Presentation on theme: "Waterproof breathable fabrics Dr. Jimmy Lam Institute of Textiles & Clothing."— Presentation transcript:
Waterproof breathable fabrics Dr. Jimmy Lam Institute of Textiles & Clothing
Learning Objectives n What are waterproof breathable fabrics n Type of waterproof breathable fabrics –Densely woven fabrics –Membrances –coatings
Waterproof breathable fabrics Definition n Waterproof breathable fabrics are designed for use in garments that protection from the weather, that is from wind, rain and loss of body heat. n Waterproof fabric completely prevents the penetration and absorption of liquid water, in contrast to water-repellent fabric, which only delays the penetration of water. n Traditionally, waterproof fabric was made by coating (like animal fat, wax, vegetable oils). Nowadays, uses polyvinylchloride (PVC) polymer. n Coated fabrics are, however, considered to be more uncomfortable to wear than water-repellent fabric, as they are relatively stiff and do not allow the escape of perspiration of vapour.
Waterproof breathable fabrics Definition n Water-repellent fabric is more comfortable to wear but its water- resistant properties are short lived. n The ideal fabric should be waterproofed (do not allow water get into the fabric) and breathable (allow water vapour escape from skin). n Breathable fabrics allow water vapour (gas) to diffuse through fabric and still prevent the water penetration of liquid water. n Production of water vapour by the skin is essential to maintenance of body temperature. The normal body temp. is 37 C, and skin temp is between 33 to 35 C. n During physical activity, the body provides cooling by producing perspiration. If the water vapour cannot escape to the surrounding, the relative humidity of the microclimate inside the clothing increase and clothing becomes uncomfortable to wear.
n Table 12.1 shows the perspiration rates and activities from sleeping to max work rate. n If the body is to remain at the physiologically required temp. clothing has to permit the passage of water vapor from perspiration rate as shown in Table 12.1. n The ability of fabric to allow water vapour to penetrate is commonly known as breathability. n The waterproof breathable fabrics prevent the penetration of liquid water from outside to inside the clothing. n It can, however, permits the penetration of water vapour (gas) from inside the clothing to outside atmosphere.
How to make a waterproof and breathable fabric n We want to prevent water molecule (liquid) to get it the fabric and allow water vapour (gas) to pass from skin to fabric. n The size of water droplet (liquid) is 100 μm and the water vapour (gas) is 0.0004 μm and we need to make a fabric with porous space around 10 μm. n In this way, it allows water vapour to pass through (from skin to fabric) and prevent water droplet to penetrate (from outside to fabric).
Types of waterproof breathable fabric n There are several methods which can be used to obtain fabrics which are both breathable and water proof. They are: 1.Densely woven fabrics 2.Membranes (Gore-tex fabric) 3.Coatings
Densely woven fabrics n Probably the first effective waterproof breathable fabric was developed in the 1940s for military purposes and is known as Ventile. n Ventile fabric uses the finest cotton yarn, combed and piled together. The yarn is woven using Oxford weave, which is a plain weave with two threads acting together in the warp. n When the fabric surface is wetted by water, the cotton fibres swell reducing the size of the pores in the fabric and requiring very high pressure to cause penetration. n The fabric is thus rendered waterproof without the need for any water repellent finishing treatment.
Ventile fabric in dry state Ventile fabric in wet state, closely packed by swelling of cotton fibres
Highly dense fabric Results n The use of very fine fibres and filaments and dense construction (setts) results in fabrics with very small pore size compared with conventional fabrics. n Typical pore size for waterproof fabric is about 10 μm compared with 60 μm for conventional fabric. n Ventile fabric has a pore size of about 10 μm when dry and 3-4 μm when wet. n Fabric made from micro-filaments is claimed to have 7000 filaments per cm.
Membranes n Membranes are extremely thin films made from polymeric material and engineered in such a way that they have a very high resistance to liquid water penetration, yet allow the passage of water vapour. n A typical membranes is only 10 μm thick and is laminated to a conventional textile fabric to provide the necessary mechanical strength.
Microspores membranes (Gore-Tex) n The first and probably best known microporous membrane, developed by Gore in 1976. (http://www.gorefabric.com) http://www.gorefabric.com n This is a thin film of polytetrafluoroethylene (PTFE) polymer with 1.4 billion tiny holes per cm 2. n These holes are much smaller than the raindrops (2-3 μm compared with 100 μm), yet very much larger than water vapour molecule (0.0004 μm).