Test for the harmful azo colorants in textiles Bookmark and Share

Posted by Sazid Rahman

Azo colorants are the most important class of synthetic dyes and pigments, representing 60 - 80% of all organic colorants. They are used widely in substrates such as textile fibres, leather, plastics, papers, hair, mineral oils, waxes, foodstuffs and cosmetics.

Hence azo colorants are part of our everyday colorful life, they are all around us and we could not do without them.

It allows colors with outstanding colorfastness and wide huge spectrum of colors.

Some of these dyes have the capacity to release certain aromatic amines which pose cancer risks. For this reason, the European Union has laid down legislation to prevent exposure to these hazardous amines. This implies that azo dyes containing aromatic amines can no longer be used to dye textile and leather products that may come into contact with the skin.

Please note that all the different parts of the finished product should be tested, and if there are several colors involved, it is not necessary to test them all separately. Only if the general test proves that there are banned azo dyes in the product, more tests will be needed.

Restrictions

EU legislation specifically prohibits the use of the 22 aromatic amines included in the next table in a concentration above the threshold limit of 30 ppm(mg/kg) (detection limit). Please note that all parts of a product should comply with this limit, and that this limit applies to each amine separately. E.g. a textile shoelace of leather footwear needs to comply with the limit of 30 ppm, as well as the leather parts of footwear. It is not allowed to take the average concentration of a certain amine in the complete product.

Table: List of aromatic amines according to the EU Directive 2002/61/EC

Sl. No.

Substance Name

CAS Number

01

Biphenyl-4-ylamin 4-aminobifenyl Xenylamine

92-67-1

02

Benzidine

92-87-5

03

4-chloro-o-toluidine

95-69-2

04

2-naphthylamine

91-59-8

05

o-aminoazotoluene

4-amino-2’,3-dimethylazobenzene

4-o-tolylazo-o-toluidine

97-56-3

06

5-nitro-o-toluidine

99-55-8

07

4-chloroaniline

106-47-8

08

4-methoxy-m-phenylenediamine

615-05-4

09

4,4'-methylenedianiline

4,4'-diaminodiphenylmethane

101-77-9

10

3,3'-dichlorobenzidine

3,3'-dichlorobiphenyl-4,4'-ylenediamine

91-94-1

11

3,3'-dimethoxybenzidine

o-dianisidine

119-90-4

12

3,3'-dimethylbenzidine

4,4'-bi-o-toluidine

119-93-7

13

4,4'-methylenedi-o-toluidine

838-88-0

14

6-methoxy-m-toluidine

p-cresidine

120-71-8

15

4,4'-methylene-bis- (2-chloro-aniline)

2,2'-dichloro-4,4'-methylenedianiline

101-14-4

16

4,4'-oxydianiline

101-80-4

17

4,4'-thiodianiline

139-65-1

18

o-toluidine

2-aminotoluene

95-53-4

19

4-methyl-m-phenylenediamine

95-80-7

20

2,4,5-trimethylaniline

137-17-7

21

o-anisidine

2-methoxyaniline

90-04-0

22

4-amino azobenzene

60-09-3


Articles covered in the EU Directive

Textile and leather products that may come into direct and prolonged contact with the human skin or oral cavity. The examples of products listed are:

• clothing, bedding, towels, hairpieces, wigs, hats, nappies and other sanitary items, sleeping bags;

• footwear, gloves, wristwatch straps, handbags, purses/wallets, briefcases, chair covers, purses worn around the neck;

• textile or leather toys and toys which include textile or leather garments;

• yarn and fabrics intended for use by the final consumer.

Test Methods:

 General Textiles: EN14362-1:2003

 Polyester: EN14362-2:2003

 Leather: CEN ISO/TS 17234:2003

 Determination of P-aminoazobenzene (4-AAB)

Chemistry of aromatic amine release

Azo dyes contain one or more nitrogen-nitrogen double bonds called azo groups in their chemical structure, see Fig. 1.

-N=N -

Fig.1: Azo group

Under reductive conditions using sodium dithionite these azo groups can be cleaved to form 2 amines, which can be schematically shown as in Fig. 2.



Fig.2: Reductive cleavage of the azo dye to form amines

A small number of the aromatic amines are classified as being carcinogenic or potentially carcinogenic to humans. Only those few azo dyes that can release these amines upon reductive cleavage are affected. It has been estimated that less than 4% of known azo dyes structures may release the corresponding amines.

False positive results
For certain dyed goods a listed amine is detected under the conditions of the analytical test even though no banned azo dye is present in the consumer good. The amine is an artifact of the test procedure, resulting from a chemical reaction other than azo cleavage. So, care should be taken that detected aromatic amines originate from azo colorants and not from other materials such as Polyurethane.

Click here to download a test report sample from ITS.

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1 comments

Industry Analysis  
September 1, 2012 at 6:02 PM

Very informative blog provides great description on Azo colorants..
Azo colorants are the most important class of synthetic dyes which allows colors with outstanding colorfastness and wide huge spectrum of colors..
keep continue sharing such interesting blog..I appreciate for this great work

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