**Pretreatments of Textiles Prior to Dyeing: Plasma Processing**

R. R. Deshmukh1 and N. V. Bhat2

*1Physics Department, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai, 2Bombay Textile Research Association, LBS Marg, Ghatkopar (w), Mumbai, India* 

#### **1. Introduction**

32 Textile Dyeing

borohydride/bisulphite method, compared with the conventional procedure involving sodium hydrosulphite/NaOH. Furthermore, the SBH/bisulphite procedure produced less

Sodium borohydride is more expensive than sodium hydrosulphite. However, the cost difference between the auxiliaries is likely to be offset by the better colour yield and, for an expensive substrate such as wool, by the lower fibre damage produced by the

Financial support for this work was provided by Australian Wool Innovation Ltd and the

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Harrison W. F. & Hinckley A. A. (1963). Vat Dyeing with Sodium Borohydride, *Am. Dyest.* 

Hug G. T. (1948). The Dyeing of Woolen Fibers and Fabrics with Vat Colors, *Am. Dyest.* 

Latham F. R. (1995). Dyeing with Vat Dyes, in *"Cellulosics",* Ed. J. Shore, Soc Dyers and

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Fastness, *Proc. 11th Int. Wool Text. Res. Conf, Leeds*, paper number 29 CCF. Medding G. L. (1980). Vat Dye Reduction System, *Am. Dyest. Reptr*, vol 69, p 30- 42.

Nair G. P. & Shah R. C. (1970). Sodium Borohydride in Vat Dyeing, *Text. Res. J*, vol 40, p 303-312. Neale C. E. (1961). US Patent 3127231, Vat Dyeing or Dye Stripping with Alkaline

Rohm and Haas Technical Information: ChromaclearTM (Jan 2007) and private communication.

Schoots H. P. & Stevens L. F. (2003). US Patent No.6663677B2 (Rohm & Haas Company). Technical Manual. (2010). Superwhite Australian Merino Using ColorClearTM WB Bleaching

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SBH/bisulphite reducing system, compared with sodium hydrosulphite/NaOH.

We also thank Jill McDonnell and Anne Parnell for skilled technical assistance.

Dyeing, *Melliand. Textilber*. Vol 47, p 286-294.

fibre damage than the conventional method.

Australian Government through CSIRO.

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**5. Acknowledgements** 

**6. References** 

Synthetic fibres have acquired an important part of the current textile industry. A great disadvantage of some of the synthetic fibres is their low surface energy. This causes poor wettability and dyeability. Surface modification techniques are mainly carried out to remove loosely bound materials, foreign particles/impurities and to improve hydrophilic nature and thereby improving dyeability. Manipulation of surface characteristics of textile materials is of fundamental importance in the production of advanced functional textiles. Textile fibres can be classified in two main groups: Natural and Synthetic. Natural fibres are of animal origin or plant origin such as silk, wool, hair, jute, cotton, cellulose etc. whereas there are a number of manmade/synthetic fibres such as viscose, polyester, polypropylene, nylon, PLA fibres, polyamide and acrylic fibres. Natural fibres are limited and are not sufficient and not always suitable for many applications. Hence synthetic fibres have acquired greater importance in the present era. Synthetic fibres form an important part of the textile industry, with the production of polyester alone surpassing that of cotton. Improving the surface properties suitably is a very important aspect of the textile processing. Low surface energy of the synthetic fibres affects the processing of the fibres, especially during wet treatments. The surfaces are not easily wetted, thus impeding the application of finishing compound and colouring agents. In addition, a hydrophobic polymer hinders water from penetrating into the pores of the fabric. For a number of applications it is necessary to modify surface properties of textiles from hydrophobic to hydrophilic and vice versa. Plasma processing has a potential to render and change such surface properties. Recent advances in textile chemistry have resulted in imparting various functional properties such as decreased skin irritations, enhancing antimicrobial activity and fragrance to the textile material. The surface composition and structure of a textile material plays an important role in the textile's performance in specific applications. E.g. The surface of apparel / textile garment that is in contact with human skin could be modified to absorb the body moisture while the outside surface could be modified to repel water. Several studies showed that properties of polymeric substrates could be altered through surface modification (Deshmukh and Bhat, 2003 (a); Deshmukh and Shetty, 2007; Jahagirdar and Tiwari, 2004; Navaneetha P., et al., 2009; Yen et al., 2006).

