Choosing a fabric for your new sofa

14 10 2013

Design decisions influence our health –so your choice of a sofa fabric could influence you and your family in ways far beyond what you imagined.  Our children start life with umbilical cords infused with chemicals that affect the essence of human life itself  –   the ability to learn, reason and reproduce.  And fabric – which cocoons us most of the time, awake and asleep – is a contributor to this chemical load.  One thing I know for sure is that the textile industry uses lots of chemicals. During manufacturing, it takes from 10% to 100% of the weight of the fabric in chemicals to produce that fabric.(1) And the final fabric, if made of 100% natural fibers (such as cotton or linen), contains about 27% , by weight, chemicals(2) – let’s not even talk about synthetic fabrics.

Since 1999, the Centers for Disease Control (CDC) has tested Americans every two years in order to build a database of what are called “body burdens,”(3) in order to help toxicologists set new standards for exposure and definitively link chemicals to illness, or else decouple them. The study attempts to assess exposure to environmental chemicals in the general U.S. population – and the more chemicals they look for, the more they find: The CDC started with 27 worrisome chemicals in 1999 and now tests for 219. Their findings have shown that no matter whether you’re rich or poor; live in the center of a city or a pristine rural community; east coast, west coast or in between; are elderly or newborn; Republican, Democrat or Socialist – you have BPA in your blood, as well as polybrominated diphenylethers (PBDE)s – which can retard a fetus’s neurological development; perfluorooctanoic acid (PFOA) – which impairs normal development; perchlorate – which can keep the thyroid from making necessary hormones and methyl tert-butyl ethers (now banned in most states) and mercury.

And the correlation between chemicals to illness seems to be on the rise (4) – certainly from studies done linking various chemicals to human disease and illness, but also because the spectrum of both “rare” and “common” illnesses is on the rise. The National Institutes of Health defines a rare disease as one affecting 200,000 or fewer Americans. Yet 25 – 30 million Americans suffer from one of the nearly 6,800 identifiable rare diseases. That compares to the 40 million Americans with one of the three “major” diseases: heart disease, cancer or diabetes.

Specifically with regard to fabrics: The 2010 AATCC (American Association of Textile Chemists and Colorists) Buyer’s Guide  lists about 2,000 chemical specialties in over 100 categories offered for sale by about 66 companies, not including dyes. The types of products offered run the gamut from antimicrobial agents and binders to UV stabilizers and wetting agents. Included are some of the most toxic known (lead, mercury, arsenic, formaldehyde, Bisphenol A, PBDE, PFOA). There are no requirements that manufacturers disclose the chemicals used in processing – chemicals which remain in the finished fabrics. Often the chemicals are used under trade names, or are protected by legislation as “trade secrets” in food and drug articles – but fabrics don’t even have a federal code to define what can/cannot be used because fabrics are totally unregulated in the U.S., except in terms of fire retardancy or intended use. It’s pretty much a free-for-all.

Why does the industry use so many chemicals? What are they used for?

Most fabrics are finished in what is called “wet processing” where the process is accomplished by applying a liquid – which accomplishes some sort of chemical action to the textile – as opposed to “dry processing”, which is a mechanical/physical treatment, such as brushing. It is a series of innumerable steps leading to the finished textile, each one of which also has a complex number of variables, in which a special chemical product is applied, impregnated or soaked with the textile fiber of the fabric. A defined sequence of treatments can then be followed by another sequence of treatments using another chemical substance. Typically, treatments are arranged to permit a continuous mode of sequences.

The chemicals used can be subdivided into:
Textile auxiliaries – this covers a wide range of functions, from cleaning natural fibers and smoothing agents to improving easy care properties. Included are such things as:

  • Complexing agents, which form stable water-soluble complexes
  • Surfactants, which lowers the surface tension of water so grease and oil to be removed more easily
  • Wetting agents, which accelerates the penetration of finishing liquors
  • Sequestering agents
  •  Dispersing agents
  • Emulsifiers

Textile chemicals (basic chemicals such as acids, bases and salts)
      Colorants, such as:

  • Dyes
  •  Dye-protective agents
  • Fixing agents
  • Leveling agents
  • pH regulators
  • Carriers
  • UV absorbers

Finishes
The chemicals used get very specific: for example, Lankem Ltd. is one such manufacturer of a range of textile chemicals. According to their website, their Kemtex AP, for example, is an “anti-precipitant” to be used “where dyes of opposing ionicity may be present in the same bath” and their Kemtex TAL is a levelling agent for wool which is a “highly effective level dyeing assistant for acid, acid milling and prematallised dyes on wool.”

