Dyes – synthetic and “natural” part 2

8 09 2009

After last week’s discussion, I think you understand why it’s important to remember that whether one uses natural or synthetic dyes a major concern is not only what type of dye the dyer uses, but whether the dyer has water treatment in place!    That’s because neither natural dyes nor synthetic dyes (plus the associated mordants, etc., used in the dyeing process) should ever be returned to the local waterways.  Even benign chemicals like potato starch will kill fish and other aquatic life because they encourage the growth of algae which depletes all available oxygen, among other issues (known as BOD or Biological Oxygen Demand).  And some so called “natural” dyes are themselves toxic.  So be sure to buy fabric from a supplier who has water treatment in place.

The other part of the equation is how the dye is formulated, because if toxic chemicals are used in the formulation then most of these chemicals remain in the fabric.  If synthetic chemical dyestuffs contain chemicals which can poison us, then the use of natural dyes seems to many people to be a safer alternative.  Additionally, the  question of natural dyes remains a romantic notion and is aesthetically pleasing to many people.  So what are natural dyes?

picture-1

Natural dyes are dyes derived from animal or plant material without any synthetic chemical treatment. They are obtained from sources like flowers, leaves, insects, bark roots and even minerals. The most common natural dyes (all from plants except cochineal, from an insect) are:

  • Madder
  • Cutch
  • Cochineal
  • Weld
  • Indigo

Contrary to popular opinion, natural dyes are  neither necessarily safer nor more ecologically sound than synthetic dyes:

1)      “Natural” does not mean safe – they are not synonyms.  Mushrooms can be poisonous. Arsenic is perfectly “natural,” meaning occurring naturally in nature.  Some natural dyes are almost perfectly safe; others are quite toxic. Some synthetic dyes are safe even to eat; others are too toxic to bring into your home.  A few  natural dyes, such as logwood, which contains hematein and hematoxlyn, are themselves significantly poisonous – they’re toxic whether inhaled, absored through the skin or ingested.  Indigo is a skin, eye and respiratory system irritant.  Proper health and safety equipment must be supplied when working with any dyestuffs and workers need to be trained properly so they treat the dyes and mordants with respect.

2)       Just because dyes are natural does not mean that they are sustainably or organically raised or harvested.   Pesticides, herbicides, defoliants, etc., may have been used on the crop or perhaps the crop itself may be genetically modified or irrigated unsustainably.   Extraction of madder is often done by dissolving the roots in sulphuric acid.  Sodium hydroxide is needed to produce natural indigo dye.[1]

3)      The physical amount of natural dyestuff needed to color fabric is much greater than that required by synthetic dyestuffs.  The amounts needed vary by dyestuff used and fiber type, but as an example, we have summarized the usage from an article in the Clothing and Textiles Research Journal[2]:

To dye 2 yards of upholstery weight fabric:

ounces

synthetic dye

0.7

freshly picked leaves

160 – 320

To dye 2 lbs of wool using:

ounces

low range

high range

Brazilwood chips

2

12

cutch

2

4

madder

6

16

To dye 5,000 yards of cotton fabric per month:

pounds

low range

high range

synthetic dyestuff

109

109

madder

938

2500

freshly picked leaves

25,000

50,000

4)      The quantity of dyestuff required is not a trivial consideration as the quantity of natural dyes that would be required to fulfill commercial dye demand would overwhelm  resources.  Some dyestuffs come from forest products, depleting valuable natural resources. Some can be wild harvested, but the population of creatures or plants required to fill human dye demand could not be supplied from current stocks of plants or animals.  (The third class of natural dyes, minerals, are most likely less objectionable in this regard.)  According to Ecotextile News (April 2009), it has been calculated that even if 2/3 of the world’s agricultural land was used to grow only natural dyes, there would scarcely be enough produced to dye the current volume of textiles.

