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LECTURE DIRECT DYEING OF COTTON

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					      DYE CONSUMPTION (TONNE)
DYE CLASS   1988a     1992      2004b
SULPHUR     90 000    70 000    70 000
DIRECT      74 000    60 000    68 000
VAT         36 000    21 000    22 000
INDIGO      12 000    12 000    12 000
AZOIC       28 000    18 000    13 000
REACTIVE    60 000    109 000   178 000

TOTAL       300 000   290 000   354 000
       WORD FIBRE CONSUMPTION
       CONSUMPTION (1000 TONNE)

YEAR    COTTON   REGENERATED   WOOL   SYNTHETIC   TOTAL


1990    18700 2700             2000   14900       39300
        (49%)                         (39%)
1995    20700 2500             2000   17300       42600
        (49%)                         (41%)
2000    23400 2400             2200   20500       48500
        (49%)                         (42%)
   DYEING OF COTTON WITH DIRECT
               DYES
• TYPICAL DYE STRUCTURE
                                           NH2
      NH2


               N   N               N   N




      Na2SO3                               Na2SO3


                       CONGO RED
                   DIRECT DYES
    FEATURES
•   PRESENCE OF SULPHONIC ACID GROUPS
•   WATER SOLUBLE
•   ANIONIC IN NATURE
•   SUBSTANTIVITY/AFFINITY TO COTTON
•   APPLIED FROM AQUEOUS DYEBATH CONTAINING
    ELECTROLYTE
•   SIMPLE DYEING OPERATION
•   LOW WASH FASTNESS
•   WASH FASTNESS IMPROVED TO SOME EXTENT AFTER
    TREATMENT WITH CATIONIC DYE FIXING AGENT
•   WASH FASTNESS STILL NOT ADEQUATE COMPARED TO
    OTHER DYE CLASSES SUCH AS REACTIVE DYES
              DIRECT DYES
 USES
• USED FOR DYEING OF LOW PRICED COTTON OR
  VISCOSE FABRIC, CUTAIN, FURNISHING OR
  CARPETS WITH GOOD LIGHT FASTNESS AND
  MODERATE WASH FASTNESS
• CHEAP COTTON DRESSING GOWNS AND BED
  SPREADS WHICH ARE NOT WASHED REGULARLY
• DUE TO LOW WASH FASTNESS, LIMITED USE.
• BEING REPLACED TO GREAT EXTENT WITH
  REACTIVE DYES WHICH HAVE BETTER WASH
  FASTNESS AND PRODUCE BRIGHT SHADES.
             CLASSIFICATION
• CLASSIFIED ACCORDING TO DYEING BEHAVIOUR
 CLASS A SELF LEVELLING
• DYES WITH GOOD MIGRATION OR LEVELLING
  PROPERTIES i.e. DYES WHICH PRODUCE UNIFORM
  SHADE. NOT SENSITIVE TO DYEING CONDITIONS.
 CLASS B SALT CONTROLLABLE
• UNIFORM SHADE PRODUCD ON CONTROLLED
  ADDITION OF SALT DURING DYEING
 CLASS C TEMPERATURE CONTROLLABLE
• UNIFORM SHADE PRODUCED ON CAREFUL
  CONTROL OF DYEING TEMPERATURE AND SALT
  ADDITION
  EFFECT OF VARIOUS PARAMETERS
            ON DYEING
  TEMPERATURE
• RATE OF DYEING AND PENETRATION INCREASES
  TEMPERATURE. DYES BEING HIGH MOLECULAR WEIGHT
  DYEING CARRIED OUT AT BOIL FOR GOOD PENETRATION.
  DYEING TIME
• PRODUCTION OF LEVEL AND WELL PENETRATED DYEING IS
  FAVOURED BY INCREASED DYEING TIME. HOWEVER,
  PROLONGED BOILING CAUSES DECOMPOSITION OF MANY
  DIRECT DYES. THE DYEING TIME IS USUALLY 1 hr. AT BOIL
  LIQUOR RATIO
• DYEBATH EXHAUSTION IS USUALLY DECREASED WITH
  INCREASE IN M:L RATIO. HOWEVER, UNIFORMITY OF
  DYEING IS IMPROVED.
  EFFECT OF VARIOUS PARAMETERS
            ON DYEING
 ELECTROLYTE
• ELECTROLYTE IS ESSENTIAL FOR DYEING WITH
  DIRECT DYES
• COMMON ELECTROLYTE USED COMMON SALT
  (NaCl) OR GLAUBER’S SALT (Na2SO4)
• CONCENTRATION OF ELECTROLYTE IS GOVERNED
• DYE CONCENTRATION: LESS SALT FOR LOW DYE
  CONCENTRATION
• No OF SULPHONIC ACID GROUPS IN DYE
  MOLECULE: HIGH SALT WITH MORE No. OF
  SULPHONIC ACID GROUPS
          ROLE OF ELECTROLYTE
• COTTON IN WATER : NEGATIVE SURFACE POTENTIAL
• ANIONIC DYES DISSOLVED IN WATER : NEGATIVE CHARGE
  DUE TO IONOIZATION OF WATER SOLUBILIZING SO3Na
  GROUPS
• DUE TO SIMILAR CHARGES: REPULSION BETWEEN DYE AND
  FIBRE SURFACE
• FOR THE DYE TO GO ON FIBRE: NECESSARY TO REDUCE –Ve
  CHARGE OF FIBRE
• ACHIEVED BY ADDITION OF ELECTROLYTE
• ELECTROLYTE DISSOCIATE IN WATER, RELEASE +Ve
  CHARGE Na+
• Na+ ACCUMULATE AT THE –Ve CHARGED FIBRE SURFACE
• NEUTRALIZE –Ve SURFACE POTENTIAL OF FIBRE
• FACILITATE –Ve DYE MOLECULE ATTRACTION/ADSORPTION
  ON FIBRE
       BATCHWISE DYEING OF COTTON
    DYE DISSOLUTION
•   USE SOFT WATER FOR DYE DISSOLUTION AND DYEING. PASTE WITH
    COLD WATER. ADD SUFFICIENT QUANTITY OF BOILING WATER.
    STIRR. FILTR TO REMOVE ANY INSOLUBLE DYE PARTCLES
•   ADDITION OF 0.5-1 g/l WETTING AGENT HELPS TO WET OUT THE
    FIBRE DURING DYEING.
    GENERAL DYEING PROCEDURE
    CLASS A DYES
•   THE DISSOLVED DYE IS ADDED TO DYEING MACHINE
•   MAKE TO TOTAL VOLUME ACCORDING TO M:L RATIO
•   IF DYE IS SENSITIVE TO HARDNESS OF WATER, ADD 1-2 g/l SODIUM
    HEXAMETA PHOSPHATE OR SODA ASH
•   ADD SODIUM CHLORIDE, FOR PALE SHADE 5% OWM, MEDIUM SHADE
    10%OWM AND HEAVY SHADE 20% OWM.
•   ENTER THE FABRIC AT 40-500C
•   RAISE THE TEMPERATURE TO BOIL IN 30-40 MIN.
•   CONTINUE DYEING AT BOIL FOR 30-45 MIN
•   RINSE WITH COLD WATER
•   AFTER TREAT WITH CATIONIC DYE FIXING AGENT.
•   DRY WITHOUT RINSING.
              CLASS B DYES
 SALT SENSITIVE DYES
• ADD SALT IN INSTALMENTS DURING RAISING THE
  TEMP. TO BOIL

