| 摘要 |
Viscose containing 4.8-7.5% by weight, preferably 6-7% by weight, of total alkali (calculated as sodium hydroxide) is spun into an aqueous spinbath containing sulphuric acid, sodium sulphate and 0.1-2% by weight of zinc sulphate, and the filaments so formed are stretched, the percentage by weight of sulphuric acid in the spinbath lying between a minimum and a maximum calculated respectively from the formul A-1-2B 1/3 and A+0.5-B 3/2 , where A is the percentage of total alkali in the viscose and B is the percentage of zinc sulphate in the spinbath. The sulphuric acid content of the spinbath is preferably at least 3%. The cellulose content of the viscose may be 5.0-8.5%, preferably 6-8%, and in the xanthation step the proportion of carbon bisulphide based on cellulose may be 25-50%, preferably 32-40%. The sodium sulphate content of the spinbath is preferably 12-26% and the temperature of the spinbath may be 30-70 DEG C., preferably 40-60 DEG C. The freshly-formed threads may be stretched in the spin bath but are preferably stretched at least 50% in a hot second bath consisting of a hot dilute aqueous solution of sulphuric acid, e.g. a 1-3% solution at 80-100 DEG C. In an example, viscose containing 7.3% of cellulose, 6.8% of total alkali (expressed as sodium hydroxide) and 2.25% of total sulphur is spun at a Hottenroth number of 10.5 into a spinbath at 50 DEG C. containing 5% of sulphuric acid, 18% of sodium sulphate and 1.0% of zinc sulphate. The threads are then stretched 110% in a second bath maintained at 90 DEG C. Cation-active compounds may be incorporated in the viscose and/or the spinbath to prevent deposition of zinc sulphide on the thread-guides &c. when the sulphuric acid and zinc sulphate concentrations in the spinbath are low and high, respectively. The stress-strain diagrams of threads produced according to the invention resemble those of natural cotton threads, and the threads are therefore suitable for making yarns composed of mixtures of the two types of fibres.
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