15 Introduction to Textile Auxiliaries

P. Mageshkumar

Introduction

Textile auxiliaries are defined as chemicals of formulated chemical products which enables a processing operation in preparation, dyeing, printing of finishing to be carried out more effectively or which is essential if a given effect is to be obtained. Certain Textile Auxiliaries are also required in order to produce special finishing effects such as wash & wear, water repellence, flame retardancy, aroma finish, anti odour, colour deepening etc. The prime consideration in the choice of Textile materials is the purpose for which they are intended, but colour has been termed the best salesman in the present scenario. The modern tendency is towards an insistence on colour which is fast to light, washing, rubbing, and bleaching; this movement makes a great demand on the science of dyeing. Auxiliaries, dyes and dye intermediates play a vital role in textile processing industries.

Learning Outcome

• After learning this topic, you will be able to list the auxiliaries used in textile industry.
• You can able to describe the functions of auxiliaries.
• You will know about the chemistry of auxiliaries.
• You can select the proper auxiliaries for particular end use.

1. CLASSIFICATION

The textile auxiliaries/chemicals in one way are classified depending on whether they are permanent or temporary, into two groups: viz. those which are used in textile processing and are removed from the textile material afterwards and those which form an integral part of the processed textile material. These two classes are called temporary and permanent textile auxiliaries. Temporary textile auxiliaries include a variety of products such as detergents, wetting  agents, sizing agents, desizing agents, levelling agents, retarding agents, carriers, dispersing agents solution aids etc. Permanent textile auxiliaries are usually applied in finishing processes. Softeners, water proofing and water repelling agents, crease resist finishing agents, flame retardants, rot proofing agents, antistatic agents, binders and fixers, dye fixing agents are some examples.

In another classification, the textile auxiliaries may be divided into essentially three groups:

i.surface active compounds

ii. nonsurface active compounds

iii. water insoluble solids or water immiscible liquids, dispersed or emulsified in water with the help of dispersing agents or emulsifiers.

Nonionic ethylene oxide condensates are better suited as wetting agents in desizing. Sodium bromite oxidises starch very rapidly into alkali products which are removed by the subsequent scouring operation. The rate of desizing with sodium bromite is very rapid. The nature of the desizing process depends upon the nature of the sizing materials to be removed. Most of the size mixing are combinations of starch, modified starches carboxymethyl cellulose (CMC) and natural gum, acrylic polymers and polyvinyl alcohol, wax or self emulsifying wax, tallow or water dispersible oil. Starch sizes can be removed by enzymes. As a general rule, nonionics do not harm enzymes whereas anionics have a widely variable effect.

2. SCOURING AND BLEACHING OPERATION

Scouring of Cotton: After desizing, cotton materials are subjected to a process known as scouring. Natural cotton contains 80-85% cellulose and small amounts of nitrogenous matter, mineral matter, pectates waxes and colouring matter as impurities. Removal of these are important for further processing of textile fabric. The fabric material is treated with alkali. Kiers, continuous scouring plants like J-Box or other systems such as padroll are used for this purpose. In scouring sodium hydroxide is the main active ingredient and its function is to saponify some of the impurities present in cotton. The efficiency of caustic scour is improved by the addition of a surfactant.

The textile auxiliaries used in scouring must be stable to hard water, stable under alkaline conditions, have good wetting power and capable of emulsifying the impurities and maintaining them in the dispersed state over a wide range of temperatures during scouring and washing. Alkyl derivatives of naphthalene sulphonic acids, fatty alcohol sulphates, fatty acid amides, phosphate esters and nonionic ethylene oxide condensates are scouring auxiliaries.

The absorbency of caustic boiled cotton is much better when nonionic octylphenol ethylene oxide condensate is used as surfactant as compared to fatty alcohol sulphate or soap. A nonionic product with 12 units of ethylene oxide was found to give the best result. Phosphate ester surfactants are good scouring auxiliaries because of their excellent compatibility with alkali.

