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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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

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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

[1]

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.