The “Ultra-Ever Dry” waterproof material developed by Ultratech has a hydrophobic and oleophobic coating that protects against damage from almost all liquids. It uses unique nanotechnology to form an air protective film on the surface of the object that can prevent the erosion of water, oil and other liquids. Another breakthrough of “Super Dry” compared to traditional technology is its super adhesion and wear resistance. It is suitable for any place where wear resistance is required and can be applied to almost any material including textiles.
The waterproof material widely used in the textile and clothing industry is polymer membrane, which is widely used in waterproof and breathable clothing, such as jackets, surgical clothing, military uniforms, etc. By controlling the appropriate air permeability, such clothing can play a protective role while also providing a certain degree of comfort. Different application fields require different polymers to construct membranes with different structures. Polymer membranes can be divided into microporous membranes, hydrophilic membranes and microporous hydrophilic composite membranes. The following mainly introduces the uses of these membranes. Application in protective clothing.
1 Microporous membrane
In a microporous membrane, the size of the micropores is 0.1 to 50 μm, which determines that only air or water vapor can pass through the membrane but liquid cannot. Electrospinning technology has low cost, easy operation and high applicable value. This technology can use natural polymers, synthetic polymers, etc. as raw materials to prepare waterproof and breathable microporous films.
1.1 Polytetrafluoroethylene (PTFE)
GORE-TEX®Waterproof and breathable technology
As a hydrophobic polymer membrane with ultra-low surface energy, PTFE membrane has good water resistance, but low air permeability. Although PTFE has very small pores and does not have many open pores, water vapor can still diffuse through the micro-voids, so this membrane can be effectively waterproof and windproof when laminated to fabrics. For example, some military poisonous gases can easily penetrate into clothing and cause harm to the human body. For this, the hydrophobicity of the surface of the protective clothing material can be increased to improve the protective performance. Modifying the PTFE microporous membrane with fluorine-containing surfactants can improve the hydrophobicity of the membrane layer. When toxic gases enter the liquid, due to the low surface tension and high surface hydrophobicity of the membrane, droplets containing toxic gases will automatically escape from the surface. Sliding off to protect skin from poisonous gases. Protective clothing with PTFE membrane as the main material can effectively block oily mustard gas, biochemical poisonous gases, etc.
PTFE laminated composite material is the material of choice for windproof, warm and anti-toxic gas. Clothing made of this material can be widely used in outdoor sportswear, fire protection clothing, military protective clothing and other products. At present, many first-class manufacturers in the world use PTFE as waterproof and breathable material. The Gore-Tex waterproof and breathable fabric developed by the American Gore Company uses a composite of PTFE film and fabric. It is currently the most advanced and durable waterproof and breathable product in the world. Japan and many European countries have also conducted relevant research, but due to the confidentiality of preparation technologies in various countries, so far only Gore, Pall, Mill-pore, Whatman, Gelman, DDS, Dominick, Sartorius and Japan’s Nitto Denko and Daikin have , Asahi Glass and other companies can produce PTFE microporous membranes. In addition, the First-Tex waterproof and breathable fabric developed by the famous American FBA International Group and the Omni-Tech waterproof and breathable fabric developed by the American Columbia Company also use PTFE as a waterproof and breathable film material, and their products have been widely used in military protective clothing. Although the PTFE microporous membrane developed in our country has been applied in the fields of environmentally friendly dust removal and functional clothing at medium and normal temperatures,�, and has basically solved many problems existing in the production technology of PTFE microporous membranes. However, compared with similar foreign products, there are still huge differences, and a large number of high-quality membranes still rely on imports.
1.2 Polyurethane (PU)
PU is widely used in many fields due to its excellent performance, involving light industry, chemical industry, electronics, textile, medical care, construction, building materials, automobiles, national defense, aerospace, aviation, etc. PU has good tensile strain, wear resistance, elasticity and toughness. It is a polymer commonly used to make breathable films.