Bleeding of colour due to formation of the leuco vat dye can be prevented by a mild oxidant such as m-nitrobenzene sulphonic acid.

2.1 Scouring of Wool

Raw wool, contains grease, perspiration salts, dirt and vegetable matter as impurities. The scouring of wool to remove impurities can be done by suint scouring, solvent extraction, or emulsion scouring. Emulsion scouring is the most widely used method. A detergent used for wool scouring possess the properties of degreasing wool at low temperature, stabilise the emulsion of wool wax with water, remove soil efficiently, hold the fine dust in suspension and not have any detrimental action on wool.

Alkyl aryl sulphonates, alkyl sulphates, alkyl sulphonates and nonionic detergents are used in wool scouring. Nonionic also give a soft handle to scoured wool.

2.2 Carbonising

Raw wool contains a considerable quantity of foreign vegetable matter in the form of straws and burrs which are not removed by scouring. Wool is subjected to carbonising after scouring, to remove them.

Wool is treated with dilute solution of sulphuric acid and/or aluminium chloride, dried, baked and washed. Alkyl naphthalene sulphonate, cationic and nonionic wetting agents are used as wetting agents in carbonising. The addition of a surfactant also reduces significantly the loss of tensile strength of the treated wool.

3. MERCERISING

Mercerisation of cotton material is carried out to improve its strength, lustre and dye adsorption. In this process, the goods are treated with 52-54° Tw sodium hydroxide, stretched and washed. A necessary condition for successful mercerisation is the rapid and uniform wetting of cotton by sodium hydroxide. A mercerizing auxiliary has high stability in concentrated alkali and good wetting power and are readily removable from the fabric by a simple washing treatment. Phenolic compounds such as cresylic acid form the basis of most of the commercial preparations.

Ordinary wetting agents used in scouring are unsuitable as wetting agents in mercerising liquors and special wetting agents effective under these conditions have been developed. Generally, there are two types-cresylic and non cresylic types of mercerizing wetting agents to be used in mercerising liquors.

Mixture of ortho-, meta-, and para–cresols (cresylic acids), are not soluble in water but dissolve in strong caustic soda solution. These are found to be stable wetting agents in this solution. Their wetting power is found to be considerably improved by incorporating certain other additives like ethyl alcohol, polyhydric alcohols having C18 chain, butanol, 2-ethyl hexanol, polyethylene glycol etc. Some of these are not miscible with water, but dissolve in caustic soda solution.

A product, obtained by the distillation of pine oil as a fraction between turpentine and rosin, has excellent wetting, penetrating and emulsifying properties. It is dispersible in mercerising liquors and improves their penetration power so as to give mercerised cotton having more even dyeing properties. This fraction may be used together with cresols, which assist the dispersion of the pine oil distillate.

Cresylic wetting agents have strong phenolic odour and are known coloured liquids. Noncresylic wetting agents include sulphated lower aliphatic alcohols such as hexyl or alcohols. These mercerising wetting agents are free from phenolic odour and foam less. Piononic acid as mercerising auxiliary is as effective a wetting agent is cresylic acid. Mercerising auxiliaries based on a substituted diethylene glycol sodium sulphates in conjunction with a sparingly soluble alcohol and solution promoter of cellosolve type is a good mercerising wetting agent.

Special wetting agents suitable for adding to mercerising liquors which are sulphoxide compounds like n-octyl-bid-(beta-hydroxyethyl)-sulphonium sulphate, n-octyl-(beta-hydroxyethyl)-sulphoxides, n-nonyl-(betahydroxyethyl)- sulphoxides and n-hexyldiethyl-sulphoxonium chloride.

