Defects of Sulpher Dyeing | Bronziness of Shades | Sulpher BlackTendering

Defects of Sulpher Dyeing:

They are mainly two defects which are common in Sulpher dyed textile materials:-

1. Bronziness or Dullness of shades
2. Sulpher Black tendering

Now they are Described below:-

Ø Bronziness of Shades:
This is a common defect found in Sulpher dyed textile materials.

☼ Causes:

The causes are as below:-
1. Excessive delay between lifting of the material from the dye bath and washing off.
2. Exposure of goods to air while dyeing.
3. Too much use of common salts as exhausting agents.
4. Insufficient Na2S (i.e. reducing agent) in dye bath. As a result of which dye is incompletely reduced.
5. Strong dye liquor in the dye bath.

☼ Remedies:

The remedies are as below:-
1. Good washing and dilute solution of Na2S (0.1%) at 300C or,
2. A treatment with boiling soap solution or a strong Na2S solution or,
3. A treatment with a solution containing 10% salponified palm oil at 600C or,
4. a) Ammonia  : 125-200 gm/100 litre or, 1.25-2 gm/litre

T.R Oil  : 200-300gm/100litre or, 2-3 gm/litre.
Time  : 15 minutes
Temperature  : Water Bath

Ø Sulpher Black Tendering:
If Sulpher dyed textile materials are stored (weakening) tentering effect is seen on the cellulose. Due to storage a part of the Sulpher colour converts in to H2SO4 by oxidizing which in turn causes degradation of cotton by hydrolysis. It is a serious problem of Sulpher dyed goods.

☼ Causes:

The causes are as below:-
1. Gradual oxidation of Sulpher to H2SO4 on storage.
2. After treatment with copper salts causes rapid tendering.
3. Presence of iron as an impurity causes rapid tendering.
4. The method of oxidation for the recon version to insoluble form influence tendering.

☼ Remedies:

The remedies are as below:-
1. Treatment of dyed material with 1-3% K2Cr2O7 and 1-3% CH3COOH at 600C temperature for 30 minutes followed by through rinsing.
2. Treatment with a little CH3COOH so that H2SO4 may be converted in to harmless acetic acid.
3. Using 5 gm/litre soda ash after dyeing followed by drying without rinsing.

Oxidizing and Reducing Used in Sulpher Dye | Reducing Steps of SulpherDyes | Oxidation Step of Sulpher Dye

Some oxidizing and reducing agent used in Sulpher Dyeing

Oxidizing  Agent	Reducing Agent
Potassium Dichromate(K2Cr2O7)	Sodium Sulphide (Na2S)
Acetic Acid(CH3COOH)	Sodium Hydro sulphide(NaHSO3)
Sodium Perborate	Thioglycolic acid
Sodium per carborate	Thio Salicylic acid
Sodium peroxide(NaO2)	Pseudo thiohydantion
Hydrozen peroxide(H2O2)

Reducing Steps of Sulpher Dyes:

Reducing step is the most important in the application of Sulpher dyes. Unless the dyes are converted in to the completely soluble form, the full colour value cannot be achieved. The solubility of reduced Sulpher dyes varies appreciably from dye to dyes. For example yellow Sulpher dyes are the last soluble dyes (i.e. most insoluble dyes)

The reducing agents are used for Sulpher dyes are:-

1. Na-Sulphide.
2. Na-Hydro Sulphide.
3. Thioglycolic Acid.
4. Pseudo-Thio-Hydantion.

But Na Sulphide is the most widely used reducing agent for dissolving Sulpher dyes. They may be replaced by Na-Hydrosulphide in some cases. But the latter is a more powerful reducing agent. So, over reducing of the dye may take place, leading to a product having lower affinity for cellulosic fibres. Hence lower colour yields are obtained along with wastage of dyestuff. In some cases lower wash fastness results if Na-Hydrosulphide is used. It also decreases the life time of the vessel.

For dissolving the Sulpher dyes, reducing agent is taken according to the weight of dye. In practice, they are taken at same weight. For example, 10 gm dye is mixed with 10 gm reducing agent. Then the mixture is boiled after adding necessary amount of water to get a good solution. For this wooden vessel or enameled iron vessel are used but not iron vessels. Because iron reacts with Sulpher.
 

Oxidation Step of Sulpher Dye:

After dyeing the reduced water soluble form of the dyes have to be converted in to the original water insoluble form by oxidation. 

The commonly used oxidizing agents are-

1. Potassium dichromate
2. Na-Perborate.
3. Na-percarborate.
4. Na-peroxide.

The method of oxidizing selection plays an important role in the development of correct shades & their optimum fast5ness properties. Rinsing off the dyeing should be done rapidly to remove as much as Na-Sulphide as possible. If even after washing some Na-sulphide or Soda-ash stays on fabric, we use CH3-COOH to neutralize them. 

