B. Tech
Seminar report
On
Dyeing of
textile fibre using supercritical fluids (CO2).
Submitted in partial
fulfillment of the requirements
For the degree of
Bachelor of
Technology
By
Mahesh Kumar
Inakhiya
(98002033)
Under the guidance of
Prof. Ms. M.
Mukhopadhyay
Department of
Chemical Engineering
Indian
Institute of Technology
CONTENTS
Acceptance certificate iii
Abstract iv
Acknowledgement v
List of figures vi
List of tables vii
1.INTRODUCTION 1.
2.CLASSIFICATION AND CHARACTERISATION OF DYES AND TEXTILE FIBRES AND DIFFERENT DYEING PROCEDURE. 4.
2.1
Classification of textile fibres.
2.2
Characterisation of fibres.
2.3
Classification of dyes.
2.4
Pretreatment.
2.5
Characterisation of dyeing.
2.6
Mechanism of dyeing.
3.CONVENTIONAL DYEING PROCEDURE. 12.
3.1
Beck dyeing.
3.2
Pad /Batch dyeing.
3.3
Transfer printing procedure.
3.4
Direct textile printing.
3.5
Package dyeing.
3.6
Beam dyeing.
3.7
Jet dyeing.
3.8
Jig dyeing.
3.9
Paddle dyeing.
3.10
Leather dyeing.
3.11
Non-woven dyeing.
4.WATER POLLUTION. 15.
5.SUPERCRITICAL FLUID DYEING. 16.
5.1
Benefits of using CO2.
5.2
Dyeing of synthetic fibres in SC CO2.
5.3 Mordant dyeing of natural fibres in SCF.
5.4
Treating cellulosic material with natural product using SCF CO2 .
5.5
Dyeing polyster fibres with disperse dyes in SC CO2.
5.6
Scouring of synthetic fibre with SC CO2.
5.7
High-pressure effect on the solubility of disperse dyes in SCF.
5.8
Parameter effects.
6. MASS TRANSFER MODEL IN SUPERCRITICAL FLUID DYEING 22.
6.1
Dyeing.
6.2
Sample analysis.
6.3
Theory.
6.4
Concentration-dependent diffusion coefficient.
6.5 Diffusivity as a function of
concentration.
7.CONCLUSIONS 26.
REFERENCES 27.
Acceptance Certificate
Department of Chemical Engineering
Indian Institute of Technology Bombay
The B. Tech seminar entitled “Dyeing of textile
fibre using supercritical fluids( SC CO2)” submitted by Mahesh Kumar
Inakhiya(Roll no. 98002033) may be accepted.
Guide (Prof. Ms M. Mukhopadhyay)
Internal Examiner
External Examiner
Abstract
In this report, we present a review of the current
stage of supercritical fluid dyeing. Processes based on aqueous systems consume
a great deal of energy and generate a large amount of wastewater. In contrast
with this in super critical fluid dyeing no wastewater is generated and also we
can do recycling with SFD very easily.
In this report we have given a method for
calculating the diffusion coefficient.
SCF accelerates the slowest mass transfer step
resulting in a faster dyeing process.
Acknowledgements
I
am grateful to my guide Prof. Ms M. Mukhopadhyay for her constant support,
encouragement and many a valuable suggestion , without which this report would
have been but an exercise in futility.
19th Oct’2000
IIT Bombay
Mahesh Kumar Inakhiya
List of figures
1. Phase diagram for carbon di oxide
2. Dependence of density and dielectric constant of CO2.
on pressure.
3. fibre shrinkage of
PP, PET and PA 6.6 after treatment in different media.
4. Quantitative dye uptake of PET after dyeing at 120 oC in different media
5. Reflectance values and quantitative dye uptake of
PET and PP after dyeing with solvent Red 27 at 120 oC in CO2.
and water.
6. Extraction efficiencies of PET fibres at various T
and P.
7. Extent to which the amount of CO2. used
influences extraction rate.
8. Solubility of AC08 in CO2. and CClF3(R13)
as a function of pressure.
9. Solubility of AC08 in CO2. as a function
of density.
10. Diffusivity versus a dimensional concentration in
the polymer (disperse blue).
List of tables
1. Typical properties of supercritical fluids compared
to those of gases and liquid.
2. Fibre characteristics of fibre and comparison
of Tm and Tg.
3. Fastness properties of dyed PP and PET fibres in
water and SCCO2.
4. Mass transfer coefficient at different working
condition.
Chapter 1:
INTRODUCTION:
Dyeing is the name given to the processes by which a
comparatively permanent colour is imparted to certain bodies, of which the most
important are the textile fibres. It appears that the production of cloth was
soon followed by a demand for coloured fabrics, for the art of dyeing is
extreme antiquity.
Textile fibres are those, of natural or artificial origin,
which are capable of being spun into yarn and made into fabrics. In order that
it may have commercial value a fibre must posses certain fundamental
properties. It must be obtainable in a large quantity at a price, which will
not make it too costly when manufactured into garments. It must also have a
certain amount of tensile strength, elasticity, and spinning power. In addition
to these fundamental properties, others are desirable, such as softness,
suppleness, luster, durability, absence of colour, and affinity for dyes.
