2. Topics:
1. What is pH ?
2. Which problems arise in fabrics if we don’t maintain proper pH
range?
3. Which problems arise in Human body if we don’t maintain proper pH
range in fabrics/ Garments?
4. How too high or low pH may cause irritation to skin?
5. What is the pH range in Dyeing & Finishing process?
6. How we can control pH in Dyeing & Finishing process?
7. How to measure/determine pH in dyeing floor & Laboratory?
3. 1. What is pH?
Answer:
pH is an abbreviation for "power of hydrogen."
pH is a measure of hydrogen ion concentration, a measure of the acidity or
alkalinity of a solution.
pH is the negative logarithm of the effective hydrogen ion concentration of a
solution.
pH = −log[H+]
pH only has meaning in an aqueous solution (in water). Many chemicals,
including liquids, do not have pH values. If there's no water, there's no pH.
For example, there is no pH value for vegetable oil, gasoline, or pure alcohol.
The pH scale usually ranges from 0 to 14.
5. 2. Which problems arise in fabrics if we don’t maintain
proper pH range?
Answer:
The pH of the processed textiles must be neutral and within the prescribed limits for a
particular end use. High or low pH value of the fabric will make the fabric easy to damage
during storage.
The textiles with higher pH value may exhibit:
a. Poor colorfastness properties,
b. Yellowing tendencies
c. Change of shade upon storage and during shipment.
Very high and very low pH results into degradation of textiles during storage and use, may
result into poor softness and harsh feel.
Greige fabric with higher pH value may result into poor dye pick up, patchy dyeing.
6. 3. Which problems arise in Human body if we don’t maintain
proper pH range in fabrics/ Garments?
Answer:pH of apparel fabrics which are in direct contact with the skin or used for
baby wear, must be controlled not to make the skin itchy.
7. 4. How too high or low pH may cause irritation/itchy to skin?
Answer:
Human skins are slightly acidic in nature to inhibit bacteria growth. pH value of skin is
achieved by body’s own secretion such as perspiration, sebum (fatty acids) and
various hormones which are acidic in nature.
Skin maintains an average pH value of 5.5-7.0. At this pH level skin protects itself
from bacterial infection, irritation, and allergic reaction.
We use a lot of chemicals in textile wet processing, which is strongly acidic or alkaline
in nature. Once the processing is finished, fabrics & garments are thoroughly washed
to remove all excessive chemicals.
However some residual chemicals are present in the fabric as well as garments which
give pH value. Too high or too low pH value of textiles will destroy the weak acid
protective layer on the skin of human body & cause irritation to skin. May cause
allergic reactions, can damage skin and make the skin vulnerable to other pathogenic
bacteria and even cause dermatitis.
Extreme pH value can cause skin itchy.
8. 5. What is the pH range in Dyeing & Finishing process?
Answer: The pH values in garments can be greatly affected by Scouring, Bleaching, After-
treatment (Dyeing & Printing) & Final washing process.
The proper range of pH values in dyeing & finishing process are given below:
Dyeing Finishing Pre-treatment & After-treatment process: pH range
1. Scouring 12.5
2. Bleaching (by H ₂O ₂) 10.5-11
3. Enzyme treatment 4.5
4. Levelling 6.5
5. Salt 7-8
6. Reactive Dyeing 10.5-11.5
7. Disperse Dyeing 4.5-6
8. Softener 6.5
9. Initial Dye bath 5.5-6.5
10. Neutralization 5.5-6.5
11. After Alkali edition 10.5-11
12. After Dyeing 5-6
13. Cationic Softener 4-5
14. Before Levelling 6-6.5
15. Silicon Softener 5.5-6
9. 6. How we can control pH in Dyeing & Finishing process?
Answer:
In Dyeing:
After scouring & bleaching process, use Acid: {citric acid/acetic acid (0.5-1.5g/l)}to neutralize
the fabric.
In dye bath, use Alkali: {caustic soda (0.5-2g/l) / soda ash (2-25 g/l)} to increase the ph.
After softening & before unload, fabrics need to neutralize, that’s why use Acid: {citric
acid/acetic acid (0.5-1.5g/l)}to neutralize the fabric.
In Finishing:
In Stentering, checked ph from softener solution (90litre water+10kg softener=100litre
solution; then add 500gm citric acid) in dram/tank, if ph range high then use acid to decrease
the ph.
10. 7. How to measure pH?
Answer:
In extraction, the water in contact with the textile will dissolve out the minute
amount of acids, bases or buffer salts contained therein. The pH of the extract
solution will be determined by the concentration of these soluble substances and
therefore, by the amount of water used for the extraction. The smaller the
amount of water used, the more accurately the pH obtained represents the pH of
the original air-dried fabric.
pH is checked by ph indicator strips.
The colors on a pH strip measure the concentration of
hydrogen ions in a solution or in soil. The color on
the strip determines the acidic or alkalinity state of
the item being tested.
11. Measure pH of solution in dyeing process:
Instrument: HANNA pH Meter
1. pH Meter keeps in water 2. Check pH of the water solution
(take from Dosing tank by run back)
3. pH Meter reading
12. During /after below process, pH range must be controlled:
1. Scouring & bleaching [need alkali media, pH =10.5-12.5]
2. Enzyme [Need acidic media, pH =4.5]
3. Levelling [Need neutral media, pH =6.5-7]
4. Color steam (after giving salt, soda & color) [Need alkali media, pH =10.5-12.5]
Take solution in Mug from Dosing tank by run back from bath, then check the pH by pH meter.
13. Measure pH of fabric in Laboratory:
Test Method: AATCC 81 & ISO 3071 (For H&M)
EQUIPMENT:
1. HANNA pH Meter 2. Mechanical shaker 3. Volumetric flask 4. Electric balance
14. EQUIPMENT:
1. Distilled water, of at least grade 3, pH 5.0-7.5.
2. 2gm fabric cut pieces (5mm*5mm).
3. Glass flasks with stopper, 150 ml.
4. Volumetric flask with stopper, 1000 ml.
5. 3 M Potassium Chloride (KCl) solution (Only for H&M buyer).
6. Electric balance, accurate to 0.01 gm.
7. Mechanical shaker, providing rotational or reciprocating movement.
8. pH-meter, with a glass electrode.
Preparation:
Fabric specimen is cut into very small pieces (5mm by 5mm) to allow test samples to wet out rapidly.
2gm fabric is soaked in distilled water (100ml) in volumetric flask. {For H&M buyer, Add Potassium chloride
solution (KCl) in concentration 0.1 M (mol/litre) in volumetric flask}
Then shake the volumetric flask by Mechanical shaker for 02 hours.
So residual influential ion is removed from textile specimen to water. This extracted water is measured by pH meter
to get pH value.
15. Pic: The process to make the solution with fabric to determine pH for H&M buyer.
RESULTS
The average value of second and third measures of one sample is calculated according to the formula
below: 𝐴𝑣𝑒𝑟𝑎𝑔𝑒=1:2+1:3/2
The result shall be reported with one decimal only.
NOTE
Note! If there should be a garment wash on the order, the pH value should be measured after the final treatment is made.
Note! The buffer solutions shall have the same temperature as the samples (room temperature
Note! Sample 1:1 shall not be included in the calculation of the result.
16. Uses of acid, alkali, salts,
bio-polishing agents &
softeners in textile dyeing &
finishing.
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