Patent GB-1175622-A (GB)
Title: Improvements in or relating to Collagen Films and Filaments and the Manufacture thereof
IPC: B29C48/03
Filed: 1967-03-07
Abstract: 1,175,622. Making collagen films and filaments. USM CORP. 7 March, 1967 [8 March, 1966], No. 10556/67. Heading B5B. Collagen filaments and films are made by treating skin material with a swelling agent and mechanically separating the swollen skin material in the presence of an aqueous medium to form a suspension of fine collagen fibres having a pH on the acid side of the isoelectric range, adding to the suspension acid-soluble collagen to provide at least 2% by weight, preferably 5 to 50% by weight, of dissolved acidsoluble collagen (based on the dry weight of collagen fibres and dissolved collagen) in the resulting suspension, if necessary adjusting the pH of the suspension so that it remains outside the isoelectric range, and extruding the suspension and coagulating the suspension using a liquid deswelling agent whereby to provide a filament or film of uniform cross-section. The suspension may have a collagen fibre contact of 3 to 6% by weight and a pH of from 3 to 3À6. The deswelling agent may be a mildly alkaline aqueous solution of a salt. The deswelling agent may be a concentrated aqueous solution of a salt soluble in water to such an extent that a saturated solution of the salt in water at ambient temperature has a concentration greater than 25%. The skin material may be limed steer hide and the swelling agent may be lactic acid. The liquid deswelling agent or coagulating bath may be a saturated aqueous solution of ammonium sulphate rendered mildly alkaline with ammonium hydroxide. The aqueous suspension containing the acid-soluble collagen is adjusted to have a pH range outside the isoelectric range of collagen but not so high or low as to cause rapid destruction of the collagen material, i.e. the pH should be above about 2À5 and below about 12. The liquid deswelling agent may be a water-soluble ketone or a concentrated, preferably at least half saturated, aqueous solution of a salt which is soluble in water, such as sodium acetate or ammonium chloride. The preferred deswelling agent is an aqueous concentrated ammonium sulphate solution. In an example, fresh steer hide is lined, unhaired, the grain surface removed in a splitting machine and the flesh side splits neutralized with acetic acid and washed with water. The splits are treated with a dilute aqueous solution of lactic acid, chopped, ground and homogenized at a pressure of 1500 to 3500 p.s.i. to form a homogenized material having a solids content of 9À5% and a pH of 3À4. Acid-soluble collagen is prepared from calfskin scrap by treating it with dilute aqueous acetic acid, the treated material is filtered, the dissolved collagen is precipitated by addition of sodium chloride to a concentration of sodium 10%, the precipitate is filtered off, redissolved in dilute acetic acid, and the salt removed by dialysis to provide a solution containing about 0À71% of soluble collagen. A mixture of 200 parts by weight of the 9À5% solids stock, 83 parts of the acid-soluble collagen solution, and lactic acid to a pH of 3À3 are mixed and extruded into a saturated aqueous solution of ammonium sulphate adjusted to pH 8À4 with ammonium hydroxide to form a collagen filament.