Patent GB-594999-A (GB)
Title: Improvements in or relating to the production of solutions comprising polymers of acrylonitrile
IPC: D01F6/18
Filed: 1944-06-23
Abstract: <PICT:0594999/IV/1> <PICT:0594999/IV/2> Clear, colourless solutions of polyacrylonitrile or copolymers containing at least 85 per cent of acrylonitrile, are prepared by mixing the polymer with a solvent having marked dissolving power for the polymer at elevated temperatures, at temperatures such that the solvent has little dissolving action, e.g. below 15 DEG  C., and thereafter heating the mass, e.g. to about 150 DEG  C., to effect solution.  Preferably, the polymer is employed in a finely-divided state, e.g. not larger than 20 mesh, and is rapidly stirred with the solvent to form a slurry, which sets to a viscous dough-like mass, from which the solution is obtained by heating.  The solvent may be mixed with a miscible volatile liquid which is a non-solvent for the polymer.  The slurry of polymer may be deaerated and forced through a heated zone, which zone may have a diameter of about 1/2 inch, to convert it into a clear colourless solution and then extruded into a coagulative or evaporative medium to form shaped articles, e.g. filaments, foils and films.  Preferably, the slurry is produced at low pressure with agitation and heating is carried out rapidly, a specified time for exposure of the slurry to heat being 40 seconds. Specified copolymers are those of acrylonitrile and vinyl acetate, vinyl chloride, acrylic acid, its esters and homologues, styrene and isobutylene.  Any of the solvents specified in Specification 579,887 may be used; listed are dimethyl formamide, dimethyl methoxy acetamide, N-formyl morpholine, N-formyl hexamethylene imine, m- and p-nitrophenols and tetramethylene cyclic sulphone. Volatile non-solvents for the polymer described are diethyl ether, water, alcohol and acetone.  When the solvent used is a solid at the low temperature, e.g. the nitrophenols, it may be first dissolved in the non-solvent, or in a mutual solvent, e.g. dimethyl formamide, or dispersed in a mutual non-solvent, e.g. petroleum ether, before being rapidly heated to form the final solution.  Apparatus similar to that described in Specification 540,967 is suitable for use in the extrusion process. In Fig. 1, mixing tank 1 has an air-tight cover 2 provided with inlets for the polymer 3 and the cooled solvent 4 (both provided with closures so that the tank may be operated under vacuum), and is fitted with stirring means and a cooling jacket 20, and at its lower end opens into passage 11 fitted with screw-feed 12 leading to a tubular member 14 provided with a heating jacket comprising oil bath 22 and heating coils 23.  The outlet of gear pump 15 is connected to an extrusion orifice 16.  Apparatus suitable for batch operation is shown in Fig. 3 in which a jacketed reservoir 60 is fitted with a piston 61 and opens into a tubular member 63 encased in a heating jacket leading to an extrusion orifice.  The piston is forced down and the viscous slurry of polymer and solvent directed into the tubular member by operation of a pump 68 which forces a displacement liquid, e.g. oil, from supply tank 69 to the reservoir 60. Specification 404,504 also is referred to.