How to identify Dyestuff mixtures?

Differentiation of Dyestuffs:

Some simple tests can be carried out to find out a dyestuff is a direct, acid or reactive or a mixture of these things.

Wet filter paper blow test:

If you blow a pinch of dyestuff on dripping wet filter paper (from a short distance):

1. Acid dyes – will create specks that do not spread.
2. Direct & reactive dyes – will form a colored dispersion.

Dissolution Test:

1. Acid dyes – will dissolve only in acid medium.
2. Direct & reactive – will dissolve in soft water and form a uniformly colored solution.

Dyed fabric test:

1. Direct dyes – weak hydrogen bond - in the presence 5 gpl soap @ 95', dye will strip out and dye a fresh RFD fabric.
2. Acid dyes – in the presence of soap, it will not strip/bleed
3. Reactive dye – covalent bond – color will not bleed and stain the adjacent rfd.

Pyridine test: P6H5N

1. Direct dye will strip completely.
2. Acid dye will not strip – but will strip in acid medium –with larger amount of leveling agent.
3. Reactive dye – will not bleed.

Dyeing Test:

1. Direct and reactive only dye cotton.
   1. Direct dyes will dye weaker in the presence of higher dosage of soda ash. ( For example a 3% depth of both, we can identify easily.)
2. Acid dyes will dye protein fibres and stain cotton.

Some More Methods:

1.      Polyester fibers were treated with 200 μL of chlorobenzene at 100 °C for 60 min. Complete extraction indicated presence of a disperse dye.

2.       Acrylic fibers were treated with 50:50 formic acid:water (total volume 200 μL) at 100 °C for 60 min. Complete extraction after this step indicated that a basic dye is present.

3.       Nylon fibers were treated with equal parts of aqueous ammonia, pyridine, and water (66 μL each), heated at 100 °C for 60 min.35 Complete extraction indicated presence of an acid dye.

4.      Cotton fibers may be dyed with direct, reactive or vat dyes. The first stage of cotton fiber extraction used 60:40 pyridine:water using (120 μL pyridine, 80 μL water) at 100 °C for 60 min; complete extraction indicated a direct dye is present. If incomplete extraction occurred, 200 μL of 1.5% NaOH solution was added, and the plate heated at 100 °C for 60 min. A complete extraction signified that a reactive dye was present. If extraction was still incomplete, a vat dye may be present. A 200 μL volume of reducing agent solution (0.8 g sodium dithionite, 0.5 g of NaOH, 5.0 mL H2O, 33.0 mL of 1,2-dimethoxy ethane, and 66.0 mL of H2O) was added to the remaining fiber sample in a 96-well plate, and heated at 100 °C for 30 min. When the plate was placed in a fume hood without the cover, air oxidized the extracted vat dye to water insoluble pigment with a corresponding color change.

Chemical Resist Process - Reactive Printing

Two Methods of Working with Two Different Families of Reactive Dyes

The chemical resist process allows you to control background coloring of printing (and other methods of direct application) without the need for additional silkscreens and without color overlays.  

The process takes advantage of differing reactivity levels of Vinylsulphone based dyes (Remazols) and Cibacron F reactive dyes (similar results can be obtained with Vinylsulphone based dyes (Remazol) and DCT and MCT reactive dyes). Since some colors of dye work more effectively with this process than others, thorough testing is necessary to achieve predictable results.

Amount of Chemical Resist

The amount of Chemical Resist that needs to be added to the Cibacron F reactive dyes is dependent upon the strength of Remazol dyes which will be applied over or under the reactive dyes (see chart).

Dye Activator Options

The chemical resist process works best with soda ash as the activator in the Cibacron F  reactive dye pastes and Basilen Fixing Agent as the activator in the Remazol dye pastes. It will work with baking soda as the activator for the Remazols, but not always reliably. (With baking soda as the activator, it is critical for Remazol dyes to dry slowly; in mid-winter, it may be necessary to prolong their dampness in the fabric by batching them in plastic for 24 hours). Method One will also work with the soda soak/batching method for fixing the dyes.

Method One - Remazol Dyes Over Reactive Dyes

1. Mix Cibacron F reactive dye pastes, using the appropriate amount of Chemical Resist (depending on the strength of the Remazols you intend to use) and soda ash (unless you have soda soaked the fabric first). Refer to the chart for quantities of Chemical Resist and soda ash.

