GB876595A - Process for the continuous manufacture of polyvinyl alcohol filaments which suffer no shrinkage in boiling water - Google Patents

Abstract

Polyvinyl alcohol filaments are made by spinning an aqueous solution of polyvinyl alcohol into an aqueous coagulating bath containing an inorganic salt, stretching the resultant filaments in the wet state, drying and further stretching the filaments at 200 DEG -235 DEG C., preferably at 210 DEG -225 DEG C., in a ratio of 1 : 2 to 1 : 5, allowing the filaments to shrink at 200 DEG -235 DEG C., preferably at 215 DEG -230 DEG C., by 5%-30% of the initial length and passing the filaments without tension at 50 DEG -95 DEG C. continuously through a single tube or two or more tubes arranged in series, each tube containing an aqueous acetalizing bath containing a highly ionizable inorganic acid, the concentration of the constituents of each acetalizing bath being maintained constant and the period of residence in the single tube (or the sum of the periods of residence in the plurality of tubes) of any given point in a filament passing therethrough being not more than 10 minutes. The temperature of the coagulating bath may be 60 DEG -75 DEG C. and the inorganic salts dissolved therein may be alkali-metal or ammonium salts such as sodium or ammonium sulphate, or mono-sodium phosphate, or other salts such as zinc sulphate. The bath may also contain an alcohol containing 1-3 carbon atoms, acetone or tetrahydrofurane, and it or the spinning solution may further contain a surface-active compound such as octadecyl-trimethylammonium bromide. The acetalizing bath may contain 2%-10% of formaldehyde and 15%-30% of an inorganic salt, preferably the same salt as is used in the coagulating bath, and about 20% of a highly ionizable inorganic acid such as sulphuric acid. The acetalizing bath temperature may be 50 DEG -95 DEG C. Up to about 20%-25% of the available hydroxyl groups of the polyvinyl alcohol may first be reacted with formaldehyde and the reaction product then treated in a second acetalizing bath with another aldehyde, such as glyoxal, terephthalic aldehyde, butyraldehyde, nonylic aldehyde, or dimethylaminobenzaldehyde. Other acetalizing compounds which may be used are chloroacetaldehyde, pyridinoaldehyde, salicaldehyde, methylcyclohexanone, diethyldiacetalyl sulphide, paraformaldehyde, paraldehyde or polyglyoxal. In an example, a solution of 4,5 kgms. of polyvinyl alcohol and 180 gms. of citric acid as stabilizer in 25,5 litres of water is spun at 70 DEG C. into a saturated aqueous solution of sodium sulphate. The resulting wet thread is stretched to twice its original length, dried successively in air at 60 DEG C. and on metal rolls at 80 DEG C. and 160 DEG C. and then stretched at a draw ratio of 1 : 3 in air in a tube heated to 220 DEG C., the period of residence of the thread in the tube being 40 seconds. The thread is next passed through a second tube heated to 225 DEG C. and allowed to shrink therein 8%, the period of residence being 20 seconds. A tow of the threads (which still contain 17,6% of sodium sulphate) is passed without tension through a glass U-tube containing an aqueous solution containing 22% of sodium sulphate, 20% of sulphuric acid and 4% of formaldehyde, maintained at 84 DEG C., the period of residence being 3 minutes. After leaving the solution the tow is squeezed to 45% solution retention (based on the dry tow). The tow (in which 33% of the OH groups is acetalized) is washed successively with cold water, dilute sodium carbonate solution and hot water and passed through an aqueous softening bath. The threads do not shrink in boiling water.