- 1 Introduction
- 2 History Of Polyester
- 3 Steps Involved In Dyeing Of Polyester
- 4 Fastness Properties of Polyester
- 5 Two Bath Dyeing Of P\C Blended Fabrics
- 6 Two Bath Dyeing Of P/W Blended Fabric
- 7 Two bath dyeing of P/V blends
- 8 Two Bath Dyeing Of P/A Blends
- 9 Applications Of Polyester And Its Blends
- 10 Conclusion
Synthetic fibres including polyester, nylon, and acrylic fibre account for nearly 46% of the total worldwide fibre consumption.During the last four decades, the textile industry has witnessed the phenomenol growth of synthetic fibres, many of which are being commonly used because of their affordability and excellent functionality.
Natural fibres like cotton, wool, and silk which served mankind for many years have been to a greater extent replaced by man-made fibre such as nylon, olefins, and polyester.Fabric woven from blends of polyester are used in large quantities for a wide range of clothing purpose.
Their performance aesthetics and versatility make woven fabric composed of polyester blends ideal for most apparel uses, hence they rank as the major commodity fabric and their price is dictated by commercial factors rather than intrinsic worth.The goal of this article describes the production of polyester fibres and its dyeing methods.It also describes the dyeing procedure of polyester blends.
Polyester is the category of polymers that contain the ester functional group in their main chain.Polyesters include naturally occurring chemicals, such as in the cutin of plant chemicals, as well as synthesis through step-growth polymerization such as polybutyrede.Depending on the chemical structure, polyester can be thermoplastic or thermoset in nature.
In recent years, the production of polyester fibres has been dynamically increased, accompanied by the common use of P/C blends.In the past decade, world production of polyester staple has grown at an average rate of 6.5 % per annum.The world situation is dominated by China, which accounted for almost 65 % of the global total in 2010 and other Asian countries.
Currently polyester occupies a major share in the global use of textile substrates.As the textile processing and coloration industries carry out processing of a wide variety of fibres, the dyestuffs selected are obviously from duvers classes of colorants such as acid, metal-complex and reactive for wool and silk; disperse for polyester, polyamide, and acetate, basic for acrylics and pigments.
Textiles made from blends of polyester and cellulose fibres constitute about 10% of the total consumption of textile material.Polyester fibre shows a definite hydrophobic character and a high degree of crystallinity, being difficult to penetrate with dyes.Besides mass coloration of polyester fibres, they can be dyed by the conventional dyeing method, but only with the use of disperse dyes.
In apparels, polyester has considerably gained over other fibres because of its better easy care characteristics and wrinkle resistance.One of the largest markets for polyester lies in the blends with cellulosic.The high modulus and resilience of PET make polyester suitable for filling fibre for quilts, pillows and sleeping bags which can be laundered. Various innovative processing techniques have produced polyester with the comfort of cotton, soft warmth of wool and glamour of silk.
History Of Polyester
It was W.H Carather’s who discovered that alcohols and carboxyl acids could be successfully mixed to create fibres.Carather’s working for DuPont at the time and unfortunately when he discovered nylon, polyester took a backseat.
PET & Terylene
Carather’s incomplete research had not advanced to investigating the polyester formed from mixing ethylene and glycol and terephthalic acid.It was British scientists – Whinfield and Dickson who patented PET or PETE in 1941.
Polyethylene terephthalate forms the basis for synthetic fibres like Dacron, terylene, and polyester. Later that year, the first polyester fibre – terylene was created by Winfield and Dicson along with Birtwhistle and Ritchiethey.Terylene was first manufactured by Imperial Chemical Industries.
It was in 1946 that DuPont bought all legal rights from ICI.In 1950 the Delaware property of DuPont manufactured another polyester fibre, which they named Dacron.Mylar was introduced in 1952 polyester was first introduced to the American public in 1951 as the magical fabric that needed no ironing.
PET & PEN are DuPont trademarks that have turned the use and consumption of polyester around.The raw materials for the production of synthetic fibres are dimethyl Terephthalate, Terephthalic acid, monoethylene glycol, etc.These raw materials are obtained from crude oil.
Steps Involved In Dyeing Of Polyester
1) Pretreatment Of Polyester
The primary objective of pretreatment process was to remove contaminants present in the grey fabric of polyester and its blends to facilitate the multifunctional finish process.
The process flow for the pretreatment on polyester is as follows:
- Grey fabric of Polyester.
- Sodium chlorite bleaching.
- Testing and analysis.
From the above flowchart in desizing and scouring processes of viscose and polyester fabric the presence of impurities such as spin finishes, coning oil and sizing agent particles were removed using enzyme and alkali treatments.
In the bleaching process, the natural color of the fabrics was removed and thereby using sodium chlorite whiteness was imparted to the fabrics.All the pretreatments for polyester fabrics were carried out to facilitate better absorbency and whiteness for the multifunctional finishing treatments.