By mixing cellulose derivatives and hydrophobic PU to form a film, the water vapor transmission rate and mechanical properties of the synthetic film are effectively improved. In PU synthetic membranes, cellulose derivatives are not only cross-linking agents but also chain extenders. In addition, an appropriate amount of cellulose derivatives can improve the water vapor permeability of synthetic membranes. When adding cellulose derivatives, temperature also has a certain impact on water vapor. At a temperature of 50°C, water vapor permeability is improved. When the PU film is fluorinated, the contact angle between the film layer and water reaches 156°, and the contact angle with oil reaches 145°, indicating that it has super hydrophobic and oleophobic properties. And this fluorinated PU membrane has higher water resistance, better air permeability and water vapor transmission rate. Polymer films have lower air permeability than inorganic films. Inorganic super-hydrophobic and super-oleophobic nanofiber membranes are prepared by dipping synthetic fluorinated PU on electrospun silica nanofibers, which have good With its waterproof and breathable properties, this composite material is ideal for protective clothing.
From the perspective of practical application, kingtex fabrics made of PU film are currently very popular in the market because of their extremely high breathability. The Texapore fabric currently developed by German Wolf Claw Company uses super-strength PU composite fabric, which has high breathability and strong waterproof properties.
1.3 Polyvinylidene fluoride (PVDF)
PVDF is a microporous fiber widely used in film materials. Compared with most polymer materials, PVDF membranes have high mechanical strength, thermal stability, chemical resistance and hydrophobicity. PVDF hydrophobic membrane can also be used to prepare microporous films due to its waterproof properties. PVDF nanofiber membranes can be successfully prepared by electrospinning technology in dimethylformamide/acetone mixed solution. When the PVDF concentration is 12% (wt%, the same below) and the volume ratio of dimethylformamide/acetone mixed solution is 6:4, a nanofiber membrane with good air permeability and excellent waterproof performance can be produced.
Since my country began to develop PVDF membranes in the 1980s, certain progress has been made, and part of the research has been commercialized. Japan, the United States, Europe, etc. have conducted in-depth research on PVDF materials, and related products have been applied in many fields. At present, foreign PVDF-related products have many varieties and grades, mature processing technology, and wider application range than domestic ones, especially in high-end fields. Recently, Cheng has successfully applied waterproof and breathable fabrics composed of hydrophobic PVDF membranes to raincoats, outdoor sportswear and other textile clothing products in his patent.
2 Hydrophilic membrane
Hydrophilic polymers are composed of copolymers. Generally, hydrophilic membranes are airtight, but breathable effects can also be achieved by adding humectants to the molecular chains. In addition, when the hydrophilic membrane comes into contact with liquid or is under a high saturated vapor pressure, it will undergo a swelling process. Through this process, the water vapor permeability of the hydrophilic membrane is also enhanced. Therefore, membrane layers composed of hydrophilic polymers are a good choice for making breathable protective clothing.
2.1 PU
Since the German Bayer Laboratory invented hydrophilic PU with water vapor permeability in 1962, hydrophilic non-porous polyurethane membranes have been gradually used as materials for breathable clothing. Hydrophilic PU is composed of water-soluble soft segments and insoluble diisocyanate hard segments. Compared with microporous PU membrane, hydrophilic PU membrane has better adhesion and durability to the material substrate, and has higher gloss.
By adding polyoxyethylene to the hydrophilic PU molecular chain, the breathability of this PEO-PUs composite film layer is not only improved, but its waterproofness and durability are balanced. Water-based PU-urea is a non-toxic and non-flammable composite material that has good adhesion to rubber, polymer fiber and other substrates. When the composite polymer contains 70% polyethylene glycol and 0.5% hardener, it has good dimensional stability, strong hydrophilicity, high water vapor transmission rate, and can be directly coated on waterproof and breathable clothing. superior. In cold environments, protective clothing is required to have good thermal insulation, and heat loss can be reduced by depositing metal on the fabric. Using the vapor deposition method to condense Al vapor in the form of nanoparticles on the surface of electrospun PU, the thermal insulation performance can be improved while maintaining moisture permeability. At present, typical hydrophilic PU products include the hydrophilic PU coated fabric Impraerm produced by the German Bayer Company, the Sympatex laminated fabric produced by the Dutch AKZO Company, and the Qualitex multifunctional waterproof and breathable fabric produced by the American Qualitex Company. These breathable membranes It can be applied to outdoor sportswear or protective clothing under severe weather conditions.