5)    Natural dyes normally require much greater energy in the dyeing process as they usually require high temperature baths for longer periods of time than the optimized synthetic dyes; they also require a copious amount of the dyestuff itself as mentioned above,  and water.

6)      Natural dyes are less permanent, often requiring the use of mordants to affix the color molecule to the fiber.     Dye can sit on top of the fabric and look fine at first, but it easily washes out or fades to light very quickly.  The mordant creates a link between the dyestuff and the fiber – it remains in the fiber permanently, holding the dye.   That’s why cottons from India (where they had discovered mordants)  in the 18th century became so popular.  The mordant allows a dye to attain acceptable wash fastness. Some natural mordants exist, like pomegranate, salt and alum, but the more effective mordants are heavy metals (lead, mercury, copper, et al), which have unsavory toxicity profiles (see last week’s post).  Each different metal used as a mordant produces a different range of colors for each dye.

7)      A primary consideration in textile manufacture is that the color possibilities for natural dyes are far more limited than synthetics.   The color of any natural dye may be easily copied by mixing synthetic dyes, but the reverse is not true:  many colors are not easily obtained with natural dyes. The non-reproduction of some shades is a drawback in commercial production. The variability of the color makes the use of natural dyes difficult in any manufacturing situation where replicability of color is important.

The use of natural dyes will almost certainly make the fabric more expensive, firstly, because large quantities of land and raw material are required to obtain the same depth of color that could be obtained from a synthetic dye – although the amount of energy needed to extract oil from the ground and convert it into useable chemicals for synthetic dyestuff is probably very high, although I have not seen studies regarding this.   Also, both growing and applying the dyes are time-consuming –  natural dyes take typically at least twice as long as synthetic dyes to get a result, and using natural dyes on vegetable fabric will be more costly still, as vegetable fibers are more resistant to taking up good strong colors than animal fibers are, and slower, longer treatments often give better results.  So the question becomes one of social responsibility also – is it responsible to use land to produce ultra low yield dye crops for the benefit of those wealthy enough to afford them?

And then there’s the problem of availability: with perhaps the exception of indigo, the most common dyeing crop, crops grown for are dye are almost non-existent. A manufacturer would have extreme difficulty making vast improvements to the environmental impacts of their dyeing processes because the supply, and the infrastructure to apply it, doesn’t exist on an industrial scale.

And yet …  many people appreciate the slight variations caused by natural human methods and feel that it adds to the beauty and interest of a fabric.  The art becomes more important than the science.   They believe that there is a richness and depth to some of these natural dyes that a synthetic just cannot match.   A company at the forefront of using vegetable dyes is Rubia Pigmenta Naturalia .   They produce a dyestuff made entirely from the madder plant, which is able to cover 40% of the color spectrum.  They have completed a long term research program to increase efficienty, yield and handling of natural colors on wool;  the dye is exceptionally stable, homogenous, colorfast and grown and processed to organic standards.  In 2008, Rubia Pigmenta Naturalia was approved for use in Global Organic Textile Standard (GOTS) fabrics.

Another source of information is Natural Dyes International, which is a nonprofit organization  to research  natural dyes,  share information and eduate the public about the history of these dyestuffs.

Researchers at the University of Leeds are investigating new technologies using both natural and synthetic materials that may revolutionize the dyeing of textiles.  The first, a process that creates colored polymers inside fibers via a catalytic dye process,  has the potential to reduce the dependence on petroleum as a starting point for synthetic dyes, be more cost effective and lower environmental impacts.  The second is a natural/synthetic hybrid using a gene modification.  As Ecotextile News says,  “Nature alone can’t meet the technical or volume demands of the modern consumer, and petroleum technology isn’t sustainable.”  (But a genetically modified dyestuff?  Yet another blog posting, due in a few weeks.)