In addition to the branded products supplied by chemical companies, which are made of unknown components because they’re proprietary, we know many chemicals are necessary to achieve certain effects, such as PBDEs for fire retardants, formaldehyde resins for crease resistance or PFOA’s for stain protection.
The chemicals used in these branded products to create the effects above include chemicals which have been proven to be toxic, or to cause cancers or genetic mutations in mammals (i.e., us too). The following is by no means an all-inclusive list of these chemicals:
• Alkylphenolethoxylates (APEOs)
• Pentachlorophenols (PCP)
• Toluene and other aromatic amines
• Dichloromethane (DCM)
• Formaldehyde
• Phthalates
• Polybrominated diphenyl ethers ( PBDE’s)
• Perfluorooctane sulfonates (PFOS)
• Heavy metals – copper, cadmium, lead, antimony, mercury among others

One of the presenters at the 2011 Living Building Challenge, inspired by writer Michael Pollan’s Food Rules,  shared a list of ways to choose products that remove the worst of the chemical contamination that plagues many products.

These rules apply to all products, including fabrics, so I’ve just edited them a bit to be fabric specific:

  • If it is cheap, it probably has hidden costs.
  • If it starts as a toxic input (like ethylene glycol in the manufacture of      polyester), you probably don’t want it in your house or office.
  • Use materials made from substances you can imagine in their raw or natural state.
  • Use carbohydrate-based materials (i.e., natural fibers) when you can.
  • Just because almost anything can kill you doesn’t mean fabrics should.
  • Pay more, use less.
  • Consult your nose – if it stinks, don’t use it.
  • If they can’t tell you what’s in it, you probably don’t want to live with it. (note: his is not just the fibers used to weave the fabric – did the processing  use specific chemicals, like heavy metals in the dyestuff, or formaldehyde in the finish?)
  • Avoid materials that are pretending to be something they are not.
  • Question materials that make health claims.
  • Regard space-age materials with skepticism.

(1)    Environmental Hazards of the Textile Industry, Hazardous Substances Research Centers, South and Southwest Outreach Program, US EPA funded consortium, June 2006.

(2)     Lacasse and Baumann, Textile Chemicals: Environmental Data and Facts; German Environmental Protection Agency, Springer, New York, 2004, page 609.

(3)    What is a “body burden”: Starting before birth, children are exposed to chemicals that impair normal growth and development. Exposures continue throughout our lives and accumulate in our bodies. These chemicals can interact within the body and cause illness. And they get passed on from parent to child for generations.

(4)    World Health Organization; http://www.who.int/healthinfo/global_burden_disease/en/index.html





Printing – part 3

19 01 2012

Yes, we’re still talking about the printing process!  As I warned you, it’s complicated.

For the past two weeks we’ve concentrated on the first two steps of the basic 5 steps in printing a fabric, which  are:

1. Preparation of the print paste.

2. Printing the fabric.

3. Drying the printed fabric.

4. Fixation of the printed dye or pigment.

5. Afterwashing.

So let’s look at the rest of the steps – drying, fixation and afterwashing.

Actually, the printing process begins even before passing  the fabric thru the printing presses, because the fabric must be conditioned.  The cloth must always to be brushed, to free it from loose nap, flocks and dust that it picks up while stored. Frequently, too, it has to be sheared by being passed over rapidly revolving knives arranged spirally round an axle, which rapidly and effectually cuts off all filaments and knots, leaving the cloth perfectly smooth and clean and in a condition fit to receive impressions of the most delicate engraving. Some figured fabrics, especially those woven in checks, stripes and crossovers, require very careful stretching and straightening on a special machine, known as a stenter, before they can be printed with certain formal styles of pattern which are intended in one way or another to correspond with the cloth pattern. Finally, all descriptions of cloth are wound round hollow wooden or iron centers into rolls of convenient size for mounting on the printing machines.

Immediately after printing, the fabric must be dried  in order to retain a sharp printed mark and to facilitate handling between printing and subsequent processing operations.

Two types of dryers are used for printed fabric, steam coil or natural gas fired dryers, through which the fabric is conveyed on belts, racks, etc., and steam cans, with which the fabric makes direct contact. Most screen printed fabrics and practically all printed knit fabrics and terry towels are dried with the first type of dryer, not to stress the fabric. Roller printed fabrics and apparel fabrics requiring soft handling are dried on steam cans, which have lower installation and operating costs and which dry the fabric more quickly than other dryers.

