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Dyeing: Short Note
1
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Singeing is a dry
process used on woven goods that removes fibers protruding from yarns or fabrics
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Singeing improves the surface appearance of woven goods and reduces pilling
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2
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Ans: There are three main types of singeing machines:
i) Gas singeing machine,
ii) Plate singeing machine,
iii) Rotary-cylinder or Roller singeing machine
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State the detail on gas singeing machine
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This is the most common type of machine used for singeing
fabrics as well yarns
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The gas-singeing machine is typically
equipped with four burners, and is capable of singeing one or both surfaces of the
fabrics
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It is
important to set a drain temperature of the water-cooled roller in a range of 50°C to 55°
C
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The fabric feed speed is preferably set at around 100 to 150m/minute
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What is de-sizing?
Ans: De-sizing is done in order to remove the size from the warp yarns of the woven
fabrics
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5
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Ans: Enzymatic de-sizing is the most widely used method for the removal of starch,
amylases being particularly suitable
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These are fairly sensitive
to temperature changes from the optimum
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For example, their activity is
destroyed they are deactivated above 75°C
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Thus diastase hydrolyses starch but does
not tender cellulose
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6
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The process
consists essentially of treatment with alkali, a good supply of water is essential
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Describe the process of scouring operation
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Natural impurities of cellulosic fabric are
normally removed by boiling off in a strong alkaline solution
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3C17 – COOH + 3NaOH= 3C17H35COONa +3H2O
Or Oil + Caustic =Soap + Glycerin
There are three types of scouring:
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Saponification

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Emulsification

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Detergency

8
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Bleaching process can be defined as the destruction of natural
coloring matter from the textile materials in order to achieve a clean white end product
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Write down the bleaching agents
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Bleaching agents essentially destroy chromophores (thereby removing the color), via
the oxidation or reduction of these absorbing groups
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Type

of

Bleaching

Agents:

1
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Reductive Bleaching Agents
3
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Describe the bleaching operation method
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One opinion is that the color producing agents in natural fibers are often organic
compounds containing conjugated double bonds
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De-coloration
can occur by breaking up the chromophore, most likely destroying one or more of the
double bonds within the conjugated system
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The major bleaching agents used in textile preparation are sodium
hypochlorite, hydrogen peroxide and sodium chlorite
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All of
these are oxidative bleaches
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So the objective in bleaching is to optimize whitening and minimize fiber damage
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What is a mercerizing?
Ans: It is a treatment for cotton articles and/or natural fibers composed by cellulose in a
concentrated solution of caustic soda (300 g/l), under tension and ambient
temperature
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Write down the mercerizing process parameters
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The quality of luster will begin
to be adversely affected
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As the temperature is
increased the quality of luster is adversely affected but on lowering the temperature no
improvement in the luster is obtained
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If the material is allowed to shrink
during mercerizing then quality of luster will be impaired on the other hand if the
material is stretched more no improvement in luster is achieved
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13
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Ans: Yarns are mostly mercerized in hank form
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A device can be used to
apply tension (to stretch) on the hanks
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The
hanks are allowed to saturate with alkali, the tension is generally applied later
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The tension is released once the residual alkali concentration drops below 60°
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5-3% is
applied, higher tension results in lower tensile strength
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Describe the fabric mercerization process

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