Some Selected Notes on Textiles- Part 4

- Colorfastness to Light: In this the samples is exposed to a light source along with blue wool sample. The fading is observed and the rating is given.  The main difference between American and European Standards is that American standard is time bound. In European standards it is not a time bound test but fading bound test- means you have to keep on exposing the sample till the sample fades to that of blue scale. Factors affecting lightfastness are the type of dyes used, depth of shade, surface structure and finishing chemicals. 

- A cotton pigment printed fabric cannot be dry cleaned . In dry cleaning solvent called Perc- Perchloro Ethylene or Tetrachloroethylene. Pigments are very susceptible to dry cleaning- they will come out. Perc is the only solvent that do not blast. In exports they use MTO . The problem with perc is that it damages Ozone layer. Perc will take out the pigments from the print. However, if you dry clean with MTO, nothing will happen.  Perc does not smell as much as MTO does.  To test for dry cleaing, a bag is prepared where instead of steel balls, stainless steel discs are added. 

- To remove smell from pigment printed fabric, it has to be cured well. To do it, maintain a temperature of 150 deg and allow the fabric for 10 minutes. It will cause phosphoric acid to get liberated and pigment get fixed- for that Diammonium phosphate needs to be added – so fixation takes place under acidic condition.  

- When testing for shrinkage, the fabric is conditioned for 24 hours. Then it is subjected to washing process for 45 minutes to 1 hours. Then it is dried and reconditiond before remeasuring.

- When testing for shrinkage, soft water is used. Alum can be used for softening. Just move the alum on the upper surface for a few times. Now decant the upper portion and use the rest of the water for testing. One can also use wetting agent. 

- Drying can be line drying, wet drying, tumble drying or drip drying. 

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Some Selected Notes on Textiles- Part 3

- Color Fastness to Rubbing – There are two types of it, dry and wet. Dry rubbing is important for the materials like sofa covers where a person sits on it. Normally it is done using Croakometer with 10cm track length and 9.8 N force.

- For all colorfastness evaluation it is done either visually or using spectrophotometer. Normally worst rating is given.

- Colorfastness to water – It is done to measure colorfastness to water under intimate contact when getting wet, for example contact of inner wear to outer garments in rain. The sample is wet in distilled water , put between two acrylic sheets and then it is clamped under a force of 4.5 kg and put in incubator at 37 degrees Celsius for  4 hours.

- Colorfastness to Water is not the same as colorfastness to washing.  In measuring colorfastness to water we use distill water, whereas in colorfastness to washing, the detergent is used which makes the pH alkaline. A case is cited where a fabric had excellent colorfastness to washing but poor colorfastness to water. It can be due to the fact that the fabric was dyed with reactive dyes. There was some hydrolyzed dye present, but it had no reactivity and hence it was unable to react with water so there was no bleeding. On the other hand that hydrolyzed dye migrated in case of pressure and water hence had poor colorfastness to water.  Thus rigorous soaping could have solved the problem. Taking the other aspect, a fabric had poor colorfastness to washing but excellent colorfastness to water. It can be due to the fact the dye is probably sensitive to the pH.

- Colorfastness to Perspiration- Test is done similar to Colorfastness to water; the only difference is that a solution is prepared which simulate perspiration and the fabric is dipped in it, rest of the procedure is the same. Two types of solutions are prepared , one simulating alkaline perspiration with a pH of 8.0 and the other simulating acidic perspiration with a pH of 5.5. To prepare this solution Sodium Chloride and Lactic Acid are the main ingredients. The test conditions of 37+- 2 deg Celcius for four hours under a pressure of 5 kg. – Picture Source and Procedure. 

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Some Selected Notes on Textiles- Part 2

- Acid dyes are used for silks. There are three categories of acid dyes- Leveling or strong acid dyes, Milling or weak acid dyes and super milling or fast acid or neutral dyes. The colorfastness of fabric is decided by which of these dyes are used.

- Colorfastness to wet scrubbing is only for pigment printing. Pigment has no affinity to fiber yet it can be applied to all the fibers.  Here a brush is used to see the shade change. 

- Colorfastness to ozone is used only for Denim, which tends to turn yellow either due to atmospheric fumes or ozone. 

- REACH- Registration Evaluation Authorisation of Chemicals is a European document which enlists 800 chemicals which are carcinogenic. Out of which 56 chemicals are SVHC- substances of very high concern. Out of these 56, only 25 are related to textiles. 

- Presence of Alkyl Phenol Ethoxylate is a compound present in cheap detergents. 

- Colorfastness is the property of a color to retain its color under different conditions of use. 

- Colorfastness to washing is checked for many different fibers using a multifiber fabric. It is important to know the colorfastness against different fibers as we don’t know which all fibers will go together in a washing load. Please see Picture Source and Procedure here.

Washing Fastness Tester

- ISO grey scales are used. There are two types of shade cards- color staining and color change ( shade change).  Grey scales are used as opposed to colored scale because only intensity of color change is seen vis-a –vis intensity of grey scale. 

- Internationally a ½ point deviation is acceptable. Normally the evaluation should be done by minimum two people. This is done with D-65 light source for evaluation. 

- This scale is used  for all tests except light fastness ( For light fastness we use 8 scale- Blue wool scales are used)

- Cross staining is transfer of color from a darker to lighter component within the fabric. 

- A case is sited where there was a red dress with white piping. The red dress had a colorfastness of 4-5. But still it was enough to make the white piping pink which was not acceptable. For this case the minimum acceptable fastness was 5. 

- When measuring colorfastness to washing, the test replicates 5 typical home launderings. 

- The Load contains multi fiber test fabric, standard reference detergent, steel balls, washing devices and grade 3 water ( grade 1 is the purest). Addition of steel balls accelates the process. In testing silks steel balls are not used. 

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Some Selected Notes on Textiles - Part 1

- Strength of Cotton is in between silk and wool. Silk is the strongest fiber.

-  Cotton is less elastic than Silk.

- Cotton wrinkles as the cellulose from which it is made has hydrogen bonds that break when washed due to agitation or mechanical action. They are formed again when ironed but in different places. Read more...

- Perspiration is of two types- Alkaline and acidic. Majority of the perspiration is alkaline. Cotton is not affected by alkaline perspiration whereas silk does.

- Coloration principle involves physical absorption of water soluble dyes, transferring of dye on to fiber, dye becoming water soluble and is retained inside the fiber.

- Reactive dyes physically react with fibers and form covalent bonds. The process involves two steps: 1. Dyeing with the dye in presence of salt to effect as exhaustion as possible ( transferring of dye from solution to fabric) and 2. Chemically reacting the dye with water in presence of alkali like soda ash.

- Reactive dyes also react with the water in which they are dissolved.  This is called hydrolysis of dyes. These hydrolysed dye has to be removed from the fiber by proper soaping else color fastness will be a major issue.

- Disadvantage of reactive dyes are that the hydrolysis accompanies fixation, as told earlier. Also there there is approximately 30% wastage of dye due to hydrolysis. Only 70% of the dye react with fiber.  To remove hydrolysed dyes there is an excessive consumption of water. Also colored effluent discharge is a major problem. It also involves large amount of electrolyte ( Common salt) as a exhaustive agent. It is also costlier. 

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