GB782956A - Polyvinyl alcohol yarn - Google Patents

Abstract

<PICT:0782956/IV (a)/1> <PICT:0782956/IV (a)/2> Polyvinyl alcohol filaments are obtained by extruding an aqueous solution of polyvinyl alcohol into an aqueous coagulating solution of a salt substantially without oxidizing action, preferably a saturated solution of sodium sulphate, and subsequently treating the filaments so formed while they still contain salt derived from the coagulating liquid with an organic liquid which is a non-solvent both for the salt and for the polyvinyl alcohol. Such an organic liquid is acetone containing not more than 5 per cent water but other suitable volatile liquids are methanol, ethanol, ethyl acetate, methyl ethyl ketone, and carbon tetrachloride. To increase the speed of coagulation the spinning solution which suitably contains polyvinyl alcohol in a concentration of 15-27 per cent, also contains a small concentration of the same salt as is used in the coagulating solution, e.g. up to 2 per cent sodium sulphate, when saturated sodium sulphate solution is the coagulant, and the coagulating solution is kept at an elevated temperature, i.e. 32-70 DEG C. To prevent any colour-forming tendency, sulphuric acid in an amount of 0.5 per cent by weight of the polyvinyl alcohol may be added to the spinning solution; more preferably, however, hydrogen peroxide as a 3 per cent aqueous solution is added. Wetting agents may, if desired, also be incorporated in the spinning solution. Salts other than sodium sulphate which may be used in the coagulating solution are sodium hydrogen phosphate, aluminium sulphate, ammonium sulphate, and potassium sulphate. As shown (Fig. 1), spinning solution passes through pipe 17 to spinning jet 16 and is spun into coagulant 12. The filaments pass to guide 19 where they converge to form a yarn, and then pass to freely-rotatable rubber covered skew-rolls 22. On leaving the rolls the yarn passes in the manner indicated through the snubbing device 23, the pins of which should have matt surfaces. By means of the rolls and snubbing pins, stretch of at least 50 per cent is imparted to the yarn. Above the pins are situated guides 24, 26, 27, 33 and 34, and bobbins 28 and 32 which are used alternately. The bobbins and snubbing device are enclosed in cabinet 36, within which the humidity is maintained at 100 per cent by means of steam pipe 37 to prevent salt from the coagulating solution crystallizing out on the yarn. The yarn fully wound up on bobbin 28 is transferred to container 41 (see Fig. 3), in which it is treated with acetone which enters through inlet 42 and leaves through outlet 43. The acetone extracts both water and salt from the yarn, aided mechanically by the whipping about of the balloon of yarn coming off the end of the bobbin and by the rubbing of the yarn against the snubbing pins 46. The yarn is then dried by dryer 49 and finally wound up on bobbin 54.