Some of the important fibres are:
·Unicellular
vegetables hairs.
·Multicellular
vegetables fibres.
·Artificial
fibres obtained by modification or regeneration of
Cellulose, generally
termed rayon.
·Artificial
fibres produced by polymerisations of relatively simple monomers
·Minerals
fibres
Depending upon application range of dyes have been developed
broadly classified as:
Sulphur dyes
Azoic dyes
Ingrain dyes
Vat dyes
Acid dyes
Mordant dyes
Metal complex
Disperse dyes
Conventionally water is used in all dyeing industries.
Processes based on aqueous system consume a great deal of
energy and generate a large amount of wastewater. Two or three decade ago there
was much concerted effort in the use of organic solvent to replace water. But
majority of the organic solvents are volatile and also vapors of organic
solvent are harmful disturbing the ecological stability; thus this approach was
seen to be flawed since it merely converted the water pollution problem into
one of air pollution.
Conventional method for scouring of textile fibres also
require a large amount of water, alkali, acid, as well as other auxiliaries.
Incontrast
with this Supercritical fluids offer advantages in textile processing as they
combine the valuable properties of both gas and liquid. The solvating power of
SCF is proportional to its density, whereas its viscosity is comparable to that
of a normal gas. Such a combination leads to highly remarkable penetration
properties. The increased power of solvation with the increase in density is
desirable in the dyeing process as it has a decisive effect on the dissolution
of disperse dyes in the supercritical carbon di oxide medium.
Optimal extent of scouring can be controlled by adjustable
solubility of supercritical fluid.
Shorter time for scouring can be obtained by high
diffusivity of SCF.
CO2 is also chemically inert, noninflammable, inexpensive,
and environmentally benign when used in closed loop system. A significant
advantage of CO2 is that it is easily driven off due to its high vapor pressure
and therefore little energy is needed for drying. SFD also give a very good
fastness properties. Fastness is defined as the resistance of the hue to
textile to the different agencies to which they may be exposed during
manufacture and subsequent use.
} Scope of report:
In this report we present the
current stage of supercritical
fluid dyeing.
In the second chapter we have
given the classification of fibres
and dyeing.
In third chapter we have given
the conventional methods of dyeing.
In the fourth chapter we have
given the supercritical fluid
dyeing. And in last chapter we
have given the mass transfer
Modeling for supercritical
fluid dyeing.
Chapter
2:
CLASSIFICATION
AND CHARACTERISATION OF
DYES
AND TEXTILE FIBRES AND DIFFERENT
DYEING
PROCEDURE
} 2.1.Classification
of textile fibres:
All the textile fibres of commerce belong to one of the
following
classes: -
1] Unicellular vegetable hairs -cotton
2] Multicellular vegetable fibres-flax, ramie hemp, jute
3] Animal secretions -silk
4] Appendages of the epidermis of animals-wool, hair
5] Artificial fibres obtained by modification or
regeneration of cellulose, generally termed `rayon’ -viscous rayon, nitro
rayon, cupramonium rayon, acetyl (cellulose-acetate) rayon.
6] Artificial fibres produced by polymerisation of
relatively simple monomers -nylon, vinyon
7] Artificial fibres produced from protein -lanital
8] Mineral fibres -asbestos, glass
Cotton consists of unicellular hairs produced by the seed to
assist its distribution, multicellular fibres are bast fibres obtained from the
stems of plants. Silk is solidified viscous liquid secreted by the silk worm to
form the cocoon.
Wool & hair are outgrowths of the epiderims of animals
and are composed of cells similar to those of the epiderims.
Artificial fibres may be either of vegetable or of animal
origin, or they maybe polymer of relatively simple organic compounds. Rayon are
made from cotton, cotton linters or paper pulp and nylon is made from
hexamethylene-diamine and adipic acid and vinyon is derived from vinyl chloride
and vinyl acetate. Protein fibres are made from casein derived from milk or
protein of vegetable origin, such as soyabean or the ground nut.
Harital consist of casein obtained from milk.
} 2.2.Characterisation
of fibres:
Vegetable fibres burn readily with a clear flame and without
producing any smell. When heated in a dry test tube they give acid vapours.
They dissolve in cold concentrated sulphuric acid, but are insoluble in boiling
5% NaOH solution.
Animal fibres do not burn freely, but frizzle, giving the
characterisation odour of burning wool, when heated in a dry test tube they
give off ammonia, and in the case of wool sulphuretted hydrogen also. They are
readily soluble in a boiling 5 % solution of sodium hydroxide, and the solution
obtained with wool contains sulphides.
All animal fibres are dyed when boiled with a decolorized
solution of magneta (schiff's reagent).
Mineral fibres are incombustible and insoluble in acid or
alkali.
} 2.3.Classification
of dyes:
According to the industrial application dyes are classified
as follows:
Acid dyes:
Acid dyes are so called because they are normally applied to
the fabric being dyed in organic or inorganic acid dyeing solution. The term
applies to a large number of anionic dyes with relatively low molecular weight
which carry from one to three sulfonic acid groups. These groups dissociate in
water or varying acidic solution to form colored anions and colourless cations.
