waterproof breathable fabric
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Basic information about Waterproof breathable fabricTRANSCRIPT
Waterproof breathable fabrics Dr Muhammad Mushtaq Mangat www.mushtaqmangat.org
Waterproof breathable fabrics
Such Fabrics which provide protection from: Weather
Wind Rain
Provides balance in heat production and heat removal from human body
Water proof and water repellant
Waterproof fabric complete protection from penetration and absorption of water
Water-repellent are shower-resistant fabric and delay the penetration of water
From long time, water proofing is being done by applying a layer of wax and oils
Now synthetic polymers such as polyvinylchloride (PVC) and polyurethane are used.
Coated fabrics are considered to be more uncomfortable during wearing, they are stiff and do not allow to escape moisture
Water-repellent fabric is more comfortable to wear but its water-resistant
Commonly used for ordinary rain and conditions
Breathable Breathable fabrics passively allow water vapor to
diffuse through them yet still prevent the penetration of liquid water [1]
Removal of sweat is must for creating of thermal balance between human body and environment
Human body core temperature is around 37 °C and skin temperature is between 33-35 °C
Narrow limit which human can tolerate is 34 °C and 42 °C
Breathable fabric contribute in thermal balance
Sweat production
Sweat production rate
http://www.occup-med.com/content/3/1/4
Severity of thermal stress
In US in1982 US fire death statistics show that only 2.6% were due to burns alone whereas 46.1% were the result of heart attacks due to thermal stress caused by stoppage of sweat evaporation [1]
Firefighters can lose up to 4 liters (4000 g) of fluid per hour when in proximity to a fire [1]
Introduction of breathable fabric
In 1991 Lomax introduced modern breathable waterproof fabrics were being claimed to be capable of transmitting more than 5000 gm-2 day-1 of water vapor
Now fabrics are available which can transmit up to 10 000 gm-2day-1
Waterproof breathable fabrics prevent the penetration of liquid water from outside to inside the clothing yet permit the penetration of water vapor from inside [1]
IMAGE SOURCE PAGE: http://dragon688.en.made-in-china.com/product/NoKJjMqxLekP/China-Breathable-Fabric-C-B478-.html
Breathable Fabric (C&B478) - China Pu Fabric,Coated Fabric
Types of waterproof breathable fabric
• densely woven fabrics
• membranes
• coatings.
Densely woven fabrics
First fabric Ventile was introduced in 1940s for US air forces
Made by using finest types of long staple cottons
Processed into combed yarn, which is then plied
Got yarn regularity and ensures that the fibers are as parallel as possible to the yarn axis, and lowest porosity
Woven using an Oxford weave, which is a plain weave with two threads acting together in the Warp
Minimum crimp in the weft Ensuring that the fibers are as parallel as possible to the surface of the fabric
On wetting cotton fibers swell transversely reducing the size of the pores in the fabric and requiring very high pressure for penetration [1]
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[1]
Dense fabric Pore size is less than 10μm in diameter
Synthetic fibers can also be used
Microfilaments are usually made from polyamide or polyester.
Water penetration resistance of the fabric is improved by application of silicone
or fluorocarbon finish.
Results are not better than cotton due to swelling property of cotton
Dense fabric pore size is 10μm in dry and 2-3 in wet conditions
Traditional fabric pore size is around 50-60 μm [1]
http://www.ventile.co.uk/uses.htmlx
Nylon High Density Fabric - China Nylon Fabric,High Density IMAGE SOURCE PAGE: http://weihetex.en.made-in-china.com/product/mqOQrDeAYMUb/China-Nylon-High-Density-Fabric.html
Membranes
Membranes are extremely thin films made from polymeric material
Engineered in such a way that they have a very high resistance to liquid water penetration
Allow the passage of water vapor
Membrane is only about 10μm thick and, therefore, is laminated to a conventional textile fabric to provide the necessary mechanical strength [1]
Tensile Membrane Structure Fabric - China pvc coated tent fabric ... IMAGE SOURCE PAGE: http://www.ecvv.com/product/2674052.html
Microporous membranes
Microporous membrane, developed and
introduced in 1976 by W Gore, is known as Gore-Tex (http://www.gorefabric.com).
This is a thin film of expanded polytetrafluoroethylene (PTFE) polymer claimed to contain 1.4 billion tiny holes per square centimeter
smaller than raindrops [1]
Water droplet size is 20 μm
Water vapor size is around 0.003 μm
Pore size is 5 μm[ http://budagear.com/index.php]
http://budagear.com/index.php
[1]
[1]
Hydrophilic membranes
Hydrophilic membranes are very thin films of chemically modified polyester or polyurethane containing no holes which, therefore, are sometimes referred to as non-poromeric.
Water vapour from perspiration is able to diffuse through the membrane in relatively large quantities
The polyester or polyurethane polymer is modified by incorporating up to 40% by weight of poly(ethylene oxide) [1]
http://www.filtsol.com/technology/super_hydrophilic.shtml
Scanning electron micrograph of hydrophilic membrane.[1]
Methods of incorporating membranes [1]
Coatings
These consist of a layer of polymeric material
applied to one surface of the fabric.
Polyurethane is used as the coating material. Like membranes, the coatings are of two types:
microporous and hydrophilic. These coatings are much thicker than membranes [1].
Microporous coatings
Microporous coatings have a similar structure
to the microporous membranes.
The coating contains very fine interconnected channels, much smaller than the finest raindrop but much larger than a water vapour molecule
Schematic diagram of a microporous coating [1]
Hydrophilic coatings
Hydrophilic coatings use the same basic water vapor permeability mechanism as the hydrophilic membranes.
The difference between microporous materials and hydrophilic materials is that with the former, water vapor passes through the permanent air-permeable structure whereas the latter transmit vapor by a molecular mechanism involving adsorption–diffusion and desorption.
These coatings are all based on polyurethane, which has been chemically modified by incorporating polyvinyl alcohols and polyethylene oxides.
Assessment techniques
Resistance to penetration and absorption of liquid water
Wind resistance
Water vapor permeability [1]
Bundesmann rain tester
Diagram of Bundesmann apparatus 1]
Air Permeability Tester Air Permeability Tester Wholesale Supplier ... IMAGE SOURCE PAGE: http://www.hellotrade.com/prism-instruments/air-permeability-tester.html
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References
1. Holmes, D.A., Waterproof breathable fabrics, in Handbook of Technical Textiles A.R. Horrocks, Anand, S. C., Editor 2000, Woodhead Publishing Ltd Cambridge.