Post on 07-Aug-2015
Vignesh Dhanabalan (M.Tech) - vigneshdhanabalan@hotmail.com
Water repellency
Water repellent is a state characterized by the non-spreading of water globules on a textile material. This term is not normally applied to a water-repellent finish impervious to air. This is generally referred to as water proof. It is generally done by treated fabric with fat, wax, rubber etc.
14/3/2014
Vignesh Dhanabalan (M.Tech) - vigneshdhanabalan@hotmail.com
Requirements of Water Repellency TextilesPurpose and Scope
• This method of test is especially suitable for screening if any textile has been given a water-repellency finishes. It is not intended for use in measuring the penetration of water through the fabric.
Terminology
• Water Repellency: in textiles, the characteristic of a fiber, yarn or fabric to resist wetting
14/3/2014
Vignesh Dhanabalan (M.Tech) - vigneshdhanabalan@hotmail.com
Water Repellency Classification
Grade Classification
100 (ISO5 ) Excellent
90 (ISO 4) Very Good
80 (ISO 3) Good
70 (ISO 2) - ---
50 (ISO 1) - ---
0 ----
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Principles of moisture vapor transfer:
Absorption, transmition and desorption of the water vapor by the fibers.
Diffusion of the water vapor through the air spaces between the fibers.
Transmition of water vapor by forced convection
Capillary pressure and capillary raise are determined using
P = 2γLV cos / Rc , L = ((Rcγ cos /2)* t1/2
P = capillary pressure L = liquid pressureRc – capillary radius t and - time and viscosity
Transport Mechanism:
Capillary’s diameter and surface energy
Properties required for breathable fabrics:
Soft feel, light weight and Durable
Easy care/launderability
Rapid drying to prevent catching cold.
Good air and water vapor permeability.Rapid moisture absorption and conveyance capacity
Optimum heat and moisture regulation (thermo-regularity effect)
Absorption of surplus heat. Dimensionally stable even
when comes in contact to waterNo/Minimum water
absorption of the layer of clothing just positioned to the skin.
Producing breathable fabrics:
Smart Breathable fabrics (PCP)SMP – PU material
Micro porous Membrane
Densely Woven Fabric (Micro denier<10 micron)
Closely woven fabrics
(oxford weave) up to 20 min
Various methods for generating microspores membrane and coating:•Mechanical fibrillation (Film) - PTFE films – biaxial stretched- negative
poissons ratio - 50– 400 µm – crystallinity of polymer >98% - 9
billion pores /inch2 -
•Wet coagulation - ultrafine pores < 1µm – salt leaching - Requires
Precise control below 3 µm.
•Thermo coagulation - volatile solvent - PU dissolved in methyl ethyl
ketone, toluene, and water, having 15–20% solid
•Foam coating - fluorocarbon (FC) polymer, PU coating – soft n
flexible - abrasion
•Radio frequency (RF)/ion/UV or E beaming - Sputtering of Teflon by Ar
gas
Application of Polyurethane coating:
• Pore dia of 0.0004 µm possible
•PU-based film designed (Permatex) by J.B. Broadley coated on fabrics offers a
vapor permeability of at least 70%.
•Grabotter membrane (Grabo Ltd.) used in waterproof shoes is a PU-based film.
•Micro porous PU film is being produced by Acordis (Tarka) is applied by a
transfer process from the release paper and it can be applied to almost any type
of substrate.
Knife coating
Floating knife
Extrusion
Calendaring
Curtain coating
Gurave coating
Reverse roll
Testing of Breathability of Fabrics using different techniques:
S.no Methodology Standard Purpose
1 Sweating Guarded Hot Plate
Tests
(ISO 11092, ISO 1999, and ASTM F 1868)
Measurement of thermal and water-vapor resistance
under steady-state conditions
2 Upright Cup Method ASTM E96 Water Vapor Transmission of Materials , permeability,
plastics (general), plastic sheet and film, sheet material3 Inverted Cup Method ASTM E96
4 Desiccant Inverted Cup Test Method
E96 M-05
5 Dynamic Moisture Permeation Cell Test
ASTM F 2298
Standard Test Methods for Water Vapor Diffusion
Resistance and Air Flow Resistance of Clothing Materials
Using the Dynamic Moisture Permeation
6 Moisture vapor transmition cell
ASTM D1653 - 13 Moisture vapor transmition behavior of fabric
7 Dynamic moisture permeable cell
ASTM F2298-03(2009) e1
Moisture transmition capability of cell
Relative water vapor permeability (%):
Heat loss when the fabric is placed on the measuring head X 100 Heat loss from bare measuring head
The main requirements for WVPI are based on
•Water vapor permeability index percentage.•Resistance to water penetration.•Cold cracking temperature.•Surface wetting (spray rating) after cleaning.
For a typical breathable fabric the acceptable parameters should have
•Water-vapor permeability (min 5000gm-2 for 24 hrs)•Water proofness min 130 cm (hydrostatic pressure)•Wind proofness less than 1.5 ml/cm2/second @ 1M bar
Water Proof rating:Waterproof Rating (mm)
Resistance provided Withstand capabilities
0-5,000 mmNo resistance to some resistance to moisture
Light rain, dry snow, no pressure
6,000-10,000 mmRainproof and waterproof under light pressure
Light rain, average snow, light pressure
11,000-15,000 mmRainproof and waterproof except under high pressure
Moderate rain, average snow, light pressure
16,000-20,000 mmRainproof and waterproof under high pressure
Heavy rain, wet snow, some pressure
20,000 mm+Rainproof and waterproof under very high pressure
Heavy rain, wet snow, high pressure
For example : 10000/10000 – First number represents water proofness of fabric and second number represents breathability of the fabric. Higher the value better is the result
Application
3M incise tape 9948Neo-G knee support
Breathable snow protect mountain wear
Fire man Protective Apparel
Racer Suite
Ventile Roofing Membrane
Somatex Casing layer
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Conclusion:
• Comfort property has become the most prime objective of the buyer/consumer where breathability of the fabric with water proofness has been the primary importance in areas that do not enjoy the evergreen nature.
• Extensive research is required to understand the relationship between segmental ventilation and local comfort of the fabric subjected to active usage of the person.