The dyes are used commercially for polyamides and wool as well as silk,
acrylic, polypropelene, and blends of these materials. The majority of the acid
dyes used commercially are azo, anthraquinone, and triarylmethane dyes.
acid dyes find their main application in the textile field
on wool, but are also used on silk, polymide, acrylic, regenerated protein
fibres, paper and leather: they are normally applied from a dye liquor
containing sulphuric, formic, or acetic acid; neutral and even slightly
alkaline dye bath are occasionally used. Chemical types involved are azo,
anthraquinone, triarylmethane, azine, xanthene, ketonimine, nitro and nitroso
compounds. They include dyes giving very bright hues and have a wide range of
fastness properties from very poor to very good.
·Sulfur
dyes:
Sulfur dyes are largely indeterminate complex heterocyclic
molecules or mixtures formed by melting or boiling organic compounds with
sodium polysulfide and/or sulfur. The organic intermediate used typically have
amino or nitro groups which are reacted with sulfur. Sulfur dyes are mainly
used for cellulosic fibres. The chief advantages are low cost, fair to good light fastness, and
high water fastness.They are applied from a sodium sulphide bath, the dyes
being reduced to a water-soluble form, reoxidation to shade occurring on the
fibre by contact with air.
·Azoic
dyes:
Azoic dyes(also called napthols or "ice
colors")are produced through an in-situ process which creates the colored
material directly on the fabric by coupling a C.I. Azoic-Diazo component and a
C.I. coupling component. The cloth first is impregneted with the coupling
component and then immersed in an ice water solution of the diazonium salt
prepared from the azoic-diazo component. Major application of Azoic dyes is the
dyeing and printing of cellulosic fibres especially cotton, giving shades of a
high standard of fastness to light and wet processing. They give bright,
intense hues particularly in the yellow, orange and red ranges.
·Vat
dyes:
Vat dyes are so called because they are employed in the
"vatting" process - a reversible chemical reduction procedure used to
solubilize and then precipitate a dye.
Vat dyes are of two type -
1.Indigoid and thioindigoid dyes
2.Anthraquinonoid dyes
They are applied from aqueous medium as leuco compounds
(vats) obtained by alkaline reduction using sodium hydrosulphite (hydros),
subsequent oxidation reforming the original insoluble dye on the substrate.
Water-soluble leuco esters are valuable for producing pale shades, or for
colouring material that are difficult to penetrate. The original dye is
regenerated by simultaneous hydrolysis and oxidation.
The major
application is the dyeing and printing of cotton. Such are the outstanding
fastness properties of this group that special methods for dyeing and printing
of substrate other than cotton, e.g. wool, silk, and cellulose acetate, have
been developed.
·Mordant
dyes :
in the C.I. the group covers "dyes sold by their makers
under such name as mordant dyes, chrome dyes, metachrome dyes, affterchrome
dyes, chrome printing colours".
It does not include the basic dyes which are dyed on tannic
antimony mordanted cotton, a mordant being a substance e.g. tannic acid, with
which cloth (cotton) must be treated before being dyed, the dye otherwise
having no affinity for the fibre. Certain type of acid dyes can form complexes
with metals. In particular chromium, the lake formed on the fibre conferring
better wet fastness than that of the acid dye itself.
·Disperse
dyes:
Disperse dyes, as their name implies, are colloidal in
nature and have very low, but finite, water solubilities owing to the absence
of sulfonic acid functionalities. In the pure state, they are crystalline
material which must be ground with dispersing agents to produce powders, and
mixed with water to make near-coloidal aqueous suspension and pastes.
C.I. definition is "a class of water insoluble dyes
Originally introduced for dyeing cellulose acetate and usually applied from
fine aqueous dispersion".
They belong to three main classes, viz. nitroarylamine, azo
and anthraquinone. Almost all contain amino- or substituted amino groups, but
do not contain solubilizing groups such as sulphonic acid groups.
The principle uses are the dyeing of cellulos acetate,
nylon, polyster and polyacrylonitrile fibres. The mechanism in each case is
believed to be one of solution in the fibre, no specific electrical charged dye
sites being needed for dyeing to take place.
·Metal
complex - These are of two kinds.
1.acid dyeing premetallized dyes
(1 metal atom usually Cr, combined with one molecule of azo
dyes)
Known as 1:1 dyes. The chief use in wool dyeing, but the
large amount of sulphuric acid needed in the dye bath is often a disadvantage.
2.neutral dyeing premetallized dyes
(1 metal atom, Cr or Co, with two molecules of azo dyes)
They are 1:2 complexes dyed from a neutral or slightly acid
bath. They give dyeing of very high all round fastness properties, and they
posses particularly good leveling properties.
} 2.4.Pretreatment:
There are many fibres for which we have to do some sort of
pretreatment otherwise these fibres cannot be dyed.
·Wetting
agents -
Is a chemical, which is used to assist the penetration of
scouring, dyeing, or other liquors used in a textile process. Soap is a wetting
agent but the term is generally reserved for more specialized products. They
may act directly or indirectly .organic solvent such as toluene and pyridine
act indirectly by dissolving grease and then facilitating penetration.
·Bleaching
agents -
Some residual natural colouring matters remains in the fibres
after scouring .We can change it into a colourless leuco compounds by these
bleaching agents.