Using of different oxidizing agents may give following results-

1. Use of perborate or percartborate in presence of acetic acid gives brighter shade.
2. Treating dyed material with dichromate without rinsing reduces colour losses but causes dull shade.

The chemistry of oxidization is as below:-

Dye-S-S-Dye +2[H] = Dye- SH + HS-Dye

Dye- SH + HS-Dye +[O] = Dye-S-S-Dye +H2O

Chemical Structure of Sulpher Dye | Chemical Nature of Sulpher Dyes |Chemistry of Dyeing with Sulpher Dye

Chemical Structure of Sulpher Dye :

Sulpher dye contain Sulpher atom in their molecule and is characterized by the thiozine ring.

Chemical Structure of Sulpher Dye

The structure formula is incomplete because the complete composition and structure of Sulpher dye is mot known.
 

Chemical Nature of Sulpher Dyes

The manufacturing method of Sulpher dyes may be shown as below:-

Thionation Sulphorization

Aromatic Hydro Carbon Containing Hydroxy amino or nitro group  =  Sulpher Dye

This reaction is carried outb in a closed vessel in the presence or absence of solvents. For this (Thionisation/Sulphorisation) purpose Sulpher or Na- polysulphide is used. The features of the products of thionation are controlled by organic compounds, conditions of reaction (time, temp etc). Condition of separating dyes from reaction mixture etc.

After the reaction is over the dye is precipitated acidification or oxidation or both. Generally Sulpher dyes are marketed in forms of powder pastes or liquid solutions. The dyes are amorphous colloidal materials of high molecular weight and variable composition. Their exact chemical composition is not yet established. However they are complex in structure. Some amorphous present in Sulpher dyes are as below:

Chemistry of dyeing with Sulpher Dye:

The Sulpher dyes contain Sulpher linkage within their molecules. They are insoluble in water but can be made soluble in water by treating them with reducing agents. This also makes them substantive towards cellulosic fibres. Na2S acts as reducing agent that breaks the Sulpher linkage and break down the longer molecules in to simple components which can penetrate the material (fiber/fabric) surface easily.

Dye-S-S-Dye +2[H] = Dye- SH + HS-Dye

This thios containing the –SH groups are readily oxidized by the action of atmospheric O2 or any other oxidizing agents. This reconverts the water soluble luco form of Sulpher dye in to previous water insoluble form which has a very good wash fastness property.

Dye- SH + HS-Dye +[O] = Dye-S-S-Dye +H2O

Sulpher dyes are negatively ionized. No Vander wall’s force effect on them is activated. Addition of salt improves efficiency of dyeing by increasing physical force.

Properties of Sulpher Dyes | Characteristics of Sulpher Dyes | Featuresof Sulpher Dye

The main properties and characteristics features of Sulpher dyes are mentioned below:-

1. Sulpher dyes have Sulpher linkage within their molecules.
2. Sulpher dyes are highly colouerd water insoluble dyes. Some dyes are partially soluble in water.
3. They have no direct affinity towards cellulosic fibres. To make them substantive they are to be converted in to soluble lucoform by treating them with reducing agents (Like dilute Na2S solution)
4. Sulpher dyes have good light fastness with rating about 4. This light fastness may be improved by an after treatment with metallic salt.
5. These dyes have excellent wash fastness with rating about 3-4. This good wash fastness is due to its larger molecular size & insolubility in water.
6. They are not applicable to wool due to strong alkaline condition.
7. They are exclusively amorphous, few of them show crystallinity.
8. Important for producing a wide range of shades on a varity of cotton and rayon.
9. Sulpher dyes are suitable for heavy & durable shades
10. Available in powder and soluble form
11. Sulpher dyes are cheap & easy to manufacture.

Heat and chemical resistance of Sulpher dyes are moderate to good. They have poor fastness to chlorine and are not applied to goods which are bleached with hypochlorite.

Features of Sulpher Dye

1. Amorphous Colloidal materials.
2. High molecular weight with various composition
3. Complex molecular structure –heterocyclic molecules containing Sulpher linkage.
4. Decomposed by acids, with the liberation of H2S.
5. Characterized by thiozine ring, containing Sulpher atom.

Classification of Sulpher Dyes

Sulpher dyes may be classified in many ways:- But according to their solubility there are essentially 3 classes of Sulpher dyes as below:-

1. Conventional or Water insoluble dyes
2. Leuco Sulpher dyes (Partially soluble) and
3. Solubilised Sulpher dyes.

These in turn are subdivided in to 6 sub classes, depending on the method of application. Namely–

i) Method i
ii) Method ii
iii) Method iii
iv) Method iv
v) Method v
vi) Method vi

Ø Method-i:
Conventional Sulpher dyes (i.e. water insoluble Sulpher dyes) are dyed in method i. They have slight affinity to textile fibres of cellulosic origin. Method is as below:-

Dye pasted with cold wateràAdd required amount of Na-sulphideàDissolved by adding boiling wateràBoiled for 100 minutes to complete desolationàTaken in dye bath containing soda ashà Material immersed in dye bathàRaising temperature & adding Glauber’s salt for exhaustion.