2. Apply Cibacron F reactive dyes and allow them to dry naturally. (Batch in plastic if using the soda soak/batching method of activation.)

3. Mix thick Remazol dye pastes, using the appropriate amount of dye activator (see chart).

4. Roll or squeegee Remazol dye(s) over the dry Cibacron F dyes.

5. Allow dyes to dry naturally (unless using the soda soak/batching method for fixing the dyes).

6. Unless you have used Basilen Fixing Agent as the Remazol dye activator, you must

steam the fabric within 1 day of applying the Remazol dyes in order for the chemical

resist process to work. That timing is not necessary with Basilen Fixing Agent as the dye activator, because it does not begin fixing the dye to the fabric until it is steamed.

7. Wrap fabric in paper, tie, and steam for 8-12 minutes.

8. Wash out excess dye and then boil the fabric for about ten minutes to achieve the full chemical resist effect. Use a drop of synthrapol in the rinse water and also in the water to be boiled.

9. The halos which occur around the Cibacron F reactive dye areas will be more or less apparent, depending on the amount of Chemical Resist used as well as on the strength and thickness of Remazol dyes you used.

Method Two - Remazol Dyes Under Reactive Dyes

1. Mix thin Remazol dye pastes with the appropriate amount of dye activator (see chart).

2. Apply Remazol dyes as desired. Allow them to dry naturally.

3. Mix Cibacron F reactive dye pastes with the appropriate amounts of Chemical Resist and soda ash (see chart).

4. Apply Cibacron F reactive dyes. Allow them to dry naturally.

5. Wrap fabric in paper, tie, and steam for 8-12 minutes.

6. Wash out excess dye and then boil the fabric for a few minutes to achieve the full

chemical resist effect. Use a drop of synthrapol in the rinse water and also in the water

to be boiled.

7. Little or no halo effect should occur around reactive dye areas using this method.

Courtesy : patricia williams

Nano and Micro Silicone softeners – how to differentiate?

The processing of textiles to achieve a particular handle is one of the most important aspects of finishing technology. Softeners are one of the main compounds in finishing process and can improve some properties of textiles, depending on the chemical nature, including soft handle, smoothness, elasticity, hydrophilic, antistatic and soil release properties. They are classified according to their ionic character and the main classes are: anionic, cationic, nonionic, amphoteric, reactive and silicone. Macro- and micro-emulsion silicone softeners are commercial classes of softeners but nano-emulsions are new class of softeners in textile industry. The purpose of this research was to study the effect of micro and nano-silicone softeners on different properties of polyester fiber.


Polyester fabrics were first scoured with nonionic detergent and were then treated with three concentrations (10, 20 and 30 gr/lit) of micro and nano-emulsions of silicones. The drape length of treated samples with 10 gr/lit of solution was decreased and more decrease was observed with increase in silicone concentration. Colorimetric properties of softener treated fabrics were evaluated with a reflectance spectrophotometer. Nano-emulsion silicones changed a little the surface reflectance of fibers compared to micro-silicone softener. Increase in weight of all samples was observed which shows the coating of silicones on fiber surface. Nano-emulsion silicones showed better results on samples treated compared to micro-emulsion silicones.

1. The abrasion resistance of nano-silicone treated fabric will be more than that of micro-silicone softener treated fabric.
   
2. Anti-pilling effect will also be more when compared against micro emulsion treated fabrics.
   
3. Under powerful micro-scope one can see, micro emulsions will found to form surface coating on fibre more than that of nano-emulsions, that will penetrate more to the core of fibre than that of micro emulsions.
   

However, I do agree, that there should be some simple test to differentiate between nano and micro silicone softeners. If anybody knows well, they can share the message in this plat form.

Heat Setting

This operation is crucial for fabrics made of synthetic fibres (PE, PA, elastomers), for triacetate, and partly for PAC fibres (setting), since it grants excellent dimensional stabilization and crease proof properties, maintained till the fabric is exposed (by air blowing) to temperatures exceeding the heat setting one (after being treated with water at a temperature above the second order glass transition temperature, i.e. 80-85°C for acrylics).

 

Heat setting is carried out on gray fabrics (scarcely applied), on scoured fabrics (frequently applied) and on dyed fabrics (scarcely applied).

 

The process grants excellent dimensional stability and good crease-proof properties.

As far as operating conditions are concerned, the fabric must be treated in accurately controlled moisture and temperature conditions.

