Waterproof breathable membranes (WBMs) characterized by a specific internal structure, allowing air and water vapor to be transferred from one side to the other while preventing liquid water penetration, have attracted much attention from researchers. WBMs combine lamination and other technologies with textile materials to form waterproof breathable fabrics, which play a key role in outdoor sports clothing, medical clothing, military clothing, etc. Herein, a systematic overview of the recent progress of WBMs is provided, including the principles of waterproofness and breathability, common preparation methods and the applications of WBMs. Discussion starts with the waterproof and breathable mechanisms of two different membranes: hydrophilic non-porous membranes and hydrophobic microporous membranes. Then evaluation criteria and common preparation methods for WBMs are presented. In addition, treatment processes that promote water vapor transmission and prominent applications in the textile field are comprehensively analyzed. Finally, the challenges and future perspectives of WBMs are also explored.
For more information, please visit our website.
Skin is a type of human tissue that comes into direct contact with the external environment, with functions such as protection, respiration, secretion and the perception of external stimuli [1]. Skin allows moist vapor to effectively propagate from the inside to the outer atmosphere, while protecting the human body against the penetration of liquid water such as rainwater and snow. This special property is defined as breathability, which is of great significance in regulating the function of organisms. Skin has the ability to regulate body temperature to a certain extent [2], but in extreme environments such as high temperature and extreme cold, the comfort and safety of the human body cannot be guaranteed. Therefore, waterproof breathable materials have been developed to ensure the normal operation of skin. Figure 1 shows the relationship between skin and fabric [3]. Natural fibers were the earliest waterproof breathable materials, but barely meet peoples needs because of their small variety, strong hydrophilicity and poor adhesion to the skin. Compared with natural fibers, synthetic fibers occupy the main market of high-quality functional clothing due to their high strength and no deformation [4]. With the development of science and technology, scientists developed the first waterproof breathable membranes (WBMs) in the s and combined them with textile materials by laminating composite methods, while ensuring the waterproof breathable property and strength of the fabric.
At present, commercial WBMs are generally divided into two types, namely hydrophilic non-porous membranes and hydrophobic microporous membranes. There is no pore structure on the surface and inside of hydrophilic membranes, and liquid water cannot penetrate them. Hydrophobic microporous membranes, more widely used than hydrophilic non-porous membranes, have an appropriate pore size and high porosity. These membranes can distinguish between water droplets (diameter > 100 μm) and small gas molecules (diameter < 1 nm), so as to allow water vapor to transfer from the body to the outside and prevent water penetration [5], thus forming a microclimate between the skin and fabric. WBMs provide protection and wearing comfort for the human body, and are widely applied in ski suits, nautical suits [6], military clothing, police jackets [7], etc.
By allowing water vapor to pass through and limiting the entry of liquid water, WBMs not only can be used as a waterproof breathable layer for clothing to ensure human comfort, but have also had significant development in fields such as construction materials [8], batteries [9], water treatment [10] and electronic equipment [11]. For example, in contrast to relatively expensive proton-exchange membranes, WBMs introduce oxygen and remove water vapor on the cathode side of membrane fuel cells (MFCs) [12], which are a kind of gas diffusion layer material with easy preparation, low cost and stable cathode structure. In addition, with the development of science and technology, mechanical and electronic products have begun to use a large number of WBMs to protect internal electronic components, as they can block liquid, dust, etc., from entering the interior [13]. More importantly, compared with completely sealing electronic devices to achieve waterproofing, the breathability of WBMs allows them to remove toxic gases generated by batteries, preventing internal leakage and affecting use.
