The flammability of flame retardant fabrics is evaluated primarily in two respects: ignitability and fabric flammability (ie, flame retardancy).
There are two main methods for assessing the burning performance of flame retardant fabrics:
First, the burning rate of flame retardant fabrics. That is, the flame retardant fabric is removed from the flame after being in contact with the flame for a certain period of time according to a prescribed method, and the flame-retardant time of the flame retardant fabric and the time of the flameless burning, and the degree of damage of the flame retardant fabric are determined. The shorter the time of flame burning and the time of flameless burning, the lower the degree of damage of the flame retardant fabric, the better the flame retardant performance of the flame retardant fabric; on the contrary, the flame retardant performance of the flame retardant fabric is poor.
Second, the oxygen index (also known as the polar oxygen index) method. Oxygen index (LOI) is the expression of oxygen required for fiber combustion. Therefore, the flame retardancy of flame retardant fabric can be determined by measuring the oxygen index. The higher the oxygen index, the oxygen concentration required for combustion. The higher, the harder it is to burn. The index can be expressed as the minimum volume percentage of oxygen required for the candle to burn in a mixed gas of nitrogen and oxygen: LOE = oxygen concentration / (oxygen concentration + nitrogen concentration) * 100% oxygen index below 20%, is flammable Fiber; oxygen index between 20~26%, is a combustible fiber; oxygen index is between 26~34% is a flame retardant fiber; oxygen index above 35% is not a fiber.
There are various combustion test methods, and the test results of various test methods are difficult to compare with each other. The experimental results can only explain the combustion performance of the flame retardant fabric to a certain extent. The combustion test method is mainly used to test the combustion extent (carbonization area and damage length) of the flame retardant fabric, the afterburning time and the smoldering time. According to the relative position of the flame retardant fabric and the flame, it can be divided into a vertical method, a tilt method and a horizontal method.
The oxygen index method is to vertically place the clamped flame retardant fabric sample into a transparent combustion tube. The cylinder has an upward moving oxygen-nitrogen flow, ignites the upper end of the sample, and then observes the combustion phenomenon, and continuously burns compared with the specified limit. The time or the distance of combustion, the oxygen index method is more suitable for use in process experiments.