Requirements for waterproof breathable fabrics
Ø Waterproof
ness
Ø Breathability
Ø Windproof
ness
Ø Abrasion
resistance(wet and dry conditions )
Ø Tear
conditions
Ø Strength of
the coating
Ø Easycare
Ø Durability
Ø Flexability
Ø Stretchability
Mechanism of water vapour transmission
In tightly woven fabrics
Ø simple
diffusion through the inter yarn faces
Ø Capillary
transfer through fibre bundle. The liquid water is wicked up
through the
yarns and desorbed and evaporated at the outer surface
Ø The diffusion
through individual fibres.
Methods of
waterproof breathable fabric making
v High Density
Wovens
Ø Thin and
smooth yarns that are usually called microfibres are used
Ø This type
weaving gives an excellent wind proof with water
vapour
permeability.
Ø The major
advantage of this type of fabric is their grip.
Ø These are
mostly used in skin clothing where water vapor permeability,
wind proof
are required rather than water impermeability
v Coatings
Ø Microporous coatings
Foam made
out of aqueous polymer dispersion, it will be pressed after being dried
Ø Phase separation
ü Wet coagulation
The coagulated PUR polymer will
be precipted with salts.
ü Dry Coagulation
An emulsion containing
solvent and non solvent will be applied to the textile. During the evaporation
of the solvent, the polyurethane will be coagulated in the non solvent forming
a microporous structure.
Hydrophilic coating
From the
hydrophilic groups containing polyurethane
solution the solvent will be evaporated leaving a compact film behind.
The water
vapour can transit the film through the hydrophilic group built into the
polymer.
v Laminates
Ø It lies between the inner and outer textile fabrics.
The film is both
waterproof
and breathable, and will never wash away.
Microporous membranes
Ø Microporous
fluorocarbon film.
Ø Microporous
PUR film
Ø Photo
polymerized polyacrylate film
Hydrophilic membranes
Ø Hydrophilic
groups built into the polymer chain bring the water vapour
molecules
through the film.
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