They are of two types,
1.reducing bleaching agents
(SO2, Na2SO37H20,
NaHsO3 etc)
2.oxidizing bleaching agents
(Cl2, HOCl, aqua regia etc)
·Organic
solvent -
Are used as a substitute for scouring with soap and water.
It also used in conjunction with soap and in the preparation of liquids, which
are employed for removal of local grease patches, as a levelling agents in the
dye path or as capillarizing solution.
There are several organic solvent some of them are
following-
1.CnH2n+2
2.C6H6
3.chlorinated hydrocarbons
4.hydrogenated aromatic hydrocarbons
·Mordant
dyes-
Many classes of dyes use or have used mordant materials to
bind to fibres and provide a colorable substrate in case where the dyes are not
otherwise directly substantive to the fabric. Mordant /chromes dyes are those
that form coordination chelate complexes with metal ions .It follows then that
substantivity increases with increased coordination (i.e. molecular size,
stability and bond strength). Co, Cu and especially Cr are used to treat
unmetallized dyes by a variety of methods. Three commonly used procedure are-
1.prechroming
2.metachroming
3.afterchroming.
} 2.5.Characterisation
of dyeing:
Following are the properties by which we characterise the
effectiveness of dyeing:
·Fastness
properties-
Colour fastness-resistance of the hue to textile to the
different agencies to which they may be exposed during manufacture and
subsequent use.
Light fastness-light fastness is assessed on a scale of
eight .One represents the least fastness and 8 the best.
(Fastness to all the other agencies is assessed on a scale
of 5)
Standard wool dyes are all blue dyes.
·Washing
fastness-
-Hand washing
-Rubbing fastness-is the resistance of dyed textile to
rubbing off and staining other materials.
-Perspiration
-Burnt gas fumes-is the resistance of dyed hydrophobic
fibres, polyamide, polyester and especially cellulose acetate ,to the action of
oxides of nitrogen which may be produced.
} 2.6.Mechanism of
dyeing:
There are four kinds of forces by which dye molecules are
bound to fibre:
(1) Ionic forces, (2) hydrogen bonding,
(3) Van der Waals' forces, and (4) covalent chemical
linkages. In the dyeing of wool, which is a complex protein containing about 20
different -amino acids, the sulfuric acid added to the dye bath forms ionic
linkages with the amino groups of the protein. In the process of dyeing, the
sulfate anion (negative ion) is replaced by a dye anion. In the dyeing of wool,
silk, and synthetic fibres, hydrogen bonds are probably set up between the azo,
amino, alkyl amino, and other groups, and the amido -CO-NH-, groups. Van der
Waals' forces (the attractive forces between the atoms or molecules of all
substances) are thought to act in the dyeing of cotton between the molecular
units of the fibre and the linear, extended molecules of direct dyes. Covalent
chemical links are brought about in the dye bath by chemical reaction between a
fibre-reactive dye molecule, one containing a chemically reactive center, and a
hydroxy group of a cotton fibre, in the presence of
alkali. In any dyeing process, whatever the chemical class
of dye being used, heat must be supplied to the dye bath; energy is used in
transferring dye molecules from the solution to the fibre as well as in
swelling the fibre to render it more receptive. The technical term for the
transfer process is and synthetic fibres; it may be attained by control of
dyeing conditions, that is, by agitation to ensure proper contact between dye
liquor and substance being dyed, and by use of restraining agents to control
rate of dyeing, or strike.
Chapter 3:
CONVENTIONAL
DYEING PROCEDURES
} 3.1.Beck dyeing:
Process uses a type of exhaustion method. Exhaustion method
use chemical agents and physical condition to force dye stuffs onto yarn or
cloth. Dye is transferred from a bath usually aqueous to the fibre. Basic
dyeing operations are
1.) Preparation of fibre
2.) Preparation of dye bath
3.) Application of dye
4.) Finishing
} 3.2.Pad /Batch
dyeing:
The pad /batch dyeing is defined as a padding system with a
beam machine for semi continuous beam.
Various versions are pad roll, pad bath, pad system
A jig machine is used for controlling shade development from
certain dyeings
} 3.3.Transfer
printing procedure:
Wet transfer printing utilizes the migration properties of
soluble dye under not aqueous condition, to enable a dye to transfer from an
ink layer on paper into water filled interstices of an adjustable fabric. To
assist the dyeing some textile auxiliary products are introduced into water
phase consequently a thickener act as a catalyst or fixation agent for the dyes
during transfer.
} 3.4.Direct textile
printing:
This uses direct printing methods that do not utilize transfer
paper as a temporary substrate. The two printing methods are roller and
screen-printing.
} 3.5.Package dyeing:
Is an exhaustion process similar to beck dyeing. However
beck dyeing moves the material through the dye liquor while package-dyeing
machines move the dye liquor through the material.
} 3.6.Beam dyeing:
Principle of beam dyeing is the same as the package dyeing,
but fewer forms are dyed on a beam in comparison with package machinery.
} 3.7.Jet dyeing:
Is an exhaustion process similar to the beck dyeing, but
beck dyeing machines having the movement of material through the dye liquor
while the movement both the material and dye liquor.
