pH Value Test

1. pH Value in Textiles

pH value, also known as hydrogen ion concentration index or acidity-alkalinity value, is a scale measuring the activity of hydrogen ions in a solution, commonly used to gauge the acidity or alkalinity of a solution. Typically (at 25°C, around 298K), when pH < 7, the solution is acidic; when pH > 7, it is alkaline; and when pH = 7, the solution is neutral.

pH value is a safety indicator for textiles, with the standard requiring a pH range of 4.0 to 9.0. Excessively high or low pH values not only affect the performance of the textiles themselves but also impact human skin. Healthy skin has a pH between 5.0 and 5.6, which is weakly acidic. When the pH value exceeds the skin's suitable range, it can cause irritation and corrosion, trigger skin inflammation, damage the sweat gland and nervous systems, and harm overall health.

2. Standard Limits for pH Value

The "National Technical Specification for Basic Safety of Textile Products" stipulates that Class A (mandatory for infant and children's textiles) has a pH limit of 4.0-7.5; Class B (at least required for textiles in direct contact with skin) has a pH limit of 4.0-8.5 (e.g., underwear); and Class C (at least required for textiles not in direct contact with skin) has a pH limit of 4.0-9.0 (e.g., outerwear). Under the Oeko-Tex Standard 100, Class B has a pH limit of 4.0-7.5, and a new limit for decorative materials is set at pH 4.0-9.0.

3. Factors Causing Abnormal pH Values

Pre-treatment process: Conducted under alkaline conditions, which can result in excessively high pH values.

Dyeing and printing process: Dyes typically react with fibers under alkaline or acidic conditions during dyeing. Improper handling can lead to textiles exceeding pH standards.

Post-treatment process: Inadequate washing during post-treatment or failure to thoroughly clean auxiliaries used in dyeing can also affect the pH value of textiles.

4. Principle of pH Value Testing

At room temperature, use a pH meter with a glass electrode to boil the sample in distilled or deionized water. After cooling the water extract to room temperature, measure the pH value of the textile's water extract using the pH meter. Equipment: Test vessels including stoppered Erlenmeyer flasks, chemically stable glass beakers, glass rods, scissors, tweezers, graduated cylinders with stoppers, volumetric flasks, balance (accuracy 0.01g), reciprocating or rotary shaker, pH meter. Testing process: