What is the technological development of waterproof and breathable fabrics
The development of science and technology has also promoted the continuous development of the textile industry. Clothing in the 21st century will develop in the direction of comfort, functionality and return to nature. Various smart fabrics and functional fabrics have received widespread attention and development. Waterproof breathable fabric is one of them.
Waterproof and breathable fabrics refer to fabrics that are both rainproof and windproof, perspiration wicking, breathable, and comfortable to wear. During the wearing process, water does not penetrate the fabric under a certain pressure, but sweat emitted by the human body can In the form of water vapor, it passes through the fabric or is transmitted to the outside world, without condensation and accumulation between the human body surface and the fabric, keeping the wearer dry and warm. The continuous improvement of people’s requirements for wearing comfort and functionality prompts us to use various new technologies to improve the various properties of fabrics. The combination of different processes and technologies is the main means to give fabrics new functions, among which the coating/layer of fabrics Pressure technology is one of the important methods.
Fabric coating/lamination is a composite of fabric and high molecular polymer. It not only retains the original function of the fabric, but also increases the function of the covering layer. Fabric coating/lamination technology brings great benefits to the textile industry. Functional fabrics provide more possibilities, greatly broadening the uses of textiles, and their application fields are becoming wider and wider. They are not only used in the production of clothing textiles, but also their applications are expanded to the shoe industry, civil or military uniforms, extreme climate Condition clothing, tarpaulins, tents, wraps, etc.
The waterproof and breathable mechanism of fabrics includes physical moisture permeability and functional moisture permeability. There are mainly the following four methods:
First, the use of the small diameter of water droplets and the diameter of water vapor or air This is achieved by using the pores between the warp and weft interweaving of the fabric or the pore diameter of the fabric composite between the small diameter and the diameter of water vapor or air to achieve the purpose of waterproofing and breathability. The waterproof and breathable fabric designed based on this principle There are ultra-fine high-density fabrics, ultra-high-density cotton fabrics, etc. The moisture permeability type of this type of fabric is due to the natural diffusion of pores between yarns. High-density fabrics are widely used in sports and outdoor activity clothing due to their lightness, durability, good moisture permeability, softness, good drape, and wind resistance. The main disadvantage is poor waterproofness. Due to the high density of the fabric, the tearing performance of the fabric is poor. The spinning must be specially treated, which results in high production costs and difficult processing.
Second, a microporous film is used to make the film’s micropores (micropore diameter about 1nm) have a pore size between water droplets and moisture, and the film and fabric are combined to give the fabric waterproof and breathable functions, as shown in Figure 1. The microporous polymer film can be combined with the fabric through lamination or coating processes to give the composite waterproof and breathable functions. There are many ways to produce micropores: micropores can be produced by biaxial stretching of the film, fillers (such as ceramics) can be added to the polymer to form pores between the polymer and the filler, or through phase Separation (wet process of polyurethane) produces micropores, and drilling technology (such as laser) can also be used mechanically to create gaps in the non-porous membrane to achieve breathability.
Third, the hydrophilic component of the polymer film is used to provide enough chemical groups as stepping stones for water vapor molecules. Water molecules adsorb water molecules on the high humidity side due to hydrogen bonds and other intermolecular forces. By transferring the hydrophilic groups on the polymer chain to the low-humidity side for desorption, a process of “adsorption-diffusion-desorption” is formed to achieve the purpose of breathability, as shown in Figure 2. The hydrophilic component can be the hydrophilic group in the molecular chain or the hydrophilic component of the block copolymer; its waterproofness comes from the continuity of the film itself and the larger surface tension of the film. Lamination/coating of film and fabric makes the fabric waterproof and breathable.
Fourth, the characteristics of shape memory polymers are utilized. In the glass transition temperature region, the breathability of shape memory polymers undergoes a qualitative mutation due to the micro-Brownian motion of the molecular chains, and its breathability changes with the external temperature. Changes with changes, that is, intelligent functions, just like human skin, can adjust with changes in external temperature and humidity, as shown in Figure 3. Using this shape memory polyurethane to produce waterproof and breathable fabrics can use non-porous lamination/coating methods, which reduces shortcomings such as micropore blockage due to micropores during use. More importantly, the moisture vapor permeability of the fabric can be improved over time. It changes with changes in human body temperature to achieve an “intelligent” effect, making it suitable for wearing under various conditions.
