Introduction:
The merit of a fabric intended for rainwear, wagon covers or tents is judged, amongst other properties, by its ability to keep water out; conversely, when intended for hose pipes or canvas buckets, to keep water in. In another direction, some fabrics must exhibit the ability to absorb water rapidly, toweling being an obvious example. So there is a relation between water and textile materials which is very necessary for their end use.
Theory:
Water repellent is a state characterized by the non-spreading of water globules on a textile material. This term is not normally applied to a water-repellent finish impervious to air. This is generally referred to as water proof. It is generally done by treated fabric with fat, wax, rubber etc. This addition may be in form of physical film or coating or physical combination. The feature of a waterproof fabric is the low degree of air permeability. Spray tester is such an instrument which measures the water repellency of a fabric. In this test a small amount of shower is produced by pouring water through a spray nozzle. The water falls on to the specimen which is mounted over a 6 in. diameter embroidery hoop and fixed at an angle of 45 degrees. To carry out the test, 250 cm3 of water at 70oF are poured steadily into the funnel. The American Association of Textile Chemists and Colorists recommend the use of a chart of photographs against which the actual fabric appearance is compared.
The ratings are as follows:
Apparatus:
Spray tester
Water
Fabric
Sample: 100% cotton, polyester, umbrella, parachute cloth.
Atmosphere:
Temperature – 25oC and relative humidity – 67%
Standard atmosphere: temperature – 20oC and relative humidity - 65%.
M/c specification:
Name: Spray tester
Brand: DAIEI KAGAKUSEHCI SEISAKUSHO LTD., Kyoto Japan.
Template: 50 cm circumference.
Working Procedure:
The sample fabric is mounted on the embroidery hoop and fixed on the instrument at 45o.
Now the beaker is filled with 250 cc water and poured on the funnel.
The water is showered through spray nozzle on the fabric.
After spraying has finished the sample holder is removed and the surplus water removed by tapping the frame 6 times against a solid object, with the face of the sample facing the solid object.
The water repellency is assessed from the spray rating chart.
5 tests should be made and the nearest rating assigned to each, since no interpolation is allowed, i.e. a rating for a specimen cannot be 75.
The mean of the 5 ratings is taken as the result.
Data:
Result:
Water repellency of a 100% cotton fabric is 0.
Water repellency of a polyester fabric is 0.
Water repellency of a umbrella fabric is 70.
Water repellency of a parachute fabric is 100.
Remark:
According to the type of fabric water repellency varies from 0-100. From the experiment we can understand this. It is mainly selected depending on the end use of fabrics.
