MODULE 7 CHROMIUM VI MANAGEMENT A Practical …corporate.marksandspencer.com/documents/policy-documents/ecp... · version 1.0 marks & spencer march 2014 environmental & chemical policy

VERSION 1.0 MARKS & SPENCER MARCH 2014

ENVIRONMENTAL & CHEMICAL POLICY FOR TEXTILE PROCESSING

ECP

MODULE 7

CHROMIUM VI MANAGEMENT

A Practical Guide

VERSION 1.0

MARCH 2014


MODULE 7 ENVIRONMENTAL & CHEMICAL POLICY FOR TEXTILE PROCESSING Page 2 of 10

MODULE CONTENT

1 INTRODUCTION ........................................................................................................................................ 3

1.1 Purpose of the Module ...................................................................................................................... 3

1.2 What are the risks of chromium VI? ................................................................................................... 3

2. CHROMIUM VI MANAGEMENT: A PRACTICAL GUIDE ....................................................................... 4

2.1 Chromium tanned leather ................................................................................................................. 4

2.2 Oxidation/reduction .......................................................................................................................... 4

2.3 What can the tannery do to avoid the formation of chromium VI during processing?.......................5

2.3.1 Chemical purchasing .......................................................................................... 5 2.3.2 The influence of fats on the conversion of chromium III to chromium VI ........................ 5 2.3.3 The effect of pH ................................................................................................. 6 2.3.4 Free chromium .................................................................................................. 6 2.3.5 Do not use oxidative chemicals ............................................................................. 6 2.3.6 Addition of proprietary chemicals .......................................................................... 6 2.3.7 Transportation and storage of leathers ................................................................... 7 2.3.8 Support and advice ............................................................................................ 7 2.3.9 Checklist for tanners ........................................................................................... 8

3. OTHER COMMON TANNAGES ............................................................................................................... 9

3.1 Aldehyde tanning (wet white) ......................................................................................... 9

3.2 Vegetable tanning ....................................................................................................... 9 4. ENVIRONMENTAL CONSIDERATIONS .............................................................................. 10 4.1 Aldehydes ........................................................................................................................................ 10 4.2 Vegetable tanning ........................................................................................................................... 10



1. INTRODUCTION

1.1 Purpose of the Module

Chromium VI (or hexavalent chromium) has been on the Marks & Spencer Restricted

Substances List for many years because of concerns over its carcinogenic, dermatitic and

allergenic properties. Chromium dyeing of wool and other protein fibres has long been prohibited

for Marks & Spencer products.

Chromium is widely used in the tanning of leather, and there is a risk of the formation of

chromium VI unless the process is managed well.

This practical guide has been created using the British Leather Council‟s (BLC) industry

knowledge, experience and a range of reference documents, including Life Cycle Assessments

(LCAs) of chromium and alternative aldehyde and vegetable tannages.

This Module is intended to provide a practical guide to the management and minimisation of

chromium VI in leather supply. The best practices described here are recommended for all

tanneries supplying material for Marks & Spencer.

1.2 What are the risks of chromium VI?

Extensive epidemiological studies have shown that the inhalation of chromium(VI) may cause

cancer of the lungs, nose and sinuses, while handling chromium VI can cause severe skin

irritation leading to allergic contact dermatitis.

In response to these risks, premium leather tanners and the major product manufacturing

brands have voluntarily worked to reduce the incidence of chromium VI to below the official test

method detection limit of 3ppm.

Recently, the European Commission decided to enforce this standard by developing regulations

that will prohibit chromium VI in leather any leather product that may come into contact with the

skin. The European prohibition will be implemented in 2014 under Annex XVII of REACH.



2. CHROMIUM VI MANAGEMENT: A PRACTICAL GUIDE

2.1 Chromium tanned leather

The bulk of leather produced around the world (85% approximately) is tanned with basic

chromium sulphate (chromium powder) and the resulting leather is known as chromium tanned.

The chromium used in tanning is in the form of chromium III which cross links the carboxyl side

chains. This tannage is typically more efficient that other tannages, meaning less use of

chemicals such as dyes, retanning agents, polymers, fatliquors and other auxiliaries.

A typical leather used for shoes, clothing, sofas and leather goods will contain around 3-5%

chromium III.

There are two types or forms of chromium that can be found in leather. The first is the tanning

chemical described above – chromium III. The second that can be found in very low levels and

is a restricted substance is chromium VI.