} 3.8.Jig dyeing:
Principle is based on a very low liquor ratio, in this
dyeing take place in the roll and it is important that the dye is distributed
uniformly in order to avoid shade variations from side to side and end to end.
} 3.9.Paddle dyeing:
There are two procedures in this category. One procedure
uses disperse dyes while other uses basic dyes. With both procedure, garments
are prepared by being turned inside out and washed, then loosely bagged in the
paddle dyeing machine. The washing relieves knitting tensions.
} 3.10.Leather dyeing:
Three main type of dyes are used to color leather are
1.) Acid,
2.) Direct and
3.) Basic
Generally, leather dyeing requires two or more dyes or dye
types to produce a given shade.
} 3.11.Non-woven
dyeing:
Non-woven dyeing are generally dyes in top forms in batch
type equipment such as package machine. Direct dyes are used for synthetic
non-woven fabric.
Chapter 4:
WATER
POLLUTION
Water is very necessary part of dyeing technique and water
is
frequently used in many dyeing procedure and this creates
wastewater problem and hence water pollution. The chief sources of water
pollution within the industry are as follows
Cotton: wool: Synthetic -fibres:
Desizing top making desizing
Scouring
scouring scouring
Mercerizing carbonizing dyeing
Bleaching fulling
Dyeing dyeing
Printing finishing
Textile industry uses synthetic fibers, polymers and
finishes and many of these products are resistant to biological degradation so
these products should be removed from waste.
Textile industry also uses a large amount of salt, ionic
dyes, inorganic catalyst, detergents and bleaching agent that add to dissolved
solids concentration of wastewater.
The constant introduction of new fibers finishes, chemicals,
process, machinery and techniques and an ever-changing consumer demand for
different styles and colors of fabric yield a highly variable waste load.
Chapter 5:
SUPERCRITICAL
FLUID DYEING:
A supercritical fluid can be characterized
best by referring to a
Phase diagram, as shown for carbon
dioxide in Figure 1.
A liquid can be converted to a
supercritical fluid by increasing
Its temperature(and consequently its
vapor pressure p) and simultaneously increasing pressure p. A closed system
reaches critical values where no boundary between the liquid and gaseous state
can be distinguished, i.e. the supercritical state. Further increase in
pressure, will greatly increase the dielectric constant of such a system, thus
imparting dissolving powers even to a system that under normal condition of p
and T has almost none (Figure 2).
The critical values of T and p for CO2
is following:
Boiling point -78.5 C, Tc
31.3 C, pc 72.9 atm
Table
1: Typical properties of
supercritical fluids compared to those of gases and liquid.
|
|
Symbol |
Unit |
Gas |
Liquid |
Supercritical Fluid phase |
|
Density Diffusion coefficient Viscosity |
r D n |
g.cm-3 cm2.s-1 g.cm-1.s-1 |
10-3 10-1 10-4 |
1 5.10-6 10-2 |
0.6 10-3 10-4 |
} 5.1 Benefits of using
CO2 :
CO2 is non toxic, it is used
in the food and beverage industry, it is non inflammable, it is supplied in
large amounts either from combustion process or volcanic sources without the
need of producing new gas, and it can be recycled in a closed system.
The low viscosity of supercritical fluids
and the rather high diffusion properties of the dissolved molecule are
especially promising aspect for dyeing process. A supercritical dyeing fluid
can easily dissolve solid dyestuffs and it can penetrate even the smallest
pores without the need of vigorous convection procedures.
To use supercritical system in dyeing,
some other properties must be known. The phase behavior of a system consisting
of solids and gas has to be considered. Phase behavior is best documented by
the Bakhuis-Roozeboom diagram,
showing phase composition as it depends on p, T and the mole fraction x. Here
solubility of CO2 in solid dyestuff and within the fiber has been
neglected.
Those phase state planes (section through
a diagram like figure 1)
That relate to dyeing in supercritical CO2
lie above the critical pressure pc (7.38 Mpa) and the critical
temperature Tc of 304.2 K. In most cases the melting point of a dye
is not reached, and the isotherms of dye solubility then displace continuous
behavior with changing pressure, and it will show a maximum.
Using reasonable experimental conditions,
this maximum will not be reached, as spectroscopic investigation of
supercritical CO2 have shown. The isothermal solubility of a
disperse dye will therefore be between 0 and 10-3 on a molar basis,
and can be adjusted by changing the system pressure.
PET microfilament fabrics, which
are difficult to dye conventionally, one can achieve a excellent levelness
grades with the CO2 procedure and even better abrasion resistance
,then conventional dyeing technique(saus and knittel 1993). Saus and knittel
found that polyamides can be dyed with disperse dye using SC CO2,
resulting in slightly lighter shades than that with PET. They also found that elastomeric
materials like Dorlaston can be dyed successfully in sc CO2. They
found lowering of Tg of the polymer of about 20-30 oC, because of
this there will be some change in fibre structure such as swelling. Increasing
the temperature decrease the density of the fluid ,so it reduce the dye supply
but it increases diffusion and they found that dye is dissolving
monomolecularally in SC fabrics ,so there no need of aftertreatment such as
washing. So main benefits of this scf dyeing is following complete elimination
of water pretreatment and water pollution, energy saving in drying textile
,since fabric treated in supercritical system will be completely dry after
expansion of the system ,no need of auxiliary agents.
