Water repellency & Waterproof Breathable Fabrics and repellency test method

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.

Thanks to all.