Advances in the Dyeing and Finishing of Technical Textiles || The use of nanotechnology in the finishing of technical textiles

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  • Woodhead Publishing Limited, 2013

    280

    12The use of nanotechnology in the fi nishing of

    technical textiles

    M. L. GU LR A JA N I, Indian Institute of Technology Delhi, India

    DOI: 10.1533/9780857097613.2.280

    Abstract: The use of nanotechnology in the fi nishing of technical textiles has resulted in imparting new and more complex functions on textile substrates as well as improvements in existing functions such as durability without losing the fabrics feel and texture, with the minimum use of chemicals. The evolution, advancement, theory and technology of application of some of the commercially successful nano-fi nishes that impart hydrophobic, super-hydrophobic, self-cleaning and antimicrobial properties are discussed in this chapter.

    Key words: Lotus Effect, NanoSphere, oleophobic fi nish, silanes, fl uorocarbon, photocatalytic, nanosilver, titania, hydrophobic, super-hydrophobic, self-cleaning, antimicrobial.

    12.1 Introduction

    Finishing of technical textiles is generally carried out to give them a par-ticular function. Nanotechnology allows the development of new and more complex functions as well as improvements in existing functions such as durability without losing the fabrics feel and texture. Application of various types of nanotechnologies for the fi nishing of textiles has been recently reviewed (Gulrajani, 2006; Holme, 2007; Siegfried, 2007; Sawhney et al., 2008; Dastjerdi and Montazer, 2010; Gowri et al., 2010).

    The most signifi cant early development of nano-fi nishes for textiles came through the research of Dr David Soane. After almost 20 years at the Uni-versity of California, Berkeley, Dr Soane left academe and, using his garage as a lab, began devising ways of using nanotechnology to add unusual prop-erties to natural and synthetic textiles, without changing a fabrics look or feel. He fl oated the fi rst nanotechnology-based company, Nano-Tex, in 1998, specifi cally catering to the textile industry. The main attribute of the tech-nology was to directly bind functional chemicals to the fi bres, instead of binding them as a side chain of a polymeric compound, thereby improving their durability with minimal effect on the basic properties of the substrate.

    At about the same time the pioneering work of Professor W. Barthlott of the University of Bonn, Germany, led to an understanding of the

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    mechanism by which the leaves of the lotus and other plants utilize super-hydrophobicity as the basis of self-cleaning. Barthlott now owns a patent and the Lotus Effect trademark, which has formed the basis of the NanoSphere-based stain protection and oil- and water-repellent textile fi nishes of Schoeller Textil A G of Switzerland.

    Further impetus for the development of nano-fi nishes for textiles came from the work of Dr Walid Daoud and Dr John Xin of Hong Kong Poly-technic University. These scientists invented an effi cient way to coat cotton cloth with tiny particles of titanium dioxide. These nanoparticles act as catalysts that help break down carbon-based molecules, requiring only sun-light to trigger the reaction. The inventors surmised that these fabrics could be used to make self-cleaning clothes, able to tackle dirt, environmental pollutants and harmful microorganisms.

    Today we have a plethora of textile fi nishes, all based on the basic research and development carried out by the above-mentioned pioneers. Applica-tion of inorganic nanoparticles such as titanium dioxide, silver, zinc oxide, copper, gallium, gold nanoparticles, carbon nanotubes, nano-layered clay, and their nanocomposites, to textile substrates to impart antimicrobial properties, is another area where the application of nanotechnology to the fi nishing of textiles is being explored extensively. New methods of applica-tion of nanoparticles by nano-coating, electro-spraying, layer-by-layer deposition, chemical vapour deposition, sol-gel deposition and polymer fi lm roughening are being researched and commercially exploited to impart super-hydrophobicity to textile substrates (Xue et al., 2010a). A large number of functionalities can be imparted to textiles by the application of nanoparticles and nanostructured materials. These have been discussed by Siegfried (2007) and are summarized in Table 12.1. The evolution and pro-gression of nano-fi nishes and their application to textiles will be discussed in this chapter.

    12.2 Hydrophobic nano-fi nishes

    Most commercial hydrophobic fi nishes are based on fl uorocarbon copoly-mers. These are dispersions of fl uorinated acrylates having comonomers that have reactive methalol or epoxy groups that may react to form a cross-linked network and become covalently bonded to the surface of the fi bres. These fi nishes form low-energy semi-permeable fi lms that protect the fi bres in treated fabrics and considerably reduce surface tension. The critical surface tension (C) of CF3 is 6 mN m1. In fl uorocarbon fi nishes the critical surface tension (C) depends on the chain length of the fl uorinated side chain and requires a minimum chain length of n = 9 (Holme, 2003).