2.2 Oxidation / reduction

In the case of leather, only a small quantity of the chemical present may be oxidised – where only a very small part of the chromium III is oxidised to chromium VI

Chromium III is oxidised to chromium VI

Chromium VI is reduced chromium III

The factors that influence this are the presence of “oxidising agents” (either air or chemicals),

the chemical conditions eg pH and temperature (higher temperature increases the chance of

chemical reactions) and the tanning process / process chemicals used.

The reason leathers can pass the chromium VI test at source and fail later may be due to

any of these issues, so they should all be controlled.



2.3 What can the tannery do to avoid the formation of chromium VI in leather

during processing?

The following list is intended to show the tannery what to do to avoid the possible formation of

chromium VI in leather.

It must be noted that there is no single item or step that will avoid the formation of

chromium VI in leather. The factors listed below should be taken into account to give the

highest level of assurance that leathers will not form in situ chromium VI.

Buy chrome tannaging salts from reputable suppliers

Check the fat content of leathers and make up of fatliqours used

Manage the pH of the process

Manage the free chrome content

Do not use oxidising chemicals

Use chemicals that will minimise the risk of chrome VI

Understand the risks associated with transportation

2.3.1 Chemical purchasing

When buying chromium tanning powder, make sure that the supplier is capable of providing

guaranteed chromium VI free chemicals.

BLC recommend, for example, Lanxess and Elementis.

This is the main point to consider but there may be other chemicals used in the process that

contain chromium (a few types of retanning agents). All materials containing chromium should

be guaranteed in writing to be chromium VI free by the supplier.

2.3.2 The influence of fats on the conversion of chromium III to chromium VI

Some fats can influence the chemical change from chromium III to VI. These are naturally

occurring fats and are of the chemical type known as “unsaturated fats”. These fats contain

double bonds and these double bonds can make it easier for the chromium to convert to

chromium VI. There are two things to consider:

i) If the raw material has a high level of natural grease it is important to carry out the degreasing

process correctly.

This applies particularly to greasy skins such as pigskin and lambskins or intensively fed cattle.

A grease content of less than 3% is desirable.

ii) If fatliqours or finishing oils are made using natural oils that contain “unsaturated fats” then the

risk of chromium VI formation is increased.



Check that the oils used in fatliqours do not contain unsaturated fats, and check that finishing

chemicals used in oily/ waxy products do not contain unsaturated fats. Non-oxidising synthetic

fats are available as replacements.

2.3.3 The effect of pH

High pH can affect the formation of chromium VI. The normal pH for finished leather is 3.5 to

4.0, which is ideal.

The part of the process to consider is the retanning process. Typical processes take the wet

blue (chromium tanned leather) and reduce the acidity (by adding alkali) to allow the retanning /

fatliquoring and dyeing chemicals to penetrate the leather.

Sometimes ammonia solution (NH4OH) , and occasionally ammonium salts eg ammonium

bicarbonate (NH4HCO3), will be used to do this. The use of these chemicals can create a high

pH (the processing water can go above pH 8), and this is not recommended.

The pH of the processing water should be kept below pH 6.5. Do not use ammonia in the

retanning process. Sodium bicarbonate is a preferred processing salt, but pH control still

remains critical and needs to be maintained below pH 6.5.

2.3.4 Free chromium

Not all the chromium in the leather is fixed to the hide or skin fibre - this is normal. A small

quantity is free or not fixed.

This free chromium should be kept to a low level to reduce the risk of chromium VI formation.

There are some regulatory standards (for example, EN71-3) where limits for the amount of

extractable chromium are set.

This can be achieved through washing the leather well after the neutralisation step, and after

the waterproofing process, where chromium salts may be added at the end of the process to

improve the performance of water resistant fatliqours.

2.3.5 Do not use oxidative chemicals

For most tanneries, the addition of chemicals that are oxidative (ie can oxidise other chemicals)

is very rare. Such chemicals might be used in bleaching processes. Do not use these

chemicals on chromium tanned leathers.

2.3.6 Addition of proprietary chemicals

Some chemicals used in the retanning process can help prevent the formation of chromium VI.

These are usually vegetable tannins - eg tara extract has been reported as being good for this –

but most vegetable extracts used in retanning will assist in reducing the risk.

Some chemical companies offer specific chemicals that can be incorporated into, or added at

the end of, the retanning process. These will increase the process cost slightly but do add an

extra layer of insurance.



