TEXTILE TESTING METHODS

Fabric testing is an important segment of the textile industry. We can easily detect the faults of machinery and materials during test of textiles.

Textile standards: Standard is a prescribed required level of performance of material. These standards are:

• NFPA: National Fire Protection Association• ANSI: American National Standard

Institute• ISO: International organization for

Standardization

INTRODUCTION

COTTONCotton fiber is a single elongated cell.

Under a microscope, cotton fiber looks like flat, spirally twisted ribbon-like tube with rough granular surface.

Mercerized cotton does not have natural twist. The finishing process makes them swollen, straight, smooth and round with a shining surface.

Microscopic view of cotton

WOOLWool fiber has irregular, roughly cylindrical, multi cellular structure with tapered ends.

Under a microscope, three basic layers are shown- epidermis (outer layer), cortex (middle layer) and medulla (inner layer).

Medulla is seen only in coarse and medium wool fibers and that too under a highly powerful microscope.

MICROSCOPIC VIEW OF WOOL

LINENLinen fiber, under a microscope, looks like having multiple sided cylindrical filaments with fine pointed edges.

The filaments show nodes at intervals.

It, in fact, looks like a bamboo stick having joints that results into a little unevenness.

Microscopic view of linen/flax

SILK• Silk fibers are straight and

smooth.• Raw silk fiber, composed of

two filaments, has elliptical shape under the microscope.

• The two fine and lustrous filaments are shown clearly looking like transparent rods with triangular shape.

• Wild silk or tussah fiber has different appearance than the cultivated silk. It is flattened, coarse, thick and broader fiber having fine, wavy lines all across its surface whereas cultivated silk is narrower fiber with no marks on it.

MICROSCOPIC VIEW OF SILK

POLYESTER• Polyester (aka Terylene ) is a category of polymers

which contain the ester functional group in their main chain.

• Generally, polyester fibers are smooth and straight and the cross-section is round.

• With various finishing processes, its appearance changes in context of texture and luster.

MICROSCOPIC VIEW OF POLYESTER

NYLONThe basic microscopic appearance is generally fine, round, smooth, and translucent.Sometimes it has shiny appearance. If it looks dull, it will also be dotted under the microscope. It is also produced in multilobal cross-sectional types.

MICROSCOPIC VIEW OF NYLON

PHYSICAL TESTSBREAKING STRENGTHTEARING STRENGTHBURSTING STRENGTHPILLING PROPENSITY

AIR PERMEABILITYABRASION RESISTANCE

BREAKING STRENGTH• Breaking strength is the force

required to break a fabric when it is under tension (being pulled).

• Breaking longation is the increase in length that has occurred when the fabrics breaks.

BREAKING STRENGTH• Mainly used for woven fabric because the

tests are unidirectional and woven fabrics have unidirectional yarns.

• Factors that produce a strong fabric include fiber content, yarn size and type, weave, and yarns per inch.

• Breaking strength is expressed in pounds and the elongation is expressed as a percent and in both cases a number of warp tests and weft test are performed.

IMPORTANCE OF BREAKING STRENGTH TEST

• Breaking strength is important in various end uses such as automotive safety belts, parachute harness and pants.

• Breaking strength can also be used to test the effects of destructive forces upon a woven fabric including sunlight, abrasion, laundering etc.

TEARING STRENGTHTearing strength is the force required to continue a tear or rip already stated in a fabric.

• This test is used mainly in woven fabrics because the test is unidirectional and woven fabrics have unidirectional yarns.

• A number of tear strength test is carried out and the average is taken to determine the tear strength.

• Tearing strength is expressed either in pounds or grams.

BURSTING STRENGTHBursting strength is the amount of pressure required to rupture a fabric.

• In this test, the testing force is applied radially and not in one direction as in breaking or tearing strength tests.

• Fabrics like knits, felt, non woven, lace and netting are usually tested in this manner because these fabrics either do not have yarns or yarns are not in any given direction.

• The bursting strength is expressed in pounds.

PILLING PROPENSITYPilling is the formation of small balls of fibres called pills on the surface of the fabric.

• Pilling occurs only when there is rubbing or an abrasive action on the surface of the fabric.

• Pilling usually occurs during normal wear and also while clothes are in the dryer

• Evaluation should be made taking into account the size, number, and visibility of the pills as well as the type and degree of other surface change.

PILLING PROPENSITYAfter each test, each of the specimen is first evaluated for pilling usually on a 5-4-3-2-1 pilling scale, then surface appearance is evaluated both for colour change as well as for fuzz.An average of ratings is usually taken as a result.