 

Fibre	Min T. °C	Max. T. °C	Time (in seconds)
Polyester (PE)	170	210	15-50
Polyamide (PA) 6.6	170	210	15-40
Polyamide (PA) 6	160	180	15-40
Triacetate	160	180	15-40
Acrylic (PAC)	160	180-200	15-40
Elastomers	170	180-200	15-40

 

Machines used: stenters.

 

Fluctuating temperatures inside the stenter cause a consistent variation of crystallinity in the fibre structure, which leads to different affinity for dyes.

 

The moisture in the fibre produces soft hand, but variable moisture percentages in the different fabric sections create the above mentioned defect (variable crystallinity).

 

Too low temperatures do not allow a good setting while too high temperatures and too long setting times cause yellowing (PA and elastic fibres), stiff hand (acrylics), and loss of elasticity (elastic fibres).

 

The presence of combustion gas (NOx) produces a yellowing of the elastomers.

 

The heat setting process carried out before scouring could fix the stains on the fabric or make the scouring process more difficult due to the modification of the lubricating products (cracking with emission of polluting gas).

 

Heat setting after dyeing could lead to the sublimation of disperse dyes (if not accurately selected).

Testing of Vinyl sulphone/ Mono-chlorotriazine Dyestuffs by print strike off method

Although a comparative exhaust dyeing method is always recommended for comparing two samples of dyestuffs, people in printing industry prefer to make strike off prints to compare the standard and sample.

Print Paste preparation for strike off:

Materials used	Vinyl Sulphone dyes	H/P type of dyes
Dyestuff	40 grams	40 grams
3-4% Sodium Alginate gel	720 grams	720 grams
Sodium Bicarbonate	30 grams	20 grams
Soda Ash	---	15 grams
Resist Salt	10 grams	10 grams
Urea	100 grams	100 grams
Water	100 grams	95 grams
Total	1000 grams	1000 grams

 

Method of printing:

On a well mounted RFD fabric on printing table, using the above paste prepared separately for standard and sample, two strikes off would be printed with the test screens.

After the print, gets dried properly, the fabric will be passed through saturated steam chamber (in a Star Ager) at 105⁰C for 10-15 minutes or dry curing chamber at 150⁰C for 4 to 5 minutes. This is followed by hot wash, cold wash, neutralization with acetic acid 2gpl and 2 soaping, hot and cold washes.

Final pH is set at 6 by doing an acetic acid treatment at the end of all washings.

 

Application of disperse dyes on 100% Polyester and its blends with cotton and viscose

General process sequence for PC blended fabric is:

 

 

 

Recipe:

• Disperse dyestuff = x %
  
• Nugen LFT = 0.5 %
  
• Acetic Acid = 1.5 %
  
• Carrier = 0.5%
  

If the recipe contains a Navy Blue dyestuff, then pH should 4.5 to 5.0 during dyeing, otherwise navy will tend to exhaust partially and hence unlevel dyeing. (If Formic Acid is available replace Acetic acid 1.5% with 1.0% of it, it is the most stable acid at high temperatures rather than Acetic).

Nugen DFT concentration need not be increase more than 0.5%. It is in fact, leveling and retarding agent; that will impair the depth and fastness.


Dyeing Procedure:

1. Pretreatment:
   
   1. Acetic Acid = 1.5 g/l
      
   2. Nugen DFT = 0.3 g/l
      1. Treat at 50⁰C for 10 minutes
         
2. Dyeing:
   
   1. Add dissolved disperse dye solution at 50⁰C = addition time = 10 minutes
      
   2. Raise the temperature to 115⁰C @ 2⁰C/minute; at 115⁰C hold for 10 minutes
      
   3. Raise the temperature to 135⁰C @0.5⁰C/minute; at 135⁰C hold for 30 to 45 minutes
      
   4. Cool to 80⁰C and drain
      
3. Reduction Clearing:
   
   (Alkaline)
   
   
   1. Caustic Soda = 2 gpl
      
   2. Hydros = 2 gpl
      
   3. Dispersol VLH = 1 gpl
      
      1. Treat at 50⁰C for 20 minutes
         
      2. Cold wash – Acetic acid wash with acetic acid – 1 gpl 10 minutes.
         
   (Acidic)
   
