The main quality index of chemical fiber

(cN/tex).

The breaking strength is an important index to reflect the quality of fiber, high breaking strength, fiber in the process of processing is not easy to break, roll, yarn and fabric fastness is high, but the breaking strength is too large, fiber rigidity increases, feel hard.

The strength of the fiber measured in the dry state is called dry strength; The strength measured in the wet state is called the wet strength. The wet strength of the fiber with higher moisture regain is lower than that of the dry strength. Most synthetic fibers have very low moisture regain, and wet strength is close to or equal to dry strength.

2. Elongation at break

The elongation at break of a fiber is generally expressed as the relative elongation at break, that is, the ratio of the length of the fiber extended to break to the original length.

Y= (L-L0) L0*100%

Where: Lo - fibrous length

L - The strength of the fiber at elongation to break.

Elongation at break is an index of fiber toughness. For the clothing filament, the greater the elongation, the softer the feel, the less hair and broken end in the post-processing, but when it is too large, the fabric is easy to deformation. For industrial filaments, the smaller the elongation, the less susceptible the final product is to deformation.

3. Initial modulus

The initial modulus of the fiber is the elastic modulus, which refers to the stress required when the fiber is stretched to 1% of its original length.

The initial mode indicates the resistance of the fiber to small deformation. In clothing, it reflects the stiffness of the fiber against small stretching or bending. The larger the initial modulus of the fiber, the easier it is to deform. Among the main varieties of synthetic fibers, the initial modulus of polyester is the largest, followed by acrylic fiber, and nylon is smaller. Therefore, polyester fabric is crisp, not easy to wrinkle nylon is easy to wrinkle, poor shape preservation.

Five, resilience

The deformation of the material under the action of external forces (stretching or compression), after the removal of external forces, the ability to return to the original state is called elastic recovery. The deformation of fiber under load includes three parts: common elastic deformation, high elastic deformation and plastic deformation. These three kinds of deformation do not appear one by one in turn, but develop simultaneously, only at different speeds.

Therefore, when the external force is removed, the recoverable general elastic deformation and the part of the high elastic deformation (rapid rebound deformation) with short relaxation time will quickly shrink, and leave a part of the deformation, that is, the residual deformation, including the high elastic deformation with long relaxation time (slow rebound deformation) and the irreversible plastic deformation. The smaller the residual deformation value, the better the resilience of the fiber.

Six, dry uneven rate

Dry irregularity is an indicator of the evenness of the filament, expressed as CV value (coefficient of variation) or mouth (Uster%). This index is particularly important for top oriented and drawn filaments. Filament dry uneven, in the process of processing is easy to produce hair and dyeing uneven.

Seven, crimp degree (mainly for short fibers)

The fiber is chemically, physically or mechanically crimped and deformed to give the fiber a certain crimp.

The purpose of crimping is to improve the adhesion of the fiber, while increasing the fluffiness and elasticity of the fiber, so that the fabric has a good appearance and warmth.

Eight, boiling water shrinkage rate

After the fiber is boiled in boiling water for 30 minutes, the ratio of the length after contraction to the original length is called the shrinkage rate of boiling water.

Boiling water shrinkage is an index of fiber thermal setting degree and dimensional stability. The smaller the shrinkage rate of boiling water, the better the structural stability of the fiber, the more stable the size of the fiber in the process of processing and taking the wet heat treatment (such as dyeing, washing, etc.), the less deformation; At the same time, the physical and mechanical properties and dyeing properties are good. The boiling water shrinkage rate of the fiber is only controlled by the heat setting process conditions of the fiber.

9. Combustion performance

The flammability of fiber refers to how easily the fiber burns in air. International regulations adopt the "limiting oxygen index" method, referred to as LOI method. The so-called limiting oxygen index is the lowest percentage of oxygen in the nitrogen and oxygen mixture in the environment when the fiber is removed from the fire source and the fiber can continue to burn.

LOI and fibers are classified as follows.

① Combustible or flammable fibers with LOI < 21%

② Flame retardant or flame retardant fiber LOI > 21% of the fiber

③ Flame retardant fiber LOI > 26% fiber

A lot of research has been done on the flame retardant treatment of chemical fibers at home and abroad, mainly using copolymerization, blending, surface treatment and other methods to introduce organophosphorus compounds, organohalogen compounds or both in fibers or fabrics.