novel dyeing techniques

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Novel Dyeingtechniques

PREPARED BY:

Danish Raja (12TE62)Danish_raja1@hotmail.com

Contents:Introduction

History

Types & Mechanism

Merits and Demerits 

Uses & Conclusion

Introduction

Dyeing Microencapsulation

Electrochemical dyeing

Dyeing is the process of adding color to textile products like fibers, yarns, and fabrics. 

Dyeing is normally done in a special solution containing dyes & particular chemical material.

After dyeing, dye molecules have uncut chemical bond with fiber molecules. The temperature and time controlling are two key factors in dyeing.

There are mainly two classes of dyes, natural and man-made.

(‘.’)

• Dyeing

The first synthetic dye was William Perkin's mauveine in 1856, derived from coal tar. Alizarin, the red dye present in madder, was the first natural pigment to be duplicated synthetically in 1869

The earliest surviving evidence of textile dyeing was found at the large Anatolia, where traces of red dyes, possibly from ochre, an iron oxide pigment derived from clay, were found In China.

Dyeing with plants, barks, and insects been traced back more than 5,000 years.

Early evidence of dyeing comes from Sindh province in Pakistan, where a piece of cotton dyed with a vegetable dye was recovered from the Archaeological site at Mohenjo-Daro (3rd millennium BCE)

 Natural insect dyes such as Tyrian purple and kermes 

plant-based dyes such as woad, indigo and madder

HISTORY

1) Microencaps

ulation in Dyeing

2) Electrochemi

cal dyeing

1 Types Of Novel Dyeing

Microencapsulation in Dyeing

MICRO-ENCAPSULATION IS A PROCESS IN WHICH TINY PARTICLES OF DYE OR DROPLETS OF DYES ARE SURROUNDED BY A COATING TO GIVE SMALL CAPSULES MANY USEFUL PROPERTIES.

IN A RELATIVELY SIMPLISTIC FORM, A MICROCAPSULE IS A SMALL SPHERE WITH A UNIFORM WALL AROUND IT.

THE MATERIAL INSIDE THE MICROCAPSULE IS REFERRED TO AS THE CORE, INTERNAL PHASE, OR FILL, WHEREAS THE WALL IS SOMETIMES CALLED A SHELL, COATING, OR MEMBRANE.

Introduction•Introduction

There are over 50 different known wall materials; both natural and synthetic polymers can be used to form the microcapsules

In recent years microencapsulation techniques have been used in the Textile, pharmaceutical, agricultural, bulk chemical, food processing, and cosmetic and toiletry industries.

The textile industry, although initially slow to exploit the technology, is now generating innovative ideas and inventions within the field.

2 •Introduction

Microencapsulation

Microencapsulation Process (a) Spray coating methods, e.g Wurster air suspension Coating

(b) Wall deposition from solution, e.g. coacervation or phase separation

(c) Interfacial reaction

(d) Physical processes, e.g. annular jet encapsulation

(e) Matrix solidification, e.g. spray drying or chilling

(f)Naturally occuring microcapsules

Textile Applications of Microencapsulation

Microencapsulation of Disperse dye CI Disperse Blue 56 (1) CI Disperse Red 60 (2)Microencapsulation of Acid dyes

These will be discussed briefly: Dyeing of polyester requires water and certain chemical auxiliaries such as

dispersing agents, penetrating agents and levelling agents, in the dye bath. Unfortunately, residual auxiliaries and dyestuff may be present in the effluent and may cause pollution.

Polyester fabric was dyed with microencapsulated CI Disperse Blue 56 using a high temperature dyeing process without dispersing agents, penetrating agents, levelling agents or other auxiliaries. The quality of the polyester fabric dyed in this manner without reduction clearing was at least as good as that dyed traditionally

ConclusionMicroencapsulation of disperse dyes provides the

opportunity to carry out dyeing in absence of auxiliaries and without dyeing without affecting other properties

.Different disperse dyes having different dyeing behavior

can be make to behave similarly by microencapsulation. So this technique is a very useful tool in compound shade dyeing.