} 5.2 Dyeing of
synthetic fibre in SC CO2:
Cleve E. investigated the synthetic fibre
and dyeing behavior of some synthetic fibre in water, CO2 and
cosolvent/CO2 mixture. They found decrease in the melting T with
increasing CO2 pressure caused by the diffusion of CO2 into
polymer. The highest decrease of Tm in CO2 at 280 bar compared to
air 1 bar was measured for PP followed by PET and lowest for PA.
Table
2:Fibre characteristics of fibre and
comparison of Tm and Tg:
|
Fibre Type |
Air Tm 1 bar |
CO2 Tm 280 bar |
Water retention value(%) |
Dielectric constant at
1 KHZ |
Tg (oC) |
|
PA 6.6 |
258 |
254 |
10-15 |
2.0 |
»50 |
|
PET |
250 |
237 |
3-5 |
2.3 |
»(70-80) |
|
PP |
167 |
145 |
0 |
3.7 |
-(15-20) |
That was because of presumption that
decrease of Tm correlates with the amount of CO2 in the fibre.
Dyeing in SC CO2 is more comparable to dyeing in water because water
is not able to diffuse into the inner of hydrophobic polymers.
They found that fibre shrinkage was same
in CO2 ,H2O ,CO2/H2O (figure 3).
They carried out dyeing of PP, PET and,
PA at 120 oC water , dyeing was made according to standard recipies.
The dye concentration was 4 % in relation to the fabric weight. They used azo
dyes ,namely C.I. disperse Yellow disperse red and disperse blue 79. Dyeing
result are characterized by the reflactance of the fibres in the absorption
maximum of the dyes. So lower reflactance value then higher color depth for PP
only light colors are obtained. They found the dyeing with pure CO2
was most suitable. Color depth of PA 6:6 is comparable to PET although the
affinity of disperse azo dyes to PA 6:6 is generally lower. And the reflectance
value obtained were comparable to a purely H2O water system. They
found that in a static high-pressure system without circulation of CO2
the dye uptake of PET (figure 4 & 5)
is lowest in sc CO2 with all dyes tested and it can be enhanced by
circulating CO2 through the fibre. The fastness properties of PP and
PET were found and generally if grade is high then the better the fastness.
Generally the more aggregated the dye in the fibre is, the higher the light
fastness and conversely the nearer the dye is to the monomolecular state the
lower the light fastness.
Table
3: Fastness
properties of dyed PP and PET fibres in water and SCCO2:
|
Properties |
H2O |
CO2 |
||
|
PP |
PES |
PP |
PES |
|
|
Light fastness |
5 |
1-2 |
5 |
2 |
|
Washing fastness |
1-2 |
3 |
5 |
- |
|
Sublimation fastness |
- |
- |
3-4 |
- |
} 5.3 Mordant dyeing of natural fibres in SCF:
The optimum condition for mordant dyeing
and the dyeing period is controlled by the solubility of the dyestuff in SC CO2(B.guzel).
B.guzel studied the wool fibres dyeing with mordant dyes dissolved in scCO2
.They used three different type of mordant dyes.
2-nitroso-1-napthol,5-salicylic acid and 1,2-dihydroxyanthrraquinone when the
CO2 was used as the solvent, because of it's solubility in water,
the Ph of the moisture on the yarn is reduced to ~ 3.5. So they got excellent
wash fastness when mordant dyeing is applied from a SCCO2.
} 5.4 Treating
cellulosic material with natural product using SCF CO2 :
The dyeing process of cotton in CO2-SFC
can be carried out using a non polar disperse dye soluble in CO2-SFC.
Dyebility of cellulose material in CO2-SFC is greatly
unfavorable, due to the glassy state of
polymer and to impossible interaction between disperse dyes and cellulose
chains. In order to remove this handicap the cotton fabric and bacterial
cellulose film can be pretreated with a plastifiant agent as the PEG.
M.l.colombo and others have done some
work on adding of natural product such as colours, aromes and essential oil
soluble in SCCO2 to cellulosic material. They used natural dyes,
soluble in CO2 -sfc and this dye penetrate in the form of molecular
solution in the cotton. They estimated the dye uptake by measuring the
reflectance value R according to `Kubelka
–Mumk’ equation
K/S=(1-R)2/2R ----(1)
The higher the K/s value the greater is
the dye receptivity of the cotton fabric.
} 5.5 Dyeing polyster
fibres with disperse dyes in SC CO2.
The dyeing of synthetic fibres such as
PET with disperse dyes in aqueous medium requires high temperature and the
presence of auxiliary agents. Polyster fiber are more difficult to dye because
of their low dye sorption rates at temperature below their Tg. Adequate rates
were achieved when the dyeing temperature exceeds Tg, Due to the increased
motion of the chain segment as the temperature is raised. M.Rita de giorgi and
others studied the dyeing polyster fibre with disperse dyes in CO2
(super critical). They obtained intense and uniform dyeing with the series of
examined thiadiazole dyes at a temperature of 80 oC and a pressure
of 3800 psi.
