Nanofinishing of textiles
Nanocoatings
§ Nanocoatings may be defined as the application of one-phase
solid structures, of which one dimension is smaller than 100nm
onto a surface, adding a specific property which otherwise would
not be accomplished.
§ These coatings may be built up by layers or by the combination of
particles thinner than 100nm that offer enhanced surface
properties.
§ While this definition is widely accepted, it is arguable that any
coating with a “nano” aspect, i.e., containing nanostructures or
possessing a nano quality may bedefined as a nanocoating.
§ Moreover, coatings may be built from nanolayers or
nanostructures exceeding the dimension of nanometers while
retaining nano properties.
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Nanofinishing in textiles
• Enhanced functionality by incorporating various
nanoparticles or creating nanostructured
surfaces, which led to enhance level of textile
performances such as stain resistant, hydrophilic,
antistatic, wrinkle resistant and shrink proof abilities.
• Nanofinishes can be applied in nanoemulsion form,
which enables a more thorough, even and precise
application on textile surfaces.
• They are generally emulsified into either
nanomicelles, made into nanosols or wrapped in
nanocapsules that can adhere to textile substrates
easily and more uniformly.
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Increase of surface area
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Surface properties and applications
of nanocoating
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Manufacturing methods
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Manufacturing methods
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Nanofinishes in market
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Hydrophobic finishes
• Hydrophopbic surfaces can be produced
mainly in two ways
– By creating a rough structure on a
hydrophobic surface
– By modifying a surface using materials with
low surface energy
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Lotus leaf effect
The surface topography of lotus leaf presents two different scales to the outside
environment and is textured with 3–10 micron sized hills and valleys that are
decorated with nanometer sized particles of a hydrophobic wax like material.
The hills and valleys ensure that surface contact area available to water is
very low while the hydrophobic nanoparticles prevent water into the valleys. The
net result is that water cannot wet the surface and therefore forms nearly spherical
water droplets, leading to superhydrophobic surfaces.
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Lotusan
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Self cleaning effect
In water-repellent surfaces, water contracted to form droplets, which came
off the leaf very quickly even at slight angles of inclination (< 5) without
leaving any residue (self-cleaning effect).
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Contact angle and wettability
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Nanocare technology
• The premier range of NanoCare® and
NanoPel® nanofinishes marketed by NanoTex Inc.
• Tiny whiskers aligned by proprietary
‘spines’ are designed to repel liquids and are
attached to the fibers utilizing molecular
‘hooks’.
• These whiskers and hooks are minute, in fact
no more than 1/1000th the size of a cotton fiber.
These whiskers cause the liquids or semisolids to
roll off the fabric thus causing minimal staining and
can be removed with simple washing
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Contact angle models
• Cassie and Baxter were the first to explain
that water repellency of rough surfaces
was due to the air enclosed between the
gaps in the surface, which minimizes
the substrate to water interface.
• Hence water does not spread and forms a
droplet, which easily rolls off.
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Surface energy
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Degree of wetting
Total Wetting: S > 0 , θe = 0 liquid spreads completely in order to minimize its
surface energy. e.g. silicon on glass, water on clean glass.
Partial wetting: S < 0, θe > 0. A liquid is “wetting” on a particular solid when θe < π/2,
non-wetting or weakly wetting when θe > π/2. For H2O, a surface is hydrophilic
if θe < π/2, hydrophobic if θe > π/2 and superhydrophobic if θe > 5π/6.
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Hydrophobic vs. hydrophilic
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Young’s law
Young’s Law: what is the equilibrium contact angle θe ?
Horizontal force balance at contact line:
γLV cos θe = γSV − γSL
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Wetting of rough solids with drops
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We#ng equa*on
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Wetting equations
A Wenzel state arises when the fluid impregnates the rough solid
In a Cassie state, the fluid does not impregnate the rough solid, leaving a
trapped vapour layer. A fluid placed on the rough surface thus sits on
roughness elements (e.g.pillars or islands)
Wenzel state breaks down at large r ⇒ air trapped within the surface
roughness ⇒ Cassie State
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Hydrophobicity of cotton
• During the last few decades, many methods of
imparting hydrophobic character to cotton have been
developed.
• These methods include attaching hydrophobic
polymer films, and attaching hydrophobic
monomers via physical or chemical sorption
processes.
• Monomeric hydrocarbon hydrophobes include
aluminum and zirconium soaps, waxes and wax-like
substances, metal complexes, pridinium compounds
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and methalol compounds.
Fluorocarbon nanofinish
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Finishes with multifunctions
Wrinkle resistance by cross-linking cellulose chains via maleic anhydride
residues.
In cotton,
1. Wrinkle resistance
2. Water repellency
3. Detergent free washing
4. Increased speed of drying
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Titania coated cotton fibers
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Titania coated cotton fibers –
discoloration of coffee stains
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Colored and Functional Silver Nanoparticle−Wool
Fiber Composites
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Nanosilver
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Antibacterial action of silver
• Attachment to the bacterial cell membrane
• Absorption/diffusion into the cell
• Coagulation with bacterial proteins/
enzymes
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