Popular Science | What performance indicators must be possessed by super cotton-like polyester fiber in order to achieve the effect of imitating cotton like cotton and imitating cotton better than cotton!

The development of my country’s chemical fiber imitation cotton has gone through three stages:

The first stage is to imitate cotton in terms of feel, gloss, and softness. Generally, combing, abnormal shrinkage, etc. are used to change the surface shape of the fiber, thereby changing the feel of the fiber;

The second stage is to imitate cotton from the perspective of moisture regain. The moisture-absorbing and sweat-wicking products currently on the market belong to the second stage. Substitute imitation cotton, mainly using special-shaped cross-sections, and then through post-finishing to achieve high moisture absorption and perspiration effects;

The third generation of imitation cotton is the current development of super imitation cotton products. The foundation of super-imitation cotton technology began with the fiber material design in the 1980s, emphasizing the integration of differentiated and functional series technologies and the mutual integration of polymerization, spinning, weaving, dyeing and finishing technologies. It is obviously different from the previous development of single differentiated technology or single functional products. Super cotton imitation products not only pursue the closeness to cotton fabrics (similarity) in fiber surface morphology and fabric style, but more importantly, they imitate cotton and super cotton in terms of fabric product functions. (Similar), especially in achieving ultra-cotton in terms of dynamic thermal and moisture comfort performance closely related to underwear and casual sportswear.

Cotton-like products are positioned to have the excellent characteristics of both cotton and polyester (PET) fibers, achieving the effect of imitating cotton like cotton and better than cotton.

In layman’s terms: looks like cotton (visually), feels like Like cotton (touch), wear like cotton (compatibility), super cotton (comfort), and more convenient to use than cotton (washability).

Scientifically speaking: super-imitation cotton products must ensure that the fibers have the excellent softness and warmth of cotton fibers, as well as the good mechanical properties of polyester. , heat resistance, color fastness, and even anti-static, anti-pilling, antibacterial, flame retardant, far-infrared, and anti-UV functions

This article interprets the performance indicators of super-cotton-like PET fiber from aspects such as gloss, feel, dyeability, and comfort.

Cotton, looks soft and mercerized, while Pure PET fiber that has not been modified has a high gloss and looks very bright, and the fabric made of it is transparent. Therefore, in order to look like cotton, the luster of PET fiber must be controlled. Fiber is a translucent body, and its luster depends on both the surface reflected light and the transmitted light. The gloss of fiber is affected by factors such as fiber surface state, fiber cross-sectional shape, and fiber internal structure. Fibers with good macromolecular orientation. The internal structure is relatively uniform, the reflected light of the fiber is strong, and the luster is bright.

Therefore, the gloss can be implemented by adding inorganic particle matting or adjusting the fiber cross-sectional shape, surface structure, etc. Regulation. In order to make PET fiber close to the luster of cotton fiber, inorganic particles can be added during the polymerization process. The inorganic particles are dispersed in PET and destroy the crystallization and orientation of PET, thus making the fiber surface appear matt. The added amount of inorganic particles is generally 1.0%-2.0% by mass. The actual added amount can be adjusted during the production process according to product requirements.

When observing cotton fibers under a microscope, you can see that the cross-section of the cotton fibers is irregular and hollow (as shown in Figure 1), and there are many spiral twists on the flat ribbon fibers. , this distortion is caused by the cotton fiber growingFormed naturally, it is called “natural twist” (as shown in Figure 2). This characteristic makes cotton fibers feel soft, fluffy, and warm to the touch. The feel of the fiber is related to the modulus of the fiber. The modulus of cotton fiber is small and soft.