AIR PERMEABILITYAir permeability is the rate of air flow through a material under a differential pressure between two fabric surfaces.This property is important for a wide range of textile applications.

With some products like curtains high air permeability is required and for other products like parachutes and gas filters air permeability required is very less.Air permeability is expressed as cubic feet per square foot of fabric at a stated pressure differential between two surfaces of fabric.

VARIABLES WHICH AFFECT AIR PERMEABILITY

Fiber content: more crimp, lower air permeability.

Yarn Twist: less twist, less air permeability.

Yarn size: heavier yarns, lower air permeability.

Fabric Thickness: thicker fabric, lower air permeability.Multiple layers: more layers, lower air permeability.Fabric yarns per inch or stitches per inch: greater density, lower air permeability.

ABRASION RESISTANCEAbrasion resistance is the wearing away of any part of a material when rubbed against any other material.

Nylon is extremely high in abrasion resistance so it is used widely in action outer whereas Acetate has poor abrasion resistance so it does not last long when used for lining in jackets and coats.

Garments that are made from fibres that possess both high breaking strength and abrasion resistance can be worn often and for a long period of time before signs of physical wear appear..

CHEMICAL TESTING• COLORFASTNESS PROPERTIES.

• CHEMICAL SOLUBILITY TEST .

COLORFASTNESS PROPERTIES• Used to determine the resistance of dyed

or printed fabrics to color change under various conditions.•There are various reasons as to which a fabric changes colors like sunlight, pollution gases, abrasion, perspiration, dry cleaning etc.•A fabric that experiences little color alteration when exposed to a fading force is said to have a good colorfastness while if the color does not hold, then the fabric has poor colorfastness.

COLORFASTNESS PROPERTIES

There is a scale from 5 to 1 for evaluating colorfastness.

Class 5 means no shade change and class 1 means very great shade change.

Problem persists with deeper colors like red rather than pastel colors.

Colorfastness to light is rated on L9 to L1 scale with L9 being the best rating and L1 the worst .

DIFFERENT TYPES OF COLORFASTNESS TESTS.

1. COLORFASTNESS TO SUNLIGHT .

2. COLORFASTNESS TO WASHING.

7. COLORFASTNESS TO BURNT GAS FUMES( GAS FADING ).

3. COLORFASTNESS TO CROCKING.

4. COLORFASTNESS TO FROSTING.

5. COLORFASTNESS TO PERSPIRATION.

6. COLORFASTNESS TO DRY CLEANING.

COLORFASTNESS TO SUNLIGHT

• Dyed fabrics when exposed to sunlight will in time fade or change color. This property is called as colorfastness to sunlight.

• Many apparels are tested up to 40 hours because certain fabrics have to resist the fading effect of the sun to a much greater degree.eg men's suit.

• Drapery fabrics are usually tested for 8 hours whereas canopy fabrics for 160 hours.

COLORFASTNESS TO SUNLIGHT

• The device used is called a weather- ometer.

• A combination of artificial light, heat & moisture is used.

• the no of hours that the specimens are in the machine should be indicated .

• This machine offers accelerated weathering and light fastness test for chemicals.

COLORFASTNESS TO WASHING

• A no of variations are followed to test colorfastness to washing because there are differences in washing procedures of different fabrics.• Eg wool fabrics cannot be washed like cottons i.e. with same considerable mechanical action in hot, soapy solutions.

• The machine used is called launder-ometer.

COLORFASTNESS TO WASHING

• The specimens are placed in containers in which there is either dry cleaning solvent or water.

• This instrument determines a materials colorfastness to washing and staining as well as to dry cleaning .

• The container rotate inside the machine, agitating the specimens.

IMPORTANT CONSIDERATIONS BEFORE WASHING

• The washing temperature should have a great affect on colors.Often the dye is loosened from fabrics by the action of hot water.

• Additions to bathBleaching and sodium carbonate should be included to intensify the washing action.

• Time is importantArticles from which dye runs should be washed without soaking and for less time so that less amount of color runs out.

IMPORTANT CONSIDERATIONS BEFORE WASHING

• Mechanical action.Mechanical action subjected to laundering should also be included in washing test.

•Proportion of liquid.The proportion of liquid to the amount of material washed is important because if volume of liquid is too high, the material would just float without the squeezing . Whereas in smaller amount there would be twisting action.

