Process Flow of Effluent Treatment in a Textile Industry-1

Process Flow of Effluent Treatment in a Textile Industry

Typically the following process flow of effluent treatment is followed in a typical textile industry;

Screening

The purpose of screening is to filter out the loose impurities. Thus wood, paper plastic bags etc. can be removed by this method. A method of progressive filtering is followed where first the matter is passed through coarse screens and then through fine screens.

Oil and Grease Removal

Many units discharge water mixed with oil. The purpose of this equipment is to remove the oil. Since surface density of oil and grease is less than water, the oily substance come on the surface of the water and can be skimmed.

Cooling and Equilization

The effluent from the primary treatment is cooled ( cooling towers are employed for this purpose) and then uniformly mixed using equlisation tank. It takes in any sudden gush of effluents as well as slow rate of effluent and feeds to the subsequent processes in a uniform way.

pH Adjustment ( Acid or Alkaline Dosing)

The waste from the Textile Industry is rarely pH neutral. To increase the efficiency of biological treatment and coagulation/flocuculation a pH of 6-8 is needed. Generally Sodium hydroxide is used to neutralise acidic waste and hydrochloric acide is used to neutralize alkaline waste. Generally the effluents from the dyeing industry have high pH and hence an acid addition is required.

Aeration 

It is reuqired to control BOD. Two main methods are used: one in which water is mechanically agitated so that air from atomoshphere may enter into the water, second method is introducing the air in the water through blowers and using diffusers to diffuse the air uniformly.

Prechlorination

Generally organic matter present in the effluent takes oxygen from the water, which increases its oxygen demand, to avoid that chlorine is added to oxidise the matter.

Clarification

The purpose of clarification is to remove any suspended solids by coagulation and flocculation. It is done using flash mixer. In flash mixer, alum solution is dosed as coagulant.

The flocculated water flows upwards towards tube settler. The suspended solids settle down.

This settling can also be done using lamella filter

Lamella Filter

It achieves solid liquid separation by directing the liquid between a seris of inclined plates called lamellae. It settles suspnded solids by gravity.



To be continued

An Excellent Document on Denim Effluent Treatment Process is here

Sources:

http://www.scribd.com/doc/4678823/Etp-Manual-Std-Denim

http://www.sharpengineering.co.in/Iffluent_Equipments.aspx

http://www.jfc-cetp.com/envinfo.html

http://www.iichemrc.org/Lamella.pdf

Now that you've finished reading this post, what are you going to do? You should join the Forum.

Effluent Generated at various Processes of Textile Manufacturing

Effluent Generated at various Processes of Textile Manufacturing

Textile manufacturing involves conversion of Fibers into garments. At each process some amount of liquid is used. However, it is not that each process leads to generation of efflents. Typically coversion to yarn involves no generation of effluents. It is the sizing and processing where most of the efflent is generated which needs to be treated. Given below is a list of the processes along with the information about effluent generated.

1. Fiber Preparation and Yarn Spinning: 

There is very little effluent generated in these processes.

2. Slashing/Sizing

The Effluent contains BOD, COd, metals, cleaning waste and size.

3. Weaving, Knitting and Tufting

There is very little effluent generated in these processes.

4. Desizing

The effluent contains BOD from water-soluble sizes, synthetic size, lubricants, biocides and anti-static compounds.

5. Scouring

The effluent contains disinfectants and insecticide resudes, NaOH, detergents, fats, oils, pectin, wax, knitting lubricants, spin finishes and spent solvents.

6. Bleaching

The effluent contains hydrogen peroxide, sodium silicate or organic stabilizer. The effluent also contains high pH.

7. Singeing and Heat Setting

There is very little effluent generated in these processes.

8. Mercerising

The effluent contains high pH and Sodium Hydroxide.

9. Dyeing

The effluent contains metals, salts, surfacftants, toxics, organic processing assistants, cationic material, color, BOD, sulfide, acidity or alkalinity and spent solvents.

10. Printing

The effluent contains suspended Solids, urea, solvents, color, metal, heat , BOD and foam.