} 5.6 Scouring of
synthetic fibre with supercritical CO2:
The extent of spinning and finishing oil
removed from synthetic fibres is critical to level dyeing performance. The
conventional means of scouring fibres requires a large amount of water and
other auxiliaries. In supercritical scouring there is no need of water and
other auxiliaries. So for that we should know about extraction efficiency of
SCCO2. Supercritical CO2 extraction efficiency varies
with different temperature and pressure(chi-ying hung). An extraction
efficiency above 80% can easily be achieved under moderate operating condition,
and spinning oil can be completely removed under severe condition. At constant
temperature, the extraction efficiency increases with higher pressure,
meanwhile, at a constant pressure, an increasing temperature implies a
decreasing extraction efficiency(figure
6). A higher CO2 density benefits extraction efficiency. The
extraction efficiency can therefore be increased with a lower temperature and a
higher pressure. A higher CO2 to fibre weight ratio cause a higher
extraction efficiency (figure 7).
} 5.7 High-pressure effect on the solubility of Disperse dyes
in SCF:
Disperse dye which is more polar will be
less soluble in SCF than that of less polar (Dirk tuma).
Dirk tuma and others studied the
solubility data of disperse dyestuff in CO2. They used two disperse
dye AC01 and AC08. They determined the Concentration of dissolved dye spectroscopically
by recording the wavelength range from 400 to 750 nm. They calculated the
Result from integral absorbance. They found that the more polar AC01 is less
soluble. And for AC 08 CO2 is a much better solvent then CClF3.
They found that solubility is a function of pressure and density (figure 8 & 9).
} 5.8 Parameter effects:
Amount of dyes sorbed into a polyster
fibre is affected, not only the dyeing temperature, pressure and time, but also
by the type of dyeing equipment. Researcher from solvenia found out the effect
of changing parameters. They used 3
special disperse dye CO2 PES Gelb SM2P(yellow), Blau SMLP (blues)
and Rot SM2P(red).They found that dyeing temperature has the greatest influence
on the amount of sorbed dyes. The effect of a higher temperature was greater
for the dyes with higher molar masses.They also found the affect of changing
processing condition when using mixtures of dyes. Every changes cause a change
in colour-lightness, chroma and especially hue. They found that dyeing with a
mixture of 3 dyes gave a lower total amount of fixed dyes than two dyes or
single dyes ,indicating that the dyes compete for accessible location in the
fibres. Varying the pressure at constant temperature cause a change in the
ratio of dyes in the fabric.
Chapter
6:
MASS TRANSFER MODEL IN SUPERCRITICAL FLUID DYEING
In SCCO2 textile fibre dyeing
system one can measure the diffusion coefficient(S.sicarbi 2000) of different
dyes which have been used at different working condition (pressure and temperature).
S.Sicarbi and Banchero did some work to
propose an experimental technique to evaluate diffusion coefficient of disperse
dyes in a PET films. They used `film role method. Sc CO2 reduces the
Tg , resulting an increased in mass transfer rate inside the polymeric matrix.
The use of sc CO2 allows lower operating temperature and use of
thermally labile dyes in scf dyeing. CO2 can be recycled and dye
stuff can be recovered. `Film roll method' belongs to the concentration
-distance curve technique.
} 6.1 Dyeing:
They used a 12 mm thick PET film. It was tightly wrapped
around a threaded stainless steel tube, producing a film roll. The roll is
secured in a proper position by a thin rod. Film roll is introduced in an
autoclave provided with a dyestuff container and a stirrer dyeing system is a
well stirred sc CO2 bath at constant temperature and pressure. Dye
stuff concentration in scCO2 is constant and the bath can be
considered infinite. They used two different dyes disperse blue and disperse
yellow .Apparatus used was a batch system. It was operated through 3 main step
charge, dyeing, discharge.
} 6.2 Sample analysis:
At the end of dyeing period the film is
unrolled and cut into section representing the successive layers. The dye
concentration in each layer is determined, via a spectrophotometer from the
intensity of the light absorbance in the UV -vis spectral band
by the `Lambert-Beer law ’
A=abc ------(2)
where
a :is molar absorvity ,
b:path length ,
c:dye molar concentration
A:absorbance
They found the maximum
absorption wavelength as 680 nm for disperse blue and 450 nm for disperse
yellow.
Also C/Co=A/A0
Where Ao and Co
are,respectively, the absorbance and the dye concentration, in the polymer at
the polymer-bath interface; A and C are the values measured in a generic layer
of the roll. Co is assumed to be the same as the concentration of dye in flap.
} 6.3 Theory:
By taking the various assumption
they got the following differential equation
And the following boundary condition
t=0, x > 0 C=0
t³0 x=0 C=Co
t³0 x®¥
They got the solution of above
equation by assuming the constant diffusion coefficient.
C=c/co=erfc(x/2 t1/2
D1/2) -----(3)
As a consequence of the above
equation a dimensional concentration c=C/Co only depends on a variable w
defined as follows
w=x/2 t1/2
After that they got the
diffusion coefficient D by fitting the experimental data with equation (3).
} 6.4 Concentration-dependent diffusion coefficient:
Equation (3) does not give any
information about the dependence of the diffusion coefficient on concentration.
