Testing of flame retardant properties of fabrics
Almost all fabric materials are flammable, and even if they are treated with fireproof technology, it is difficult to prevent the fibers from burning in flames. It’s just that after fireproofing, the burning speed of the cloth material will be reduced to varying degrees and it can stop burning quickly after leaving the fire source. Therefore, fireproofing is relative rather than absolute.
With the progress of urban modernization, people’s awareness of fire prevention of fabrics is increasing day by day. In order to reduce fire accidents caused by fabrics and avoid unnecessary losses, the testing of fabric burning properties has attracted attention from countries around the world in recent years: Due to the different uses of fabrics, the fire protection regulations formulated by various countries also started from aircraft interior fabrics, carpets and building materials, and expanded to pajamas, furniture sofa covers, scented cushions and interior decorations: the United Kingdom, the United States, Japan and other countries have also responded with laws Formal regulations: work clothes and pajamas for women, children, the elderly, and disabled people must be marked “fireproof.” Our country’s work in this area is also constantly increasing its efforts.
1. Test method for fire resistance
There are various combustion test methods, and it is difficult to compare the test results of various test methods with each other. The experimental results can only illustrate the combustion performance of the sample to a certain extent. The combustion experiment method is mainly used to test the combustion extent (charring area and damage length), afterburning time and smoldering time of the sample. According to the relative position of the sample and the flame, it can be divided into vertical method, tilt method and horizontal method.
China currently mainly uses GB/T 5455~1997 “Vertical Method for Testing the Combustion Performance of Fabric Products” for the test method of fire resistance of work clothes. The principle is to place a sample of a certain size vertically in a specified combustion test chamber and ignite it with a specified fire source for 12 seconds. After removing the fire source, measure the afterburning time and smoldering time of the sample. After the smoldering stops, press Determine the length of damage using prescribed methods. This method can be used for the fire resistance of workwear fabrics, decorative fabrics, construction tent fabrics, etc.; the 45° tilt method is suitable for aircraft interior decoration fabrics; the horizontal method is suitable for carpets and other matting fabrics and automobile interior decoration fabrics.
The oxygen index method is to clamp the sample. Put it vertically into a transparent combustion tube. There is an upward moving oxygen and nitrogen flow in the tube. Light the sample end, then observe the combustion phenomenon, and compare the burning time or burning distance with the specified limit: through a series of tests at different concentrations This kind of experiment can measure low oxygen concentration, and the oxygen index method is more suitable for process experiments.
2. Evaluation of fabric fire resistance
Evaluating the flammability of fabrics is mainly considered from two aspects: on the one hand, the ease of ignition, that is, the level of the ignition point, which indicates the difficulty of the fabric catching fire; on the other hand, the burning performance of the fabric, that is, the fire resistance.
There are two criteria for evaluating the burning performance of fabrics: one is based on the burning rate of the fabric. That is, the fabric after fireproofing is exposed to the flame for a certain period of time according to the prescribed method, and then the flame is removed, and the time for the fabric to continue burning with flames and the time for burning without flames is measured, as well as the degree of damage to the fabric. The shorter the flame burning time and the flameless burning time, and the lower the degree of damage, the better the fire resistance of the fabric; on the contrary, it means the fabric has poor fire resistance.
The other is to judge by the oxygen index (also called extreme oxygen index) method: fabrics require oxygen to burn. The oxygen index (LOI) is an expression of the oxygen required for fiber burning, so it can be determined by measuring the oxygen index. For the fire resistance of fabric, the higher the oxygen index, the higher the oxygen concentration required to maintain combustion, which means the more difficult it is to burn: this index can be expressed by the small volume percentage of oxygen required to maintain candle-like combustion of the sample in a nitrogen and oxygen mixed gas. : LOI = oxygen concentration/(oxygen concentration + nitrogen concentration) × 100%
The oxygen index is less than 20%, which is a flammable fiber; the oxygen index is between 20 and 26%, it is a flammable fiber; the oxygen index is between 26 and 34%, it is a flame-retardant fiber; the oxygen index above 35% is a flammable fiber Non-flammable fiber.
3. China’s regulations on combustion performance
At present, countries all over the world attach great importance to the fire resistance of workwear fabrics. Some countries have even included it in national fire safety regulations, indicating that the fire resistance of clothing fabrics has become a particularly important test in the functional testing of workwear. project. China’s regulations on the fire resistance of fabrics are as follows:
As can be seen from the table, my country’s standards are based on the burning rate of fabrics. Only fabric products that meet the requirements of the above standards can be regarded as fire-proof products. With the progress of urban modernization, to reduce fire accidents caused by fabrics, relevant laws and regulations must be improved. my country’s current fire protection product standards have been more than five years old, and there is a certain gap between the content and advanced countries. Therefore, we should carefully learn from foreign countries. Use advanced experience to speed up the improvement of standards for testing methods for the combustion performance of fabrics. Formulate product standards for fire-resistant fabrics, strengthen quality supervision and inspection of fabrics, and promote the development of fire-resistant fabrics.
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