4. DYEING

Dyeing is production of coloured fabrics. A wide variety of dyestuffs are available and each class of dyes have different method of application.Chemicals (auxiliaries) are used in dying process to obtain satisfactory dyeing process. The auxiliaries used in dyeing are:

1.  Wetting and penetrating agents

2.  Dispersing agent

3.  Levelling agents

4.  Sequestering agents

5.  Antifoaming agents

6.  Accelerators

7.  Migration inhibitor

8.  Dye fixing agents

9.  After washing agents

10.  Stripping agents

4.1 Wetting agents

There are surfactants added to the dye bath to ensure penetration of dye liquor into the yarns and fabrics. Sulphated fatty alcohol, sulphated oil and anionic surfactants like sulphonic acids are used.

4.2 Dispersing agents

Dispersing agents are also surfactants used for uniform dye dispersion. These are particularly used in disperse and vat dyes. Sulphated fatty alcohol, alkyl aryl sulphonates, sulphated fatty acid amides are used.

4.3 Levelling agents

Levelling agents are added in dye bath to uniformly dye the yarns or fabrics. An ionic surfactants like alkyl aryl sulphonates, fatty alcohol sulphates, fatty amide sulphonates are used. Non ionic surfactants are used for direct dyes, cationic surfactants and non ionic surfactants are used in vat dyeing.

In case of dyeing of acrylics, retarding agents like cationic and anionic surfactants are used as retarders. Non ionic surfactants are used in polyester/blends dyeing as levelling agent.

4.4 Sequestering agents

Sequestering agents are chemicals which complexes heavy metal and do not allow these heavy metal to react with fibre or dyes. EDTA, NTA are common sequestering agents.

4.5 Antifoaming agents

Antifoaming agents are used in dye bath to prevent foaming of the bath which affects dyeing adversely. The best antifoaming agents are silicone polymers such as dimethyl polysiloxane with a viscosity of 100-500 centiposie at 25°C. Polyamino alkyl substituted hydrocarbons are based organo poly siloxanes are also used as effective agents.

4.6 Carriers

Carriers are used in dyeing of synthetics particularly polyesters with disperse dyes. It imbibes deep shades on the polyester and blended fabrics. O phenyl phenol, monochloro o phenyl phenol, p phenyl phenol, diphenyl, mono methyl naphthalene, trichloro benzene, dimethyl pterephthalate, methyl salicylate etc. are good carriers.

  4.7 Migration inhibitor

Migration inhibitor effects uniform dyeing of fabrics by preventing migration of dye molecules along with liquor during drying operation. Sodium alginate non ionic polyelectrolyests, carboxymethyl cellulose, ethoxylated and propoxylated guar gums are good migration inhibitors.

4.8 Dye fixing agents

Dye fixing agents fixes the dye on the yarns and fabric in a permanent fashion, so that their fastness properties are manifested properly. Usually cationic surfactants are used as dye fixing agents.

4.9 Stripping agents

Stripping agents are used for dye removal from bad dyed cloth produced by faulty dyeing. Quartery ammonium compound with long chain alkyl are effective. Poly vinyl pyrrolidone based agents are used for stripping vat, sulphur and direct dyes.

Cetyl trimethyl ammonium bromide are efficient in stripping azoic dyes. These are usually effective in presence of oxidizing or reducing agents. Nonionic surfactants with caustic soda and hydrosulphite are formed useful.

Sulphoxylate of formaldehyde, polyvinyl pyrrolidone in presence of acetic strips disperse dyses from nylon. 1-20% diphenyl with 3- 5% zinc sulphoxylate and 5% acetic acid at boiling temperature strips colour from polyester.

5 Auxiliaries in printing

Printing is a process to decorate textile fabrics with colours and colour motif. Textile printing may be considered as a specialized dyeing process. It is a controlled application of dyes and pigments to exactly defined locations on the fabric leaving rest of the fabric essentially unaffected. There are three major methods of printing viz. direct printing, resist printing and discharge printing. In the direct printing method a paste of dyes and auxiliary chemicals are directly fixed on the fabric by a pattern block or silk screen. In discharge printing a reducing agent is used to destroy the oxidizing agent at the printed area needed to develop a particular dye (vat dye) or an acid is used to destroy the alkali needed for development and fixing of a dye. In discharge printing stable reducing agents are used to discharge the dye on the fabric. Vat dyes, pigments, basic dyes, are used for discharge printing.