   
   1. Cyclonon ECO = 2gpl
      
   2. Acetic Acid = 2 gpl
      
      1. 
         Treat at 80⁰C for 20 minutes
         
      2. Cold Wash 10 minutes; unload.
         

Please find below a general process sequence for Polyester Cotton blend:

Process Flow for PC and PV blends:

 

 

 











Some reasons for un-level dyeing:

• Highly pH sensitive disperse dyes – almost all navy's and blacks
  
• Too much loading
  
• Liquor Circulation problems
  
• Improper heat setting/no heat setting
  
• Too less quantity of Leveling /dispersing agent
  
• Inadequate quantity of Acetic/Formic acid (please check acid concentration- acetic acid is being manufactured from different sources.) pH plays a major role in disperse dyeing levelness – take care.
  

Other Defects noticed in polyester dyeing:



Moire Effect on PC or PV – woven/knitted:

A watered, clouded, or frosted wavy appearance produced upon either woven or knitted textile fabrics is said to be moiré effect.

The moiré effect is caused mainly due to the differential shrinkage of polyester and cotton or viscose at high temperature and high pressure dyeing. This problem can be avoided by taking proper precautions before and after dyeing.

1. A perfect head setting on pins at a temperature of 200 to 210⁰C for 30 to 45 seconds with an over feed of 6 to 8% may be done.
   
2. In case of PV blends, caustizisation with 10 to 12⁰TW of caustic soda at room temperature may minimize moiré effect.
   
3. Moire effect after dyeing may be corrected either by caustizisation or treating the fabric with 3 to 5 gpl of carrier at 130⁰C for 30 minutes in a jet or soft-flow machine.
   
4. This can also be corrected by subjecting the fabric to high temperature at 200⁰C with an over feed of 6 to 7% and redye in HT + HP machine using 10% of disperse dye recipe for 30 minutes.
   

Poor Sublimation Fastness:

• Some of the disperse dyes tend to crystallize while cooling down the exhausted bath from 135⁰C to 80⁰C. 100⁰C is the most critical temperature at which some of the red disperse dyes ( C.I.No. 53, 60, 131, 132 and 159) give problem of crystallization when they are dyed at higher depths and especially if the dyeing is carried out in hard water. The hardness of water should be nil for disperse dyeing.
  
• Some of the disperse dyes are very sensitive to metal ions and shade changes considerably bluer to duller side. Spinning assistants, spinning oils, alkaline residues and other factors cause crystallization of disperse dyes to produce dye specks. This problem may be solved by proper pretreatment.
  
• The chromophore of the azo based disperse dyes is reduced and become soluble when an alkaline reducing agent (caustic & hydros) at 60C thus promoting poor sublimation and rubbing fastness
  
  Na2SO4 + 2 H2O -------à 2H + 2NaHSO3
  
  (alkaline condition)
  
  -N=N- + 4H --------à -NH2-NH2- (soluble disperse dye)
  
  Azo dye
  
• Use of non-ionic auxiliaries in the dye bath may also tend to aggregate some of the disperse dyes causing poor sublimation and rubbing fastness.
  

These problems can be overcome by using the following recipe:

• Disperse dye = x %
• Acetic acid = 1.0 gpl
• Sodium Acetate = 0.5 gpl
• Anionic dispersing agent = 1.0 gpl
  

Or

• Disperse dye = x %
  
• Formic acid = 0.35 to 0.5 gpl
  
• Ammonium Sulphate = 1.0 gpl
  
• Anionic dispersing agent = 1.0 gpl
  

Dye Specks:
Dyeing auxiliaries like carrier, leveling agents (non-ionic) are liable to nullify the effect and impair the solubilizing effect of dispersing agents thus promoting aggregation and agglomeration of disperse dyes causing specks.
Also use of non-ionic silicones during final finishing tend to aggregate disperse dye and reactive dyes; reduces the sublimation /rubbing fastness of the dyed fabric.
Non-ionic products in the form of wetting, leveling and finishing agents may be curtailed to avoid these problems.


Pilling:
Factors responsible for pilling:

1. Fiber Characteristics such as morphological, chemical and fine structure of the fiber, fiber length, fineness, strength etc.
   
2. Yarn Characteristics – viz., blend, count, twist, hairiness
   
3. Fabric Characteristics – such as weave, ends and picks etc.
   
4. Frictional and abrasive force – such as linear or rotational rubbing forces encountered during wear or processing.
   

Remedies:

• Surface treatment: The protruding fibres from the yarn or fabric can be removed mechanically/chemically or by burning out or cropping, surface carbonizing, singeing, heat setting etc reduces pilling.
  