Pretreatments of Textiles Prior to Dyeing: Plasma Processing 35

In this surface modification technique, the textile surface is treated with liquid reagent to generate reactive functional groups onto the surface. Chemical agent penetrates in the textile material / substrate, thereby damaging the bulk property. The commonly used chemical processing agents are chromic acid and potassium permanganate which introduce oxygen containing functional groups on synthetic fibres such as PET, PP, Nylon and PE. The degree of functionalization is therefore not repeatable between the polymers of different molecular weight and crystallinity. The another disadvantage is that it can lead to the generation of hazardous chemical waste and can cause skin irritation, even with very small amount of residual on the textile material. The effect of pretreatment of polyester with DMF, DCM and PCE on dyeability of polyester fabric was studied for disperse dyes (Jahagirdar and Tiwari, 2004; Patel and Bhat, 1986). The dye uptake depended on the solvent and the temperature and duration of pretreatment. All the pretreated samples showed a higher dye uptake than the untreated one. The temperature close to the boiling point of the solvent was found to be the best temperature for increased dyeing. The enhanced dyeability was associated with the plasticization and reduction in glass transition temperature of polyester. Similar studies on effect of swelling treatments with benzyl alcohol and formic acid was carried out for nylon-6 filaments. When the pretreated filaments were dyed with disperse dye, a considerable increase in the equilibrium dye uptake was observed. Although these filaments showed increase in lateral order (as evident from X-ray diffraction), the increase in dye uptake was explained due to structural rearrangement creating larger voids (Subramanian et al., 1982). In the chemical grafting, the first step is to create radicals on the textile to initiate copolymerization reactions with different monomers. Deo and Gotmare have carried out grafting of acrylonitrile monomer on grey cotton to impart high water absorbency (Deo and Gotmare, 1999). They have used KMnO4 as an initiator. Tsukada et al. have used ammonium peroxysulfide as an initiator to graft benzyl methacylate on wool fibres (Tsukada et al., 1997). They have also reported that the tensile strength of grafted fibres increases while

It also leads to non uniform and non repeatable surface modification. We do not have good control over the process as in wet processing. This in turn hampers mechanical properties of

The reactive oxygen is generated by burning an oxygen rich gas mixture. It incorporates hydroxyl, aldehyde and carboxylic acid functional groups onto the surface and is utilized to enhance surface properties for better printability, adhesion and wettability. Flame treatment is non-specific surface funcationalization technique that bombards the polymer surface with ionized air generating large amounts of surface oxidation products. One drawback of flame treatment is that it can reduce the optical transparency of polymers. It depends upon flame temperature, contact time and composition that must be accurately controlled to maintain

Enzymatic surface modification of textile material involves processing of fibres to modify physical and chemical surface properties or introduction of functional groups on the surface.

**2.1 Wet chemical processing** 

elongation and breaking strength decreases.

uniform and reproducible treatment and to avoid burning.

**2.4 Enzymatic surface modification** 

**2.2 Mechanical abrasion** 

the materials under process.

**2.3 Flame treatment** 

In the history of dyeing, right from early days, when natural dyes derived from extracts of trees, leaves, roots and flowers were used till the modern concept with the use of several synthetic dyes, it can be seen that each one has its own peculiarities. An efficient dyeing process needs good adhesion and penetration of dye molecule into the fibre structure. Thus the structure of the fibre – both Physical and Chemical – becomes important. If not found to be suitable, these need to be modified. Various pretreatments such as chemical, enzymes, plasma, irradiation have been tried.

Textile technology deals with several processes such as desizing, scouring, bleaching, calendaring, singeing, dyeing, printing etc. During each of these stages the structure, properties and behavior of fibres undergo many changes. The assembly of the fibres and fabrics as well as bulk of each fibre undergoes transformations. Of these changes, the surface modifications of the fibres is of profound importance as it improves properties such as softness, adhesion, wettability, dyeability, printability etc. Apart from clothing, textiles find use in a variety of applications such as furnishing, carpets, medical, automobile, geo-textile etc. Each of these can benefit from specially designed characteristics which are governed by surface properties. Wettability, adhesion, friction, biocompatibility, absorption, all begin at surface and thus surface composition is more important than bulk. The properties depend on surface chemical and physical structures which vary according to types of fibres, polymers and the assemblies. The surfaces offer a platform for functional modifications to meet specific needs. The surface modification can be achieved by various techniques such as traditional wet solution treatment, physical treatment, biological approach etc. New technologies using high energy beam process, vapour deposition, nano-particles etc. can have potential for modification of surfaces.

Textile industry is one of the most pollutant industries because of the various processes involved such as singeing, desizing, scouring, bleaching, mercerization, dyeing etc. These processes pollute the environment and water resources. Economical and ecological pressure on textile industry requires the development of economic and environment friendly "green" processes. So one has to select a proper pretreatment for the modification of surfaces amongst the available processes.
