Fabric Repellency and Surface Tension Quiz

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Questions and Answers

What is the required surface tension of a liquid for fabric to be considered water repellent?

20-35 mN/m

15-20 mN/m

73 mN/m (correct)

40-50 mN/m

How is surface tension most simply defined in relation to liquid molecules?

The angle of interaction between a liquid and a solid

The ability of a liquid to absorb energy

The total surface area of a liquid

The cohesive force keeping molecules together at the surface (correct)

What phenomenon is described as a result of spontaneous wetting in a capillary system?

Capillary force

Surface tension

Wicking (correct)

Cohesive energy

Which of the following chemical finishes is NOT commonly associated with repellent treatments?

Polyester finish Signup and view all the answers

What is the purpose of hydrostatic pressure tests in evaluating fabric repellency?

To measure the water penetration under pressure. Signup and view all the answers

What does the contact angle measure?

The degree of wettability of a liquid on a solid Signup and view all the answers

Which fabric feature has a significant impact on its repellency?

Fibre composition Signup and view all the answers

Which of the following describes surface energy in relation to solids?

It is evaluated at the solid-gas interface to determine wettability Signup and view all the answers

For fabric to be oil repellent, what is the required surface tension of the liquid?

20-35 mN/m Signup and view all the answers

What does hydrophobicity describe in the context of surface interactions?

Resistance of a surface to wetting by liquids Signup and view all the answers

What is considered a borderline pass in the grading of drops?

Three or more drops show a rounded drop with partial darkening. Signup and view all the answers

At what stage can the AATCC hydrocarbon resistant test be carried out?

As received or after the agreed number of washes Signup and view all the answers

Which grading represents a well-rounded drop without darkening?

A Signup and view all the answers

In the context of soil release, what does 'soil' refer to?

Substances not normally present on a substrate. Signup and view all the answers

How is the grade determined for a borderline pass?

By subtracting one-half from the number of the borderline pass test liquid. Signup and view all the answers

What grade indicates a complete failure in the drop grading system?

D Signup and view all the answers

What does the oil repellency grade indicate in AATCC testing?

The highest numbered test liquid that does not wet the fabric Signup and view all the answers

What is the minimum specimen size required for the AATCC 70 test?

20 × 20 cm Signup and view all the answers

How long should specimens be conditioned before applying stains?

4 hours Signup and view all the answers

What is the purpose of the AATCC 70 test method?

To detect the presence of a fluorochemical finish Signup and view all the answers

What is the preferred surface for conducting the test procedure?

A horizontal smooth surface Signup and view all the answers

Which of the following describes a standard test liquid used in the AATCC oil repellency test?

Hydrocarbons with varying surface tensions Signup and view all the answers

What temperature and humidity conditions are required for specimen conditioning?

21 ± 1°C and 65 ± 2% RH Signup and view all the answers

What is the reason for conducting the test with at least two layers of the fabric?

To prevent the test liquid from wetting the underlying surface. Signup and view all the answers

Which factor must be ensured to maintain the integrity of the oil repellency grade?

Equipment and gloves must be free of silicone. Signup and view all the answers

What is the advised method for placing drops of the test liquid on the fabric?

Hold the dropper tip about 0.6 cm from the fabric surface. Signup and view all the answers

How should the drops of test liquid be spaced on the fabric?

4 cm apart. Signup and view all the answers

What should be observed for at the liquid-fabric interface after placing the drops?

No penetration or wetting at the interface. Signup and view all the answers

What is the duration for which drops should be observed during the test?

30 ± 2 seconds. Signup and view all the answers

What indicates that the next higher-numbered test liquid should be used?

If there is obvious wetting or wicking around the drop. Signup and view all the answers

What is the appropriate action if drops of the test liquid are observed to penetrate the fabric?

Stop the testing procedure immediately. Signup and view all the answers

What conditions must be met when preparing fabric specimens for testing?

At least three specimens should be taken diagonally. Signup and view all the answers

Which of the following best describes the environmental conditions for conditioning the test specimens?

21 ± 2°C (70 ± 5°F) and 65 ± 2% relative humidity. Signup and view all the answers

What should be specified on each fabric specimen before testing?

The surface exposed to water. Signup and view all the answers

Which testing condition involves a constant rate of water flow?

Dynamic conditions. Signup and view all the answers

What is the minimum size for fabric specimens to allow proper clamping?

200 × 200 mm. Signup and view all the answers

What should be verified about the water in contact with the test specimen before starting the test?

Its temperature should be regulated at 21 ± 2°C. Signup and view all the answers

How many washes must be agreed upon for testing a fabric after washing?

It should be agreed upon but typically 3 washes. Signup and view all the answers

What is the appropriate gradient setting for the test procedure?

60 mbar/min. Signup and view all the answers

Study Notes

Repellency of Textile

Water repellency is a common functional property for protective clothing, needed for comfort and ability.
Water repellency is the ability of a textile material to resist wetting.
Water repellent textiles have industrial, consumer, and apparel uses.
Water repellency treatment modifies surface tension, causing fibers or fabric to repel water drops. This also improves soil repellency.
Water resistance is needed for outdoor clothing to protect against rain, and for furniture and bedding to protect against liquid spills.