Moreover, as the demand for fresh water increases, methods of water treatment are constantly developing. Among them, reverse osmosis (RO), forward osmosis (FO) and membrane distillation (MD) are common desalination methods. RO achieves seawater desalination by driving water molecules and ions through a hydrophilic membrane under high pressure [14], and its water transport mechanism is explained by the solutiondiffusion model. But recently, Elimelechs team [15] proposed that the migration of water and solvent in RO can be predicted by a solutionfriction model, in which water molecules travel in clusters through tiny transient holes within the polymer that exert friction on them as they pass through. As a permeation-driven membrane process, FO has the characteristics of low energy consumption, good separation effect and simple operation. Al-Furaiji et al. [16] prepared a thin-film composite (TFC) membrane with polyacrylonitrile (PAN) as the supporting layer. PAN-TFC membrane has excellent porosity, water flux and mechanical properties that are no less than those of the RO membrane. MD technology is a combination of membrane separation and thermal distillation [17], which utilizes the temperature difference on both sides of the membrane to generate a vapor pressure difference [18], enabling WBMs to separate liquid feed from a penetrant.
Common methods of preparation and processing of WBMs mainly include melt extrusion, biaxial stretching and electrospinning. The melt extrusion method has strong adaptability and uniform coating, but most processed membranes have poor water vapor permeability. Microporous membranes can be manufactured by biaxial stretching, but the preparation process is complicated and pore size adjustment is difficult. Currently, the electrospinning technique is considered to be the most effective method for fabricating WBMs. By adjusting the process parameters, electrospinning membranes with suitable fiber morphology and pore structure can be produced. In order to obtain WBMs with better comprehensive performance, two modification methods can be applied: doping modification and post-treatment. In the past few years, WBMs have developed rapidly in the textile industry, showing promising application prospects in fields such as outdoor clothing, protective clothing, wound dressing and smart clothing.
In this review, we focus on analyzing the waterproof and breathable mechanisms of two types of WBMs: hydrophilic non-porous membranes and hydrophobic microporous membranes. The advantages and disadvantages of three common WBM preparation methods are compared, and doping modification and post-treatment methods are introduced from the perspective of optimizing waterproof and breathable properties. Then, the latest progress and application of WBMs in the textile field are summarized in detail, including daily outdoor sportswear, special protective clothing, wound dressings and bionic textiles. In addition, the future development trends of WBMs are discussed in the hope that this review can promote a deeper understanding of WBMs and provide more inspiration for its applications in the textile field.
"Waterproof Breathable"
Huichen are exported all over the world and different industries with quality first. Our belief is to provide our customers with more and better high value-added products. Let's create a better future together.
Is that Waterproof AND Breathable or is it Waterproof OR Breathable?
Gore-Tex, Neo Shell, eVent and other waterproof membranes are funny things. For many people it's the layer they reach for anytime the weather isn't perfect. The thing is that those waterproof breathable membranes just don't seem to breathe very well when it's wet out and as far as I can tell, nothing does. The problem is physics.
Okay, so I talked about membranes, what are those? There's two classes of waterproof jacket out there - membranes and coatings. Membranes work by bonding a membrane to an outer material (and often another layer or two) while coatings are just that - something basically slathered onto the outer material with maybe a protective layer or raised profile on the inside. Membranes - like Gore-Tex and eVent tend to breathe better, but the jackets also tend to be heavier, less packable and more expensive. Coatings - like Marmot's NanoPro or Pertex Shield+ are lighter, less expensive, but less breathable and often less durable that their membrane counterparts.
Waterproof breathable membranes and coatings work on the principle of diffusion. Diffusion needs a difference in humidity on each side of the membrane in order for your jacket to accomplish anything. The bigger the difference, the higher the rate of diffusion. When you are working hard, it's wet inside your jacket, so it's best at moving that sweat to outside your jacket when it's dry out.
Pissing rain means it's pretty damn humid out - which means the driving pressure for diffusion is low or straight up zero which means maybe your jacket is waterproof, but it just isn't very breathable. If you are sweating while it's pouring raining, you're getting wet. If the humidity outside your jacket is the same as the humidity inside your jacket - then there's just nowhere for your sweat to go, so unless there's some crazy voodoo going on that I don't know about, I don't know how a breathable jacket could keep you dry while you are working hard in a humid environment. It's certainly what I've experienced during my time in the super wet coast mountains of BC.
If you want more info on how waterproof breathable membranes and coatings work, REI has a really good article on it.
What it really comes down to, is if it's raining out, you have three realistic options:
Notice that there's no solution for 'stay dry while working hard in the rain'. There just isn't anything out there that can do that at this point.