Don't you collect the main quality indicators of chemical fibers?

Fiber quality refers to the overall quality of many indicators that have a decisive impact on the use value of fibre products. The main indicators reflecting the quality of fibers are physical performance indicators, including fiber length, fineness, specific gravity, gloss, moisture absorption, thermal performance and electrical performance; mechanical performance indicators, including breaking strength, elongation at break, initial modulus, resilience, multiple deformation resistance; and stability performance indicators, including high temperature and low temperature. Temperature stability, light-atmosphere stability, chemical reagent stability and microbial stability; processing performance indicators include fiber cohesion, electrostatic and dyeing properties; additional quality indicators of staple fibers include fiber length, crimp, fiber defects and so on.

1. Fineness
Fineness is the degree of fiber thickness. There are two kinds of indirect indicators and direct indicators. The direct index is usually expressed by the diameter and cross-sectional area of the fibers. Because the cross-sectional area of the fibers is irregular and difficult to measure, the direct index is usually used to express the thickness of the fibers, so the indirect index is often used. Indirect indicators are determined by the quality or length of the fibers, that is, the quality (fixed length) or length (fixed weight) of the fibers at a fixed length or weight.
In the production of chemical fibers, the uneven evenness of non-drawn and drawn yarns will be caused by the fluctuation of raw materials, equipment operation and process conditions. Therefore, the measurement of evenness of fibers along length direction is an important index to measure the change of fibre quality. It affects the physical-mechanical properties and dyeing properties of fibers, as well as the textile processing properties and appearance of fabrics.

Two. Hygroscopicity
Hygroscopicity is one of the physical properties of fibers. Usually the ability of fibers to absorb moisture from gaseous environment is called hygroscopicity. The indicators of hygroscopicity are as follows:
1. Moisture regain and moisture content: moisture content in fiber materials, i.e. adsorbed water content, is usually expressed in terms of Moisture regain or Moisture content. The former refers to the percentage of moisture content in fibers to the quality of dry fibers, while the latter refers to the percentage of moisture content in fibers to the actual quality of fibers. In chemical fiber industry, moisture regain is generally used to indicate the strength of hygroscopicity of fibers.
2. Standard moisture regain and definite moisture regain: The actual moisture regain of various fibers varies with environmental temperature and humidity. In order to compare the moisture absorption capacity of various fibers, the moisture regain of various fibers is set at &ldquo after a certain period of time in a unified standard atmospheric condition (20 C, 65% relative humidity). When a steady value is reached, the moisture regain rate is the standard moisture regain rate.
In trade and cost calculation, fiber materials are often not in the standard state. In order to meet the needs of weighing and nuclear price, the moisture regain rate of various fiber materials must be artificially uniformly stipulated, which is called the public moisture regain rate. The moisture regain of main textile fibers is as follows:

Three, density
Densities of fibers refer to the quality (weight) of fibers per unit volume, commonly used in g/cm3 . Due to the different material composition, macromolecule arrangement and fiber morphology, the density of various fibers is different. Among the main chemical fibers, the density of polypropylene fibers is the smallest, and that of viscose fibers is the largest. The density of main textile fibers is as follows:

Four. Tensile properties
Fiber materials are subject to tension, bending, compression, friction and torsion in use, resulting in different deformation. Tension is the main external force that chemical fibers are subjected to in the course of use. The flexural properties of chemical fibers are also related to their tensile properties. Therefore, tensile properties are the most important mechanical properties of chemical fibers. It includes strength and elongation, so it is also called strength and elongation.
(1) Fracture strength
Fracture strength is the main index to characterize the quality of fibers. Increasing the fracture strength of fibers can improve the service properties of products. The breaking strength of fibers is usually expressed in the following ways:
1. Fracture strength: also known as absolute strength or fracture load, referred to as strength. That is to say, the force needed for the fiber material to be stretched directly to fracture by the outside world is Newton (N), and the derivative units are centimeter Newton (cN), millinewton (mN), thousand Newton (kN), etc. The readings measured on various forceful machines are all forceful. Strength is related to the thickness of fibers, so there is no comparability of strength for fibers of different sizes.
2. Relative Strength: The strength required to break a fibre per fineness is called relative strength, i.e. the ratio of breaking strength to linear density of the fibre, which is used to compare the tensile fracture properties of fibers with different fineness in units of N/tex.
The breaking strength is high, the fibers are not easy to break ends and roll in the process of processing, and the fastness of the yarns and fabrics is also high, but the breaking strength is too high, the rigidity of the fibers increases, and the handle becomes hard.
(2) Fracture elongation
The elongation at break is called elongation at break, which indicates the ability of the fibers to withstand tensile deformation.
The fibers with high elongation at break have soft handle, which can cushion the force they are subjected to while textile processing, and have fewer wool and broken ends. However, the elongation at break should not be too large, otherwise the fabric will be easily deformed. The elongation at break of ordinary textile fibers is in the range of 10% & nbsp; - 30%. However, for industrial high-strength yarns, high breaking strength and low elongation at break are generally required.Make its products not easy to deform.
(3) Initial modulus
Initial modulus, also known as Young's modulus or Young's modulus, indicates the difficulty of specimen deformation under small load and reflects the rigidity of material.
The initial modulus of the fiber depends on the chemical structure of the polymer and the intermolecular interaction force. The stronger the flexibility of macromolecule, the smaller the initial modulus of the fibers, and the more easily the fibers are deformed. For fibers made from the same polymer, the higher the intermolecular force, orientation or crystallinity, the greater the initial modulus of the fibers. Among the main chemical fiber varieties, the initial modulus of polyester is the largest, while that of nylon is smaller, so the polyester fabric is stiff and not easy to wrinkle, while the polyamide fiber is easy to wrinkle and has poor shape retention.
Tensile properties of several common chemical fibers are as follows:

(four) resilience
Elastic recovery is the ability of a material to recover its original state after being deformed (stretched or compressed) by an external force. The deformation of fibers under load includes three parts: general elastic deformation, high elastic deformation and plastic deformation. These three kinds of deformation do not appear one by one, but develop at the same time, but at different speeds. Therefore, when the external force is removed, the recoverable elastic deformation and the part of high elastic deformation with short relaxation time (rapid resilience deformation) will quickly retract, leaving behind a part of deformation, i.e. residual deformation, including high elastic deformation with long relaxation time (slow resilience deformation) and irreversible plastic deformation. The smaller the residual deformation, the better the resilience of the fibers.
The resilience of fibers is closely related to the dimensional stability and crease of their products. Clothing made of high resilient fibers (e.g. polyester) is not easy to wrinkle and has the characteristics of stiffness.
Five, fatigue resistance
Fatigue resistance usually refers to the damage or damage of fibers under repeated loads or long-term static loads.
From the point of view of energy, the mechanism of fatigue failure can be considered as that the work consumed by the external action reaches the binding energy (fracture work) within the material, which makes the material fatigue; from the point of view of deformation, it can also be considered that the accumulation of deformation and plastic deformation caused by the external force reaches the elongation at break and makes the material fatigue. Lao. Generally speaking, fibers with better resilience have higher fatigue resistance, such as nylon, which has better resilience and fatigue resistance.


Six. Wear resistance
The so-called wear generally refers to the phenomenon that material loses a small amount of material from the solid surface due to mechanical action, that is, the contact between two solid surfaces makes relative motion, accompanied by the reduction process caused by friction.
The factors affecting the wear resistance of fibers are very complex. The first is the molecular structure and microstructure of the fibers. Generally speaking, the main chain bond energy is strong, the molecular chain flexibility is good, the degree of polymerization is good, the orientation is high, the crystallinity is appropriate, the crystalline particles are fine and uniform, and the glass transition temperature of the fibers is near the service temperature, the wear resistance is better. From the aspect of fiber properties, the surface hardness of the fiber is high, the recovery rate of rapid elasticity is high, the specific work of tensile fracture is large, and the wear resistance is better when the recovery coefficient is high. In addition, temperature and humidity, sample tension, abrasive type, shape, hardness and so on have an impact on wear resistance.
The order of wear resistance of common fibers is as follows: nylon & gt; Polypropylene & gt; vinylon & gt; polyethylene & gt; polyester & gt; acrylic & gt; polyvinyl chloride & gt; wool & gt; Silk & gt; Cotton & gt; linen & gt; strong fiber & gt; copper-spandex fiber & gt; viscose & gt; acetate fiber & gt; glass fiber.
Heat Resistance and Thermal Stability
Fibers and their products are subjected to high temperature (such as dyeing, finishing, drying, etc.) in the process of processing, and they are often exposed to high temperature (such as washing and ironing) in the process of using. Industrial and technical fibers are more subjected to high temperature for a long time. Therefore, the stability of high temperature is one of the stability performance indicators of materials.
Heat Resistance: Characterizes the changes in mechanical properties of fibers measured at elevated temperatures, which can often be restored to normal temperature (a reversible change), so it is also called physical heat resistance.
Thermal stability: characterizes the irreversible change in mechanical properties of fibers after heating. This change is measured by heating and cooling the fibers to room temperature. It is caused by the degradation or chemical change of polymers, so it is also called chemical heat resistance.
The chemical structure of polymers is one of the main factors affecting the heat resistance (including thermal stability) of fibers. Natural cellulose fibers and regenerated hydrated cellulose fibers have high heat resistance. These fibers are not thermoplastic, so they will not soften or bond at elevated temperature. At elevated temperature, the strength of synthetic fibers decreases more than that of hydrated cellulose fibers. Among the main chemical fibers, viscose fibers have the best heat resistance, while polyester fibers have the best thermal stability.
The formation of cross-linking structure in polymer molecules can improve the heat resistance of fibers, such as the acetalization of polyvinyl alcohol. By adding a small amount of antioxidant or chain cracking retardant, the degree of pyrolysis and thermal oxidation cracking of the fibers can be greatly reduced, and the thermal stability of the fibers can be improved, but the heat resistance of the fibers can not be improved.