11. Finishing

The effluent contains BOD, COD, suspended solids, toxics and spent solvents.

Read Also

Textile Effluent Treatment-1
Textile Effluent Treatment-2

Now that you've finished reading this post, what are you going to do? You should join the Forum.

Effluent Treatment in Textile Industry-2

Bleaching and Dyeing

It is estimated that to dye 1 kg of cotton with reactive dyes, 0.6-0.8 kg of NaCl, 30-60 grams of dyestuff and 70-150 liter of water is required. Once the dyeing operation is over, the wastewater must be treated before reuse. Coagulation and Membrane Technique ( nanofilteration  or reverse osmosis) are among the processes suggested for the treatment of water. 

Coagulation and Flocculation

Natural and wastewater contain small particles. They are suspended in water in a form called as a colloid. These particles carry the same charges, and repulsion prevents them from combining into larger particles to settle. Thus, some chemical and physical techniques are applied to help them settle. The phenomenon is known as coagulation. A well known method is the addition of electrolyte. Charged particulates combine with ions neutralizing the charges. The neutral particulates combine to form larger particles, and finally settle down. Historically Alum is used for this purpose but it makes the pH of the solution slightly basic. 

Another method is to use high-molecular-weight material to attract or trap the particulates and settle down together. Such a process is called flocculation. Starch and multiply charged ions are often used.

Here the basic advantage is that the dye molecules themselves are removed which is better than other methods where dye molecules are decomposed and produce harmful and toxic aromatic compounds. 

The disadvantage is that in coagulation process, large amount of sludge is created which may become  a pollutant itself and increase the treatment cost.

This method is useful for removing the insoluble dyes, but the cost of treating the sludge increases.

Ultrafilteration and Nanofilteration


Ultrafilteration filters substances with sizes less than  than 10^-7 to 10^-8 m . It can effectively remove suspended organic solids. It can not remove multivalent ions. It needs low water pressure to operate.

Nano filteration filters substances with size less than 10^-8 to 10^-10 m. It can remove multivalent ions. 

Reverse Osmosis

It can remove substances with size less than 10^-9 to 10^-11m. It can remove multivalent as well as monovalent ions.

When a compartment containing a dilute solution is connected to another compartment containing a concentrated solution by a semipermeable membrane, water molecules move from the dilute solution to concentrated solution. This phenomenon is called osmosis.

By applying pressure in the higher concentration solution, water molecules migrate from a high concentration solution to a low concentration solution. This method is called reverse osmosis water filter system. ( Source )

An excellent FAQ on Reverse Osmosis can be found here .

Previous    Next

Now that you've finished reading this post, what are you going to do? You should join the Forum.

A Note on Medical Textiles

Textiles act as an interface between man and treament. Depending upon the area of application, the medical textiles are categorises as Non-implantable, implantable and healthcare and hygiene products.

Non implantable material are external to the body, with or without skin contact. It includes absorbant pad, bandages and plasters among others. These material should have good padding characteristics and should be non sticking to the wound. Air and vapor permeability is requrired so that the material is comfortable to the patient. They should have high absorbancy and should be soft and pliable.

Implantable materials are used in place of defective body parts. It includes sutures and soft tissue implants. These materials should have compatibility with the natural body systems. They should be durable and resistant to alkali and acidic media. Of course, they should have functionality for the purpose for which they are applied.

Healthcare and hygine products are not directly used in medical treatment, rather they are used for good hygiene application and healthcare. It includes surgical clothing and surgical covers. They should have high bacterial and viral resistance. They should be hygienic and should have softness and breathablitity. They should have required strength.

Source of image: 1

Now that you've finished reading this post, what are you going to do? You should join the Forum.

Textile and Comfort

People have always been interested in the connection between clothing and physical well-being.Comfort has its physiological, physical-chemical and psychological components. Major components in case of textiles are Warmth, Absorbing capacity and humidity, General comfort , Cloth convenience , Skin perception , Weight and Softness. Out of these major part of comfort is directly related to the body temperature. Thus any clothing can be measured on comfort by the fact that how well it can regulate the temperature of the body. Sweating is the most effective way the human body has of cooling down. How well can a clothing provide comfort depends upon (among other factors) how well it can handle sweating.