The auxiliaries used for printing of textiles are thickeners, wetting agents, dispersing agents, antifoaming agents, hygroscopic agents, reducing and oxidizing agents, binders, after washing agents and miscellaneous auxiliaries.

5.1 Thickeners

These chemicals act as vehicles for carrying the dyes onto the cloth. The prevent the colour spread on the fabric beyond desired limit, starch, natural gums like locust bean, senegal, arabic, karaya, guar bean are used commonly. Modified starches like British gums dextrin, sodium alginate, sodium carboxy methyl cellulose are also used with satisfactory results. Kerosene, water emulsions with non ionic surfactants are also used.

5.2 Wetting agents

These are usually various surfactants compatible with other auxiliaries used for a specific printing formulation. These have already been discussed earlier.

Dispersing agents

Dispersing agents used are diethylene glycol, thio diglycol, sodium benzyl sulphanilate, nonionic surfactants are use for prevention of agglomeration of dye particles.

5.3 Antifoaming agents

Antifoaming agents are the same as used for dye bath. They are usually siloxanes. Hygroscopic agents used are glycerine, diethylene glycol etc.

5.4 Oxidising and reducing agents

Oxidising and reducing agents are sodium chlorate, chromate, dichromate, nitrate, ferrocyanide hydrosulphite, bisulphite, glucose and stannous and ferrous salts.

5.5 Carriers

Carriers are the same chemicals used for dyeing with disperse dyes and already been discussed earlier.

 5.6 Binders

Binders are used in pigment printing. It forms a film at the printed portion. The film should be colourless, clear, have high resistance to washing liquids and chemicals, should have good adhesion with the fabric and should have good abrasion resistance.

Large number of synthetic resin based binders is used. They are vinyls, acrylics, melamine formaldehyde, UF precondensates, chlorinated rubbers etc. SBR, acrylonitrile, butadiene based binders are also used.

5.7 After washing

After washing removes thickeners and to bring out the true shades, usually mild detergents are used for after washing.

6 Finishing of textiles

The auxiliaries used in finishing can broadly be divided as below:

1.  Stiffening agents

2.  Durable press/crease resistance agents

3.  Optical brighteners

4.  Softeners

5.  Water repellents

6.  Flame retardants

7.  Antistatic agents

8.  Soil release agents

9.  Antipilling agents

6.1 Optical brightening agents

All types of textile fibres, natural or synthetic, do not appear perfectly white but exhibit a yellow tinge because of the presence of certain coloured impurities which absorb some of the incident light in the blue end of the spectrum. Three methods are available to remove the yellow tinge. The first one is the destruction of the colouring matter by bleaching agents. This method is invariably used to remove most of the colouring impurities from the fibre but it is not possible to eliminate totally the slight yellowish tinge without degradation of the fibre itself. The second method employs the use of blueing agents on the bleached fabric. These agents correct the yellowness of the fabric by absorption of yellowness of the fabric by absorption of yellow light by the applied blue pigment. In this case the yellowish white fabric acquires a greyish white appearance. The third method which is the most popular today involves the use of optical brighteners or fluorescent brighteners. The optical brightening agents are for the most part similar to dyes, and posses affinity for the fibre. They contain fluorescent chromophores instead of colour chromophores, and make the white fabric whiter without adversely affecting the strength and other useful properties.

Fluorescent brighteners, also known as fluorescent whitening agents, fluorescent dyes and optical brighteners, are special types of fluorescent organic compounds which are used to enhance the coloristic performance or brightness of the various materials such as natural fibres, synthetic fibres, textiles, polymers, papers and paints. In general, these molecules are capable of absorbing radiation of short wave length and high energy, normally invisible to the human eye and emitting the radiation of longer wavelength, i.e., in the visible light.

