GB931678A - Improvements in and relating to the production of artificial threads of poly-gamma-methyl glutamate - Google Patents

Abstract

Polypeptide fibres consisting of at least 90% by weight of units of an optically active form of gamma-methyl glutamate are produced by extruding a birefringent solution of the polymer into a liquid coagulating bath at a "spinning speed" of at least 140 metres per minute and stretching the resultant fibre while the polymer is still in the alpha configuration to convert it into the beta configuration and to orient the fibre along its axis. "Spinning speed" is defined as the mean linear speed at which the filaments are withdrawn from the coagulating bath by the first gobet, reel or roller to which the filaments are passed when they leave the spinning bath. The polymers have a "reduced viscosity" of at least 1,4 and preferably at least 2,0. "Reduced viscosity" is defined as Nsp/C where Nsp is the specific viscosity of a solution having a concentration of C grams per 100 c.c. of solution of the polymer in a 1:9 V/V mixture of trifluoroacetic acid and trichloroacetic acid. The viscosity of the spinning solution is preferably at least 50 poises at 25 DEG C. and may range from 70 to 10,000 poises. In the wet spinning process the "pull-off ratio", i.e. the "spinning speed" divided by the linear rate of extrusion is preferably at least 1,2. The polymerization solvent used is preferably a methylene chloride-ethyl acetate mixture containing a major proportion of methylene chloride and the polymerization step may conveniently be carried out at or near 40 DEG C. The preferred coagulating liquid is acetone. If the viscosity of the spinning solution is at least 50 poises and the pull-off ratio at least 1,0, fibres can be produced having a tenacity of at least 2 grams per denier and an extensibility of at least 10%. At concentration of the polymer in the spinning solution up to about 10% the solution is isotropic and at concentrations above 12% it is birefringent. Even at spinning speeds as high as 300 metres per minute to produce fibres having desirable mechanical properties may be obtained. Specifications 864,692 and 931,677 are referred to.