2) Dyeing Of Polyester
Polyester is difficult to dye because of a high degree of orientation and high cohesive forces and compact structure.Hence for the dye to diffuse in the fibre, certain dyeing conditions which will loosen the fibre structure must be selected. The dyeing methods are divided into exhaust methods and continuous methods.
1) Exhaust method
This method involves dye transfer from aqueous baths into the fibre.Exhaust dyeing is carried out at boil using carriers and high-temperature conditions.Woven, knitted and texturized polyester fabrics are dyed by this method.
2) Continuous method
The dye is mechanically fixed on the fibre and then made to diffuse into the fibre by a thermal treatment called “thermosolling”, where the dye is applied to the fibre mechanically and then thermofixed at 200-200°C.
The polyester may be dyed by the following methods.
Certain chemicals called “Carriers” are added to the dye bath to act as swelling agents for the polyester fibres.They swell the fibres in an aqueous dye bath held at the boil and thus enable the chain molecules in the fibre to move about more easily.
Carrier enables dyeing to be carried out at boiling temperature under normal atmospheric pressure, without the need for special equipment such as high-pressure machines which are expensive.
A typical method involves the use of a closed automatic jigger with a direct or indirect heating system, which is a must in order to get satisfactory dyeing.The bath is set with an anionic wetting agent, a carrier, and acetic acid to adjust the pH at 5.5 to 6.5.
The fabric is run in the blank bath with the carrier for 30 mins at 60°C and then previously dispersed dye is added to the bath after filtration.The dispersion is added in two lots at 60 °C.The temperature is then slowly raised to the boil and dyeing continued for 90 minutes.
After the dyeing is complete, the bath is run off and the fabric is treated with the boiling water or scoured with 1 GPL non-ionic detergent to remove the loosely held carrier.The dyed material is then given a reduction clearing treatment with 2 GPL caustic soda and 2 GPL sodium hydrosulfite at 60°C for 30 minutes to remove the unfixed color from the fabric.
The fabric is now washed thoroughly with hot and cold water. To remove the carrier completely from the fibre a heat treatment is given at about 150-180°C for 30-60 seconds, depending upon the type of carrier used.
- Disperse dye : X%
- Anionic wetting agent : 0.1 to 0.5 %
- Dispersing agent : 0.1 to 0.5 %
- Carrier :Y%
- Acetic acid : 0.1 to 0.5 %
High-Temperature High Pressure (HTHP) Dyeing Method
In this method, the polyester fibre is dyed at high temperature and high pressure in an aqueous bath.The HTHP conditions help to bring the fibre to the temperature well above the Tg of the fibre, so excellent diffusion can take place and good dyeing results are obtained.
- Disperse dye: X%
- Dispersing agent: 1 gpl
- Wetting agent : 0.5 gpl
- Levelling agent: 0.5 to 1 gpl
- Acetic acid: enough to get pH
The batch of the fibre is entered into the autoclave and the vessel is filled with water.Complete removal of air should be ensured before starting the actual dyeing process. The dye bath is set at 50°C with 1 gpl dispersing agent and 0.5 gpl wetting agent; 0.5 -1 gpl leveling agent is also included if required.
The pH of the bath is adjusted to 5-6 with acetic acid.The liquor is circulated through the beam for 15 minutes at 50°C.The dyestuff is pasted and then dispersed in 10 to 20 times its weight of water at 40-50°C for 5 minutes to ensure uniform and thorough wetting.The dye dispersion is added to the dye bath and temperature of bath raised to 90-95°C within 10 minutes.
Further, increase in the temperature from 95°C to 110°C should be very slow and uniform as this is the critical zone for the dyeing of polyester fibre and the dye uptake and the levelness of dyeing depend very much on it.A rate of temperature rise of half a degree per minute from 90-95°C to 110°C would be suitable and take about 30-40 minutes.
The temperature increase is kept at this rate while the dyeing is continued for another 30 minutes when the dye bath temperature reaches 125-130°C.The heating is then adjusted to maintain this temperature and the dyeing continues for 30-45 minutes at this temperature.
After dyeing at 125-130° C for the required time a sample is taken out for shade matching and if any addition of dyestuff is necessary, it is done after cooling the dye bath to 80-90°C so as to avoid uneven dyeing. After every addition, the dyeing should be done for at least 15 minutes at the dyeing temperature.
Reduction clearing: This treatment is given after dyeing step to remove any unfixed dye from the fabric.It is carried out with caustic soda and sodium hydrosulfite at 60°C for 20-30 minutes.The batch is then washed and unloaded.
Thermosol Dyeing Technique
The Du Pont thermosol process is a continuous process in which dry heat is utilized effectively in the dyeing of synthetic textiles.It involves padding a fabric through a dispersion of the dye, drying, and heating for about one minute at 200°C.