COLORFASTNESS TO CROCKING

• Crocking is the transference of color by rubbing from one colored textile material to another .

• Wet fabrics will crock more easily than dry ones because the moisture present assists in removing the dye.

• Similarly, printed fabrics often will crock more easily than dyed fabrics because in printed fabrics the dye is on the surface than inside the fabric.

• Dark shades are more likely to crock than light colors because there is more dye in dark colors than light ones.

COLORFASTNESS TO CROCKING

•The arm is rotated back & forth causing the white crock test cloth to rub against the specimen.

•The cloth is removed and evaluated on a scale of 5 to 1.(class 5:negligible or no crocking; class 1 : large amount of crocking).

The device used is crock meter

COLORFASTNESS TO CROCKING

•The arm is rotated back & forth causing the white crock test cloth to rub against the specimen.

•The cloth is removed and evaluated on a scale of 5 to 1.(class 5:negligible or no crocking; class 1 : large amount of crocking).

Colorfastness to frosting

•Frosting is a localized color change produced by a relatively severe, localized flat abrasion action. Eg back pocket of a pair of trousers.•Fabrics with poor dye penetration will fade quickly from abrasion as on the surface will wear, leaving a very little color.•Blended fabric can change colors if each fiber has different abrasion resistance.•Eg in a dark grey fabric, the black cotton will abrade more quickly than a white polyester fabric, developing a light grey color.

•The device used is a surface Abrader.

Colorfastness to perspiration

•Perspiration may change the color of a fabric.•Three things may take place :1. color change of the dyed fabric.2. Loosening and uneven repositioning of color on

colored fabric.3. Staining of material next to the colored fabric.

• Perspiration maybe slightly acidic but through bacterial action, it becomes alkaline. The dye may get affected by both.

• The device used is the perspiration tester.• a slightly acid solution on one cloth & alkaline on

another is used. Both specimens are tested.• The one with the most color change is used to

represent the fabric and its class rating is used as a result.

Colorfastness to dry cleaning

•Color may change due to dry cleaning too.•This test indicates what will happen to the color of textile materials after repeated commercial dry cleaning.•Perchlorethylene is used in the test:•Commonly used dry cleaning solvents.•It is slightly more severe in solvent action.•A color that may get affected by perchlorethylene will not get affected by Stoddard solvent (petroleum base).

•Device used for this test is the launder- ometer.•Dry cleaning solvent instead of water is used as liquid.

Colorfastness to burnt gas fumes

•Lastly, color changes due to the presence of nitrous oxide in the atmosphere.•Acetate is the most susceptible to this gas.•When disperse dye is combined with acetate , severe color changes take place.eg blue which changes to purple.•Solution dyeing & inhibitors can be used to reduce or eliminate color fading .

•The device used to perform the test is called gas fading chamber.•The source of burnt gas fumes is a Bunsen burner placed at the bottom of the instrument.

Chemical test

•In these types of tests , chemicals are used as a part of the test procedure.•the specimen is dissolved in the chemical to check its solubility .

•The test include :

•Colorfastness•Fiber identification using the solubility test.

Chemical solubility test

COTTON & FLAX:They can be differentiated by observing their longitudinal appearance with a microscope.

SOLVENTS CONCENTRATION TEMPERATURE MINUTES FIBER

SULPHURIC ACID 70% 38*C 20 COTTON

SULPHURIC ACID 70% 38*C 20 FLAX

SILK & WOOL:Differentiate visually

SOLVENTS CONCENTRATION TEMPERATURE MINUTES FIBER

SODIUM HYPOCHLORITE

5.25% 20*C 20 WOOL

SODIUM HYPOCHLORITE

5.25 % 20*C 20 SILK

Polyester:SOLVENTS CONCENTRATION TEMPERATURE MINUTES FIBER

META-CRESOL 100% 139*C 5 POLYESTER

Acetate :SOLVENTS CONCENTRATION TEMPERATURE MINUTES FIBER

ACETIC ACID 100% 20*C 5 ACETATE

Rayon:

SOLVENT CONCENTRATION TEMPERATURE MINUTES FIBER

HYDROCHLORIC ACID

38% 24*C 5 RAYON

Nylon:SOLVENTS CONCENTRATION TEMPERATURE MINUTES FIBER

META-CRESOL 100% 139*C 5 NYLON

Spandex:

SOLVENT CONCENTRATION TEMPERATURE MINUTES FIBER

DIMETHYL FORMAMIDE

100% 90*C 10 LYCRA/ SPANDEX