Patent GB-1145790-A (GB)
Title: Process for the preparation of filaments of poly--ß-lactams
IPC: D01F6/60
Filed: 1967-12-21
Abstract: 1,145,790. Poly-beta-lactam filaments. FARBWERKE HOECHST A.G. 21 Dec., 1967 [21 Dec., 1966], No. 58146/67. Heading B5B. A process for the preparation of filaments of a poly-beta-lactam, comprises spinning a solution of the polymer in formic acid into an aqueous precipitating bath which contains formic acid and at least one alkaline earth metal formate. Preferably, the poly-beta-lactam is poly-4-methyl-azetidin-2-one. If desired, the precipitating bath may contain two or more alkaline earth metal formates, and specified formates include those of calcium, magnesium, barium and strontium. The aqueous precipitating bath may contain from 0.5 to 4% by weight, and preferably from 1 to 2%, of formic acid, and from 8 to 15% by weight, preferably 9 to 12% by weight of alkaline earth metal formate. In addition, the aqueous precipitating bath may contain up to 18% by weight, and especially from 5 to 10% by weight, of one or more additional inorganic alkali metal or alkaline earth metal salts. Salts so specified include magnesium sulphate, magnesium chloride, calcium chloride, sodium chloride and/or sodium sulphate. The precipitating bath may also contain an alkaline metal formate, preferably sodium formate. It is advantageous to add free formic acid to the precipitating baths before spinning and to keep the amount of free formic acid entrained into the bath during spinning as constant as possible. This may be effected by introducing a fresh, neutral solution of the alkaline earth metal formates into the precipitating bath or by neutralizing the formic acid using hydroxides of the alkaline earth metals. The combination of the alkaline earth metal formates with magnesium sulphate, e.g. 12% by weight of magnesium formate and 10% by weight of magnesium sulphate, is especially advantageous. Precipitating baths containing e.g. 2% by weight of formic acid, 11À2% by weight magnesium formate and 8À9% by weight of sodium formate, remained entirely clear in spinning tests conducted over long periods of time. In addition to freedom from turbidity, the use of these baths has the advantage that filament precipitation takes place gradually and the filament thus remains elastic while in the precipitating bath and so can be drawn off more rapidly without breaking, final draw-off rates of up to 90 m. per min. being possible. In addition, the alkaline earth metal formates being only sparingly soluble in water, they can readily be separated by partial evaporation of the exhausted precipitating baths. Partial evaporation is also advantageous for recovering the formic acid from the precipitating bath because the enriched formic acid can be neutralized readily using oxides or hydroxides of the alkaline earth metals, and the salts formed can be isolated together with the coagulation salts. Even with precipitating baths containing other salts in addition to the alkaline earth metal formates, partial evaporation results in a deposited salt mixture containing a preponderant amount of the alkaline earth metal formates which may be recovered together with the neutralized formic acid. Examples are given.