PET contains aromatic benzene rings, and the molecular chain segments are relatively rigid, so it feels hard. To make it feel like cotton, it is necessary to control the molecular chain segments, fiber cross-section, and fiber modulus of PET. Introducing flexible segments during the polymerization process of terephthalic acid and ethylene glycol can increase the flexibility of PET segments, thereby improving the feel. In the spinning stage, hollow, cross, and U-shaped spinnerets are generally used to finally produce special-shaped fibers (as shown in Figure 3) with a hand feel close to cotton. There is a warm feeling when touching the cotton fiber. This is mainly related to the instantaneous moisture absorption and heat transfer of the fiber. The surface of the cotton fiber is not smooth and has many grooves and pits (as shown in Figure 4), so the fiber can form a static layer on the surface. air layer.

As we all know, the thermal conductivity of the still air layer is less than that of any fiber material, so the hand feels warm when touching the fiber. Using this principle, appropriate alkali reduction treatment is performed on the fiber during the post-processing process to form pits and micropores on the surface of the fiber (as shown in Figure 5b), which can store a large amount of still air, thereby increasing the warmth of the cotton-like fiber. feel.

In addition, the warmth of cotton fibers is due to their instant moisture absorption properties. When in contact with the human body, cotton fiber can instantly absorb the gaseous water on the surface of the human body and convert it into liquid water. At the same time, it releases heat, making the skin feel warm. Based on this principle, in the process of developing super-cotton-like PET fiber, by adding inorganic particles, the fiber can instantly absorb the gaseous water on the surface of the human body when it comes into contact with the human body, thereby producing a sense of warmth.

Generally, fibers must be dyed after being made into fabrics. Cotton fiber has soft molecular segments and contains a large number of hydroxyl groups, which is conducive to the entry of dye molecules and can interact with dye molecules. The hydroxyl group is combined, so the dyeability is better than that of PET. PET fiber has a very small number of hydroxyl groups and a very rigid molecular chain segment, which is not conducive to the entry of dye molecules. It also has no groups that can combine with dye molecules, so its dyeing performance is poor. Therefore, sulfonic acid groups are introduced during the polymerization process, and the sulfonic acid groups are combined with dye molecules to improve the dyeing performance of PET fibers. In addition, the introduced flexible segments and hydrophilic groups destroy the regularity of PET, reduce the crystallinity, and also improve the dyeing performance of the fiber.

The comfort of fabrics includes many aspects, among which thermal and moisture comfort are the most basic and core elements of comfort. Fabric thermal and wet comfort is a comprehensive balance of biothermodynamics between people, fabrics, and the environment. It is a combination of moisture, humidity, human activity level, fabric’s heat transfer performance, moisture transfer performance, breathability and other factors. coordination. The physical indicators of thermal comfort include warmth retention rate, thermal conductivity, thermal resistance value, etc. The physical indicators of wet comfort include water absorption rate, moisture regain rate, water retention rate, dehumidification rate, wicking rate, moisture permeability rate, and are proposed on this basis. Humidity release performance, etc.

4.1 Heat transfer performance

The thermal conductivity of general materials is expressed by the thermal conductivity (λ). The greater the thermal conductivity, the higher the thermal conductivity of the material, and the lower its thermal insulation or warmth retention. As a fiber aggregate, the fabric has many pores, and the total volume of these pores is about 60%-80% of the fabric, that is, air occupies the largest volume of the fabric. The thermal conductivity of still air is less than that of any textile fiber, so fabric structural design is very important for heat transfer in fabrics. The heat transfer of fabrics is a complex process, which includes four forms of heat conduction through the air and moisture in the fibers and fabrics, as well as convection and radiation of heat through the gaps between fibers or yarns.

4.2 Wet transfer performance

When the human body dissipates heat, it must rely on sweating to obtain heat production and heat dissipation. Thermal balance, if a large amount of sweat vapor accumulates in the microclimate between clothing and skin and cannot be diffused or transferred to the environment in time, the human body will feel very uncomfortable. Therefore, the moisture absorption and breathability of the fabric are related to the moisture transfer performance of the fabric. Closely related.