Having weighted all the options and looked at costs and prices, we decided that a fully optimized GOTS compliant synthetic dyestuff, applied in a facility that follows the GOTS water treatment standards, is the best choice for O Ecotextiles fabrics at this point in time.  We are always hoping that the industry will develop better choices as time goes by, because as mentioned in the previous posts, the GOTS and Oeko Tex requirements do not prohibit the chemicals that are so egregious in terms of toxicity, they just establish threshhold limits for these chemicals.  Again, the Europeans are at the forefront, with their REACH legislation which mandates finding replacements for up to 2000 of the worst chemical offenders by a certain date.  We’ll all benefit from their strong and forward-thinking leadership.


[1]http://greencottonblog.com/2008/06/natural-dyes-are-they-an-alternative-to-synthetics/

[2] Chen and Burns, “Environmental Analysis of Textile Products”, Clothing and Textiles Research Journal, 2006; 24; 248.





Dyes – synthetic and “natural”

1 09 2009

hand_dyed_yarn_8i98

I thought we’d take a look at the dyeing process because so many people ask if we use “natural” dyes.  The answer is no, we don’t (although we’re not entirely objecting to natural dyes), and I hope the next two blogs will explain our position!  Let’s first take a look at what makes the dyes (and how they are applied) an area of concern.

Dyeing cloth is one of our oldest industries;  people used natural products found around them to change the color of the fibers used to make their cloth  – things like leaves, berries, or roots.   The first synthetic dye was created in 1856.  Today the use of natural dyes on a commercial scale has almost disappeared (except for a resurgence in the craft market) in favor of the newer synthetic dyes.  The production of synthetic chemical dyestuffs has become big business, but unfortunately the production and use of these synthetic dyes is one of the world’s most polluting industries.  Conventional synthetic dyes present health risks to those working with them and to those who wear them, as well as damaging the environment in a number of ways.  Why?

Dyes are compounds that can be dissolved in solvents, usually water.  The process of dyeing cloth uses a great quantity of water – according to the United States EPA, it takes an average of 5 – 35 gallons of water for every pound of finished fabric.  That translates into 125 – 875 gallons of water to dye 25 yards of fabric – enough to cover one sofa![1]

The dyes in solution are absorbed by the fibers.  The process of transferring the dye from the water to the fiber is called exhaustion or “fixation rate”, with 100% exhaustion meaning there is no dye left in the dyebath solution.   Most conventional dyes have an exhaustion rate of 80%, meaning the dyestuff which is not affixed to the fiber is flushed into our rivers with the spent process water.  Each year the global textile industry discharges 40,000 – 50,000 tons of dye into our rivers, and more than 200,000 tons of salt.[2]

One of the most pressing issues today is the lack of fresh drinking water, and as one of the most polluting industries, textiles – and especially the dyeing of textiles – is responsible for many instances of pollution making fresh water undrinkable.  In the worst cases, communities have to use polluted water to drink, wash clothes, bathe and irrigate crops and the toxins they’re exposed to can have catastrophic effects.  Even in those instances where water treatment is in place, toxic sludge is a byproduct of the process.  Often  sludge is sent to the landfill, but the toxicity of the sludge remains – containing, among others,  heavy metals, gypsum, malachite green (identified by the U.S. Food and Drug Administration as a priority chemical for carcinogenicity testing).

pink-sewage-300_tcm18-156872

The 40,000 to 50,000 tons of  synthetic dyestuffs expelled into our rivers are complex chemical formulations containing some things that are very toxic to us,  such as heavy metals (like lead, mercury, chromium, zinc, cobalt and copper), benzene and formaldehyde.  Many certifications, such as the new Global Organic Textile Standard and Oeko-Tex, restricts the kinds of chemicals allowed in certified products.  For example, GOTS restricts amine releasing AZO dyes and disperse dyes (must be <30 mg/kg); chromium, cobalt, copper, nickel, mercury, lead, antimony and arsenic are all restricted (rather than prohibited as many people believe).  So the dye formulation means a lot when you’re evaluating the eco credentials of a fabric – but almost never will you be able to find out what dye was used in any  particular fabric.                                                                                                              Copyright: Jucheng Hu

In addition to the formulation, there are requirements that dyestuffs must meet regarding oral toxicity, aquatic toxicity, biodegradability, eliminability and bi-accumulation in fatty tissues. The GOTS details are on their website: www.global-standard.org. Some dyestuff producers advertise that they have a dye group that meets these standards, such as Huntsman and Clariant.  So the formulation of dyes used makes a big difference – look for dyestuffs that have been certified by a third party, such as GOTS.

