Patent ES-347598-A1 (ES)
Title: Improvements relating to Regenerated Cellulose Filamentary Materials
IPC: D01F2/06
Filed: 1967-11-14
Abstract: "Alkali-resistant" regenerated cellulose filaments characterized by an "orientation angle" of 35 to 47 degrees and a "degree of organization" of 0À42 to 0À48 may be produced by spinning into an aqueous coagulation bath containing less than 25 g./litre of sulphuric acid, sodium sulphate, and zinc sulphate, the bath containing not more than 2 g./litre of zinc sulphate (reckoned as anhydrous), at a temperature below 40 C. a viscose the cellulose in which has a D.P. of at least 400, and which has a gamma index between 60 and 100 and viscosity above 300 poises measured at 15 C., so as to form gel filaments of gamma index above 45, and, after the gel filaments have been withdrawn from the bath, stretching them by 30-80% and simultaneously squeezing them so as to remove from them adhering acid spinning bath liquid, the stretching and squeezing conditions being adjusted to give filaments which, immediately after the stretching operation, have a gamma index [gamma] 1 of 28-40 and a "swelling index" G of 5-8, and also to cause the acid concentration of the liquid which is squeezed out of the filaments during the final stage of the stretching operation to be 6-9À5 g./litre, and subsequently completely regenerating the cellulose in the filaments by treatment with an acid regenerating bath. The term "alkali-resistant" is stated to denote regenerated cellulose filaments having an elongation when wet lower than 8% under a load of 0À5 g./den. after they have been treated with a 5% aqueous caustic soda solution at 20 C. for 15 minutes. This elongation is measured on a single filament. The term "orientation angle" is defined as being the mean angle which results from the mean orientation of the crystallites in the fibrils and from the mean orientation of the fibrils in relation to each other. In filaments having a low orientation angle the crystallites are highly oriented in relation to the axis of the filaments. The "degree of organization" is stated to be directly related to the sum of the crystalline parts which constitute the filaments and is stated to be also related to the degree of order. An X-ray technique for measuring the degree of organization of fibres is described. The gamma index is defined as the number of CS 2 equivalents on 100 glucose units. The "swelling index G" is defined as the ratio between the weight of the gel filaments and the weight of cellulose contained in the filaments after the gel filaments have been centrifuged under such conditions that they are subjected to a centrifugal force 300 times that of gravity. The gel filaments may be subjected to a second stretching operation in air in which they are stretched by up to 100% of their length immediately before the operation. The gamma index of the filaments after the second stretch may be 18-28. The stretched gel filaments may be relaxed, e.g. in an aqueous bath containing less than 2 g./litre of sulphuric acid. The relaxation may be effected at 20 to 80 C. The gel filaments may be shrunk by 8-20% in the relaxation step. The relaxed gel filaments may be completely regenerated in a hot dilute acid bath, e.g. a bath at 95 C. containing 10 g. sulphuric acid and 20 g. sodium sulphate per litre. The regenerated filaments may be acetylated to form cellulose acetate filaments.