ASTM D2810-18 Standard Test Method for Leather pH Value

The "ASTM D2810-18 Standard Test Method for Leather pH Value" standard developed by the American Society for Testing and Materials (ASTM) describes a test method for determining the pH value of all leather types. This test method is not applicable to wet blue or wet white.

For the purposes of this standard, the following terms and definitions apply:

• The pH of a solution is defined as the negative logarithm of the hydrogen ion activity. A solution with a pH of 7 is neutral at 24 degrees Celsius. Lower numbers indicate increasing acidity, and higher numbers indicate increasing alkalinity.
• The pH difference figure (delta pH) expresses the difference between the pH value of a solution and its tenfold dilution.

This test method is designed to measure the pH value of a distilled water extract of leather. The calculated value is considered a measure of the acidity or alkalinity of the leather. Excessive acidity or alkalinity may have a detrimental effect on the ageing properties of the leather. This test method is suitable for the development, control and service evaluation of leather.

If the leather contains excessive amounts of oil or grease or has been treated with a material to achieve water repellency, wettability and therefore removability may be affected. If the sample is difficult or impossible to wet, it can be treated by any of the following procedures:

• A vacuum may be used to ensure wetting.
• It is mixed with the required amount of water in a disintegrator for 1 minute.
• The weighed sample is extracted with a fat solvent in a Soxhlet apparatus for 5 hours. The Soxhlet apparatus is designed to extract fat from a solid sample, but can be used in any case where it is difficult to extract a compound from a solid. The sample is allowed to aerate until all the solvent has evaporated, then proceed as described in this standard.

The main equipment used in these tests includes:

• Electronic pH meter with a suitable electrode (this device must have an accuracy of at least 0,01 pH units and a repeatability of 0,05 pH units).
• Analytical balance (must be accurate to 0,01 g or greater).

The reagents used in these tests are:

• Purity of reagents: Reagent grade chemicals should be used in all tests. Unless otherwise specified, all reagents are intended to conform to the specifications of the American Chemical Society Committee on Analytical Reagents, where such specifications exist. Other grades may be used, provided it can be assured that the reagent is of sufficiently high purity to permit its use without diminishing the accuracy of the determination.
• Purity of water: Unless otherwise stated, the term water shall be understood to mean distilled water or water of equal purity. Distilled water shall have a pH value of not less than 5,5 or more than 7,0 and shall give a residue of not more than 100 mg when 0,5 mL is evaporated and dried in a platinum dish.
• Standard pH solutions:
  • Alkaline phosphate buffer solution: Dissolve 1,42 g of anhydrous disodium hydrogen phosphate in 100 mL of 0,1 N noncarbonated sodium hydroxide solution and dilute to 1 L with water.
  • Borax buffer solution: Dissolve 3,81 g of sodium tetraborate decahydrate in water and dilute to 1 L.

The pH value is important in the production of leather and leather products, because leather is produced at a pH value of approximately 4,5 to 5,5. This pH value allows the bound oils and tannins to remain in the leather. The pH value of a substance is a logarithmic interval of ten, indicating how acidic or basic that substance is. Distilled water has a pH value of 7. A substance with a pH value of 8, such as seawater, is ten times more basic, and a substance with a pH value of 5, such as coffee, is a hundred times more acidic.

As skin ages, the acid-base ratio shifts to alkaline (i.e. the pH value rises above 7). This makes the skin unbalanced. The skin darkens, hardens and becomes brittle. This change occurs due to age, moisture, sun and sweat. For example, steering wheels react to skin contact over time. The skin is more susceptible to mold due to the pH change.

Another cause of leather deterioration is alkaline cleaners. Most cleaners are alkaline because they have a good cleaning effect. However, leather cleaners should not be alkaline.

Sulfuric acid is one of the strongest acids and is well below the minimum pH value for skin, which is 3,5.

Among the numerous testing, measurement, analysis and evaluation studies that our organization has carried out for businesses in various sectors, it also provides testing services defined in the "ASTM D2810-18 Standard test method for leather pH value" standard with its trained and expert staff and advanced technological equipment.