Eight. Thermal shrinkage
Heat shrinkage is one of the thermal properties of fibers. It refers to the shrinkage of fibers'morphology and size under heating conditions.When the temperature decreases, it is irreversible. The thermal shrinkage of fibers is due to the internal stress of the fibers. The thermal shrinkage is expressed by the heat-shrinkage, which is the percentage of the shortened length of the fibers to the original length after heating.
According to the different heating medium, there are boiling water shrinkage, hot air shrinkage and saturated steam shrinkage. For the heat shrinkage treatment of fibers, the heat treatment conditions for different varieties are also different. Common heat shrinkage treatment conditions for chemical fibers:


The shrinkage of fibers is related to heat treatment, temperature and time. Generally, the shrinkage of fibers is the largest in saturated steam, the second in boiling water and the smallest in hot air. The shrinkage of polyvinyl chloride fibers is over 50% in hot air at 100 C, the shrinkage of vinylon fibers in boiling water is about 5%, and that of polyester staple fibers processed normally is about 1%.
Nine. Flame retardancy
Fiber combustion is the result of rapid thermal degradation and intense chemical reaction of fibers at high temperature in open fire. Flame retardancy is one of the stability indexes of fibers, also known as flame retardancy. The indexes describing the combustion performance of fibers are LOI, ignition temperature T, combustion time T, flame temperature TB and so on. Limited oxygen index (LOI) is widely used.
Limit oxygen index (LOI) refers to the lowest oxygen integral required for a sample to maintain complete combustion in a mixture of oxygen and nitrogen. The higher the oxygen limiting index is, the higher the concentration of oxygen required for combustion is, the more difficult it is for fibers to burn under normal conditions. According to the LOI value, the combustibility of fibers can be divided into four categories:

Limit oxygen index of common chemical fibers:

X. Chemical Stability
The stability of chemical action is one of the stability properties of materials, also known as chemical resistance. It is a measure of the resistance of fibers to chemical reagents. The stability of microbial action refers to the ability of fibers to resist the action of borers and fungi, also known as microbial resistance.
The stability of chemical fibers to chemical reagents depends mainly on the structure of their polymers. Generally, carbon-chain chemical fibers are more stable to acid and alkali than hetero-chain chemical fibers, but also related to side groups. For example, acrylic fibers have cyano groups on the macromolecular chain, so they are not resistant to strong alkali.
The chemical stability of polyester fibers depends mainly on their molecular structure. Apart from poor alkali resistance, polyester fibers have excellent resistance to other chemical reagents. Polyester fibers are resistant to microorganisms, not to borers, fungi and other effects.
Nylon fibers have good alkali resistance and reductant resistance, but poor acid resistance and oxidant resistance. The microbial resistance of nylon fibers is better than that of polyvinyl chloride fibers in sludge water or alkali. However, the microbial resistance of nylon fibers with oil or sizing agent decreases.
Acrylic fibers have good acid resistance and alkalinity. 35% hydrochloric acid, 65% sulphuric acid and 45% nitric acid have no effect on their strength. The strength of acrylic fibers in 50% caustic sodium and 28% ammonia water almost does not decrease. Insect resistance of acrylic fibersIt has good resistance to mildew.