At this temperature, many disperse dyes are molten whilst the fibre is plastic with its chain molecules vibrating vigorously.Thus, the dyeing consists essentially of a liquid dye dissolving in a fibre, which itself is like a “viscous liquid”, hence the name “thermosol process”.
Basically, the mechanism of thermosol fixation of the dye is the same as for exhaust dyeing.The dye is dissolved directly in the fibre when exposed to temperatures of the order of 20°C.Complete penetration is obtained in 60 seconds.
Dyeing by this method is a relatively simple process and consist in general of the following four steps:
- Padding the material with disperse dye or a combination of dyes used for P/C blends.
- Drying the padded fabric.
- Fixation of dyestuff within the material by means of dry heat at 180-210°C for 60-90 seconds.
- After treatment of the material for synthetic fibres and dyeing and development of the other component fibre in case of blended textile.
Fastness Properties of Polyester
The fastness properties of disperse dyes on the polyester cover a wide enough range for an adequate dye selection for most end uses.The same dyes generally show poorer fastness on nylon. Lightfastness ratings at the IS0 standard depth (1/1 SD) can easily be in the 6-7 range on the Blue Wool Scale of 1-8, although they do drop slightly if the light source is a carbon arc as opposed to the xenon lamp.
As the depth of shade decreases, lightfastness drops, a phenomenon shared by dyeings of all application classes of dyes. If extremely high lightfastness is needed (automotive fabrics), a nonionic UV inhibitor may be added to the dyebath and applied to the fiber along with the dye.
These compounds, often benzotriazoles, work much like sunscreen, screening out and dissipating UV radiation to prevent sunburn. Wet fastness tests are frequently conducted after the goods have been reduction cleared and heat set; e.g., at 180°C (356F) for 30 seconds. They are assessed in terms of the staining on multifiber or adjacent nylon piece goods. Ratings of 4+ out of 5 are readily achieved on regular denier fibers.
The ratings are very dependent on the extent of clearing of the fiber surfaces, the duration, and temperature of the heat treatment and whether the fabric has been treated with a finish of any kind. Heating disperses dyed goods causes the dyes to tend to migrate towards the fiber surfaces and some of the disperse dyes are quite soluble in hydrophobic surface films; e.g., in softeners which may have been applied.
Fastness to crocking or rubbing as well as drycleaning suffers if dye migrates to the fiber surface or surface layer. For those dealing in imports and exports of dyed goods, it is vitally important to be aware that the methods of fastness testing, and consequently the ratings for dyed goods, vary from country to country. The International Organization for Standardization (ISO) has developed a series of fastness tests which are often very different from test methods (6) used in the U.S.
Two Bath Dyeing Of P\C Blended Fabrics
In the modern & highly competitive area of textile dyeing the key to uniformity, reproducibility and high-quality fabric lies in the correct pretreatment of fabric prior to dyeing.
It is commonly experienced that common 70%of the faults in the finished fabric may be treated back to some faulty pretreatment. Dyeing of the cellulosic polyester blend is now more commercially important then dyeing of either fibre alone.This is the dye extensive use of P/c blends including regenerated cellulose.
P\c blends are subjected to a variety of pretreatments to ensure good results in dyeing.two typical routes are stated below
1)Singeing ⇒ Desizing ⇒ Washing ⇒ Bleaching ⇒ Mercerising ⇒ Drying ⇒ Heat setting
2)Desizing ⇒ Washing ⇒ Drying ⇒ Heat setting ⇒ Singeing ⇒ Mercerising ⇒ Drying
Dyeing Of Polyester Component
Prepare dyebath for following recipe
X% -Disperse dye.
1 g/l – Dispersing agent.
4.5-5.5 – pH with acetic acid.
Set the dye bath at 60°C and material there in 15 minutes.Raise the temperature up to 90° C.Slowly raise the temperature from 90°C to 110°C.Increase the temperature to 130°C.Work out the material for 30 minutes at 130°C temperature.Cool down at 80°C.
Remove the sample and wash with cold water.Carryout reduction clearing treatment by 4cc/ liter NaOH at 70°C for 30 minutes.Rinse the fabric with cold water.
Dyeing Of Cotton Component
Take the dyed sample in the bath with required quantity of reactive dye with 1:30 MLR.Start the dyeing at room temperature.Raise the temperature at 60°C.Then add 40 gpl salt and raise the temperature to 80°C.
Add 20 gpl soda ash and continue dyeing for 45 minutes at same temperature.Remove sample and wash thoroughly with cold water.Soap with 2 gpl soap solution for 20 minutes.Wash with hot and cold water.