So they used the crank and park’s derivation
So they got the following
differential equation
Where c=C/Co is the dimensional
concentration inside the polymer
By integrating the above
equation they got the following expression for D
Results they obtained is given
in table 4
Table
4.Mass transfer
coefficient at different working condition
Unit of D is m2s-1
|
No. |
T(oC) |
P (Mpa) |
Disperse yellow |
Disperse Red |
|
1. |
90 |
22 |
1.4x10-14 |
2.3x10-14 |
|
2. |
110 |
22 |
1.2x10-13 |
1.1x10-13 |
|
3. |
110 |
25 |
1.5x10-13 |
1.6x10-13 |
so
they found that increase in temp from 90-110 oC(at constant pressure
of 22 Mpa implies an increase in the diffusion coefficient D. this result can
be ascribed to the increase in flexibility of the polymer chain due to temperature.
The rubbery and amorphous region of polymer increase compared to the harder and
more brittle ones, resulting in more permeability to dye molecule.
Diffusion coefficient also depends upon
pressure(table 4). Increase in
pressure from 22 to 25 Mpa (at constant temperature 110 oC) result
in small increase in the diffusion coefficient D for both dyes. This
improvement in the kinetics of dyeing can be justified with the CO2
plasticising effect. Increasing pressure result in swelling the polymers chain
thus promoting dye diffusion.
} 6.5 Diffusivity as a
function of concentration:
Diffusion coefficient D appears to be
strongly influenced by concentration at low value of C/Co until a
maximum is reached. After that diffusion coefficient decreases more gradually
with increasing concentration (figure 10).
So
from this work they calculated the D for two different disperse dye in SCCO2
and that is in good agreement with the literature.
Conclusions:
So
we can conclude that the SFD is more beneficial then conventional dyeing.
The
benefits of using supercritical fluid CO2 as a dyeing medium for textile fibres
are as follows :
Complete
elimination of waste water problem and hence water pollution; energy saving in
drying textiles, since fabrics treated in supercritical system will be
completely dry after expansions of the system; no need of auxiliary agents. Any
residual dye stuff is easily recovered
after expansion of the SC system . There is
no shortage of carbon
di oxide, it is non toxic, it can be obtained from natural sources and it can be easily recycled in a dyeing
process.
The
experience from industrial extraction
technology will enhance the realization of commercial dyeing facilities. High
investment costs will be balanced by ecological and processing time profits.
Dye manufacturer will have to adapt their dyestuff sorting process in order to
supply materials best suited for this new
procedure.
At
present this procedure is very new and there is only preliminary uhderstanding
of this procedure, and quite a lot of further research is necessary.
References:
S.Sicardi,
L.Manna & M.Banchero . Diffusion of disperse dyes in PET films during
impregnation with a supercritical fluid. Vol. 17, Issue 2 ,2000 ,Pp 187-194.
Wolfgang
Saus, Dierk Knittel, and Eckhard Schollmeyer. Dyeing of textiles in
supercritical carbon di oxide. Textile
Res. J., Vol. 63, 1993, Pp 135-141.
Dirk
Tuma & Gerhard M. Schneider. High pressure investigation on the solubility
of disperse dyes in near and supercritical fluids: measured up to 100 Mpa by a
static mrthod.
J.
of supercritical fluids Vol. 16, 1999, Pp 81.
M.
Rita De Giorgi , Enzo Cadoni, Gianluca Poma. Dyeing polyster fibres with
disperse dyes in supercritical carbon di oxide. Dyes and pigments Vol. 45, Pp
393-396.
A.
Akgerman, B. Guzel. Natural fibres mordant dyeing from supercritical fluids. J.
of chemical and Engg. Data, Vol. 44 ,Pp 351-355.
M.L.Colombo, A.Mossa, L.Sala, A.Seves,
G.Testa, E.Rossi, A.M.Bonfatti. Treatment of cellulosic material with natural
products dissolved in SCF carbon di
oxide. Pp 357-360.
Chi
Ying Hung, Chih Wei Lai, Li Chuan Huang, and Wen Fa Lin. Scouring of synthetic
fibres with supercritical carbon di oxide. Pp 403-408.
Batch
E., Cleve E., and Schollmeyer E. dyeing of synthetic fibres in supercritical
carbon di oxide. J. Text. Inst. 1998. Pp 345-350
Michael
Bork. Supercritical fluid dyeing of synthetic fibres. Pp 387-391
Some
journal which were not available:
A.S.Ozcan,
A.A. Clifford, K.D. Bartle and D. M. Lewis. Dyeing of cotton fibres with
disperse dyes in supercritical carbon di oxide. Vol. 36, Feb 1998, Pp 103-110
J.V.
Scnitzler and R. Eggers. Mass transfer in polymer in a supercritical carbon di
oxide- atmosphere. J. of supercritical
fluid Vol. 16 ,1999 Pp 81.
Texts:
Dyes
and their pigments :
By: E. N. Abrahart
The
bleaching, dyeing and chemical technology of textile fibres
By: S.R. Trotman & E.R.
Trotman
Textile
dyeing operation
By: A.L. Blackard, S.V. Kulkarni, M.W.
Alexandre.