Remember that if the average exhaustion rate is 80% for most dyes (i.e., that 20% of the dyestuff is expelled with the wastewater) then that means that 80% of the dyestuff remains in the fabric!  In other words, those toxic chemicals remain in the fabrics you bring into your homes.  What do I mean by “toxic” – if you can stand it, I’ll give a short synopsis of the effects some of these chemicals found in many dyestuffs have on us:

  • Mercury:  Easily absorbed thru the skin or inhalation of dust which contains residues; effects the immune system, alters genetic and enzyme systems, damages the nervous system.  Particularly damaging to developing embryos, which are 5 to 10 times more sensitive than adults.
  • Lead: Easily absorbed thru the skin or inhalation of dust which contains residues. Impacts nervous system.   Even low levels of lead can reduce IQ, stunt growth and cause behavior problems.
  • Chromium:  Necessary for insulin activity and an essential trace metal; at toxic levels it causes squamous cell carcinoma of the lung.
  • Copper:  Fatigue, insomnia, osteoporosis, heart disease, cancer, migraine headaches, seizures. Mental disorders include depression, anxiety, mood swings, phobias, panic attacks and attention deficit disorders.
  • Cadmium:  Extremely toxic to humans because of its inhibition of various enzyme systems; primary target organ is the kidney; but also causes lung cancer ; also causes testicular damage and male sterility. Plants readily absorb cadmium from the soil so it easily enters food chain. Chronic exposure is associated with renal disease.
  • Sodium chloride (salt): not toxic in small doses (thankfully for me and my salt addiction), but the industry uses this in such high volumes it becomes an environmental hazard; an organochlorine (the class of organochlorines are very stable (i.e. does not break down into other compounds) and they bioaccumulate; 177 different organochlorines have been found in the  average population in Canada and the US.  Each person has a unique level at which this build-up becomes critical and triggers a wide range of health problems.)  Well known effects of chronic organochlorine contamination include hormonal disruption, infertility and lowered sperm counts, immune system suppression, learning disabilities, behavioral changes, and damage to the skin, liver and kidneys. Newborns, infants, children, childbearing women and the elderly are even more vulnerable to these health impacts.
  • Toluene:  affects the central nervous system; symptoms range from slight drowsiness, fatigue and headaches, to irritation of the respiratory tract,  mental confusion and incoordination; higher concentrations can result in unconsciousness and death.  Prolonged contact can cause dermatitis.  Teratogenic, embryotoxic.
  • Benzene:  Highly carcinogenic, linked to all types of leukemia but believed to cause the rarer forms (acute myelogenous leukemis (AML) and acute lymphocytic leukemia (ALL); effects the bone marrow and decrease of red blood cells, leading to anemia, excessive bleeding and/or immune system disfunction. Low levels cause rapid heart rate, dizziness, headaches, tremors, confusion.  Easily absorbed by skin

Better Thinking Ltd., a UK based organization, took a look at the dyes used in the industry and what they do to us and our environment.  They published their findings in a paper called “Dyeing for a Change” which explains the various synthetic dyes available and how they’re used.  (Click here to read about it.)

