pH value refers to the determination of the pH value of textile water extract. Since the promulgation and implementation of the compulsory standard GB 18401 "National Basic Safety Technical Specifications for Textile Products", pH value, as an important textile safety performance index, has always been the quality index tested by various regulatory agencies, and it is also one of the frequently unqualified indexes. In recent years, consumers have become more and more concerned about the inherent quality of textile and apparel products that directly contact the skin. In recent years, according to the results of random inspections by the national and local quality supervision departments, the problem of unqualified pH has always been high, and it has almost become textiles. The “old problem” of quality, whether the pH index is within the specified range has attracted great attention.
The harmful of pH value exceeding standard
The pH value of normal human skin is between 5.5-6.5, and the chemical reaction is weakly acidic. The sweat and oil secreted by the sweat glands and sebum of the skin have their own pH. If the pH of the outside world is too different from the normal pH required by the human body, it will cause people to defecate. The body is unwell, and there are many diseases on the skin. The pH test of textiles is based on this demand. The deviation between the pH value and the standard value will result in improper acid-base of the clothing, which will destroy the natural barrier of the skin surface. The neutral and acidic skin of the human body will be irritated, causing burns, breeding bacteria, and causing diseases. Therefore, the country has formulated GB 18401 and other standards. The pH value of category A infant textile products should be in the range of 4.0 to 7.5, the pH value of category B textiles that directly contact the skin should be between 4.0 and 8.5, and category C indirect contact pH value of skin should be in the range of 4.0 to 9.0, when the human body is most comfortable to wear.
The Reasons for the unqualified PH value:
There are many reasons for the pH value of textiles to exceed the standard. If the various dyestuff and finishing auxiliaries used in the printing and dyeing and finishing processes of textiles are not fully washed or neutralized, and various finishing agents are added during the washing process, they are not regulated and controlled. Will make the pH of the final product exceed the standard. In summary, there are several reasons as below:
1). In order to reduce costs, the factory arbitrarily reduces the production process, and does not fully wash or neutralize the product after dyeing, finishing or special processing, resulting in higher or lower pH.
2. Manufacturers use some cheap and unstable direct dyes and paints for dyeing and printing. After the products produced by using these dyes are neutralized with weak acids and weak bases, the products are dark, without luster, and even change in hue or leave an unpleasant smell. Therefore, in order to maintain the bright luster of the product, some companies know that the pH value of the product is too high and do not neutralize it, resulting in substandard product quality.
3. Some small factories lack technical talents in printing and dyeing, and the staff in important positions have not received systematic professional training, and some even rely on experience to determine the number of washing times and the amount of acid and alkali. The pH value is unstable, and the phenomenon of unqualified pH value is prominent.
4. Some corporate laboratories lack the necessary testing equipment and just use pH test paper for testing. Studies have shown that pH test paper is only suitable for testing the pH of solutions with larger electrolyte concentrations. The pH value of textile extracts is generally close to neutral, and the electrolyte concentration of the solution is very low, so it is not suitable for pH test paper measurement.
5. The influence of operating errors of enterprise test personnel. The textile pH test is a test operation that requires particularly high instrumentation and test conditions. Test temperature, sampling quality, extraction time, pH meter calibration, etc，will all affect the results of pH determination.