GB415042A - Process for the production of artificial filaments, threads, films and the like - Google Patents

Abstract

Films and filaments of alginic acid, free from opacity, are produced by preparing an aqueous solution of an alkali-metal alginate which solution is both sterile and clear and whose concentration, expressed as alginic acid, does not exceed 10 per cent, forming the said solution into a film or filament without delay and drying the film or filament in fifteen minutes or less. For part of the alkali-metal alginate in the solution there may be substituted ammonium alginate provided that the proportion of ammonium constitutes not more than 85 per cent of the total alkali present. The invention also comprises the preparation of films and filaments consisting in preparing an aqueous solution of an alginate, forming this material into films or filaments and drying, characterized by the employment of some or all of the following precautions, viz.: (a) limiting the concentration of alginate, preferably to not more than 10 per cent; (b) forming into filaments or films as rapidly as possible after preparation of the solution; (e) evaporating rapidly (e.g. to dryness in 15 minutes; (d keeping the solution acid, neutral, or weakly alkaline (e.g. pH value between 5 and 6); (e) keeping the apparatus and solutions sterile; (f) using ammonia along with the alkali hydroxides or carbonates as solvents, these precautions being employed to a sufficient extent to give a product whose freedom from opacity is not inferior to that of the products obtained by the process described above. Broadly speaking it is desirable to employ all the precautions referred to, but very rapid working may render sterilization unnecessary, or if the solutions are sterilized and of suitable concentration they need not be formed into filaments as rapidly after production, and so forth. Alginic acid and its compounds are stated to be capable of existing in two chemical forms referred to as the "A" form and the "B" form, the first of which gives non-transparent and opalescent films, and the second, clear and brilliant films. Moreover, alginic acid and its solutions offer a ready home for the growth of bacteria and films produced therefrom rapidly lose alginic acid and become discoloured and useless. All the above mentioned precautions except (e) tend to preserve the "B" form, while precautions (b), (c) and (e) keep down bacterial action. A feature of the invention comprises preparing an aqueous alginate solution, forming the solution into films or filaments and drying the product, characterized by sterilizing the solution, e.g. by addition of copper salt, so that bacterial action during the process is obviated. A further feature comprises the preparation of an aqueous alginate solution, the formation of films and filaments therefrom and drying, characterized by the adoption of steps as hereinbefore set forth so as to maintain the solution in the "B" form. The films or filaments produced may be tanned by treatment with a material, for example, a solution of a calcium salt, which converts it into an insoluble alginate. In examples, alginic acd is obtained by treating wet laminaria digitata with sodium carbonate solution. After dilution and filtration the solution is bleached and sterilized by adding sodium hypochlorite. Alginic acid jelly is then precipitated by adding dilute hydrochloric acid. In the first two examples, alginic acid jelly is dissolved in a solution of sodium carbonate and ammonia, and the solution spread within a day or two, on to a moving band which passes over steam coils so as to effect drying of the film in rather less than fifteen minutes. In other examples, solutions of alginic acid are made up with sodium hydroxide and ammonia, the amount of the latter varying between 10 and 85 per cent of the total alkali. Alternative methods of effecting sterilization are by heating the solution to 100 DEG C., and by incorporating a germicide with the solution, e.g. one part in ten thousand of copper ions. The first Provisional Specification includes a method of forming the films and filaments by flowing or squirting the solution of alginic material into a salt bath or an acid bath. Specifications 22069/03, [Class 2], 343,702, and 402,807 are referred to.