2.2 Polyvinyl alcohol (PVA)
PVA was synthesized by German chemists W O Herrmann and Dr. W W Hachnel in 1924. It has strong adhesion and wear resistance. It is a hydrophilic polymer with many excellent properties, which makes it useful in daily life. The uses are very broad. PVA can remove moisture from the human body and transfer it to the atmosphere. Polyacrylic acid (PPAc) is used as a cross-linking agent to coat high molecular weight polyvinyl alcohol on cotton fabrics. The carboxyl groups in the polyacrylic acid, which acts as a cross-linking agent, are combined with the hydroxyl groups in PVA to form a breathable film layer. When the molar ratio of PVA to PPAc is 25:1, this hydrophilic coating has excellent breathability. In addition, this kind of film layer is continuous without gaps, so it is very fast when applied to fabrics. Compared with developed countries, my country is relatively lagging behind in the application of PVA and its derivatives. It can be predicted that with the expansion of my country’s economic scale and the improvement of quality, PVA and its derivatives will be widely used in China’s protective clothing.
2.3 Polyoxymolybdate
Some researchers have proposed that selective membranes with polyoxymolybdate as the main component can be used in protective clothing against chemical gases. On the nanocomposite membrane with ethylene-PVA copolymer and polymolybdate as the main components, water molecules can pass through the hydrophilic holes, but large hydrophobic molecules are blocked outside the membrane layer. The moisture permeability of this membrane is very high, while the permeability of organic solvents is very low. Therefore, films with polyoxymolybdate as the main component can effectively block harmful chemical gases in the environment and can currently be used in chemical protective clothing in factories and military protective clothing. Outdoor sportswear made of breathable membranes can provide protection in extreme weather conditions. In addition, hydrophilic membranes made of PVA and PVDC can effectively block toxic chemical gases when used in chemical protective clothing.
3 microporous hydrophilic composite membrane
Figure 1 Schematic diagram of PU/c-PVA composite fiber membrane
Some researchers used the electrospinning method to directly coat the PU microporous membrane layer on the prepared hydrophilic membrane layer (Figure 1). The prepared composite membrane contained a hydrophobic PU membrane layer and hydrophilic polyvinyl alcohol ( c-PVA) film layer. In the composite membrane, the hydrophobic section is waterproof, and water can spontaneously flow from the hydrophobic section to the hydrophilic section; water vapor can pass through the hydrophilic section. At present, microporous hydrophilic membranes have not been widely used in protective clothing, but this kind of composite membrane with special properties has great development prospects.
4 Conclusion
Microporous membranes, hydrophilic membranes and composite membranes can all be used in many fields and play a protective role, but each has its own characteristics:
(1) Microporous membranes have a certain degree of air permeability. Hydrophilic membranes can also achieve breathability by adding moisturizers to their molecular chains. However, the water vapor permeability is not as high as that of microporous membranes. For composite membranes, , increasing strength and toughness will lead to a decrease in breathability;
(2) Hydrophilic membranes are generally continuous without gaps, and the pore size of hydrophilic membranes is generally smaller than that of microporous membranes. Therefore, hydrophilic membranes have higher adhesion to the substrate, while composite membranes have higher adhesion to the substrate due to the addition of Hydrophilic film layer, so its adhesion is also enhanced;
(3) Hydrophilic membranes have better wear resistance than microporous membranes and can maintain their original performance after washing;
(4) Hydrophilic membrane has better dimensional stability and higher wind resistance.
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