After printing and drying, the fabric is often cooled by blowing air over it or by passing it over a cooling cylinder to improve its storage properties prior to steaming, which is the process which fixes the color into the fabric.  Steaming may be likened to a dyeing operation.  Before steaming, the bulk of the dyestuff is held in a dried film of thickening agent.  During the steaming operation, the printed areas absorb moisture and form a very concentrated dyebath, from which dyeing of the fiber takes place.  The thickening agent prevents the dyestuff from spreading outside the area originally printed, because the printed areas act as a concentrated dyebath that exists more in the form of a gel than a solution and restricts any tendency to bleed.  Excessive moisture can cause bleeding, and insufficient moisture can prevent proper dyestuff fixation.  Steaming is generally done with atmospheric steam, although certain tyepes of dyestuffs, such as disperse dyes, can be fixed by using superheated steam or even dry heat.  In a few instances, acetic or formic acid is added to the steam to provide the acid atmosphere necessary to fix certain classes of dyes.  Temperatures in the steamer must be carefully controlled to prevent damage from overheating due to the heat swelling of the fabric, condensation of certain chemicals, or the decomposition of reducing agents.

Flash aging is a special fixation technique used for vat dyes. The dyes are printed in the insoluble oxidized state by using a thickener which is very insoluble in alkali. The dried print is run through a bath containing alkali and reducing agent, and then directly into a steamer, where reduction and color transfer take place.

After steaming, the printed fabric must not be stored for too long prior to washing because reducing agent residues may continue to decompose, leading to heat build up in the stacked material and defective dyeing or even browning of the fibers. If a delay of several hours is anticipated before the wet aftertreatment the fabric should be cooled with air (called “skying”) to oxidize at least some of the excess reducing agent.

Finally, printed goods must be washed thoroughly to remove thickening agent, chemicals, and unfixed dyestuff.  Washing of the printed material begins with a thorough rinsing in cold water.  After this, reoxidation is carried out with hydrogen peroxide in the presence of a small amount of acetic acid at 122 – 140 degrees F. A soap treatment with sodium carbonate at the boiling point should be begun only after this process is complete. This washing must be carefully done to prevent staining of the uncolored portions of the fabric.  Drying of the washed goods is the final operation of printing. 

And there you have it – a beautifully printed fabric that you can proudly display. Bet you know the subject of the next post – the environmental consequences of all this. Stay tuned.





Printing – part 2

13 01 2012

Bear with me – I’ll eventually get to the environmental aspects of printing – including digital printing.  But I think it’s important to know the basic steps and processes in order to be able to understand green claims.  So there will still be a Printing – part 3 before we get to the environmental topics.

Specific fiber materials and dye types interact with each other in well defined ways, and it is these interactions that determines the best composition of a printing paste or ink.  The preparation of this paste is one of the most important steps in printing. (note:  paste and ink seem to be interchangeable names for the same substances).

It requires a set of special characteristics  – one of the most important is that the paste be viscous (like paint or pudding).

Printing paste ready to use.

This quality is called “flow”.  The choice of an agent to create this flow (called a thickening agent) is a critical component. In addition, each printing method we talked about last week (flat bed, screen or rotary), as well as the nature and sequence of fixation and aftertreatment steps  requires a specific kind of printing ink or paste.

For direct printing, a printing paste is prepared by dissolving the dyes in hot water to which is added urea and a solvent (ethylene glycol, thioethylene glycol, sometimes glycerine or a similar substance – and sometimes water).   This solution is stirred into a thickener that is easily removed by washing.  Small amounts of oxidizing agents are added.[1]

After making the printing paste, it is essential to strain or sieve all colours in order to free them from lumps, fine sand, and other foreign objects, which would inevitably damage the highly polished surface of the engraved rollers and result in bad printing. Every scratch on the surface of a roller prints a fine line in the cloth, and too much care, therefore, cannot be taken to remove, as far as possible, all grit and other hard particles from every color.

The straining is usually done by squeezing the paste through filter cloths as artisanal fine cotton, silk or industrial woven nylon. Fine sieves can also be employed for pastes that are used hot or are very strongly alkaline or acid.

All the necessary ingredients for the paste are metered (dosed) and mixed together in a mixing station. Since between 5 and 10 different printing pastes are usually necessary to print a single pattern (in some cases up to 20 different pastes are applied), in order to reduce losses, due to incorrect measurement, the preparation of the pastes is done in automatic stations. In modern plants, with the help of special devices, the exact amount of printing paste required is determined and prepared in continuous mode for each printing position, thus reducing leftovers at the end of the run.