Ø Method-ii:
These dyes are also insoluble in water and are called specialized conventional Sulpher dyes. Its application method is as below:-

Pasting of dye with 25-30 times soft water and reducing agent à Dissolved dye added to dye bath (mixture of soda ash & rongalite C) and boiled for sometimeà Material put in dye bath and dyeing carried out for 20 minutes à for exhaustion common salt or Glauber salt is added and dyeing continued for 30-40 minutes.

Ø Method-iii:
This method is used for leuco Sulpher dyes; they have distinct affinity for cellulosic fibres. These Sulpher dyes are dyed as in the case of method –I except that little or no Na-sulphide is required for their volatilization.

Ø Method-iv:
These dyes are soluble in water having substantivity to cellulosic fibres. They are mixture of Sulpher dyes and Na- sulphide. The dyeing method is as below:

Dye pasted with little amount water at 300Cà Diluted with 10-20 times water at same temperatureàDissolved dye is added to required quantity of water in dye vessel àcommon or Glauber Salt and soda ash is added in dye bathàMaterial is put in dye bath and kept at 400-600C for 25-30 minutes.

Ø Method-v:
These dyes are also soluble in water & are substantive to cellulosic fibres. They are dry mixture of the dyes and Rongallite-C. The dyeing method is as below:

Dye pasted with water & dissolved by boiling at 10-20 times soft water à Solution is added to dye bath containing required amount of wateràTemperature is raised to 900 c à material is entered in to the dye bath after 20 minutesà Glauber salt is added & dyeing continued for some times.

Ø Method-vi:
These dyes are solubilized Sulpher dyes. They have no affinity towards cellulosic fibres. Chemically they are thio-sulphuric acid derivatives and are applied either by Na-sulphite method or by Na-Hydrosulphite method.

Sulpher Dyes | History of Sulpher Dyes | Trade Names of Sulpher Dye

Sulpher dyes are complex heterocyclic molecules or mixtures formed by melting or boiling organic compounds containing amino or nitro groups with Na-polysulphide and Sulpher. Sulpher dyes are so called as they all contain Sulpher linkage within their molecules.

Sulpher dyes are highly coloured, water insoluble compounds and have to be converted in to water soluble substantive forms (lucoforms) before application to the textile materials. This conversion is carried out by a treatment with a reducing agent like dilute aqueous Na2S. Since this lucoform of Sulpher dye is substantive to cellulosic materials. They are absorbed on the fibre surface. Then they are reconverted original water insoluble form of dye by oxidation. This oxidation is carried out by “airing” (exposure to air) or by using an oxidizing agent like Na-dichromate (Na2Cr2O7).

The reducing agents converts the “S” in dye in to –SH group and the Sulpher linkages. Then inside the material the thiols containing –SH groups are oxidized & thus reconverted to original form of dye.

This is shown in the bellow:
Dye-S-S-Dye + 2[H] = Dye-SH + HS-Dye

Dye-SH + HS-Dye +[O] = Dye-S-S-Dye + H₂O

Sulpher gives best result (Bright Tone) when they are used to produce black, Black & brown shades but red shades cannot be obtained by Sulpher dyes.
 

History of Sulpher Dyes

The history of Sulpher dyes may be summarized as below:
1. The first Sulpher dyes where made in 1873 heating saw dust, caustic soda and Sulpher. It occurred by chance when a reaction vessel containing Na2S was leaking and the saw dust was used to wipe the solution coming out. Later a cotton fabric come in contact with this contaminated sawdust and become stained.

2. The real pioneer of Sulpher dyes was vidal who produce vidal black (Name of Sulpher dye) by fusing para-phenylene diamine with Na2S & Sulpher in 1893.

3. In 1897 Kalischer produced Immedial Black FF by heating 2, 4-dinitro-4-dihydroxy diphenylamine with Na-poly sulphide.

4. In 1896 Read Holliday introduced a range of grey, brown and black Sulpher dyes by the action of Sulpher, alkali sulphides and many organic compounds.
 

Method of manufacture of Sulpher dye

Aromatic Hydro Carbon Containing Hydroxy amino or nitro group      =        Sulpher Dye

Trade Names of Sulpher dye

 

Trade Names	Name of Manufacturer	Country of origin
Calcogen	Dyes Dept. American Cyanamid Co.	USA
Pyrogene	Ciba	Switzerland
Thional	Sandoz	Switzerland
Solfo	ACNA	Italy
Sulfogene	Du pont	USA
Thional	Imperial	UK
Mitsui Sulpher	Mitsui Chemicals Ind. Co. Ltd	Japan