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The Chlorination Of Wool






The employment of chlorine in wool dyeing and wool printing has of
late years received an impetus in directions previously little thought
of. The addition of a little chlorine to the decoction of logwood has
been recommended as increasing the dyeing power of the wool. Treating
the wool with chlorine has a material influence in increasing its
capacity for taking dye-stuffs, and although but little attention has
been paid to this circumstance by wool dyers, yet among wool printers
it has come largely into use, and enables them to produce fuller and
faster shades than would otherwise be possible.

The method involves the treatment of the wool first with an acid, then
with a solution of a hypochlorite. The staple becomes soft and supple
and assumes a silky character; in dyeing it shows a greater affinity
for the dyes than it did previously. Although not deteriorated in
strength, it almost entirely loses its felting properties. On account
of this feature the process cannot be adopted for wool which has to be
fulled, but it is of service where felting of the goods is to be
avoided, for worsteds, underwear, woollen and half woollen hosiery,
etc., in which the felting property that occurs on washing is rather
objectionable.

By the chloring of the wool the intensity of the shade dyed is
increased to such a degree that when dyeing with Acid black, Naphthol
black, Naphthol green, Nigrosine, Fast blue, Water blue, and some
others dyed in an acid bath, but little more than half the dye used on
unchlored wool is required, while with Induline, more even and intense
shades are obtained than is otherwise possible.

The operation of chlorination can be done either in one or two (p. 038)
baths. The choice depends upon circumstances and the judgment of the
dyer. The process by the two-bath method, with subsequent dyeing in
the second or separate bath is (for 100 lb. of wool), as follows. The
first bath contains, for light cloths, yarn, etc., from 3 to 4 lb.
sulphuric acid, 168 deg. Tw., and for heavier cloths and felt, where the
penetration and equalisation of the colour is difficult, from 8 lb. to
10 lb. of acid. Generally speaking, a temperature of 170 deg. to 175
deg. F. is sufficient, although for heavy wool and for wool with poor
dyeing qualities it is well to use the bath at the boil. The treatment
lasts for half an hour, in which time the acid is almost completely
absorbed.

The second bath contains a clear solution of 10 lb. bleaching powder,
which solution is prepared as follows. Dry bleaching powder of the
best quality is stirred in a wooden vat with 70 gallons of water, the
mass is allowed to stand, the clear, supernatant liquor is run into
the vat and the sediment stirred up and again allowed to settle, the
clear liquor being run off as before, and 5 gallons more water is run
in. The clear liquors of these three treatments are then mixed
together to form the chloring bath. Special care should be taken that
no undissolved particles of the bleaching powder should be left in,
for if these settle on the wool they result in too great a development
of chlorine, which injures the wool.

The goods after being in the acid bath are entered in this chlorine
bath at a temperature of 70 deg. F., which is then raised to the boil. If
the acid bath has been strong, or been used at the boil, it is perhaps
best to rinse the goods before entering into the chlorine bath. The
hypochlorous acid disappears so completely from this bath that it may
at once be used as the dye-bath, for which purpose it is only necessary
to lift the goods, add the required amount of dye-stuff, re-enter the
goods and work until the bath is exhausted, which generally happens when
acid dyes are used. If a separate dye-bath be preferred, this is (p. 039)
made and used as is ordinarily done.

To perform all the operations in one bath the acid bath is made with
from 3 to 4 lb. sulphuric acid, and the wool is treated therein for
thirty minutes at 170 deg. F., until all the acid has been absorbed. Then
the bath is allowed to cool down to 70 deg. or 80 deg. F., the clear
bleaching powder solution is added, the goods are re-entered, and the
bath is heated to the boil. When all the chlorine has disappeared add the
dye-stuff, and dye as directed above.

In printing on wool the chlorination of the wool is a most important
preliminary operation. For this purpose the cloth is passed for
fifteen minutes at 170 deg. F. through a bath containing 3/4 oz. sulphuric
acid per gallon of water. Then it is passed through a cold bath of 3/4
oz. bleaching powder per gallon of water, after which the cloth is
rinsed and dried and is then ready for printing.

Another method of chloring the wool is to pass the goods through a
bath made with 100 gallons of water, 2 gallons hydrochloric acid and 2
gallons bleaching powder solution of 16 deg. Tw. As some chlorine is given
off it is best to use this in a well-ventilated place.





Next: Dyeing Machinery And Dyeing Manipulations

Previous: Processes Preparatory To Dyeing Scouring And Bleaching Of Wool



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