There are two main types of paste used:

  1. Pigmented emulsions: Pigmented emulsions are suitable for all fiber types,  they are able to dry by evaporation at room temperature and are able to be cured at 320 degrees F for 2 – 3 minutes, which achieves washing and drycleaning fastness.  A typical formulation of a pigment emulsion printing paste is:

COMPONENTS

RATIO

Water

10%

Emulsifier

1%

Thickener

4%

White spirit

62%

Catalyst solution

3%

Binder

15%

Pigment dispersion

5%

Pastes which are entirely water-based are obtained by replacing the white spirit  with  water.

  1. Plastisol printing pastes :  based on a vinyl resin dispersed in plasticizer; characterized by virtually 100% non-volatility (no solvent is present); used frequently for printing on dark or dark-colored fabrics.  Components of plastisol printing pastes consist of
    1. PVC homopolymer (i.e., a vinyl resin) dispersed in phthalate plasticizer;
    2.  liquid plasticizer (i.e., dialkyl phthalate or di-iso-octyl phthalate);
    3. heat and light stabilisers (i.e., liquid barium/cadmium/zinc combined with epoxy plasticizer);
    4.  high proportion of extender to improve wet-on-wet properties.

Printing pastes are made up of four main components:

  1. The coloring matter used (dyes or pigments)
  2. The binding agent
  3. The solvent
  4. The auxiliaries.

The coloring matter used can be either dyestuffs or pigments.   Dyes are in solution and become chemically or physically incorporated into the individual fibers.   The dyes used for printing mostly include vat, reactive, naphthol and disperse colours which have good fastness properties.    Pigments are largely insoluable, so often organic solvents are used (such as benzene or toluene).   The pigmented printing paste must physically bind with the fabric, so must contain a resin, which holds the pigment in place on top of the fabric.

The binder is decisively responsible for the fastness of the pigment prints during use. The most important fastnesses are wash fastness, chemical cleaning fastness and friction fastness. The handle and the brilliance of the colours are also influenced by the choice of binder.
Binders are in general “self-crosslinking polymers” based mainly on acrylates and less commonly on butadiene and vinyl acetate, with solid contents of approx.. 40 – 50%. (2)   Binders made of natural wood resin, wax stand linseed or safflower oils and chitosan were tested in order to obtain biodegradable printing paste.  Promising results were reported when using chitosan as a binder, and no solvent was necessary.

Solvents are usually added in the formulation of the thickeners.  The type of paste (emulsion vs. plastisol) and thickening agent determines the type of solvent needed.  White spirit is a commonly used organic solvent, as is water.  The organic solvent concentration in print pastes may vary from 0% to 60% by weight, with no consistent ratio of organic solvent to water.  Water based solvents may still emit VOC’s from small amounts of solvent and other additives blended into the paste. The liquid waste material of water based pastes may also be considered hazardous waste.

The most important auxiliaries are the thickening agents.  Printing paste normally contains 40 – 70% thickener solution. [3] The printing thickeners used depend on the printing technique and fabric and dyestuff used. Typical thickening agents are starch derivatives, flour, gum Senegal and gum arabic (both very old thickenings, and very expensive today) and albumen. A starch paste is made from wheat starch, cold water, and olive oil, and boiled for thickening.  Starch used to be the most preferred of all the thickenings, but nowadays gums or alginates derived from seaweed is preferred as they allow better penetration of color and are easier to wash out.

Hot water soluble thickening agents as native starch are made into pastes by boiling; the colorants and solvents were added during this step then cooled, after which the various fixing agents would be added.  Colors are reduced in shade by simply adding more stock printing paste.  For example, a dark blue containing 4 oz. of methylene blue per gallon may readily be made into a pale shade by adding to it thirty times its bulk of starch paste or gum, as the case may be. Mechanical agitators are also fitted in these pans to mix the various ingredients together, and to destroy lumps and prevent the formation of lumps, keeping the contents thoroughly stirred up during the whole time they are being boiled and cooled to make a smooth paste. Most thickening agents used today are cold soluble and require less stirring.

Almost exclusively synthetic, acrylate-based thickening agents are used in pigment printing – or none at all, since the mix of resins, solvents and water produces thickening anyway.

