Carbonizing of wool

Raw wool contains seeds and other pieces of vegetable matter. Much of this may be removed in scouring and in combing. Combing is not used in woolen system and vegetable matter is only partially removed in carding. Even in some worsted processes, small amount of residual vegetable material is present in the fabric and in such cases carbonizing is essential to remove the residues.

The scoured wool fabric is padded, either in the rope form or in open width, with liquor containing dilute sulfuric acid (5 to 7 % by wt.) at approximately 65% wet pick up. And dried at 65 -90 C to concentrate the acid. Baking at 125 C for one minute chars the cellulosic material. The charred vegetable material is brittle and easily crushed on passing the rollers. it can be removed as dust during subsequent mechanical working. After carbonizing the wool fabric should rinsed and neutralized by washing. Such neutralization should be carried out immediately after baking, otherwise fabric damage will occur during storage of wool in such as acidic state. It is convenient to neutralize prior to dyeing but uneven neutralization leads to uneven dyeings.

Polynosics fibres

“A manufactured cellulose fibre with a fine and stable micro fibrillar structure which is resistant to the action of 8% sodium hydroxide solution down to zero degree Celsius., which structure results in a minimum wet strength of 2.2 grams per denier and a wet elongation of less than 3.5% at a stress of 0.5 grams per denier”.

The word polynosic has no connection with, or similarity of meaning to, such words as polymer, polyamide, and polyester, polyvinyl and so on. It is said to mean multifibrillar.

There are 4 main ways in which the polynosic differ from ordinary rayon

1) Dimensional stability in fabric form
2) Ability to withstand mercerizing. Their alkali solubility is much less than that of ordinary rayon
3) Crisper, loftier handle more like cotton than rayon. Luster is also more like that of sea-island cotton, sometimes like that of spun silk
4) Swelling in water and imbibition of water are much lower.

Methods of mordanting for natural dyeing

The three methods used for mordanting are: -

- Pre-mordanting: - The substrate is treated with the mordant and then dyed.
- Meta - mordanting: - The mordant is added in the dye bath itself.
- Post-mordanting: - The dyed material is treated with a mordant.
The methods have different effects on the shade obtained after dyeing and also on the fastness properties. It also depends upon the dye and the substrate. It is therefore necessary to choose a proper method to get the required shade and fastness by optimisation of parameters.

Cotton:
Since metallic mordants are soluble in water and are loosely held by the cotton fibres, these mordants have to be precipitated on the fabric by converting them into insoluble form, or by first treating the fibres with oil or tannic acid and then impregnating treated fabric with solution of mordant, whereby the metallic mordants are held on to cotton via oil or tannic acid.

Wool:
Unlike cotton, wool is highly receptive towards mordants. Due to its amphoteric nature wool can absorb acids and bases equally effectively. When wool is treated with a metallic salt it hydrolyses the salt into an acidic and basic component. The basic component is absorbed at –COOH group and the acidic component is removed during washing.
Wool also has a tendency to absorb fine precipitates from solutions. These precipitates are superficially sorbs onto surface of fibres and the dye attached to these gives poor rubbing fastness.

Silk:

Like wool, silk is also amphoteric and can absorb both acids as well as bases. However, wool has thiol groups (-SH) from the cystine amino acid, which act as reducing agent and can reduce hexavalent chromium of potassium dichromate to trivalent form. The trivalent chromium forms the complex with the fibre and dye. Therefore potassium dichromate cannot be used as mordant effectively.

MERITS AND DEMERITS OF NATURAL DYES

ADVANTAGES OF NATURAL DYES: -

1) Health and safety aspects of natural dyes: Though all natural dyes are not 100% safe they are less toxic than their synthetic counterparts. Many of the natural dyes like turmeric, annatto and saffron are permitted as food additives. Many natural dyes have pharmacological effects and possible health benefits.
2) They are obtained from renewable sources.
3) Natural dyes cause no disposal problems, as they are biodegradable.
4) Practically no or mild reactions are involved in their preparation.
5) They are unsophisticated and harmonized with nature.
6) Many natural dyes have the advantage that even though they have poor wash fastness ratings, they do not stain the adjacent fabrics in the washing process because of the non-substantive nature of the dye towards the fabric. An exception to this is turmeric, which shows substantivity for cotton.
7) Natural dyes are cost effective
8) It is possible to obtain a full range of colours using various mordants.

LIMITATIONS OF NATURAL DYES

The limitations of natural dyes that are responsible for their decline are: -

Ø Availability
Ø Colour yield
Ø Complexity of textile dyeing process
Ø Reproducibility of shade
Besides these there are other technical drawbacks of natural dyes: -
These are: -
Ø Limited number of suitable dyes
Ø Great difficulty in blending dyes
Ø Non-standardized
Ø Inadequate degree of fixation
Ø Inadequate fastness properties except few exceptions
Ø Water pollution by heavy metals and large amounts of organic substances.

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.