key parameters should be checked before starting the dyeing

7/28/2019 Key Parameters Should Be Checked Before Starting the Dyeing

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How to check the fabric Suitability prior to

start the Dyeing.

Bachelor of Applied Science (Textile Technology)-2012/2013

Lasitha Nawarathna


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Key Parameters should be checked before starting the Dyeing

In order to avoid the quality problems that may arise due to the improper quality of greige(unprocessed) fabric or yarn, the following Quality Assurance measures has to be taken.

Key Parameters

1. Absorbency

2. Wettability

3. Fabric Core pH

4. Residual Peroxide

5. Water Hardness & quality

6. Residual Starch

7. Presence of Heavy metals

8. Whiteness Index/Degree of whiteness


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Absorbency

Cotton is a versatile fabric used around the world due to its softness, comfort and wash-and-wear

properties. The cotton fiber, which retains 24 to 27 times its weight in water, breathes by

absorbing and releasing moisture quickly. This absorbent quality makes cotton an easy fabric to

dye. Ideal dyes to use on cotton are cold water fiber reactive dyes, all-purpose dyes and direct

dyes.

High moisture regain Absorb water molecules in to amorphous region due toOH hydrophilic groups

Moisture regain = Mass of absorb water / Mass of dry fibre * 100

Moisture content = Mass of absorb water / Mass of wet fibre * 100

High strength due to high degree of polymerisation, Wet strength is higher (5%) than wet strength due

to polymer alignment in the amorphous region

Why cotton fabric can be less absorbency

1. Residual wax cuticle2. Residual pectin layer

3. residual Starch

4. Residual Mineral matter (Ash)5. Residual Other organic matter


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Absorbency test

Test :- AATCC/ASTM Test Method TS-018

Method:-

This test method is designed to measure the water absorbency of textiles by measuring the time ittakes a drop of water placed on the fabric surface to be completely absorbed into the fabric.

Before dye some fabric if we can do this test we can identify fabric whether good for dyeing or

no.

Wettability

Test 01 :- Draves Wetting Test (AATCC Standard Test 17)

The ability of a surfactant to wet textile substrates rapidly is a key performance property in many

applications. The Draves Wetting Test (AATCC Standard Test 17) is a widely used laboratory

procedure for ranking the relative wetting efficiencies of surfactants. This test is a timed


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Residual Starch

The processes by which we remove sizes are known asdesizing.Sizing is the need for the

weaving but is an obstacle for the dyeindg. because of errors in desizing process some sizing

starch not removing completely. Before dyeing we have to verify amount of residual starch.

Test: - Iodine Test

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:

1. 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)

No change of colour = no starch size present.

Violet = presence of starch size

Residual Peroxide

Test :- Hydrogen Peroxide Test Strips

Method :-

To assess the presence of residual Hydrogen peroxide, the part of the sample is to be cut in wet

stage and used for Stripe Test.

Stripe has to be toughed to the wet fabric and check the color change in stripe.
http://www.linkedwords.com/science/technology/textile/desizing.phphttp://www.linkedwords.com/science/technology/textile/desizing.phphttp://www.linkedwords.com/science/technology/textile/desizing.php


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If the color is not changes to bluer side, it indicates the presence of residual peroxide not

available

Whiteness Index/Degree of whiteness

Instrumental Measurement of fabric White

The color white is defined in colorimetric terms as a color with the highest luminosity, no

hue and no saturation. Instruments measure the color of white as a property of reflecting

light at all wavelengths, that is, the reflectance of the whole visible spectrum of 100%. This

defines the ideal white; a condition rarely found in nature.

Whiteness is the attribute of color perception by which an object is compared to approachthe preferred white. The Whiteness Index is a number, computed by an instrument that

indicates the level of whiteness. In the testpiece report, the higher the Whiteness Index

value, the greater the whiteness of the measured testpiece. If the preferred white fabric has

a high reflectance, then the ideal Whiteness Index for textile materials should approach 100.