Generally, the auxiliaries used for printing are the same as those used in dyeing with a dye bath.  These types of auxiliaries include:

  • Oxidizing  agents (e.g. m-nitrobenzenesulphonate, sodium chlorate, hydrogen peroxide)
  • Reducing  agents (e.g. sodium dithionite, formaldehyde sulphoxylates, thiourea      dioxide, tin(II) chloride)
  • Wetting  agents (nonionic, cationic, anionic)
  • Discharging  agents for discharge printing (e.g. anthraquinone)
  • Humectants   (urea, glycerine, glycols)
  • Carriers:  (cresotinic acid methyl ester,  trichlorobenzene, n-butylphthalimide in combination with other      phthalimides, methylnaphthalene)
  • Retarders  (derivatives of quaternary amines, leveling agents)
  • Resist agents  (zinc oxide, alkalis, amines, complexing agents)
  • Metal  complexes (copper or nickel salts of sarcosine or hydroxyethylsarcosine)
  • Softeners
  • Defoamers,  (e.g. silicon compounds, organic and inorganic esters, aliphatic esters,      etc.)
  • Resins[4]

[1] Ullman’s Fibers, page 766

(2)  Lacasse, K., and Baumann, W., Textile Chemicals: Enviornmental Data and Facts, Springer, 2004; p. 234

[3] Fritz Ullmann, editor,  Ullmann’s Fibers: Textile and dyeing technologies, vol 2; Wiley-VCH Verlag GmbH & Co, KGaA, weinheim, 2008, p. 759

[4] Ulmman, p. 743





Can it be an organic fabric if it uses synthetic dyestuffs?

3 11 2011

At the  International Federation of Organic Agriculture Movements (IFOAM ) Congress   in February, 2011, Ann Shankar from Biodye India, a company that produces natural dyes based on wild plants,  made a provocative suggestion –  that the term “organic textile” is not an accurate description of any textile where synthetic dyes and auxiliaries are used.  The Global Organic Textile Standard   allows the use of synthetic dyestuffs ( which are made from unsustainable sources and are not biodegradable).  She suggests that a separate category for such textiles be called “organic fibers with responsible synthetic dyes”.  According to Ann, even if it takes another couple of years for anyone to be able to claim a fully organic supply chain that would warrant the name ‘organic textile’ it should exist as a goal. Until then, natural dyes and auxiliaries (definitions by GOTS) should be given a separate standard such as ‘Organic fibers with natural dyes’ – a term separate but equal with the label for synthetic dyes.

She said that her company has recently overcome the technical difficulties often associated with using natural dyestuffs, especially at an industrial level.   Biodye is not the only company which produces dyestuffs from organic material which can be used for manufacturing; Rubia Natural Colors also has developed dyes in the red range from madder.

One of the major problems with synthetic dyestuffs is the pollution problems they present coupled with our “end of pipe” solutions.  Pointing out the impracticality of this end of pipe scenario, she points to two examples:

  1. The Central Pollution Control Board (CPCB) in India categorizes process waste sludge from synthetic dye production as hazardous, yet has no norms for proper disposal.  The result is that solid waste is stacked in any available space,  on riverbanks and roadsides, where it leaches back into the water or soil.

    National Geographic

  2. Water is a critical concern, since the dye process uses so much water.  In 2006, over 6.9 million acres of agricultural land in 68 villages in India was destroyed (meaning no crops could grow on the land)  by water from the Noyyal River, which had long been the recipient of untreated textile mill effluent.  The water pollution was so bad that the Madras High Court ordered the dyeing and bleaching facilities which used the river to pay fines to both the government as well as to local farmers, who had lost their livelihood.[1]  They also instituted  a “zero discharge” requirement for all dyeing units.  However, in January 2011, the Madras High Court again forced  the closure of all dyeing units in the area when it was found that pollution levels were above allowable limits.  Despite a grant from the government to build treatment facilities, the General Secretary of the Tirapur Dyes & Chemicals Association, said “At present we do not have any technology for zero discharge.”

The use of natural dyes means that there is no pollution to dispose of, and it also increases the green cover for plants and animals.   She uses as an example the differences between synthetic indigo and natural indigo:

Synthetic indigo:

  • Made from petrochemicals.
  • Impurities include toxic aniline and N-methylaniline residues.
  • Not biodegradable – incineration is the only recommended means of disposal.
  • Toxic to daphnids and algae.
  • Small creatures do not live around the rims of fermentation vats containing synthetic indigo, nor can a frog survive a dip in the vat.
  • Called “nature identical” by chemists.