The most effective cooling is achieved by sweat evaporating directly on the skin. Thus any clothing that behaves closest to the skin is comfortablee. The ability of a textile to transport perspiration in the form of vapour through itself and out to the exterior is generally referred to as its breathability. It is incorrect to use the terms breathability (or resistance to water vapour) and air permeability interchangeably, because low air permeability does not in itself result in lower breathability. The best example of this is modern wind- and waterproof membranes, which allow very little air to permeate in from outside (windproof), but still allow evaporated perspiration to pass through from the inside.

Fiber characteristics influence breathability the most. However contrary to popular belief,synthetic fibers are not always bad in terms of comfort. If textiles made from synthetic fibres were properly designed, they could not only offer the same heat and moisture management qualities as natural fibres but even exceed them.For example in in double faced clothings, layers of natural and synthetic fibres were combined, yet kept separate. The synthetic fibres of the "double face material" were next to the skin and conducted perspiration quickly and efficiently away from the body and into the outer cotton layer. In combination, the two materials were far more comfortable than cotton, because of the drier feeling on the skin."

There are some interesting developments in getting comfort characteristcs of fabrics they include a gradual variation in the fineness of the fibres and yarns from the inner surface of the textile to the outer surface. It improves moisture management; because the resulting narrowing of the capillaries (denier gradient) means that the moisture can be transported away from the skin really effectively. Other measeures include integrating electrical and electronic components such as heating or cooling elements. The latest battery technology and innovative methods of processing and wiring.


Sources:

http://www.innovationintextiles.com/articles/732.php

http://www.technica.net/NT/NT3/comfort_clothing.htm
 

Now that you've finished reading this post, what are you going to do? You should join the Forum.

Various Chemicals Used in Textile Industry

Various Chemicals used in Textile Industry


Pre-treatment Chemicals

De-sizing Agent

This is used to remove the different types of sizes (Starch, waxes etc.) from the fabric/yarn

Wetting and Penetrating Agent

This is needed to reduce the surface tension of water and thus increase the absorbency of the water to the fabric

Sequestering Agent & Protective Colloid

This is needed to reduce the hardness of water and thus make ideal conditions for washing

Scouring Agent

This is needed to remove the oil , fats etc from the fabric.

Silicone & Non Silicone Defoamers

These are needed to reduce the foam created during the process of treatment of fabric

Non-Silicate Peroxide stabilizer

This is used to stabilize the peroxide of hydrogen peroxide in the pretreatment process.

Peroxide Killer

This is used to clear the residual peroxide from the fabric

Polyester Weight Reducing Catalyst

This is used to reduce the weight of the polyester fabric during the caustic addition process

Anti-back Staining Agent

This is used to prevent the staining of the pockets during the denim fabric treatment

Dyeing Chemicals

Sequestering Agent

It is used to reduce the hardness of water and thus make ideal condition for processing

Silicone & Non Silicone Defoamers

These are used to reduce the foam created during the process

Buffering Agent

These are used to maintain the pH of dye bath throughout the dyeing process

Polyester Dyeing Carriers

These are used to facilitate easy absorption and penetration of dyes by the polyester fabric

Dispersing Agent & Oligomer Removing Agent

This is used to maintain the dispersion of dyes in the dyeing process and help to remove oligomers

Levelling Agent

This is used to get even dyeing and even colour depth effect

Lubricants

To reduce the friction between fabric to fabric and fabric to machine and to reduce the creation of creases in the fabric

Washing off Agent

To remove the unfixed dyes from the fabric

Dye-fixing Agent

To fix the dyes on to the fabric

Soda Ash Substitute

To substitute soda ash in the dyeing process of cotton.