This is the characteristic used when establishing the criteria for evaluating the results of the

Whiteness Index of NAILMs Testpiece Service.

Test 01:-

Test for measurer fabric Degree of whiteness

This test method provides procedures for measuring the whiteness and tint of textiles.

Whiteness as measured by this test method is an indication of how white the textiles

appears to an average viewer. Tint, if other than zero, is an indication of a reddish or

greenish hue having shifted away form a bluish hue. The formulas for calculation of

whiteness and tint are those recommended by the CIE.

Whiteness value - 70-80 (Tolerance + or -2)

Test 02:-

Abstract for AATCC 110


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Purpose and Scope

This test method provides procedures for measuring the whiteness and tint of textiles.

Whiteness as measured by this test method is an indication of how white the textile appears to an average

viewer. Tint, if other than zero, is an indication of a reddish or greenish hue having shifted away from a

bluish hue with a dominant wavelength of 466 nm. The formulas for calculation of whiteness and tint are

those recommended by the CIE (see 11.1).

Because reflectance is affected by the nature of the surface of the textile, comparisons can be made only

between samples of the same type of textile.

Water Hardness & other water parameters

In the textile dyeing process, water quality plays an important role in determining the

final shades of the products. One of the important factors in influencing the dye house

water quality is its hardness, which is defined as the presence of soluble calcium and

magnesium salts in the water and expressed in the form of CaCO3 equivalent. The

presence of hardness in water can cause dye precipitation and the precipitates can further

promote dye aggregations, which result in colour specks and loss of depth. Although the

influence of hardness on dyeing has been widely investigated [1-3], this paper deals with

the electrolytic effect, especially on the electro kinetic properties in the dyeing process.


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In the following table you can see how the presence of Water Hardness affects the various wet processingstages right from desizing to finishing.

Standard of water parameters

NO Water Parameter Standard

1 Colour Clear2 Smell/ Odour No Smell

3 pH 06-Jul

4 Total Dissolved Solids < 1 mg/l*

5 Total Settleable Solids < 50 mg/l

6 Total Suspended Solids < 1 mg/l

7 Total Fixed Solids < 50 mg/l

9 Total Organic Carbon < 20 mg/l

10 Chloride < 10 mg/l

11 Nitrate < 50 mg/l

12 Nitrite < 5 mg/l14 Total Hardness < 50 mg/l

15Total Iron (Ferrous &

Ferric)< 0.1 mg/l

16 Manganese < 0.02 mg/l

17 Copper < 0.005 mg/l

18 Free Carbon Dioxide ND

Process Problem

Desizing

Scouring

Bleaching

Mercerizing

Dyeing

Finishing

Deactivate enzymes and makes it in-soluble some size materials likestarch and PVA.

Combine with soap, precipitate metal-organic acids. Produce yellowingof off-white shades, reduce cleaning efficiency and water absorption.

Decompose bleach baths.

Form insoluble metal oxides, reduce absorbency and luster Combinewith dyes changing their shades, in-soubise dyes, cause tippy dyeing,reduce dye diffusion and hence results in poor washing and rubbingfastness.

Dusting and white patches appear if the hardness is very high. Form insoluble metal oxides, reduce absorbency and luster. Combinewith dyes changing their shades, make them in-soluble, cause tippydyeing, reduce dye diffusion and hence results inpoorwashing and rubbing fastness.


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Test method for measure water hardness

Test :- Titration

One of the more sophisticated tests for hardness is the EDTA titration in which

incremental small quantities of an EDTA solution are added to a test sample until a

reaction is complete and a color change occurs.

The color change signifies that enough EDTA has been added to use up all the calcium

and magnesium in the sample. A simple calculation based on how much solution was

required can then be used to calculate an accurate value for hardness, reported as parts

per million (ppm) calcium carbonate equivalent. A value of over 180 ppm signifies hard

water.

key parameters should be checked before starting the dyeing

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