Natural indigo:

  • Dye is made in the leaves of the plant Indigofera.
  • Impurities include plant polymers and soil particles
  • Biodegradable. If natural indigo ceases to be added to a natural fermentation vat, it loses its power to dye within 75 days. A sour vat will consume the indigo within 15 days.
  • Small insects and creepy crawlies live around the rims of natural fermentation vats containing natural indigo, and frogs can hop in and out without harm

Biodye uses no toxic mordants and treats its waste water so sludge is available as fertilizer and water can be used as irrigation.





What to do about salt?

16 02 2011

Last week we talked about the use of salt in textile dyeing.  We always say the textile industry uses a LOT of three resources: water, chemicals and energy.  The use of salt (a chemical – benign, essential for life, but a chemical nevertheless) bumps up the other two considerably.   And though the salt itself is not expensive, using less salt delivers substantial benefits to the mill because the fabric requires less rinsing in hot water (and hence reductions in energy and water) as well as cost savings of up to 10% of the total process costs.[1] So we promised to look at options available to avoid salt.

To recap:

When fabrics made of cotton, linen, hemp or viscose are dyed,  they’re immersed in water which contains dyes which have been dissolved in the water.   These dye chemicals are usually reactive dyes which require  the addition of salt  to “push” the dyes out of solution and into the cloth.  The salt acts like a glue to hold the dye molecules in place.  But the percentage of dye that moves from the dye bath into the fiber, and permanently bonds with the fiber (called the fixation rate) is very low.  For conventional reactive dyes, the fixation rate is often less than 80%, resulting in waste of dyestuff, and also the need to remove that 20% from the fabric.[2] But this is incredibly difficult when the “unreacted” dyes are still “glued” onto the fabric by salt.  So vast amounts of water are required  to simply dilute the salt concentrations to a point where it no longer acts as glue.

There are a few things that mill owners can do:  simple process optimization can easily reduce salt concentrations in dyebaths by 10 to 15%.  Another simple method is to reduce liquor ratios (which is simply the ratio of water to fabric in a dyeing process).  It’s easy to see that using 10 gallons of 100 oz/gal of salt uses less salt than using 5 gallons of 100 oz/gal of salt.

There are also some “low salt” dyes that have appeared on the market.  These dyestuffs  require less “glue” to fix to the fibers.  Ciba Specialty Chemicals, a Swiss manufacturer of textile dyes (now part of BASF) produces a dyestuff which requires less salt.  As the company brochure puts it:  “ Textile companies using the new dyes are able toreduce their costs for salt by up to 2 percent of revenues, a significant drop in an industry withrazor-thin profit margins.”  However,  we’re told they’re not used because of uncompetetitive pricing.  (Remember, it’s all about the cost!).

Another alternative is to recycle the salt.  The effluent can be cleaned and the salt recovered through an energy intensive process to evaporate the water.  But the carbon footprint takes a beating.

We’re back to square one: to use less salt.

And that usually means we have to look to the dyeing machines.  There are low-liquor-ratio (LLR) jet dyeing mcahines that are based on the principle of accelerating water through a nozzle to transport fabrics through the machine.  They are designed to operate efficiently and at high quality with a very low ratio of water to material.  Although these types of machines have been used for over 40 years, recent technological advances have reduced water requirements so that liquor ratios of 8:1 and even 4:1 are possible, with average water consumption of less than 50 liters per kilogram of knit fabric.  Yet there is still salt infused effluent which must be treated.  And these new ultra low liquor ratio machines are very expensive.

What about using no salt at all?

There are two ways to dye fabrics without salt:  “continuous dyeing” and “cold pad batch dyeing”.  Continuous dyeing means that the dye is applied with alkali to activate the dye fixation; the fabric is then steamed for a few minutes to completely fix the dyestuff.  Cold pad batch dyeing applies the dyestuff with alkali and the fabric is simply left at room temperature for 24 hours to fix the dye.

Both of these methods don’t use salt, so the unfixed dye chemicals are easier to remove because there is no salt acting as the “glue” – and therefore less water is used.  And an additional benefit is having a lower salt content in the effluent.

So why don’t companies use this method?  Continuous dyeing requires investment in big, expensive machines that only make environmental sense if they can be filled with large orders – because they use lots of energy even during downtime.

Cold pad batch machines are relatively inexpensive to buy and run, they are highly productive and can be used for a wide range of fabrics.  Yet only 3% of knitted cotton fabric is dyed in Asia using cold pad batch machines.

Why on earth don’t these mills use cold pad batch dyeing?  I would love to hear from any mill owners who might let us know more about the economics of dyeing operations.


[1] “A Practical Guide For Responsible Sourcing”, The National Resources Defense Council (NRDC), February 2010.