Cationising Agent for Pigment Dyeing

To provide required cationic charge to the fabric in the pigment dyeing process

Printing Chemicals:

Dispersing, Penetrating, Swelling, Levelling & Defoaming Agent

This is used to provide depth and even level printing effect, being added in the printing paste

Fixation Accelerators

These are used to provide depth and fixation of dyes to the polyester printing fabric in loopager machine during the disperse printing process

Binders Acrylic, Self Thickening for Gold & Flock

These are used to bind the pigment or dyes onto the fabric

Fixers in Pigment Printing

These are used to provide fastness to the print

Thickeners

These are used to provide viscosity to the printing paste to facilitate required printing effect

White Inks

These are used to provide printing effect onto the fabric

Washing Off Agent

This is needed to remove the unfixed dye from the printed fabric

Finishing Chemicals:

Stiffeners

This is used to provide stiff finish effect to the fabric

Softeners

These are used to provide soft finish effect to the fabric

Silicone Emulsion

This is used to provide silky and soft finish effect to the fabric

Wax Finishing Agent

This is used to provide waxy finish to the fabric

Anti Static Agent

This is used to reduce the static power of the fabric

Water Repellant & Soil Resisting Agent

This is used to provide water repellency and dust repellency to the fabric

Polyurethane Finishing Agent

This is used to provide bouncy feel to the fabric

Crease Recovery Agent

This is used to reduce the crease and provide wrinkle free effect to the fabric

Delustering Agent

This is used to remove the luster from the viscose fabric

Anti-pilling & Anti-Slip Agents

These are used to remove the hairing and pilling problems from the fabric and also provide anti-slip effect

Enzymatic Bio-polishing Agent

This is used to remove the surface protruding fibers from the knit substrates and denim and thus improvise the surface feel

Now that you've finished reading this post, what are you going do? You should go join the Forum.

Influence of Fiber Fineness and Maturity in spinning Process

Influence of Fiber Fineness and Maturity on spinning Process

Fiber Fineness

Fiber fineness determine how many fibers are present in the cross section of a yarn of given thickness. Additional fibers in the cross section not only provide additional strength but also a better distribution in the yarn. Minimum 30 fibers are needed, usually over 100 fibers are required. Fiber fineness influences spinning limit, drape of the fabric, yarn strength, luster, yarn evenness, handle, yarn fullness and productivity. Productivity is influenced by reduced end breakage rate.

In a conventional spinning process, fine fibers accumulate to the core and coarse fibers in the periphery.

Fiber fineness is measured in dtex which is equal to ratio of mass in dgrams and length in km. Decitex is equal to the product of Micronaire value of the cotton and 0.394.

Cotton fibers are generally classified as very fine if they have a micronaire value upto 3.1; fine if they have value between 3.1 to 3.9; medium if they have it between 4.0 to 4.9; slightly coarse between values of 5 to 5.9 and coarse if they have a micronaire value above 6.

Fiber Maturity

Cotton fiber consists of cell wall and lumen. The maturity index depends upon the thickness of the cell wall. The fibers are considered ripe if they have maturity index between 50-80 percent, unripe if they have MI between 30 to 45% and dead when they have it less than 25%.

Unripe fibers have neither adequate strength nor adequate longitudinal thickness. They lead to loss of yarn strength, neppiness, high proportion of short fibers, varying dyeability, processing difficulties mainly at the card.

Now that you've finished reading this post, what are you going do? You should go join the Forum.

World Textile Industry Report

Please click this link for world textile industry report

Introduction to textile Processes

Please refer to the link here.

Textile Printing-1

Printing has often been described as dyeing in a localized, patterned design. Textile printing utilizes the same dyes or pigments applied to produce a dyed fabric.The same principles of specific dye classes having select fibre affinities and the general fastness characteristics apply equally to printing as to dyeing.

Dyes or pigments used in dyeing are usually in a water bath solution. When the same dyes or pigments are used for printing, they must be thickened with gums or starches to prevent the wicking or flowing of the print design.The thickened solution, about the consistency of heavy buttermilk, is called the print paste.

Many dyes cannot be used in printing pastes. Some of the reasons include insufficient solubility, Low colour yield and poor print paste stability.

