TYPES OF TEST The
The
Non technical Test FEELING TEST BURNING TESTS
Technical Test MICROSCOPIC TEST CHEMICAL TEST
Tests for identification Handle/Feel
Test Visual Examination Burning test Twist on Drying Floatation Test Microscopic analysis Chemical Analysis
Requirements for tests: Preparation of test specimen Apparatus for microscopic examination Reagents used for chemical tests Other tools and equipment
THE NON-TECHNICAL TESTS Feeling
test Burning test
FEELING TEST The
feeling test requires perception if it is to be of any value. Skilled perception is acquired only after handling many different fabrics over a period of time. Limitations of this test become apparent when examining and comparing fabrics of different fiber content.
BURNING TEST To recognize the composition of fabrics by the burning test ,the sample of fibre, yarn of fabric should be moved slowly towards a small flame and the reaction to heat carefully observed .One end of the sample should be put directly into flame to determine its burning rate and characteristics. The burning odour should be noted and the characteristics of the ash such as amount ,form, hardness and colour should be examined.
IDENTIFICATION OF FIBRES THROUGH BURNING TEST
Cotton When ignited it burns with a steady flame and smells like burning leaves. The ash left is easily crumbled. Small samples of burning cotton can be blown out as you would a candle. Linen Linen takes longer to ignite. The fabric closest to the ash is very brittle. Linen is easily extinguished by blowing on it as you would a candle.
Silk It is a protein fibre and usually burns readily, not necessarily with a steady flame, and smells like burning hair. The ash is easily crumbled. Silk samples are not as easily extinguished as cotton or linen. Wool It is also a protein fibre but is harder to ignite than silk as the individual "hair" fibres are shorter than silk and the weave of the fabrics is generally looser than with silk. The flame is steady but more difficult to keep burning. The smell of burning wool is like burning hair.
Man Made Fibres Acetate Acetate burns readily with a flickering flame that cannot be easily extinguished. The burning cellulose drips and leaves a hard ash. The smell is similar to burning wood chips. Acrylic Acrylics burn readily due to the fibre content and the lofty, air filled pockets. A match dropped on an acrylic blanket can ignite the fabric which will burn rapidly unless extinguished. The ash is hard. The smell is acrid or harsh.
Nylon Nylon melts and then burns rapidly if the flame remains on the melted fibre. If you can keep the flame on the melting nylon, it smells like burning plastic. Polyester Polyester melts and burns at the same time, the melting, burning ash can bond quickly to any surface it drips on including skin. The smoke from polyester is black with a sweetish smell. The extinguished ash is
Rayon It is a regenerated cellulose fibre which is almost pure cellulose. Rayon burns rapidly and leaves only a slight ash. The burning smell is close to burning leaves.
LIMITATION OF BURNING TEST It
is apparent that many fibers have similar burning reactions that might cause doubt and occasional confusion.
TECHNICAL TESTS There are certain technical tests performed for identifying various fibers. These tests req uire high technology laboratory equipment a nd are much more reliable than the non tech nical fibre tests. Technicals tests require high skilled personn el and technical know how of handling chemi cals and their accurate analysis. These tests are very valuable for those fabrics that are a blend of different yarns and also have certai n special properties including flame retardan ce etc.
TYPES OF TECHNICAL TEST Microscopic
test Chemical test
MICROSCOPIC TEST
Microscopic test is a technical test that involves identifying the fabric with the help of a microscop e with a magnification of minimum 100 power. The test can easily distinguish between fibers. The test identifies the natural fibers more easily as compared to man made ones. Synthetic fibers are very similar in appearance and the increase in the number of varieties, make s it a little tough to distinguish the fibers even un der a microscope.
MICROSCOPIC TEST FOR NATURAL FIBERS COTTON: It is a single elongated cell. Under the microscope, it resembles a collapsed, spirally twisted tube with a rough surface. The thin cell wall of the fiber has from 200 to 400 convolutions per inch. LINEN: Under the microscope, the hair like flax fiber shows several sided cylindrical filaments with fine pointed ends. The fiber somewhat
WOOL:
Under the microscope , wool’s cross section shows three layers- epidermis, cortex and the medulla.
SILK: It appears somewhat elliptical and triangular in cross section when we see under the microscope. It is composed of fibroin, consisting of two filaments, called brin which is held together by sericin.
MICROSCOPIC TEST FOR MANMADE FIBERS RAYONS:
Rayon fibers have a glasslike luster under the microscope and appear to have a uniform diameter when viewed longitudinally.
ACETATE:
The cross sectional view has a bulbous or multilobal appearance with indentations. These indentations appear as occasional markings or
NYLON: The basic microscopic appearance is generally fine , round, smooth, and translucent. It is also produced in multilobal cross-sectional types.
POLYESTERS: Generally, polyester fibers are smooth and straight and the cross-section is round. This general characteristics may be altered to achieve
ACRYLICS: The methods of manufacturing of the acrylic fibres differ, the appearances vary accordingly. ACRILAN ACRYLIC: It has a bean-shaped cross section, its longitudinal appearance is straight and smooth. ORLON ACRYLIC: It has a flat, nut-shaped cross section. CRESLAN ACRYLIC: It has an almost round cross section. MOD ACRYLICS: it is of two types verel modacrylic and SEF modacrylic
SPANDEX: Spandex fibers are unique in appearance, they appear to be groups of fibers fused together.
