Metals in reactive dyes for cellulose

1. Abstract

Often people ask about the metal content of Reactive dyes.The following question comes from different sources but all on the same theme,and can therefore be grouped together. They come from Reactive dyestuffsuppliers in India and Thailand, and a Cellulosic Knit Dyehouse in Turkey.

We have been asked by customers whether or not our reactivedyes contain heavy metals. To what extent can heavy metals be found in dyestuffsand to what extent are they permitted?

All major retailers must have specifications for maximumpermissible content of toxic materials in their garments. Is there anyvariation from one retailer to another? And what sort of practical maximumvalues should have no impact on human health?

2. Full Article

2.1 The Answer

There are a number of requirements or legislations which areclosely related:

• Health and Safety at Work

• Environmental Impact

• and Ethical Clothing.

So far as reactive dyes are concerned, H&S requires thatmanual operatives must not be exposed to any materials which are:

• Carcinogenic
• Mutagenic
• Toxic
• Dusty (and could lead to breathing and asthmatic and allergy problems).

Toxicity and Mutagenicity cover a wide range of properties and constituents. Heavy Metal content is just one of them. Permitted levels will varyfrom one local Health authority to another. In Italy, for example, therequirements are set by the local USSL authority, and the requirements can evenvary for neighbouring USSLs.

The requirements cover:

• the manufacture and handling of dyestuffs (and appropriate intermediates)
• dyestuff impurities produced in manufacture
• the application of dyestuffs
• the discharge of effluent resulting from the use of the dyestuffs
• compounds residual of dyed and finished textiles
• the labelling of garments on sale to consumers.

2.2. Heavy Metal content in Dyestuff

Heavy metals of concern include:

• cadmium
• lead
• copper
• nickel
• cobalt
• chromium
• chromium 6
• arsenic
• mercury
• selenium
• antimony

Some Reactive dyes contain metal complexes in their chromophores. In these the heavy metal is bonded within the chromophore. But it is possible that free metals can be produced as impurities through incomplete reaction.

Heavy metals used in this context would include:

• Copper
• Nickel
• Cobalt
• and chromium

Reactive dye examples would include:

• copper phthalocyanines (turquoise dyes)
• nickel phthalocyanines (bright green dyes)

It is also possible for dyestuffs with metal-free chromophores to contain metallic impurities, originating from the raw materials used in manufacture. Limits for the amount of metallic impurities permitted in dyestuffs are defined by ETAD and the EU Eco-label are shown in Table 1.

Table 1:

Examples of Regulations concerning Heavy Metals are available on the internet, and a typical example would be as follows:

Another possible source of heavy metals in dyestuffs comes from the use of catalysts.

Residues of mercury, copper or chromium in reactive dyestuffs are possible from the use of catalysts in the synthesis of some dye intermediates. In this respect, it is not simply the dye structure which must be considered but also the source of manufacture. The use of mercury as a catalyst has been replaced by alternatives in Japan and Europe, but continued usage of mercury has been found in dye manufacture in some developing countries. Chromium and Copper can also be used as catalysts in synthesis of dye intermediates.

2.3. Look at the Source of Supply and Not Just the claimed Structure

Taking a reactive dye simply by Colour Index number can be no guarantee of its composition.

Take CI Reactive Blue 19 as an example:

Sumifix Br Blue R (from Japan) contains < 1.0 ppm copper impurity.

Levels > 2,000 ppm have been found in some Chinese products which are claimed by CI number to be the same product.

The quality of industrial water used in manufacture is another important consideration, and potential source of metallic impurities.

2.4. Retailer Requirements

• Most retailers follow the requirements of Oeko Tex Standard 100.

• But there are some variations across the retail spectrum. Marks & Spencer do not go into fine level of detail with respect to extractable heavy metals. Nike target Cd, Cr, Pb, Ni, Hg and Sn.

• Another potential complication arises from the fact that there are three different methods of analysis available :

• Total metal content
• EN71 (Toy Standard)
• Acid Perspiration test.

Different retailers specify different methods and different limits.

2.5. Concluding Remarks

• Always check which retailer spec you are working to.

• Assume nothing (until proven) by Colour Index number alone.

Dont Let Heavy Metal Get You Down!!

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