Some Definitions

Water resistance: The characteristic to resist wetting and penetration by water. Also called water repellency.
Water repellent: The relative degree of resistance of a fabric to surface wetting, water penetration, water absorption. Assessment is dependent on objective and/or subjective factors pertaining to the test condition.
Water proof: A condition where a textile material (treated or untreated) prevents the absorption and penetration of water. This creates a water barrier in all practical end-use conditions.

Difference Between Water Repellent and Water Proof Textile

Feature	Water Repellent	Water Proof
Pores	Open	Filled
Water vapor permeability	Small to large	Zero to very small
Air permeability	Usually large	Zero to small
Resistance to water penetrations	Resistance to wetting by rain, spreading and wicking of water. Permits water passage under external hydrostatic pressure.	Highly resistant even under external hydrostatic pressure.

Some Definitions (Wetting, Wicking, Low Energy Surface)

Wetting: Displacement of a fiber-air interface with a fiber-liquid interface.
Wicking: The spontaneous flow of a liquid in a porous substrate, driven by capillary forces. Wicking is a result of spontaneous wetting in a capillary system.
Low energy surface: Surfaces exhibiting low interactions with liquids. These surfaces are called low energy surfaces.

Some Definitions (Surface Tension, Surface Energy, Contact Angle)

Surface tension: The cohesive force of molecules at the surface of an element attracting toward one another to take up the least possible surface area. Measured in mN/m.
Surface energy: Performed on solids at the solid-gas interface, provides information about solid wettability. Expressed in mN/m. It is an expression of hydrophylicity, hydrophobicity, and olephobicity behaviors.
Contact angle: The angle formed where a liquid or vapor interacts with a solid surface.

Contact Angle and Wettability

Hydrophilic: Contact angle < 90°.
Hydrophobic: Contact angle > 90°.
Superhydrophobic: Contact angle > 150°. Lower contact angle = higher wettability

Common Finishes for Repellency

Paraffin repellent
Stearic acid (melamine repellent)
Silicon water repellent
Fluorocarbon based repellent
Produces surfaces with surface energies of 15-20 mN/m.

Typical Textile & Their Requirements for Repellency Finishes

Data is displayed in table format. Details about different textile types and finishes required are listed.

Factors Affecting the Repellency of Textiles

Fiber
Fabrics
Chemical finishes
Laundering conditions

Test Methods for Water Repellency

Class I: Spray test to simulate exposure to rain (AATCC 22, 35, 42)
Class II: Hydrostatic pressure tests. These measure water penetration as a function of pressure exerted by water standing on the fabric (AATCC 127, ISO 811)
Class III: Sorption of water by the fabric immersed in water (AATCC 70)

Oil Repellent (Hydrocarbon Resistant Test) AATCC 118

Scope: Detects the presence of fluorochemical finish and other compounds capable of imparting a low energy surface, on all types of fabrics, by evaluating the fabric's resistance to wetting by a series of liquid hydrocarbons with different surface tensions.

Standard Test Liquids AATCC Oil Repellency

Data is displayed in table format. Details about different grade number, composition, and surface tension values are listed.

Test Specimen Size and Preparation

Use two specimens of the same size from each sample. Specimen size should be sufficient to evaluate all test liquids, but no smaller than 20 x 20 cm.
Condition the test specimens for a minimum of 4 h at 21 ± 1°C (70 ± 2°F) and 65 ± 2% RH before application of stains.

Testing for Hydrocarbon Resistant Test

Testing can be carried out at:
- As received
- After the number of washes agreed
If testing needs to be done after washing, the wash procedure should follow AATCC 135 (as per care label for washing and drying).

Test Procedure (General)

Place the test specimen flat on white textile blotting paper on a smooth, horizontal surface.
When evaluating open weave of thin fabrics, the test should be done on at least two layers.
Equipment, benches, and gloves should be free from silicone, as silicone-containing products can negatively affect the oil repellency grade.

Test Procedure (Specifics)

Additional information regarding steps to follow during the testing process.

Grading of the Drops

Describes the grading system for test drops. Details about pass/fail criteria for different grades are explained.

General Requirements

Defines the general requirements for the original state and after agreed number of washes when evaluating the different testing approaches.

Soil and Stain Release Test AATCC 130

Scope: Describes the methodology for testing soil and stain release.

Some Terminologies (Soil, Soil Release, Stain)

Soil: Dirt, oil, or substances not normally intended to be present on a substrate, like a textile material.
Soil release: The degree to which a soiled substrate approaches its original appearance.
Stain: A local deposit of soil or discoloration on a substrate exhibiting some degree of resistance to removal.

Principal (Soil and Stain Release Test)

Provides the methodology on how to force stain substance to penetrate the fabric.
Details on the scale for evaluating the residual stain after the fabrics are laundered.

Test Specimen Size and Preparation (for staining)

Details about the size of test specimens.
Conditioning period for the test specimens.