Microencapsulation of acid dyes can be used for improving leveling. This can also be used improve barre dyeing. As this technique retard the rate of dyeing it can be used successfully.

ELECTROCHEMICAL DYEING

Introduction  A novel electrochemical dyeing process results in product savings, less chemicals with special safety requirements, and unsurpassed environmental compatibility. Besides, the new process also facilitates dye bath monitoring in real time, ensuring high quality of the dyed fabric

Electrochemical dyeing of cellulosics:Indigo, vat dyes and sulphur dyes are an important

class of dyestuffs for dyeing cellulosic fibres.

These dyes are applied to different varieties of products but the application procedure contains a common reduction step with strong reducing agents to attain the reduced form of dyestuff.

According to the dyeing procedure and nature of dye, different reducing agents are used

These chemicals produce toxic nature by-products, which are acidic in nature

Electrochemical dyeing of cellulosics:

These agents is used in dye reduction and the excess chemicals find their way into the waste water. By-products formed in the decomposition of hydrosulfite are sulphur compounds (eg, Na2S, NaHS, etc).

which pollute the atmosphere through the formation of H2S

At the same time, salts of sulphur in form of sulphates and sulphites (Na2SO3, NaHSO4, Na2SO4, Na2S2O3, etc.)

CharacteristicsElectrochemical dyeing process results

product saving, less chemicals with special safety requirements,

unsurpassed environmental compatibility

better fastness properties.

There are two methods by means of which electrochemical dyeing can be carried out,

Direct electrochemical dyeing:In case of direct electrochemical dyeing technique, organic

dyestuff has been directly reduced by contact between dye and electrode.

Indirect electrochemical dyeing:In this system, the dye reduction does not take place due

to direct contact of dyestuff with the cathode, like in direct electrochemical reduction.

The dye is not directly reduced at the electrode rather, a reducing agent is added that reduces the dye in the conventional manner, which in turn gets oxidized after dye reduction

DYEING PROCEDURE The electrolysis is carried out under galvanostatic

condition by maintaining the constant current. The pre-treated fabric sample is introduced into the

dye bath. The dyeing is carried out by exhaustion method for

30 minutes with constant stirring. Both electrolysis and electrochemical dyeing are carried out at 300 ± 2 K.

After completion of dyeing, the fabric sample was washed with cold water and exposed to air, for oxidation/fixation of dye molecules.

Then the fabric was soaped at boil, rinsed with cold water, and air dried 

Electrochemical

Advantages of electrochemical dyeing processEconomyThe entire textile industry gets affected because

savings in the chemical costs as chemical wastes are reduced by 80%.

Reduction of waste water recycling cost at the same time water savings around 85%,

Electrode material for cathode and anode is cheap.

simply constructed cell and easy maintenance, so economical process. 

Advantages:HealthSeveral times bath recycling is possible with this

dyeing method.

The toxic nature sulphates and sulphites are not there in effluent so no adverse effect on aquatic life.

Low concentration of chemicals and non-toxic chemicals.

Economic technique for recycling of chemicals and water used for washing

AdvantagesDyeing processFully controlled dyeing parameters. Maximum process reliability through control of reducing potential

as needed ranging from 0 to 1,200 mV just by varying the current. Dye reduction rate is very good (10 mg dye/min) Dye pick up may go up to 85 - 90%.

Quality of productsBetter overall fastness property compared with the technique

already in use. Reproducible process condition.Dyeing results was observed. Better quality product. [

Conclusion Electrochemical dyeingThe results obtained convey the conclusion that

reducing agents required in the dyeing process for vat and sulphur dyes cannot be recycled, and lead to problematic waste products.

Therefore, modern economical and ecological requirements are not fulfilled. 

The final results are similar to those obtained in dyeing with chemical reducing agents. Improvements in control of the dyeing process can be anticipated, as well as environmental benefits and saving in process chemical.

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