There are several classes of dyes:

  1. Direct dyes:  given this name because they color the fibers “directly” and eliminates the need for a mordant (the chemical fixing agent lots of dyes need).  Azo dyes are a type of direct dye made from a nitrogen compound; azo dyes are known to give off a range of carcinogenic particles and have been banned in many places, including the EU.  Effluent contains 5 – 20% of original dyestuff, plus salt and dye fixing agents.
  2. Vat dyes:  these dyes need a powerful reducing agent, such as alkali, to make them soluble.  Expensive and complicated to use, effluent contains 5 – 20% of residual dyestuffs, plus reducing agents, oxidizing agents, detergents and salts.
  3. Sulphur dyes:  90% of all sulphur dyes contain sodium sulphide, which endangers life and alters DNA, corrodes sewage systems, damages treatment works and leads to high pH and unpleasant odors.  Effluent contains 30 – 40% of the dyestuff plus alkalis and salt.
  4. Reactive dyes:  these dyes bond directly with the fibers, rather than merely remaining as an independent chemical entity within the fiber.  Applied with relatively cool water (saving energy) and

Of all the classes of synthetic dyes, a subset of  “reactive” dyes (called “low impact fiber reactive”) seems to be the best environmental choice.  As “Dyeing for a Change” explains:

Low-impact reactive dyes are usually defined as “low impact” because of the supposed lower fixation rate – however, these dyes have a fixation rate of at least 70%, which still leaves much room for improvement.  What does make them “low impact” and classified by the EU as eco-friendly:   they have been formulated to contain no heavy metals or other known toxic substances, and do not need mordants. The high cost of this dye becomes an environmental advantage, as it is cheaper to reclaim dye from the effluent rather than discharge it all and start from scratch. The water can also be recycled. The dye cycle is shorter than it is for other dye processes, meaning less water, salt and chemicals are needed. The entire process normally occurs at a pH of around 7.0, meaning no acids or alkalis need to be added to the water.

However, there are still disadvantages: like other environmentally damaging dyes, these dyes are made from synthetic petrochemicals. The process requires very high concentrations of salt (20%-80% of the weight of the goods dyed), alkali and water. Even if the unfixed dye is reclaimed, the effluent from this process can still contain high concentrations of salts, surfactants and defoamers, and is strongly alkaline. It’s also quite expensive, whereas conventional dye is cheap. This process’ effluent normally contains salt, alkali, detergent and between 20% to 50% of dye used. As reactive dyes currently make up 50% of world dye consumption, more knowledge on how to improve upon this method is needed.

Fortunately, research is being undertaken in this area, and a number of companies have produced products that improve on its impacts. It’s been found that, by pre-treating cotton with 120g of phosphate buffer per kg of fabric, no salt or alkali is needed in the dyeing process as the process can occur at a neutral pH. It also means the amount of water required can be halved and the whole dyeing process can be significantly reduced, presenting additional benefits in the form of cost savings. Compared to the other chemicals used to dye fabric the conventional way, this is a relatively low concentration, and its high exhaustion value means the effluent would only contain it in small  proportions, making it a greener alternative.  And British scientists have developed a way to use algae (called diatoms) to color the fabric – eliminating dyes entirely![3]

So you see why water treatment is critical – even if a dyestuff has a rather benign chemical formulation, the associated salts, defoamers and fixing agents must be dealt with.   We chose low impact fiber reactive GOTS approved dyestuffs for our fabrics – and we made sure that all wastewater is treated adequately before release.  But that’s not good enough – partly because there is still the question of the sludge created during the process and partly because we need to make sure that ALL process inputs have a benign chemical profile.

Tune in next week, when the subject will be “natural” dyes  – hopefully the discussion will clear up our thinking on synthetic vs. natural dyes.


[1]“Analysis of the Potential Benefits of Recycled Water Use in Dye Houses”, Water 3 Engineering, Inc., April 2005.

[2] Dyeing for a Change, page 4

[3] Madrigal, Alexis, “How Pond Scum Could Lead to Eco-Friendly Fabric and Paint”, Wired magazine, 10.11.07