• IF DESIRED SALT ADDITION MAY BE CONTINUED
  AFTER THE DYEBATH HAS REACHED TO BOIL.

• ADDITION OF DISSOLVED SALT BY DRIP FEED
  METHOD IS PREFERRED
                   CLASS C DYES
    TEMPERATURE SENSITIVE DYES
•   LOW ELECTROLYTE CONC. ADDED AT THE START
•   RAISE TEMP TO BOIL AT VERY LOW RATE
•   DYEING CONTINUED AT BOIL FOR 45-60 MIN.
•   SALT ADDITION SHOULD BE DONE IN INSTALMENTS AT BOIL.
    COMPOUND SHADES
• PRODUCED BY USING TWO OR THREE DYES TAKEN
  TOGETHER
• TAKE MIX DYES BELONGING TO THE SAME CLASS
• DYES IN MIXTURE SHOULD HAVE SIMILAR RATE OF
  EXHAUSTION
• DYE MANUFACTURER SHADE CARD GIVES INFORMATION ON
  DYE CLASS AND DYEING CONDITIONS
• FOLLOW THE INSTRUCTIONS CAREFULLY AND FAITHFLLY.
            AFTER TREATMENT
• INADEQUATE WASH AND PERSPIRATION FASTNESS
  OF DIRECT DYES
• CAN BE IMPROVED BY AFTERTREATMENT AFTER
  DYEING
• DIAZOTIZATION AND DEVELOPMENT
• COPPER SULPHATE AND POTASSIUM DICHROMATE
  TREATMENT
• FORMALDEHYDE TREATMENT
• CATIONIC DYE FIXING AGENT: MOST POPULAR
• FORMS COMPLEX WITH ANIONIC DYE. DECREASE
  IN DYE SOLUBILITY
• TRETMENT CARRIED OUT USING 1-3%OWM
  CATIONIC AGENT AT 600C FOR 30 MIN AT pH 5 WITH
  ACETIC ACID.
• NO RISING AFTER TREATMENT
CATIONIC DYE FIXING AGENT

				
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posted:8/5/2011
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