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Factors and indicators affecting the combustion characteristics of fabrics1
Due to the small thickness and large specific surface area of common fabrics, low-intensity flames can be ignited and the flame propagation rate is fast, and they are in direct and close contact with the human body. Therefore, the burning of fabrics is the main cause of fire and death. The evaluation of the combustion performance of fabrics is very complicated. The traditional combustion test methods include the combustion test method, the limiting oxygen index method, the smoke test method, the thermal analysis method, and the cone calorimeter method. 1. Factors affecting the combustion characteristics of fabrics: 1. Materials: Each fiber material has its own unique combustion characteristics, for example, polyester combustion has a melting drop phenomenon. Different moisture regains of different raw materials will also affect the heat absorption and release during combustion. Some studies have studied the heat release sequence and total heat release of six materials: polyester, acrylic, nylon, cotton, linen, silk, and wool during combustion. The research shows that the heat release sequence of fabrics of different materials in the combustion test is polyester>silk>cotton>hemp>silk>acrylic>nylon 6. The total amount of heat release per unit mass of the fabric is: cotton > acrylic > nylon 6 > polyester > hemp > wool > silk. This is due to the high moisture regain of natural fibers, the heat absorbed in this stage is mainly used to evaporate the moisture contained in the fabric itself, and the fabric begins to release heat after the temperature reaches the ignition point. Synthetic fibers have low moisture regain and absorb less heat for evaporating water. It is also related to how well the fabric burns. 2. Fabric structure and weight: When the fabric materials are the same, the shorter the average floating length of the fabric structure, the heavier the fabric weight, and the higher the limiting oxygen index of the fabric. 3. Flame retardant finishing of fabric: After the flame retardant finishing of the fabric, its flammability is reduced. 4. Test conditions: The size of the test box affects the oxygen content in the combustion environment. The distance between the test flame and the sample, the length of the flame affects the way the fabric is ignited, and the ignition time directly affects the intensity of the combustion. Therefore, the test of the combustion performance of the fabric should be carried out under the standard instrument and in accordance with the provisions of the standard to ensure the accuracy of the test results. 2. Indicators to characterize the combustion characteristics of fabrics: 1. The main evaluation indicators in the combustion test method are: afterburning time, smoldering time, and the degree of damage to the surface of the fabric. Under standard test conditions, the shorter the flame burning time and the flameless burning time, the lower the degree of damage, which means the better the flame retardant performance of the fabric. 2. Limiting oxygen index: The minimum concentration of oxygen in the nitrogen-oxygen mixture required to keep the material in a burning state under the specified test conditions. 3. According to the long-term accumulation of various fire data, analyze the smoke and toxicity of the combustion products, which are often more harmful than the flame and heat generated during combustion. In the smoke test method, the optical density, maximum smoke density, average smoke rate, light transmittance, and harmful gas content can be obtained through the smoke density test transmittance and time curve to comprehensively evaluate the combustion performance of flame retardant textiles. 4. Heat release rate. The heat release rate when a material is burned, that is, the heat released by the material in a unit time, is the most important fire parameter to characterize the burning risk of a material in a fire. 3. Common terms of combustion performance: 1. Combustion: When the flammable substance leaves the fire source, the oxidative exothermic reaction occurs, accompanied by the luminous phenomenon of the flameless combustion zone with flames. 2. Burning: When the flammable substance contacts the fire source, the flameless combustion process in the solid state is accompanied by the phenomenon of luminescence in the combustion area. 3. Afterburning: After the burning substance leaves the fire source, there is still continuous flame burning. 4. Smoldering: After the burning substance leaves the fire source, it still continues to burn without flame. 5. Flame combustion: gas phase combustion accompanied by luminescence. 6. Smoke burning: a slow burning phenomenon with no light visible, usually with smoke. 7. Flame retardant: The material has the characteristics of preventing, slowing down or terminating flaming combustion. 8. Flame spread: the expansion process of the flame front. 9. Damage length: under the specified test conditions, the maximum length of the damaged area of the material in the specified direction, also known as the carbon length. 10. Ignition temperature: under the specified test conditions, the lowest temperature at which the material starts to burn continuously, usually called the ignition point. 11. Pyrolysis: irreversible chemical decomposition of materials at high temperatures without oxidation. 12. Melt drop: the material is melted and dropped at high temperature. 13. Carbonization: The process of forming carbonaceous residues during the pyrolysis or incomplete combustion of materials. More about Textile Fire Testing Instruments: http://www.standard-groups.com/TextileGarment/
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