METHODS OF PRINTING
There are several methods for printing of textiles. Two are of significant commercial importance: the roller print method and the screen print method. A third method, heat transfer printing, is of less significance. Other printing methods, not widely used in commercial production of textiles, are block and batik printing.

Roller Printing

This method of printing is comparable to newspaper printing. It is a high speed process, capable of producing over 6000 yards of printed fabric per hour. The method is also known as machine printing.

In roller printing, the design is put into fabric by copper engraved rollers (sometimes called copper engraved cylinders). The roller engravings match exactly the artist-designer's creative sketch. A separate engraved cylinder is required for each colour in the print. The size of the engraved cylinders is governed by the printing machine and the design.

HOW ROLLER PRINTS ARE MADE

1. The Engraved Copper Roller A in rotation makes contact with Colour Furnisher B (whose surface is much like that of a paint roller used in house painting). The entire surface of Roller A becomes covered with print paste.

2. Colour Furnisher B, also in rotation, picks up a constantly fresh supply of print paste from Colour Box E.

3. Meanwhile, Engraved Copper Roller A in rotation comes in contact with Doctor Blade C. This is a steel blade which functions somewhat like a squeegee. It scrapes off all the print paste on the surface of Roller A, but cannot clean off the print paste from the engraved portion, and thus leaves behind the print paste inside the etched copper.

4. The cloth to be printed is drawn and guided between the Cylinder Roller and Engraved Copper Roller A. The pressure created at the point of contact causes the print paste to be transferred from inside the etched copper to the cloth. The pattern is now on the cloth.

5. Engraved Copper Roller A continues in rotation and comes in contact with Lint Doctor D, a steel blade which comes in contact with Roller A and removes any lint picked up from the fabric being printed.

6. The cloth being printed continues its path around the Cylinder Roller. If a 2nd, 3rd or 4th colour is to be printed on the same fabric, then Steps 1 through 5 will be repeated for the respective 2nd, 3rd or 4th sets of Engraved Copper Roller, Doctor Blades, Colour Box and so forth. The fabric makes only one pass through the roller printing machine. Successive colours do not become smudged because the pressure of the engraved roller on the fabric being printed literally squeezes the print paste into the fabric and the surface colour dries instantly.

7. The printed cloth on leaving the machine is immediately dried so that the fabric can be touched without smudging the print. Afterwards, the fabric is transferred to a steam chamber where moisture and heat will set the dyes. If pigments rather than dyes are used, the fabric is entered into a dry heat curing oven at temperatures up to 400°F.

8. 'The Back Grey is a fabric that moves through the print machine along-with and in back of the fabric being printed. Its function is to absorb the excess print paste which may strike through and stain the Cylinder Roller cover. The Back Grey is later washed out and used over and again. It eventually takes on a dingy grey colour, hence its name.

Screen Printing

Screen printing is a method whereby an open, but closely meshed screen, mounted in a wooden or metal frame, is placed in contact with the fabric to be printed and the print paste forced through the screen by a squeegee (implement edged with rubber for sweeping water from surfaces). The design is created by painting out or otherwise making opaque portions of the screen, thus preventing the print paste from passing through. Those areas where the print paste does pass through will register as the printed pattern.

There are actually three methods of screen printing, each of which embodies the same principle. The first, hand screen printing, the second method is automatic screen printing or flat bed printing or automatic flat printing and the third method is the rotary screen printing or rotary printing.

Hand Screen Printing

Hand screen printing is done commercially on long tables (up to 60 yards in length). The roll of fabric to be printed is spread smoothly onto the table, whose surface has first been coated with a light tack adhesive. The print operators then move the screen frames, by hand, successively along the whole table, printing one frame at a time, until the entire fabric is printed. Each frame will contain one colour of the print. A three colour print, for example. will require three frames and three applications to the fabric. The rate of production ranges from 50 to 90 yards per hour by this method.