    To develop a more durable hydrophobic and oleophobic fi nish that does not block the pores of the fabric by formation of polymer fi lm thereby

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    Table 12.1 Technical textiles and nanoparticles

    Functional textile Nanoparticle/nanostructure

    Product description

    Self-cleaning textiles/stain resistant

    TiO2, fl uoroacrylates, SiO2*, CNT

    Stain-repellent furniture textiles, umbrellas, easy to clean luggage, self-cleaning pants, ties, coats

    Antibacterial Ag, chitosan, SiO2*, TiO2, ZnO

    Anti-odour underwear, socks, insoles, helmets and other sports gear, furniture textiles and bed sheets, kitchen sponges, towels; biocidal facial masks, blankets, patient dresses, surgical gloves

    Conductive/antistatic textiles

    Cu, polypyrrole, polyaniline

    Smart clothes with sensing function, isolating carpets and fl oor coverings, suits with electromagnetic functions, spark-preventing fi lters

    UV-blocking textiles

    TiO2, ZnO UV-blocking sports clothing with integrated sun protection, shirt fabric, coating agents, umbrellas

    Flame-retardant textiles

    Sb3O2, CNT, boroxosiloxane, montmorillonite

    Flame-resistant suits, gloves, carpets, curtains, furniture textiles, seat cushions, linings

    Reinforced textiles CNT Bulletproof jackets and vestsControlled release

    of active agents, drugs or fragrances

    Montmorillonite, SiO2*

    Insect-repelling jackets, tents; fragrance-emitting furniture textiles, carpets, curtains; drug-releasing wound dressings

    Luminescent textiles

    Stimuli-sensitive colorants

    Textiles with colour changing effects

    Thermal insulating textiles

    Nanoporous Si structure

    Thermally insulating mountain jackets for low temperatures, shoe insoles

    * SiO2-nanosol-coating as matrix for embedded active species (biocides, dyes, fragrances).

    making it more breathable Soane and co-workers (Soane and Offord, 2002; Linford et al., 2005) patented a large number of multifunctional (nano) molecules that were capable of being covalently and non-covalently attached to cellulosic and proteinous fi bres. Some of these multifunctional molecules were block copolymers or graft copolymers, having plural functional groups such as binding groups, hydrophobic groups, hydrophilic groups and oleo-phobic groups. These groups may be present in the form of hydrophobic and hydrophilic regions. In these multifunctional molecules the hydrophilic groups, such as the carboxyl groups, act as reactive groups. These may be present in the form of polycarboxylic acid or as polyanhydrides, such as poly(maleic anhydride) polymer.

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    One such multifunctional molecule may be represented as in Fig. 12.1. A reaction scheme of a multifunctional molecule with cotton is shown in Fig. 12.2. Where a hydrophilic reactive molecule of poly(maleic anhydride) fi rst reacts with the hydro- or fl uoroalkyls, having preferably C8 or C9 (for

    R

    A

    X

    ( )m

    ( )o

    (O)n

    12.1 Multifunctional molecule of Dr Shone, where m, n = 0 or 1, o = 0 or 2. R is a linear, branched, or cyclic hydrocarbon or fl uorocarbon having C1 to C30 hydrocarbon or fl uorocarbon groups. A is SO2, CONH, CH2 or CF2. X is a nucleophilic group capable of reacting with a hydroxyl, amine or thiol group.

    Poly(maleic anhydride)

    OO O

    OO Om

    ( )

    +R

    R = hydro-and fluoroalkyls

    HO RR = hydro- and fluoroalkyls Copolymerize

    O O

    oO

    OO

    OO

    R

    ( )( )n

    OO O R

    ( ) ( )m n

    Poly(maleic anhydride-co-fluoroalkene-co-hydroalkene)

    Cotton clothingH2O, NaH2PO2, heat

    H2O, NaH2PO2,heat, cotton clothing

    Cotton

    OH OH OH OHHOOO O

    O

    Cotton

    OH OH OH OHOHOO

    OOO

    O

    RO

    O( )

    ( )no

    R

    nm( )( )

    12.2 Reaction schemes of a multifunctional molecule formation and attachment with cotton to form whiskers on the surface that are fl oating in air away from the fabric surface.

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    maximum hydro- and oleophobicity as discussed above), it forms a multi-functional molecule, having hydrophobic, oleophilic and hydrophilic groups or regions. Subsequently this multifunctional molecule reacts with the hydroxyl groups of cotton or other cel