The development of polyurethane and its application in waterproof and breathable textiles. Polymers used in waterproof and breathable fabrics originally included polyvinyl chloride (PVC), polyethylene, polychloroprene and other various synthetic rubbers. , due to its poor moisture vapor permeability, when wearing this type of clothing for activities, a large amount of sweat cannot be discharged in the form of water vapor, and condensation water is formed inside the clothing, causing the human body to feel sticky, stuffy, etc., although it has good waterproof properties. , but the taking performance needs to be further improved. Later developed polytetrafluoroethylene laminated films, thermoplastic polyurethane (TPU) coatings and laminated fabrics have good moisture vapor permeability and are developing rapidly. In particular, thermoplastic polyurethane materials have good wear resistance, chemical resistance and The advantages of hydrolyzability, insect resistance, mildew resistance, low temperature resistance, easy coloring, and wide range of process operation options have been greatly developed in terms of the scope of application and the improvement of its own performance. Different Types of Waterproof and Breathable Polyurethane for Polyurethane��, fabrics impregnated with polyethylene glycol (PEG) have the function of storing heat, that is, they absorb heat when heated and release heat when cold. This technology is applied to polyurethane fabric coatings. PEG is a component of polyurethane. By selecting and designing the polymerization degree and content of PEG, the glass transition temperature of the soft segment composed of PEG is within the temperature range that the human body feels comfortable. In this way, when the environment is higher than the critical temperature, the polymer undergoes phase change and absorbs heat. At the same time, the volume of the polymer expands, the space volume of the hydrophilic group increases, and the thermal movement intensifies, which increases the moisture vapor permeability and accelerates heat and perspiration. People feel cool; when the ambient temperature is lower than the critical temperature of the polymer, the PEG chain segments crystallize, and the polymer phase changes to release heat. At the same time, the Brownian motion is reduced, the breathability is reduced, and it plays the role of wind protection and heat preservation. In this way, moisture vapor permeability and temperature regulation play a coordinated role at the same time. In this way, the wearer will feel comfortable even when the ambient temperature changes or the human body becomes hot and sweats.
3 Innovation in coating technology Research and development of pollution-free polyurethane: Researching a completely water-dispersed, solvent-free coating agent is a hot and difficult point in current development. Whether the current PU coating is produced by dry or wet methods, most of the PU solutions used are solvent-based, containing about 70% of organic solvents such as dimethylformamide (DMF), toluene, and methylacetone. These solvents are harmful to the operation. It has certain hazards, is flammable and explosive, pollutes the environment, and is difficult to recover solvents. In recent decades, people’s awareness of environmental protection has been continuously strengthened, and relevant laws and regulations on labor protection, safety, and environmental protection have been increasingly strengthened. Therefore, water-emulsified polyurethane coatings have been developed to replace organic solvents with water during the production process to reduce environmental pollution and harm to the human body. , has important practical significance. Water-emulsible polyurethane has received attention and is also a hot spot in development. Improve waterproof and breathable performance: On the one hand, it combines the respective advantages of microporous coating and hydrophilic non-porous coating, and performs hydrophilic coating finishing on the basis of microporous coating, which increases the fabric’s breathability without affecting the microporous breathability. Waterproof and improve its durability, such as making it less likely to cause clogging of micropores during use; in addition, adding other additives to the PU coating agent can not only improve the breathability of the PU film, but also give the fabric anti-bacterial effects and Excellent hand feel, such as adding chitin to improve the breathability and hygroscopicity of PU and having a certain antibacterial effect; infiltrating metal powder into the resin to form a metal layer that reflects the radiant heat of the human body and radiates far-infrared rays to the human body. It improves the warmth retention of fabrics and promotes the function of human body microcirculation. Conclusion Waterproof and breathable fabric is a high value-added product. Products produced by different production processes have their own characteristics. Among coating materials, polyurethane coating materials have a wide range of application prospects, among which functional polyurethane (temperature regulation, shape The development of (memory) and its application in textiles are of great significance to improving the comfort of coated fabrics, and are also one of the important directions in the current development of waterproof and breathable fabrics. AAE4T45UY75T
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