In this experiment, 100% cotton double jersey knit fabrics (scoured and bleached) were used. At first fabric is finished with different types of water repellent chemicals by pad-dry-cure method. The fabrics were supplied by Essential Clothing Ltd, Bangladesh. Two types of double jersey fabrics were used here, one is rib (1 × 1) and another is interlock. Fabric specifications were given in Table 1.

Supplied fabrics which presents good hydrophilic character were first finished by using three different fluorocarbon based water repellent chemicals in three different concentrations (70 g/L, 90 g/L and 100 g/L) to analyze the performance of different water repellent chemicals and their varying concentration on water repellency and other physical properties of the fabrics. In addition, fabrics were dyed by using following recipe which is given in Table 2 in Micro Fibre lab and finished with different water repellent chemicals in 100 g/L concentration (conc.) as it showed excellent water repellency to investigate different fastness properties of the finished fabrics.

Dye application bath for double jersey fabrics

Three types of fluorocarbon based water repellent chemicals are used, first is fluorocarbon (FC) (trade name Nuva TTC, dispersion of fluorine compound, weakly cationic, Clariant), second is fluorocarbon with dendrimers (FC + D) (trade name Rucostar EEE6, fluorocarbon (C6) resin with polymeric, hyperbranched dendrimers in a hydrocarbon, weakly cationic, Rudolf chemie) and third is fluorocarbon with booster (FC + B) (trade name Lurotex protector RP ECO, C6 fluorocarbon finish with an unblocked isocyanate booster, weakly cationic, BASF).

Two types of double jersey derivative fabrics were treated with three different water repellent chemicals at three different conc. (70 g/L, 90 g/L and 100 g/L) from a separate bath with same bath condition. Fluorocarbon (FC), fluorocarbon with dendrimers (FC + D) and fluorocarbon with booster (FC + B) water repellent chemical’s solutions were prepared. The process parameters were adopted as recommended by the supplier and bath set up are given in Table 3. Horizontal Pad-Mangle machine (Rapid, Xiamen Rapid Co Ltd, China) was used

for padding with 4.5 rpm fabric speed and 2.3 kg/cm² padding pressure. Channel precision oven machine, made in China, was used for drying and Labtec Steamer machine (Newave Lab equipments Co Ltd, Taiwan) was used for curing.

1) Drop test: It checked the contact angle by using AATCC 79 method. ( one water droplet is placed on treated fabric from specific distance and checked the droplet visually to evaluate the water repellency. When water droplet is placed on finished fabric then the drop will rest up on it and will not penetrate it means that the finished material surface has lower surface tension than water surface tension, then that material is called water repellent.)

2) Spray rating test: The spray rating tests were evaluted by using ISO 4920:2012 test method.

3) Hydrostatic Head Test: It was done by Shirley hydrostatic head tester, England according to AATCC 127 method.

Each samples were tested in the standard atmosphere, 25˚C ± 2˚C temperature and 65% RH after conditioning 24 hrs.

1) GSM test: GSM test was done by GSM cutter from James H. Heal & Co. Ltd. Halifax, England according to ASTM (D 3776-79) method.

2) Bursting strength test: It was done by bursting strength tester from SDL Atlas according to ASTM (D 3786-87) method.

3) Air permeability test: It is done by using Textest FX 3300 Labair air permeability tester, Textest Instrument, Switzerland according to ISO 9237 method.

4) Color fastness to wash: Color fastness to wash was measured with ISO-105 C2S method.

5) Color fastness to water: It is done by ISO 105-E01 method.

6) Color fastness to chlorinated water: It is done by ISO 105-E03 method

7) Color fastness to perspiration: It is done by ISO 105-E04 method

8) Color fastness to rubbing: The resistance of color against rubbing of dyed fabrics (dry and wet) were evaluated with ISO-105-X 12 method.

Three fluorocarbon based water repellent solutions (trade name Nuva TTC, Rcostar EEE6 and Lurotex protector RP ECO) were prepared in 70 g/L, 90 g/L and 100 g/L conc. and applied these conc. on different 100% cotton double jersey knit fabrics. Two different double jersey knit fabrics were used in here which were 1 × 1 rib and interlock.

This is the visual test to evaluate the water repellency. If the material surface has lower surface tension than water surface tension, then that material is called water repellent. When water drop is placed on water repellent material then the drop will rest up on it and will not penetrate, then it will be called water repellent.

Here are some physical appearances of untreated and treated rib and interlock fabrics by using fluorocarbon with dendrimer chemicals (trade name is Rcostar EEE6 and expressed by FC + D) (Figure 3), showed that treated fabrics are water repellent and pictures were taken by using Projectina (Electron microscope) dmm-2000 model. 1) Untreated black color dyed of rib fabric; 2) Black color dyed of rib fabric, treated with FC + D chemicals at 100 g/L conc; 3) Untreated pink color dyed of interlock fabric; 4) Pink color dyed of interlock fabric, treated with FC + D chemicals at 100 g/L conc. (untreated fabric showed absorbing area of water droplet and treated fabric showed water droplet without penetration); 5) Untreated white rib fabric; 6) Treated white rib fabric with 70 g/L conc. of FC + D chemical; 7) Treated white rib fabric with 90 g/L conc. of FC + D chemical; 8) Treated white rib fabric with 100 g/L conc. of FC + D chemical; 9) Untreated white interlock fabric; 10) Treated white interlock fabric with 70 g/L conc. of FC + D chemical; 11) Treated white interlock fabric with 90 g/L conc. of FC + D chemical; 12) Treated white interlock fabric with 100 g/L conc. of FC + D chemical;

FC, FC + D and FC + B water repellent chemical’s solutions were prepared in 70 g/L, 90 g/L and 100 g/L conc. and applied on double jersey knit dyed fabrics. These treated fabrics were evaluated using ISO 4920:2012 method. The evaluated rating of the samples are given in chart with its graphical analysis. Schindler et al described that after completing the pad-dry-cure process, perfluoro side chains changed to almost crystalline structures by curing process to achieve optimal water repellency [8] . Compared with the untreated fabric, the finished fabrics had good water repellency with around 3 - 5 grades.

It is shown from Figure 4 and Table 4 that by applying 70 g/L conc., water repellency rating varies with different double jersey fabrics. FC + D water repellent chemical and rib fabric give comparatively better repellency for its compactness and for its heavy GSM. In 90 g/L conc., water repellency rating has improved for FC + B water repellent chemical. Among the fabric, heavy GSM of rib fabric show the best rating. FC + D water repellent chemical’s treated fabrics remain same rating like 70 g/L conc. treated fabric though FC water repellent chemical improves by 90 g/L conc. Particularly for 100 g/L conc., both FC and FC + D gives the best result for all fabrics and in high conc. all the chemicals show better result for both fabrics.

The hydrostatic head test was done according to AATCC 127 method on double jersey fabrics after water repellent finish at various conc. which are stated below in Figure 5.

From the above chart it has clearly seen that the more pressure is required to force water through the fabric. After gradually increasing the conc. from 70 g/L to 100 g/L, the pressure requires more. Rib fabric has higher hydrostatic head test rating than interlock fabric because of rib fabric has higher GSM and more compactness. An increase in repellent conc. caused an increase in wetting times of the fabric after finishing. In all conc., FC + D water repellent chemical shows better hydrostatic head test rating than FC + B and FC water repellent chemicals for both rib and double jersey fabrics. Because the water repellent chemicals form a coating on the fabric and the more conc. of chemicals leads the higher density of the coating resulting increased water repellency.