How to Identify Size of Woven Fabrics | Importance of Size of Woven Fabrics | Procedure for Identification of Starch, PVA and CMC

What is Size?

Size or sizing is defined as the composition of matter applied towarp yarns, before weaving, for the sake of their protection against abrasivestresses during weaving. These abrasive stresses are caused by movement of thewarp yarns through the heddles on the loom and mechanical actions duringinsertion of filling. Unprotected warp yarns will break during weaving, causingfrequent machine stoppages and loss of productivity. The application of sizegreatly improves the weaving efficiencies. The size also glues down loosefibers and lets the yarn slide more easily during weaving.

Why identification of type of size (on the fabric) isimportant?

Sizing is called "devil's invention" by thetextile dyer, since he must remove it in order to have a defect-free, uniform,well penetrated dyeing. In order to assure the best removal of sizing, theidentification of type of size is important, as different type of sizes needdifferent removal strategies or different optimum desizing recipes.

Scheme 1 for identification of type of size

Preparation of Test Solutions:

Solution 1: 2.4 g of potassium iodide and 1.3 g of iodinedissolved in water and diluted to one litre.

Solution 2: 0.13 g of iodine, 2.6 g of potassium iodide and4.0 g of boric acid added in that order and diluted to 100 ml.

Solution 3: 11.88 g of potassium dichromate and 25 ml ofconcentrated sulphuric acid diluted to 50 ml with water.

Solution 4: 30 g of sodium hydroxide in 70 ml of water.

Solution 5: 0.012 M ferric chloride.

Solution 6: 0.06 M potassium thiocyanate.

Solution 7: 0.005 M potassium ferrocyanide.

Solution 8: Iodine and boric acid

Solution 9: Chromic acid.

Solution 10: Sodium hydroxide

Procedure for Identification of Starch, PVA and CMC(Fig. 1)

Step 1: Spot fabric with one or two drops of solution 1. Formation of a deepblue colour indicates the presence of starch or PVA.

Step 2: (Only if you know that starch is not present) Spot fabric with one ortwo drops of solution 2. A purple colour indicates the presence of PVA.

Step 3: Apply on fabric one drop of solution 3 and immediately neutralise with3-4 drops of solution 4. Wait for 5 seconds, and then rub mixture with a glassrod. Formation of a brown spot indicates presence of PVA.

Step 4: Mix thoroughly 5 drops each of solution 5 and 6. Spot the fabric withone drop of this mixture and let stand approximately 3 minutes. Rinse inrunning water for 10 seconds and blot dry. Add one drop of solution 7 and letstand 1 minute. Rinse in running water 5 seconds and blot dry. A blue or blue-greenspot indicates CMC.

Fig. 1 Flowchart for identification of starch, PVA and CMC sizes

Procedure for Identification of Starch-PVA blends (Fig. 2)

Step 1: Spot fabric with one drop of solution 8 and allow to air dry. A blue or purple colour indicates starch and/or PVA.

Step 2: Apply one drop of solution 9 to the fabric and neutralise immediately with 3 drops of solution 10. Rub the spotted area with a glass stirring rod. A brown colour indicates PVA. A yellow or green-yellow colour indicates starch.

Fig. 2 Flowchart for identification of Starch/PVA blends

Procedure for Identification of Partially or Fully Hydrolysed Types of PVA (Fig. 3)

Step 1: First determine that PVA is present

Step 2: Add 1 drop of solution 8 and allow to air dry

Step 3: Add 1 drop of water to the centre of the spot

Step 4: Wait 10 seconds. A wine-red halo around the spot indicates partially hydrolysed PVA. Fully hydrolysed PVA does not give the halo. (Starch does not affect the reactions.)

Fig. 3 Flowchart for identification of partially of fully hydrolysed types of PVA

Procedure for identification of acrylic and polyester sizes

Step 1: Prepare a 0.025% solution of cationic dye such as Basic Blue 54 or Basic Red 29. Adjust pH to 6-7.

Step 2: Place fabric sample in dye solution for 1 minute at room temperature while stirring well.

Step 3: Rinse sample in room temperature water for 1 minute.

Step 4: Rinse sample again in 10% acetic acid and 0.2% non-ionic surfactant solution at room temperature for 1 minute.

Step 5: Rinse again in room temperature water for 1 minute and then dry.

Step 6: Medium to dark stains of warp yarns indicate presence of size.

Note: Since cationic dyes can stain many fibres, care must be taken while interpreting test results on fibres other than polyester.

Scheme 2 for identification of type of size

Another scheme for identification of type of size is given as follows:

Preparation of Reagents

Iodine Solution: To make N/50 iodine solution, dissolve 15g of Potassium Iodide into as little distilled water as possible. Dissolve 2.7g of Iodine into it. After dissolving, fill it up to make the total amount 1 litre.

Boric Acid Iodine Solution: Dissolve 30 g Boric Acid in 900 ml distilled water by heating at 50-60 C. Cool it down and add in it N/50 Iodine solution as prepared above to make the total solution of 1 litre.

Procedure for detection of starch and PVA

Take 1 g piece of fabric in 50 ml distilled water and boil for 30 minutes, with constant stirring, for extraction. Cool the extract for further analysis.

a) Take 10 ml of the above extract in a test tube and add a few drops of iodine solution. If there is any blue coloration, then starch is present. If there is no blue coloration even on adding a few more drops of iodine solution, starch is not present.

b) If presence of starch has been indicated, take another fresh 10 ml of the above extract in another test tube and add 1-2 ml of commercial heat-stable enzymatic desizing agent (amylases). Place the test tube in heated water bath for 10-20 minutes to degrade starch. To confirm the degradation of starch, take a few ml of the enzyme-treated solution in another test tube, cool it down and add a few drops of iodine solution. If there is no blue coloration, starch is completely degraded. If there is any blue coloration, then starch is not degraded. To degrade the starch fully, add in the enzyme-treated test tube, a few more drops of enzyme and/or heat for more time till the starch is fully degraded.

Once it is confirmed that the starch in fully degraded, presence of PVA can be checked by first cooling the solution down and then adding a few drops of boric acid iodine solution. If there is any blue coloration, it indicates the presence of PVA. If there is no blue coloration, PVA is not present.