6.2 Softeners

All natural fibres are associated with some oily, fatty or waxy substances in the raw state. These substances give a soft feel to the fibre. However, on scouring and bleaching the material, these waxy substances are removed and the material becomes harsh. Certain colouring matters at higher concentrations, as well as finishing agents such as starches, china clay, etc., also impart an unpleasant handle to the cloth. It is, therefore, necessary to apply some softening agent to the textile so as to impart softness, smoothness, fullness, suppleness and flexibility. Although, many hundred of preparations are available for softening textile materials, it is noteworthy that most of these substances are based on long chain fatty compounds in one form or another. The softeners are of five types-

1.  Anionic softeners

2.  Nonionic softeners

3.  Cationic softeners

4.  Reactive softeners

5.  Emulsion softeners

6.2.1 Nonionic softeners

In this group of compounds, ethylene oxide condensates with stearyl alcohol and stearic acid are quite popular. Nonionic fatty amide type of products is also sometimes used. These softeners are characterised by their excellent stability against yellowing and good tolerance of catalysts used in resin finishing. Generally, they do not have any effect on shades of dyestuffs. However, nonionics also do not have any substantivity for fibres and are not fast to washing.

6.2.2 Cationic softeners

Cationic softeners constitute a very important group of popular softeners. They are substantive to cellulosic fibres and therefore the treated textile remains soft for a few washes. These softeners impart a full and silk-like hand to the cloth. They have excellent stability in the resin finishing bath. But the major problem with them is of yellowing on white. Hence the treatment is done very carefully.

6.2.3 Reactive softeners

In order improve the durability of the soft finish, reactive softeners are developed. These softeners will react chemical with the hydroxyl groups of cellulose under suitable conditions. These softeners posses a reactive group attached to a long chain lubricating or softening group. “Velan PF” or “Zelan” is stearyl amido methyl pyridinium chloride. It is applied to the fabric in aqueous solution, usually buffered with sodium acetate. The fabric is dried and baked at 120- 150ºC for a few minutes. During this baking the softener reacts chemically with cellulose giving off pyridine. The softener is expensive, toxic and yellows the treated fabric on curing.

6.2.4 Emulsion softeners

The emulsion softeners have gained popularity by virtue of their ability to reduce the losses in tear strength or resin finishing. These are prepared by polymerization of the monomer which has been emulsified in a water phase. The important products belonging to this group are polyethylene emulsion, polyester emulsion and so on. The emulsion softeners give excellent full hand with adequate fastness to washing.

6.2.5 Silicone softeners

During last few years the use of silicone emulsions as softeners has increases considerably. The commercially important silicone polymers consist of a backbone of silicone and oxygen with organic substituents on the silicon atoms. Since silicon is tetravalent, two sites are available on each silicon member of the siloxane chain, when both the sites are substituted with organic groups a linear fluid polymer results. Network polymers or resins can be formed by selected branching along the siloxane chain with additional siloxane linkages

7 Summary

Textile auxiliaries play a vital role in textile chemical processing and finishing. It enhances, activates the main ingredient’s activity and sometimes it gives functional, performance properties also. The choice of auxiliary should be done with much care to achieve the desired results.

REFERENCES and URLs

1. EIRI consultants and engineers, “Textile auxiliaries and chemicals”, Engineers India Research Institute, 2007.
2. Derek Heywood, “Textile Finishing”, Society of Dyers and Colourists, 2003.
3. Fischer, K., et all, “Ullmann’s Encyclopedia of Industrial Chemistry”, 2000
4. NPCS Board of Consultants & Engineers, “Handbook on Textile Auxiliaries, Dyes and Dye Intermediates Technology”, Asia Pacific Business Press Inc., 2009
5. John Shore, “Colorants and auxiliaries, vol.2-Auxiliaries”, Society of Dyers and Colourist, 2002.