Leather - Chemical tests - Determination of pH and difference figure
Material
Industry
Our test laboratory performs accredited testing according to DIN EN ISO 4045 for the determination of the pH value of leather. The pH value is an important parameter for assessing the chemical condition of leather. Excessively acidic or alkaline leather may influence ageing resistance, promote material degradation, or cause interactions with adjacent materials. Particularly in chrome-tanned leathers or leathers subjected to various retanning and finishing processes, pH values may provide indications of process conditions or residual chemical substances. In addition, elevated acid contents may accelerate the hydrolysis of certain material components.
Test Procedure
In the DIN EN ISO 4045 test, defined leather samples are shredded and extracted with water under specified conditions. After a standardized extraction period, the aqueous extract is prepared and the pH value is determined electrometrically using a calibrated glass electrode. In addition, the difference figure may also be determined within the scope of the test. For this purpose, a further measurement is carried out after defined dilution of the extract. Larger differences may indicate the presence of free strong acids. The test requires defined conditioning conditions, as moisture content and material inhomogeneity may influence the measurement results.
The test is used, among others, for automotive leather, upper leather for footwear, upholstery leather, and garment leather. In the automotive sector, it is applied, for example, to leather used for seat covers, steering wheel covers, and interior trim components. The standard is frequently used together with DIN EN ISO 4047 (ash content) and DIN EN ISO 5398-1 (chromium oxide content) in order to characterize chemical properties and tanning parameters more comprehensively. In failure investigations, abnormal pH values may indicate changes in manufacturing conditions or ageing processes.