JPS4819944B1 - - Google Patents

Abstract

1,082,852. Tubular collagen films. UNILEVER Ltd. June 15, 1965 [June 16, 1964; Sept. 8, 1964], Nos. 24892/64 and 36780/64. Heading B5B. A method for the preparation of tubular casing, comprises modifying collagen by treating it with a strong alkali in the presence of an alkali metal salt capable of preventing swelling of the collagen and subsequently extruding the modified collagen in tubular form. The strong alkali is suitably an alkali metal hydroxide capable of giving a solution having a pH of 13 or above, especially sodium hydroxide. The preferred alkali metal salt is sodium sulphate. Preferably, the salt is present in a solution more than 90% saturated with respect to the salt. Desirably, the modified collagen submitted to extrusion has a gelatin conversion determined as described in the Specification, of 10 to 22%, especially 10 to 17%. The modified collagen may be swollen with a carboxylic acid, especially a hydroxycarboxylic acid, prior to extrusion. To alter the drying characteristics of the casing, and make its moisture content more uniform, a suitable plasticizer or humectant may be added to the acid swollen material, for example, glycerol. The suspension of modified collagen extruded may contain from 2À5 to 10% by weight of total solids, especially 6 to 8%. The precipitating bath may contain an alkali metal salt or an ammonium salt capable of precipitating collagen, and a preferred precipitating bath contains sodium chloride, or sodium chloride and ammonium hydroxide. Suitably the sodium chloride is in saturated solution and the ammonium hydroxide not greater than seminormal, preferably deci-normal. The precipitating solution may also contain a tanning agent. After precipitation, the casing is washed with water containing a small proportion of ammonium hydroxide, and is air dried. In a modification, the precipitated casing is partially or substantially completely dried without previously washing out the precipitating salt. During and after drying, the casing is preferably maintained at a pH of not less than 5. The salt may be washed from the product after partial or complete drying.