as stapling, curling and colouring. The Specification as open to inspection under Sect. 91 (3) (a) refers to the employment of the swelling medium in the vapor phase, and to the application of the process to cellulose xanthogenate threads; and it contains other examples in which (1) cellulose acetate threads which have been soaked in 50 per cent aqueous dioxane are drawn to 30 times their length in 8 secs., (2) the drawn cellulose acetate threads are deacetylated in alcoholic potash lye to give regenerated cellulose threads showing a further improvement in tensile strength, or alternatively are deacetylated simultaneously with drawing by adding the deacetylation agent to the dioxane solution, (3) the drawing of the threads is assisted by passage through a Thiele funnel through which a current of mercury is flowing, and (4) the drawing is carried out in two stages, in the second of which deacetylation agents may be present in the swelling bath. This subject-matter does not appear in the Specification as accepted.