Cotton fabric is suitable for close-fitting wear and is skin-friendly on the outside Cotton fabrics are very comfortable in good conditions. Cotton fiber is a hydrophilic fiber. The hydrophilic performance includes two aspects: hygroscopicity and water absorption of the fiber: the gas phase water is attracted by the fiber surface and internal chemical groups or physically adsorbed, which is called hygroscopicity. It is usually expressed as moisture regain. It means that the moisture regain rate of cotton fiber is about 8%; if the liquid water is diffused by the fiber surface or absorbed inside the fiber, this characteristic is called water absorption.

When moisture passes through the fabric, there are two phases: gas phase and liquid phase:

① Liquid water is transferred by the capillary action of the fabric. This transfer is also called wicking transfer, that is, due to the yarn and fiber structure of the fabric There are capillaries in the fabric, and liquid moisture (sweat secreted by the human body or natural water) can be transferred from one side of the fabric to the other side through capillary action, thereby also transferring heat to the other side of the fabric;

② Since sweat evaporates on the skin surface, when the water vapor partial pressure in the air layer between the material on the side of the skin and the skin is greater than that in the surrounding environment When the water vapor partial pressure is high, the gas phase moisture mainly diffuses from the side with high partial pressure to the side with low partial pressure through the gaps between yarns and fibers in the fabric. This breathability is determined by the fabric structure and its porosity and thickness. This transmission method is the main way of evaporation and diffusion of sweat.

Cotton fiber has a good ability to manage gas phase water, and can absorb water discharged by the human body and maintain the skin’s moisture content. It is dry and comfortable, but its ability to manage liquid water is weak. When the external environment changes, cotton fiber has poor adjustment performance. Due to the high water retention rate of cotton fiber, when the human body sweats during extensive exercise, although the cotton fabric can absorb the water, it cannot discharge the water, causing the human body to be damp and stuffy. That is, the dehumidification and moisture conduction capabilities of cotton fiber are poor. The moisture conduction process of fabrics is essentially the phenomenon of liquid wicking and flowing in the capillary pores in the fabric, which is determined by the wetting and moisture conduction properties.

The performance of super cotton-like PET fiber must ultimately be reflected in the end product, when the fiber moisture regain is between 1.0% and 2.0%, it can meet the requirements of human body comfort. Secondly, the fiber only needs to absorb water and moisten the surface, and does not need to absorb water into the interior of the fiber. The surface of cotton fiber contains a large number of hydroxyl groups, which combine with water molecules, so the water is not easily discharged, causing the human body to be damp and stuffy. Super cotton-like PET fiber must improve the ability to regulate both gas phase water and liquid phase water at the same time: first, the fiber must have hydrophilic properties. Only with hydrophilic properties can it absorb water discharged by the human body; secondly, it must have good wettability. By adding polyhydroxyl-containing monomers during the polymerization process, the reaction rate is controlled to ensure that both ends of the polyhydroxyl monomer are connected to the PET macromolecular chain, and the remaining hydroxyl groups do not participate in the reaction, which can improve the hydrophilic properties of the PET fiber. In addition, the fiber surface state is changed by combining fine or ultra-fine denier, surface roughening, cross-section deformation, hollowing and other means to ensure that the fiber or fabric has a good wicking effect, so that water can be exported in time, so that the fiber has good Moisture-conducting properties keep the skin surface dry and warm. As shown in Figure 6 and Figure 7: The moisture regain rate of cotton-like hydrophilic PET fiber is lower than that of cotton fiber, but it is greatly improved compared to pure PET fiber. Secondly, when the moisture absorption and moisture release of imitation cotton-like hydrophilic fiber reach a balance, It is shorter, indicating that compared with cotton, cotton-like hydrophilic fibers have stronger dynamic real-time control capabilities.

In summary, PET fiber has been comprehensively modified from aspects such as gloss, feel, dyeing, and comfort, and has been developed The fiber combines the human-friendly comfort of cotton with the washability and wearability of polyester. It is a new generation of super-imitation cotton fiber.