Development of waterproof and breathable fabrics
Development of waterproof and breathable fabrics
Waterproof and breathable fabric is a new type of textile fabric, which is composed of polymer waterproof and breathable material (PTFE membrane) and fabric. It has the functions of waterproof, moisture-permeable, breathable, insulating, windproof, and warm. Many of the outdoor sportswear we are familiar with are made 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 and breathable fabrics are one of them.
Waterproof and breathable fabrics refer to fabrics that are both rainproof and windproof, sweat-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 pass through in the form of water vapor. The fabric may be transmitted to the outside world without condensation accumulating 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 performance 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 polymer. It not only retains the original function of the fabric, but also increases the function of the covering layer. Fabric coating/lamination technology provides more opportunities for the textile industry to manufacture functional fabrics. Many possibilities have greatly broadened 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, clothing under extreme climate conditions, and protective clothing. Tarps, tents, packages, etc.
The waterproof and breathable mechanism of fabrics The waterproof and breathable mechanisms of fabrics include physical moisture permeability and functional moisture permeability. There are mainly four methods:
The first is to use the difference between the small diameter of water droplets and the diameter of water vapor or air to achieve waterproofing, either by using the pores between the warp and weft of the fabric or the pore diameter of the fabric composite between the small diameter and the diameter of water vapor or air. For the purpose of breathability, waterproof and breathable fabrics designed based on this principle include 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.
The second is to use a microporous film so that the pore diameter of the film’s micropores (micropore diameter is about 1nm) is between water droplets and moisture, and the film and fabric are combined to give the fabric waterproof and breathable functions, such as 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.
The third is to use the hydrophilic component of the polymer film to provide enough chemical groups as stepping stones for water vapor molecules. Due to hydrogen bonds and other intermolecular forces, water molecules adsorb water molecules on the high-humidity side and pass through the polymer chain. The upper hydrophilic group is transferred to the low humidity side for desorption, forming an “adsorption-diffusion-desorption” process to achieve the purpose of breathability, such as 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. The film and fabric are laminated/coated to give the fabric waterproof and breathable properties.
The fourth is to utilize the characteristics of shape memory polymers. 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 changes in external temperature. That is, intelligent functions, just like human skin, can adjust with changes in external temperature and humidity, such as 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 adjusted over time. It changes with changes in human body temperature to achieve an “intelligent” effect, making it suitable for wearing under various conditions. 1 Principle of microporosity breathability 4 Relationship between shape memory PU breathability and temperature 2 Principle of hydrophilic breathability Intermolecular pores (Tg) at low temperature 3 Principle of breathability of shape memory function Development of polyurethane and its application in waterproof and breathable textiles for waterproof and breathable textiles The polymers of the fabric initially include polyvinyl chloride (PVC), polyethylene, polychloroprene and other synthetic rubbers. Due to their poor moisture vapor permeability, when wearing such clothing for activities, a large amount of sweat cannot be absorbed by water vapor. It is discharged in the form, forming condensation water inside the clothing, causing the human body to feel sticky, stuffy and other uncomfortable feelings. Although it has good waterproof performance, the wearing performance needs to be further improved. Later developed PTFE laminate films, thermoplastic polyurethane (TPU) coatings and laminated surfaces.�It has good moisture vapor permeability and is developing rapidly. In particular, thermoplastic polyurethane materials have the advantages of good wear resistance, chemical resistance and hydrolysis resistance, insect resistance, mildew resistance, low temperature resistance, easy coloring, and a wide range of process operation options. , both in the scope of application and in the improvement of its own performance, it has achieved great development. Different types of waterproof and breathable polyurethane Polyurethane is used for coating and finishing of fabrics. It has different forms not only in terms of raw material type but also in production process. According to the principle of waterproof and breathable, various waterproof and breathable products can be produced. Polyurethane coating agents are divided into two categories: solvent and water-dispersed. Among them, solvent-based coating agents are divided into single-component and two-component. Different types of coating agents have different coating process options. 1 The microporous polyurethane porous coating mainly causes the polyurethane to form micropores during the film formation process. The diameter of these pores is less than 2mm, which can prevent water droplets (average diameter 100mm), but allows water vapor molecules (average diameter 0.0004mm) to pass, thus Get waterproof breathability. There are three ways to generate micropores: foam method, phase separation method, and phase inversion method.
Are waterproof and breathable fabrics harmful to the skin? How can ordinary people tell the difference?
Waterproof and breathable fabrics are not harmful to people. Generally, waterproof and breathable fabrics are used in outdoor sportswear. For general waterproofing, a simple test is to put some water on it. If the water droplets slide quickly, it means it is waterproof. For breathability, you can dip your fingers into some water and put it on the breathable membrane or coating to see their water absorption capacity. Introduction to the functions of this type of fabric, Bp0JdofPtN
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