DESIZING

The processes by which we remove sizes are known as desizing. Sizing is the need for the weaving but is an obstacle for the dyeing. It can be done by many ways such as acid steep, rot steep, enzymatic etc. in all these enzymatic desizing is dominating because of its eco-friendliness and also because of its characteristics that is it acts at specific sites only at definite pH, temperature and concentration. Mainly starch is used as the ingredient in sizing.

Chemically starch is poly-α-glucopyranose in which straight chain (amylase) and branched chain (amylopectin) polymers are present. Both constituents of starch are insoluble in water, but they can be solubilised by hydrolysis of these long chain compounds to shorter ones. Thus under suitable conditions starch can be progressively hydrolyzed to the following stages. In desizing the hydrolysis reaction is carried out up to the stage of soluble dextrin only and not further to a-glucose.

Like starch polyvinyl alcohol is also common. Since it is a powerful film forming sizing agent and because of the ease with which it can be removed (it is soluble in water) it is an ideal sizing agent. The molecular weight and the degree of hydrolysis are the two primary factors, which influence its solubility in water, the solubility decreasing with increasing molecular weight. The desizing of polyvinyl-treated fabrics involves three steps- swelling, dissolving and dispersing. In contrast to starch, enzymes, normally used for desizing starches, do not hydrolyze it. The principle steps in the desizing procedure are

Wetting out with suitable wetting agent.

Steeping for affecting the swelling and softening of the polyvinyl alcohol film.

Rising thoroughly in overflowing water.

Desizing efficiency is found in two ways conventional and

TEGEWA method.

Conventional Method:

In this method we first take the weight of the sized fabric, let it be W₁. Then desize the fabric, dry & take the weight, let it be W₂. After that the fabric is treated with 3gpl (35%) HCl at 70⁰ C for 30 min. dry & take the weight of the fabric. Let it be W₃.

Total size = W₁-W₃.

Residual size = W₂-W₃.

Desizing Efficiency = (Total size – Residual size)/Total size X 100.

TEGEWA RATING:

Reagent: potassium iodide (10 gm. Of KI (100%) in 100 ml water, add 0.6358 gm of iodine (100%) stir and shake; iodine is completely dissolved. Fill up to 800 ml with water then complete to 1000 ml with ethanol. (Shelf life approx 6 months only).

Method:

Spot drop wise solution onto fabric.

2. Rub in gently.

3. Assess change of colour.

Note: the test must be carried on fabric cooled down to room temperature; residual alkalinity has to be neutralities prior to the test.

Assessment:

Grey fabric:

No change of colour = no starch size present.

Pale blue to bluish = presence of starch size or blend

Violet =of starch size with synthetic size

Desized fabric:

Pale blue to bluish violet = refer to violet scale TEGEWA This indicates residual Starch content.

Colour Fastness

Fastness:

Fastness is the fundamental requirement that coloured textiles should
withstand the conditions encountered during processing following colouration
and during following their subsequent useful life.

Light Fastness:
How confident are you that your fabric will perform well exposed to light or will colors fed or the fiber loosed their strength is always a question in front of most of manufactures. For some manufactures the light stability is an oblivious concern.
Degradation to textiles from exposure to light typically includes color change, fading yellowing and loss of tensile strength. If light fastness and weathering do not seem like significant consideration for particular product, this kind of damage causes millions of dollars in product losses every year.
This degradation occurs when light breaks chemical bonds in dyes and fibers. Sunlight is made up of ultra violate light, visible light and infrared radiation. While short wave UV causes most of the physical property damage to fibers, it is generally the longer wave UV and visible light that causes textile fed. This means that both outdoor product, like balloons, tents, and awnings and indoor product like apparel and curtains are vulnerable+. Even products exposed to harsh indoor lightning or sunlight through window glass in bright retail or commercial environment are susceptible.
For manufacturers of the fabric used outdoors, light exposure is one of the several concerns. High temperature and moisture in the form of rain, dew, and humidity can also be damaging. Light, heat and moisture in combination may synergistically contribute to even greater product degradation than anyone of these elements alone.

Scope:
This method is intended for determining the resistance of the colour of textiles of all kinds and in all forms, and of leather, to the action of daylight.
If there is a possibility o a sample being photochromic, the test of photochromism shall be applied additionally.
Principle:
A specimen of textile or leather is exposed to daylight under prescribed conditions, including protection from rain, along with eight dyed wool standards. The fastness is assessed by comparing the change in colour of the specimen with that of the standards.
1. Fabric size: 1 x 6 cm
2. Fastness rating: 1 to 8
Blue wool cloth ranging from 1 to 8
i. C.I. Acid Blue 104
ii. C.I. Acid Blue 109
iii. C.I. Acid Blue 83
iv. C.I. Acid Blue 121
v. C.I. Acid Blue 47
vi. C.I. Acid Blue 23
vii. C.I. Solubilised Vat Blue 5
viii. C.I. Solubilised Vat Blue 8

Pattern dyed with 3 dyes should be deceived after dyeing. The patterns of light fastness from 1-8 may be obtained from ISI.
The BS 1006:1978 test of day light exposure specifies that sample should be tested together with standard dyed wool patterns of light fastness. 1-8 respectively cover with opaque sheet of card board or aluminum leaving the other half exposed.
When daylight is used fading is slow and quicker answer is often necessary under commercial purpose. Hence, xenon arc lamp is used. The SED of this lamp bears a close resemblance to a natural light.
Test reports:
Report the numerical rating for light fastness. It is represented by the figure alone (in the case of using the standards denominated 1-8).If this rating is equal to or higher than 4 and the preliminary assessment is equal to or lower than 3, report the later figure in brackets. If the specimen is photochromic, the light fastness shall be followed by bracketed P along with the grey scale rating.

Fastness of Dyed Textiles

Dyeing is defined as an operation or a series of operation by means of which uniform color of permanent character is produced on a substrate. This implies that it should not be possible to wash the color out easily in laundering, nor should it fade rapidly when exposed to light. There is probably no dye, which can be guaranteed not to alter shade under all condition. Wide variation in the fastness properties of dyes are observed on number of factors, e.g. chemical constitution of the dye, nature of substrate, method of application, auxiliary chemicals added during dyeing etc.
A number of tests are necessary to cover all the important properties of any one dye because good fastness to one influence is not necessarily accompanied by equal fastness to exposure to other condition.Tests may be divided into those of customer significance, such as light, wash; perspiration, rubbing, sublimation and hose concern only the unshrinkable treatment, carbonization etc.