Testing for Stain Release

Testing is required to be carried out at:
- Original state (after one wash)
- After 3 washes
If testing needs to be done after washing, the wash procedure should follow AATCC 135 (as per care label for washing and drying).

Staining Procedure

Detailed step-by-step instructions for staining fabric specimens for testing purposes.

Washing Conditions (general)

Lists different machine cycles and washing temperatures suitable for textile testing

Drying Conditions (general)

Lists different drying methods for testing the textile material, for example tumble drying, line drying, drip drying, and screen drying.

Procedure (general)

Provides general steps to perform the test, such as washing conditions, reference detergent addition, and drying conditions selection.

Evaluation (general)

Details about the evaluation procedure, rating criteria, and criteria for when mass of the blotting paper increases
Method for obtaining a complete overall picture of penetration resistance of fabric or fabric combinations. Additional considerations when evaluating results.

Evaluation (specifics)

Rating criteria for stain release. Explanation of each grade from 1-5 and their corresponding standard stains.
Assessment is in a Dark room with special lighting conditions (F96 CW).

General Requirements (for stain release)

Lists general requirements for the evaluation procedure. Criteria are provided for the original and after agreed number of washes stages.

Spray test to simulate exposure to rain AATCC 22

Details about spray tests in order to simulate exposure to rain.

Scope (spray test)

Defines the applicability of the test method for any textile fabric, finished or unfinished. Explains measuring the resistance of fabrics to wetting by water, making it suitable for measuring water-repellent efficacy of finishes.
Discusses the factors that affect results from the test method on water repellency, fibers and yarns, fabric construction.

Aparatus and Materials (spray test)

Lists different apparatus and materials needed during the spray test, for example Spray Tester, graduated cylinder, distilled water, standards spray test rating, chemicals for water repellent finish, and the fabric to be tested.

Spray Tester (detailed)

Detailed graphical representation and measures of the spray tester along with the dimensions for each component.

Testing for Spray Test

Testing can be carried out at:
- As received
- After the number of washes agreed
If testing needs to be done after washing, the wash procedure should follow AATCC 135 (as per care label).

Test Specimen Size and Preparation (spray test)

Details about specimen size for spray tests.
Conditioning period for the testing of specimens.

Test Procedure (spray test)

Detailed steps in order to perform the spray test, starting from placing the fabric test specimen in a hoop, pouring distilled water, adjusting the valve and time for spray, and evaluating the outcomes.

Evaluation (spray test)

Instructions on how to compare the wet or spotted pattern from the test specimen, assigning the rating, and handling different rating types.

General Requirements (spray test)

Criteria for the evaluation and the rating system. Specifies original and after agreed number of washes.

Spray test to simulate exposure to rain AATCC 35

Purpose and Scope (AATCC 35)

Applicability: Any textile fabric, finished or unfinished.
Measurement: Resistance to water penetration by impact.
Suitability: Predicting probable rain penetration resistance and measuring penetration resistance of fabric.

Principal (AATCC 35)

Spraying with water for 5 minutes from a fixed distance and evaluating the amount of water that penetrates the specimen. Reweighing the blotters to calculate this quantity.

Apparatus (AATCC 35)

Details about the equipment needed, including the spray tester, graduated cylinder, and distilled water.

Testing for AATCC 35

Testing can be carried out at
- As received
- After agreed number of washes.
If testing is to be done after washing, the wash procedure should follow the specifications outlined in AATCC 135 (as per care label).

Test Procedure (AATCC 35)

Detailed procedure for fabric preparation, mounting of the specimen, performing the spray test, and measuring the results.

Evaluation (AATCC 35)

Evaluation steps. Rating the result in terms of the penetrated water, amount of water, and how water affects the fabric.

AATCC 127, ISO 811 (Hydrostatic pressure test)

Scope (Hydrostatic Pressure Test)

Defining the applicability and purpose of this test method for measuring resistance of fabric to penetration of water under hydrostatic pressure. Includes fabrics treated with water-resistant or water-repellent finishes and the factors affecting the outcome.
How results obtained from this method may not be the same as AATCC, rainwater or water spray.

Apparatus (Hydrostatic pressure test)

Identifying the necessary tools /equipment to carry out the test.

Testing for Hydrostatic pressure test

Testing can be carried out in static conditions or dynamic conditions.

Sample Preparation (Hydrostatic pressure test)

Necessary steps to prepare fabric samples.
Conditioning step / period.

Test Procedure (Hydrostatic pressure test)

Detailed procedure for how to set up the specimen for testing, how to apply pressure to the fabric and recording the pressure.

Evaluation (Hydrostatic pressure test)

Detailed steps to evaluate the outcomes from the test and identifying the pressure required when water penetrates through the fabric.

Apparatus (Hydrostatic Pressure Test (detailed)

Identifying the necessary equipment and the diagrams to carry out the test.

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Description

Test your knowledge on the principles of fabric repellency, including surface tension and hydrophobicity. This quiz covers various phenomena related to surface interactions, hydrostatic pressure tests, and grading systems for water and oil repellency in fabrics. Ideal for students and professionals in textile science.