• Steaming & cropping: the loose projecting fibres are removed mechanically by sharp blades from the surface of the fabric to a certain extent and that helps in reducing pilling.
  
• Surface carbonizing: In this technique, the protruding fibres are burnt or dissolved with suitable chemicals – the nature and the amount of chemicals used depends on the constituents of the blended fabrics. The fabric is thus not only free from pilling but also gives surface feel.
  

Disperse Dyes in Printing

 Methods of printing with Disperse Dyes – a practical over view

Nuchem Dyestuffs P Ltd., (NDPL), suggests the following 3 methods for printing with disperse dyes. These methods can be used in flat-bed and rotary screen printing machines.

Method-1:

PRINTING - DRYING - BAKING - REDUCTION CLEARING - WASHING OFF

1.       PRINTING

Recipe	Full Thickening	Half Thickening
Disperse Dyes	X - parts	X – parts
Alginate thickener (10% conc)	600 - parts	450 – parts
Emulsion thickener	Nil	150 – parts
Anti-Reducing Agent (mild Oxidizing agent)	5 – parts	5 - parts
Citric Acid	2 – parts	2 – parts
Wetting Agent	20 – parts	20 –parts
Add water to make	1000 parts	1000 parts

2.  DRYING – on stenter at 100 – 105°C

3.  BAKING – on Curing machine

-    Temperature                210 ⁰C

-    Time                              60           second

4.  REDUCTION CLEARING (RC)

-          NaOH flake                                  2              gram / litre

-          Sodium hydrosulphite                 2              gram / litre

-          Dispersing agent                         2              gram / litre

-          Temperature                               60 ⁰C

-          Time                                            10 minutes

5.  WASHING OFF

Method-2:

PRINTING - DRYING - HT STEAM -  REDUCTION CLEARING - WASHING OFF

1.           PRINTING

Recipe	Full Thickening	Half Thickening
Disperse Dyes	X - parts	X – parts
Alginate thickener (10% conc)	600 - parts	450 – parts
Emulsion thickener	Nil	150 – parts
Anti-Reducing Agent (mild Oxidizing agent)	5 – parts	5 - parts
Citric Acid	2 – parts	2 – parts
Wetting Agent	20 – parts	20 –parts
Add water to make	1000 parts	1000 parts

2.           DRYING

3.       HIGH TEMPERATURE (HT) STEAM

-          Temperature                170 ⁰C

-          Time                              8 minutes

4.       REDUCTION CLEARING (RC)

-          NaOH flake                                  2              gram / litre

-          Sodium hydrosulphite                 2              gram / litre

-          Dispersing agent                          2              gram / litre

-          Temperature                                 60 ⁰C

-          Time                                              10   minutes

5.       WASHING OFF

Method – 3:

PRINTING   - DRYING   - HP STEAM   -  REDUCTION CLEARING   - WASHING OFF

1.           PRINTING

Recipe	Full Thickening	Half Thickening
Disperse Dyes	X - parts	X – parts
Alginate thickener (10% conc)	500 - parts	250 – parts
Emulsion thickener	Nil	450 – parts
Anti-Reducing Agent (mild Oxidizing agent)	2.5 – parts	2.5- parts
Wetting Agent	10 – parts	Nil
Add water to make	1000 parts	1000 parts

2.       DRYING

3.       HIGH PRESSURE (HP) STEAM

-          Temperature                130 ⁰C

-          Time                              20 minutes

4.       REDUCTION CLEARING (RC)

-          NaOH flake                                  2              gram / litre

-          Sodium hydrosulphite                 2              gram / litre

-          Dispersing agent                         2              gram / litre

-          Temperature                                60 ⁰C

-          Time                                             10   minutes

5.       WASHING OFF

Notes:

1.       Disperse Dyes                 : Nusperse Dyes (Nuchem Disperse Dyes)

2.       Alginate thickener         : Manutex F  , etc

3.       Emulsion thickener        : mixture from water , white spirit and emulsifier

4.       Anti reduction                : Matexil PAL , Ludigol , sodium chlorate , etc

5.       Wetting agent for print paste           : Matexil WA-KBN , etc

6.       Dispersing agent           : Matexil DN-VL , Solopol ZB , etc