| 摘要 |
A sequestering agent capable of chelating polyvalent cations (such as calcium, magnesium, and iron present in the pulp or liquor) in alkaline solution, e.g. the sodium salts of iminoacetic acid, nitrilotriacetic acid and ethylene diamine tetra-acetic acid is added to viscose in a proportion of 0.02-2% based on the a -cellulose, at least some being added during formation of the alkali cellulose, which need not be aged. Xanthation is effected in stages and the viscose temperature is kept below 10 DEG C. from the time it is made to the time it is spun. In a preferred method, alkali cellulose is made by steeping cellulose having a degree of polymerization of 800-1500 in 18-21% NaOH, using 2000-3000 parts of the caustic soda liquor per 100 parts of cellulose, for 20-60 minutes at 16-25 DEG C. and adding the sequestering agent to the pulp liquor. The resulting alkali cellulose is shredded at 16-24 DEG C. for 0.5-1.5 hours and charged without ageing, or with not more than 30 hours ageing, to a xanthating vessel, where it is xanthated at 18-32 DEG C. under conditions avoiding localized heating, e.g. by thorough mixing of the crumbs with the carbon disulphide, or adding the latter in stages. The amount of CS2 added may be 1.33 to 1.05 times the equivalent amount. The viscose is kept below 10 DEG C. suitably by adding it to dilute caustic soda solution at - 5 DEG to 5 DEG C. and cooling by refrigeration. Spinning is effected at a gamma number above 80, preferably above 100 and a viscosity of at least 120 poises. Such viscose has 3.5-6% cellulose and a NaOH/cellulose ratio of at least 1.
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