Two Bath Dyeing Of P/W Blended Fabric
The consumers increasing the acceptance of wool and polyester blends over the past two decades have given added impetus to research aimed at improving the economics and quality of dyeing of these blends.
Because of the vastly different chemical nature of wool and polyester, two classes of dye are employed in the dyeing method – a water-soluble dye and a disperse dye, both of which are applied to the blend either sequentially in a two bath process, or together in a single bath containing all necessary auxiliaries.
Dyeing Of Polyester Component
Prepare the bath with the following recipe:
1gpl – Dispersing agent
1gpl – anionic wetting agent
3 gpl – carrier
4.5-5.5 – pH with acetic acid
Set the bath at 60°C and work out the material therein for 15 minutes.Add the dye dispersion and continue the dyeing at the same temperature for 15 minutes.Raise the temperature to 105°C in 20 minutes.Work out the material for 1-2 hours at 105°C temperature depending on the depth of color.
Cool down the bath slowly to 90° C.Remove the sample and wash thoroughly with cold water.Carry out reduction clearing treatment 3 gpl sodium hydrosulfite, 4 ccs/lit ammonia, 1 gpl dispersing agent at 50°C for 15 minutes.Wash and rinse with 1 gpl acetic acid.
Dyeing Of Wool Component
Prepare the dyebath with above recipe:
X% – Acid dye
4 % -Acetic acid
10 % -Sodium sulfate
Set the bath at room temperature and work out the material therein for 5 minutes.Raise the temperature to boil slowly.Work out the material for 30-60 minutes at the boil for exhaustion of dye.Add 1-2 % of formic acid for complete exhaustion of dye.Remove the sample and wash thoroughly with cold water.Finally, wash with cold water.
Two bath dyeing of P/V blends
Dyeing Of Polyester Component
Prepare the dye bath with the following recipe:
X% -Disperse Dye
1 gpl -Dispersing agent
4.5-5.5 – pH with acetic acid
1:20 – MLR
Set the bath at 60°C and the material therein for 15 minutes.Raise the temperature up to 90°C.From 90°C to 110°C raise the temperature slowly.Increase the temperature to 130°C.Workout the material for 30 minutes at 130°C temperature.
Cool down the bath to 80°C.Remove the sample and wash thoroughly with cold water.Carry out reduction clearing treatment with 2 gpl sodium hydrosulfite 4 ccs/ lit NaOH at 70°C for 30 minutes.Rinse the fabric with cold water.
Dyeing Of Viscose Component
Take the polyester dyed sample in a bath with required quantity of reactive dye with 1:30 MLR.Start the dyeing at room temperature.Raise the temperature to 60°C.Then add 40 gpl salt and raise the temperature to 80°C.Add 20 gpl soda ash and continue the dyeing for 45 minutes at the same temperature.
Remove the sample and wash thoroughly with cold water.Carry out soaping with 2 gpl soap solution for 20 minutes.Wash with hot water and cold water.Add 20 gpl soda ash and continue dyeing for 45 minutes at same temperature.Remove the sample and wash thoroughly with cold water.Soap with 2 gpl soap solution for 20 minutes.Wash with hot and cold water.
Two Bath Dyeing Of P/A Blends
These mixtures posses the dimensional stability of polyester and wool like the softness of acrylic fibre.However, such disperse dyes should be selected that stain the acrylic component only to tolerable limits, under the conditions of dyeing.The rapid dyeing and constant temperature dyeing techniques for acrylics have been well developed by Bayer, Sandoz etc.
The polyester component is dyed as usual and then the material is rinsed.The second fresh bath is set at 60°C with the necessary amounts of cationic dye, acetic acid, leveling agent etc. and then the temperature is raised rapidly to 80-85°C and subsequently slowly within 30-45 minutes to 100-105°C.The dyeing is carried out at this temperature for one hour, the liquor is then cooled down slowly to 50-60°C, and then the material is well rinsed.
Applications Of Polyester And Its Blends
- Polyester fibres are the first choice for apparel and are used in trousers, shirts, dresses, suits, jackets, blouses and outdoor clothing.
- Fabrics made from polyester thread or yarn is used expansively in apparel and home furnishing products.
- Polyester fibre is used as cushioning and padding material in pillows, quilts and upholstery stuffing.
- Industrial polyester fibres, yarns, and ropes are used in tyre strengthening process.
- Polyester fabrics are used for conveyor belts, safety belts, coated fabrics and plastic supporting with high energy absorption.
- Polyester is used in jackets and quilted garments.
Environmental consideration has the great impact on the production and coloration of synthetic fibre with its blend namely polyester and its blends like P/C, P/V, P/W and P/A.It has led to the development of new fibre production, dyeing, and processing technique.
This review reveals the overview of polyester, its manufacturing process, several pretreatments carried out on polyester and its blends before dyeing, their dyeing processes with suitable dye and its end applications.
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