Certain
end use of textiles such as umbrella cloth, swim suit, sportswear, rain coat,
tarpaulin etc. need water repellency or water proofing.
When a uniform coating of suitable substances such as rubber is
produced on the surface of the fabric, the interstitches between the warp and
weft yarns are blocked by the continuous film of that substances and water will
not pass through the fabric. This phenomena is known as water repellent or
water proof finishes.
However,
the rubber treated fabric becomes impermeable to air as well as moisture, when
a treated fabric is impermeable to water and air then this type of finishes is
called water proof finish.
When
the protection from water is desired as in apparel purpose, the treated fabric
should be permeable to air but not in water. This type of finish is called
water repellent finish.
Method of Application: Water repellent or proof finishes are produced by the use of
water insoluble metal soap like aluminum stearate. This is usually done by
treating the fabric first with an aqueous solution of the metal that is
aluminum acetate or lead acetate, that passing through water soluble soap like
sodium stearate.
Paraffin
wax or vegetable waxes are used along with aluminum stearate to increase the
water repellent effect.
Agents for Water Repellent and Water Proof Finishes: The following agents are commercially used
for water repellent or proof finishes. They are,
1.
Bteanoxy methyl
pyridinium chloride
2.
Bteanamide= C17H35CONH2.
3.
Methylate methylol
stearamide = C17H35CONCH2OH
4.
Methylene
bis-stearamide
5.
Methylol
stearamide
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