GB737222A - Improvements in the production of filamentary materials of acrylonitrile polymers - Google Patents

Abstract

A solution of polyacrylonitrile or of an acrylonitrile copolymer containing at least 85 per cent of acrylonitrile is extruded into an evaporative medium to form one or more filaments; the filaments are caused to travel in contact with the evaporative medium until their solvent content has fallen to 20-40 per cent; the surfaces of the filaments are thoroughly wetted with a liquid which is a non-solvent for the polymer but is miscible with the solvent, and the residual solvent is removed while preventing any substantial lengthwise shrinkage of the filaments. The non-solvent which is applied to the filaments may be water, and it may contain a <PICT:0737222/IV (a)/1> <PICT:0737222/IV (a)/2> anti-static agent or textile lubricant. Hot water may be used to remove residual solvent from the filaments. The solvent-free filaments may be stretched to increase their tenacity, and afterwards they may be relaxed by heating them, e.g. by means of hot air, while allowing them to shrink, so as to improve their elongation at break. The solvent for the polymer may be N,N - dimethyl - formamide, gamma - butyrolactone, N-formyl-pyrrolidone, dimethyl sulphone, sulpholane, fumaronitrile or cyclic ethylene carbonate. The concentration of the polymer in the solution is preferably between 10 and 30 per cent. The heated solution may be forced through a bed of sand or other finely-divided material just before it reaches the spinning jet. This not only filters the solution but serves to disperse and homogenize solvent-polymer gel particles which might otherwise cause uneven or broken filaments. The liquid with which the filaments are wetted may be water containing an anti-static agent such as an inorganic salt or amine salt of a higher fatty alcohol sulphate or phosphate, or a salt of a quaternary ammonium compound, or a polyethylene glycol, or it may be water containing a textile lubricant such as a mineral oil, a higher fatty alcohol, olive oil, oxidized pea-nut oil or an alkylated phenol such as di-t.-amyl phenol. The stretching of the washed filaments or yarns may be effected by passing them under tension through super-heated steam at a temperature above 140 DEG C. and preferably below, but no more than 30 DEG C. below, the tacky point of the polymer. Stretching may be effected in one or more stages. The subsequent relaxation treatment may be effected by heating skeins of the stretched yarn for a few minutes in air at 140 DEG C., or by passing the yarn through a chamber in which a temperature of 140-250 DEG C. is maintained. As shown in Fig. 1, a solution of acrylonitrile polymer is extruded through the jet 8 into a spinning cell 3. Air from a blower 13 is passed through a heater 14 and then through inlet pipes 11, 12 into the cell. After passing down the cell, the air with evaporated solvent is removed through outlet 15. The extrusion speed, air speed and temperature are adjusted so that the filaments 24 still contain 20-40 per cent of solvent when they reach the ring guide 16. The resulting yarn passes in contact with roll 17 and is wetted with water from trough 18. The wet yarn is fed by rolls 19, 20 to the ring spinner 23 and perforated bobbin 22. It may subsequently be washed free from solvent while still wound on the bobbin. For the stretching operation, the yarn 40 (Fig. 2) is passed first in contact with the wick 30, which applies to it an anti-static agent, and then round forwarding roll 32 on which it may be heated by the device 34. It is forwarded at a constant speed to the heating cabinet 35 through which superheated steam is continuously passed. The yarn is drawn from the cabinet by roll 38 which is rotated at such a speed as to stretch the yarn to the desired degree. The air entering the spinning cell may be at 124 DEG C. and the walls of the cell may be heated by circulating oil at 250 DEG C. in the jacket 4 (Fig. 1) so that the temperature of the air near the bottom of the cell is about 220 DEG C. Specification 737,258 is referred to.