2.3.7 Transportation or storage of leathers

In the event that leathers have not been made using the best practice as described above then

storage and shipping conditions can cause the formation of chrome VI.

Under conditions of low humidity, high temperature and possibly direct sunlight, leathers that

have not been tanned using best practice have shown the propensity to convert from

chrome III to chrome VI. It should be stressed that leathers that have been made using the

advice provided in this document should have a low risk of conversion to chrome VI.

2.3.8 Support and advice

Members of BLC can access free advice and support on this issue when needed. Expert

chrome VI and chrome VI ageing tests are also available at discounted rates. For further

information please contact:

[email protected], [email protected], [email protected]

BLC Leather Technology Centre Ltd

Kings Park Road

Moulton Park

Northampton

NN14 4XP

Tel - 44 (0) 1604 679999, Fax - 44 (0) 1604 679998

www.blcleathertech.com, www.blc-chemicaltesting.com



2.3.9 Checklist for Tanners

The checklist is recommended to ensure that the best practices described above

are being followed.

TASK DONE

1 Check that your chromium-containing chemicals do not contain chromium

VI by obtaining a signed and dated guarantee from your suppliers. It is

recommended that this is renewed annually.

2 Check that your degreasing process is effective. A target of less than 3%

residual grease is ideal

3 Check that you are not using unsaturated oils in your fatliquoring or

finishing oils. If unsure, check with your supplier on this.

4 Check that ammonia or ammonium salts are not used in the

neutralisation process.

5 Check that the pH of the neutralisation and retanning processes is below

6.5

6 Check that the washing process is effective, and that the level of free

chromium is low. Levels below 500ppm to the BSENISO17072-1 test

method are recommended.

7 Check that you are not using oxidative chemicals in the retanning and

dyeing processes. If unsure, check with your supplier on this.



3. OTHER COMMON TANNAGES

A simple overview of the two other main tannages in leather making has been provided for

information.

3.1 Aldehyde tanning (wet white)

Aldehyde-based tannages are often referred to as „wet white‟ owing to the pale colour of the

tanned, undyed intermediate.

Aldehydes are a group of organic chemicals with excellent crosslinking capabilities. Modified

glutaraldehyde is the most common chemical used in commercial chrome-free tannage

systems.

The chemical bonds that aldehydes form with the amine side chains of the collagen protein

during the tanning process are different from those formed with chromium, which reacts with

carboxyl side chains. This means that there are fewer available sites for dye molecules to bond

which limit the range of bright, vibrant shades that can be produced.

The thermal stability of 75°C- 80°C of a wet white leather is less than for chrome tanned leather,

which limits its use in high temperature product manufacturing processes such as shoe lasting.

Because of the performance and colour limitations, this type of leather is rarely used outside the

automotive industry.

3.2 Vegetable tanning

This is the process of using tannins from plant extracts (usually the bark of trees) to tan the

leather. It is a traditional method and results in a very specific type of leather which has brown

colour tones used, for example, for leather soles. It is difficult to dye vegetable tanned leather to

colours outside the natural palette.

The chemistry is very different to both the chrome and aldehyde tanning processes. The

vegetable molecules are phenolic in nature, and very large when compared to chrome and

aldehydes. The process of collagen stabilisation is through a chemical filling reaction which can

take significant time due to the slow penetration of the vegetable tannin molecules.

The colour and performance limitations tend to limit this tannage type to heavier, less flexible

products such as soling, belting and larger leather goods.

Vegetable tanning extracts can be used in combination with other tanning agents (chrome and

aldehyde) to change the properties of the resulting leather.



4. ENVIRONMENTAL CONSIDERATIONS

4.1 Aldehydes

Effluent containing aldehydes can contribute to water based pollution through eutrophication

(the deterioration of quality of the watercourse).

Also, this tannage is typically much less efficient than chrome tanning, requiring significantly

more chemicals such as dyes, retanning agents, polymers, fatliquors and other auxillaries.

4.2 Vegetable tanning

Effluent loadings can be high, and generally vegetable tanned leather has poor biodegradability

due to the filling action of the tannage preventing microbial penetration.

Documents

MODULE 7 CHROMIUM VI MANAGEMENT A Practical …corporate.marksandspencer.com/documents/policy-documents/ecp... · version 1.0 marks & spencer march 2014 environmental & chemical policy