GB963072A - Method of making clear cellulose films from green viscose - Google Patents

Abstract

963,072. Regenerated cellulose films. FMC CORPORATION. Feb. 19, 1962 [March 28, 1961], No. 6387/62. Heading B5B. A clear film is made from a green viscose having a salt point of at least 5, coagulation being effected in the presence of glyoxal or formaldehyde. Preferably, the viscose contains 6-12%, especially 8-10% by weight of cellulose, 4-8%, especially 5-7% by weight of sodium hydroxide, 20-40%, especially 25-35% by weight of carbon disulphide, all based on the alpha cellulose content of the pulp, and has a salt point of at least 10. The coagulating bath may contain 0.5-2% by weight, based on the bath, of formaldehyde or glyoxal, and is preferably an aqueous liquid containing 7-15% by weight sulphuric acid and 10-25% by weight anhydrous sodium sulphate. In place of formaldehyde or glyoxal, paraformaldehyde or sym-trioxane may be utilized, and if desired, the aldehyde may alternatively or additionally be added to the viscose, suitably shortly before casting. The film may be regenerated in a separate bath containing 4-10% by weight of sulphuric acid and 7-15% by weight anhydrous sodium sulphate. In an example, a viscose containing 8.0% cellulose, 6.0% sodium hydroxide and 30% carbon disulphide and having a salt point of 12 is cast on a glass plate and immersed in a bath containing 13.5% by weight sulphuric acid, 22% anhydrous sodium sulphate and 2% by weight formaldehyde. Regeneration is effected in a bath containing 4.5% by weight sulphuric acid and 14.5% anhydrous sodium sulphate. The film is then washed with water, desulphurized in 0.5% anhydrous sodium sulphide solution, washed, bleached, re-washed, plasticized with 5% by weight glycerine solution, and dried.