Automatic Screen Printing (Flat Bed Printing)

Automatic screen printing (flat bed printing) is like hand screen printing except that the process is automated and therefore, faster. Instead of the long table on which the fabric to be printed is spread (as in hand screen printing), the fabric is moved to the screens on a wide rubberized belt. Like hand screen printing, it is an intermittent rather than a continuous process. In this instance, the fabric moves to the screen, then stops for the screen squeegee action (which is done automatically). After the squeegee action, the fabric moves again to the next screen frame. The rate of production is about 500 yards per hour. Automatic screen printing is utilized for whole rolls of fabric only.

Rotary Screen Printing

Rotary screen printing is different from the other methods of screen printing in several important respects. Rotary printing is continuous like roller printing. The fabric being printed is moved on a wide rubber belt under the rotary screen cylinders which are in continuous movement. Rotary screen printing is the fastest method of screen printing, with production of 2500 to more than 3500 yards per hour. Seamless, perforated metal or plastic screens are used. The largest rotary screens have a circumference of about 40 inches and the maximum repeat size of patterns is, therefore, about 40 inches.

Heat Transfer Printing

Heat transfer printing is sometimes called thermal transfer printing. In this method, the design is first printed on paper with printing inks containing dyes of the disperse dye class. The printed paper (called transfer paper) is then stored until ready for use by the textile printer or converter.

When fabric is to be printed, it is passed through a heat transfer printing machine which brings paper and fabric together face to face and passes them through the machine at about 400°F. Under this high temperature, the dye on the printed paper sublimates and is transferred onto the fabric.The process, resembling somewhat the familiar decal transfer, is relatively simple and does not require the expertise necessary when producing roller or rotary screen prints.

Disperse dyes are the only dyes which can be sublimated. and thus the only ones which will respond in a way that permits heat transfer printing. The process is therefore limited to fabrics which are composed of fibres having affinity to this class of dyestuff. This includes acetate, acrylics, polyamides (nylon) and polyesters.

The Above table give a list of the printing methods and their advantages and disadvantages.

PRINTED FABRIC IMPERFECTIONS

The following is a listing and description of the more frequently occurring imperfections that may result from printing processes. These imperfections may result from faulty or improper printing procedures, faulty or improper preparation of the fabric prior to printing or to imperfections in the material being printed.

Since the printing of textiles is in many respects similar to the dyeing of textiles, many of the imperfections found in dyed fabrics are also found in printed fabrics.

A. Colour Drag- Colour of the print smears or smudges from rubbing against an object before it becomes dry.

B. Colour Splatter-The print paste instead of being placed on the fabric is thrown or splattered onto the fabric surface.

C. Fuzzy Pattern - The edges of patterns are not sharp, clear lines, but are instead rather fuzzy lines. Most frequently caused by improper singeing or improperly thickened print paste.

D. Off-register- Printing rolls or screens improperly aligned so pattern parts do not meet properly. This imperfection is also called out-of-fit or out-of-register.

E. Stop Mark- Colour streak across the fabric resulting from the printing machine being stopped during the printing process and then starting again.

F. Tender Spots- In printed fabrics, one or more colours of the print may cause weakened areas where they were printed. Usually due to excessive use of injurious chemicals in the print paste. May also be found in the discharged area of discharge prints.

Textile Dyeing-1

Textile Dyeing

There are three distinct categories by which color is imparted to textiles . These are:

By Dyeing
By Pigment Application
By Solution or Dope Dyeing

Of the three categories, the most widely used is dyeing.

Essentially, dyeing involves the use of highly complex organic chemical dyestuffs, which will under proper conditions, actually combine with the textile fibre molecule. Usually the fibre, yarn or fabric is immersed in a water solution of the dye, frequently under carefully regulated high temperature, untile the dye in the bath combines with the material to reproduce the desired colour.

Textile colouring by use of pigments differs from dyes in that pigments do not combine with the fibre molecules as dyes do. Pigments physically hold onto the textile material with resin binders in much the same way that paint holds to a wall.

Solution dyeing differs from the previous two categories mentioned because the coloration of the textile is part of the fibre manufacturing process of man-made fibres. In solution dyeing, appropriate coloring agents are added to the man-made fibre solution before it is extruded from the spinnerette.