Why Leather Manufacturers Should Test the Chemical Properties of Leather

Testing the chemical properties of leather determines the quality and durability of leather goods, and lets you know whether your finished product meets the legal trading requirements for the international market.

We’re going to look at how manufacturers benefit by performing chemical and physical tests on leather, as well as at some common lab testing methods used to ensure that leather products are fit for the consumer market.

How Do Manufacturers Benefit from Testing Leather Products?

• Protect your brand with quality assurance and customer confidence
• Ensure you comply with REACH regulations
• Earn an Ecolabel
• Be prepared for risk assessment

Leather tanneries and manufacturers use a wide variety of methods to give leather a certain look and feel, depending on the hide’s ultimate application. Some of those treatments are detrimental to the quality and durability of the leather, but could go unnoticed by the manufacturer unless the material is professionally tested before shipping to stores.

Under EU trade regulations, leather good manufacturers must be able to prove their products are safe for customers and the environment. Testing the chemical properties of leather products will ensure compliance, as well as the right to use the Ecolabel.

Chemical Tests for Toxic Dyes in Leather

The leather dyeing process uses azo colorants that can break down to produce toxic chemicals known as aromatic amines. These carcinogens are tightly regulated by the EU and other nations, so manufacturers using leather must be confident their products don’t contain the banned substances.

What Are The Legal Limits For Chemical Properties of Leather?

Under the EU’s REACH regulations, the restricted chemicals for leather products are specified in Appendix 10.

Annex XVII defines the detection limit of 30 mg/kg for each amine in leather. Products tested as being within the EU limit of 30 mg/kg can acquire an Ecolabel. Meanwhile, China’s regulations set a limit of 20 mg/kg for the toxic substances.

Testing Methods

Two standard chemical tests are used to detect restricted chemicals in leather products by leather extraction and chemical reaction:

• EN ISO 17234-1:2010, Part 1: Determination of certain aromatic amines derived from azo colorants
• EN ISO 17234-2:2011, Part 2: Determination of 4-aminoazobenzene

Testing Leather for pH Value

The measure of leather’s acidity or alkalinity tells you about the durability of your finished product. The pH value can also indicate the quality of the tanning or dyeing process used.

There are two standard methods for testing the pH of leather. The tests can be done in a solution or on the material itself.

What Are the Testing Methods?

Using damp indicator paper on the product is non-destructive and gives an approximate result. A more accurate method involves cutting the leather and testing it using the EN ISO 4045:2008 standard.

The pH value is measured on the a logarithmic scale of 0-14. Actual values can be less than 0 and higher than 14, but as a rule of thumb, the following ranges apply:

Acidic: pH 1-7

Neutral: pH 7

Alkaline: pH 8 - 14

What Do The Test Results Mean?

Chromium-tanned leather is quite acidic: pH 3.2 - 5.5, which is normal. However, higher levels of acidity could indicate that low-quality tanning procedures were used, and the leather will degrade prematurely.

By contrast, an extremely alkaline result could indicate that dye fixation was performed poorly, and the leather’s color won’t last a long time.

Testing Leather for Chromium VI compounds

Chromium (VI) is a chemical produced during the leather tanning process. As it is known to cause severe allergic reactions on contact with skin, leather products placed on the EU market must not contain chromium VI in concentrations over 3 mg/kg.

What Are the Testing Methods?

EN ISO 17075 Chemical Determination of Chromium(VI) Content in Leather lists various extraction methods involving chemical solutions that can be used for the tests. The results are defined as colorimetric or chromatographic.

What Do the Test Results Mean?

A result of pH 7.5 - 8 indicates the presence of chromium(VI), which should not be equal to or exceed 3 milligrams per kilogram (0.0003%) of the total dry weight of the leather.

Physical Tests for Leather

The durability and quality of leather products is evaluated in physical tests that emulate how the finished product will be used by the end user. Here are some examples of the tests conducted at QIMA labs. Note that these tests do not apply to wet blue leather.

• Resistance to Wetting (spray test)
  • A qualitative evaluation of the leather surface or coating’s repellency to water.
• Adhesive Properties of Finishing
  • Tests the tendency of cloth to adhere to finished leather.
• Tear Load Test
  • Measures the load required to tear leather through two holes in the test specimen. Also used to determine the stitch tearing resistance of leather using a double hole tear.
• Tensile Strength Test
  • Gives a reliable indication of the quality of the leather for development, control, specification acceptance, and service evaluation of leather. Uses a 12.7-mm wide specimen to test the load required to rupture.
• Colorfastness Test
  • Intended specifically for colored leathers, with or without surface coating, this test determines how well leathers withstand frequent laundering and whether staining of adjacent textile materials occurs.
• Relative Stiffness Test
  • A torsional apparatus is used to measure the relative stiffness of gloving leathers

How Can QIMA Help You?

QIMA provides a full range of professional chemical and physical tests for leather to help clients ensure their products meet international compliance requirements and protect their brands.

We operate three ISO accredited in-house laboratories located in the US, Hong Kong and China. Tests can also be conducted at labs that are part of our extensive worldwide network of vetted associates.

Whether you are a manufacturer or supplier of leather goods, we are here to help give you transparent and rapid results that will save you time and money, and give you additional peace of mind with our expert quality control services.

Contact us today for an instant quotation or for more information on specific tests and quality assurance programs.