GB940621A - Improvements in and relating to the production of isotactic polystyrene fibers - Google Patents

Abstract

940,621. Polystyrene filaments. UNION CARBIDE CORPORATION. Nov. 2, 1959 [Oct. 31, 1958], No. 37047/59. Heading B5B. Isotactic polystyrene filaments having uniform molecular orientation are made by extruding isotactic polystyrene having a melt index from 1 to 30, through a die at from 230-330‹ C. to form a continuous filament, hot drawing the filament as it emerges from the die through a heated zone maintained at a temperature at least as high as the extrusion temperature and not higher than 330‹ C. without permitting the temperature of the filament to fall below the extrusion temperature until all the filament molecules are completely relaxed, and thereafter bringing the filament to a temperature of 120-140‹ C. and cold drawing the filament at this temperature to a degree sufficient to induce molecular orientation in an amount of 750- 900%. The heated zone may be a heated liquid bath containing an inert non-solvent for polystyrene, or a heated gas stream, or, as described below, a heated chimney of metal or refractory material capable of withstanding elevated temperatures. Preferably, the melt index of the polystyrene is 2-20, extrusion is effected at 250-300 C., and cold drawing at 125-135‹ C., at a rate of 200-3000 ft./min. to a ratio of at least 8.5: 1. Isotactic polystyrene of melt index 1-30 may be obtained by pyrolysis of isotactic polystyrene of melt index 0.01-1.0 at 325-425‹ C. After extrusion and hot-drawing, the filaments may be cooled and wound on bobbins or drums prior to cold-drawing. As the hot-drawn filaments are brittle when cold, they are heated, after the cooling step, to 75-100‹ C. before winding. Preferably, however, hot-drawing and colddrawing are carried out as a continuous process, without an intermediate wind-up step. In Fig. 1, isotactic polystyrene fed into hopper 10 is forced by a screw extruder into a heated zone 16, held at 230-250 C., then into a second heated zone 18 held at 250-290‹ C., and then into extrusion die 12, at 230-330‹ C. The extruded filaments are maintained at the die temperature by means of the heated chimney 14, hot-drawn and passed around pulley 20 at a temperature sufficient to prevent the fibres from being too brittle for handling, but at which the polymer will not flow or permit orientation. The tow is now passed around rolls 22, through which the force is applied to the filaments in the relaxing chimney to effect the hot-drawing, heat being supplied from infra-red lamps A to prevent cracking of the filaments while passing around rolls 22. Next the tow is cold-drawn in bath 24, suitably of glycerine, maintained at 120-140 C., force being applied through godet 26. Fig. 2 shows the extruder head construction. The extruder head and spinning die are maintained at the required temperature by an electric band heater 40, and chimney 42. close to the die orifices, and preferably attached to the die shown, is heated by heater bands 44, the temperature of the chimney interior being measured by thermocouple 46. Specification 823,306 is referred to.