GLASS: The fiber is smooth, round, translucent, highly lustrous, and quite flexible.
Asbestos fibre
CHEMICAL TESTS
Chemical tests are another technical means of identifying fibers. But chemical tests are not intended for the general consumers. Different types of chemical tests are undertaken to establish the identity of the fibers used. These tests give accurate and precise analysis.
The tests are conducted in research laboratories.
TYPES OF CHEMICAL TEST
Stain Test: Also known as the Double Barrel Fibre Identification (DBFI), the test is based on the theory that each fibre has its own distinct two- colour reaction when treated with stain. A fibre will turn to a particular colour in the presence of dilute acetic acid and to some other specific colour when stained in the presence of a mild alkali.
Solvent Test: The test involves treating the fibres in certain solvents for identifying them. The technical test is becoming difficult to conduct as most of the manufactured fibres and their blends are chemically similar. There is no individual chemical or solvent test for separating or identifying the fibres in combinations.
Distinguishing
animal from vegetable fibres with an acid As strong alkali destroy animal substances, a 5% of soda lye solution in water can be used to eliminate wool and silk fibers from a sample that contains a mixture of fiber. The vegetable fibres will not be affected by this solution.
Distinguishing
vegetable from animal fibres with an acid As dilute acid destroy vegetable fibers, a 2% sulphuric acid solution can be used. A drop of solution is placed on the sample, which is then pressed with a hot iron. The spotted area will become charred if the sample is cotton linen or rayon.
DISTINGUISHING SILK FROM WOOL: The use of concentrated cold hydrochloric acid will dissolve the silk and the wool fiber swells.
DISTINGUISHING NYLON FROM OTHER FIBRES: If the fabric is thought to contain nylon, the fabric may be immersed in a boiling solution of sodium hydroxide. The nylon is insoluble in such a solution.
DISTINGUISHING POLYESTERS FROM OTHER FIBRES: Polyester is soluble in hot meta cresol; however , unlike acetate it is not soluble in acetone, and unlike nylon it is not soluble in concentrated formic acid.
DISTINGUISHING ACRYLICS FROM OTHER FIBRES: Acrylic fibers will dissolve in 70 percent solution of ammonium thio cyanate at 130 degree Celsius but the other fibers will not.
DISTINGUISHING LINEN FROM COTTON Cotton and linen are immersed in a 1% solution of fuchsine in alcohol to give red rose colour. Later , they are washed and immersed into ammonia, linen retains the red coloration but cotton does not. DISTINGUISHING GLASS FIBERS FROM OTHER FIBRES: There are two specific solvents for quick identification of glass fibers, they are hydrofluoric acid and hot phosphoric acid.
This technical fibre identification test has the following advantages and limitations Advantages • More reliable than the non technical tests. • Used for both man made fibres and natural fibres. • Easily conducted. Limitations • Certain manufacturing and finishing processes like mercerizing, affects the appearance of the fibres under the microscope. • Very dark coloured fabrics cannot be identified under microscope. • Dye stuffs must be removed from fabrics.
Fiber Identification Soda ash 40% sol.
Caustic soda 25% sol.
Sodiu m hypo chlorid e
Hydro chloric acid 40%
Nitric acid 15%
Nitric acid 70%
Sulphur ic acid 15%
Sulphur ic acid 70%
Burning in Flame
Microscopic View
Remarks
swells
Swells& Shines
Whitened
Turns yellowish
Opens up
&looses strength
Dissolves on heating
Dissolves quickly
Burns continuously leaving grey ash of burning paper smell
Longitudinal twists.
Resistance to alkalis.
test fiber Cotton
Dissolves slowly
jute
-do-
-do-
-do-
Coir
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---
Color turns pale
Viscose
Swells
Swells & slowly dissolves
Silk
Looses strength
Wool
-do-
---
---
-do
-do
Dissolves
-do
Longitudinal irregular lines
-Rough handle
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---
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Dissolves on prolonged heating
Dissolves slowly
-doblack ash
Opaque thick
serations Brittle & resistant to chemicals
Gets weakene d
Turns yellow
Dissolv es on heating
Dissolves
Dissolves
Dissolves quickly
Burns continuously leaving grey ash of burning paper smell
Longitudinal regular lines
Soft filaments good luster
Dissolves
Dissolve s slowly
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---
Dissolves partial;ly
---
Dissolves
Self extinguishing Leaves crushable Black beads
Densed centre line Uneven
coating Delicate lustrous filaments
-do-
Dissolves
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---
Dissolves slowly
---
Dissolves slowly
Self extinguishing Leaves crushable Black beads Fish
Scales structure
Rough crimpy fibers
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Dissolves slowly on prolonged treatment
transpera nt hard beads.
Dissolves slowly
Burns& stops leaving semi
Translucent& uniform
Resistant to chemicals
-
Polyeste r
---
Acrylic
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---
---
---
---
Looses strength & dissolves slowly
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Turns yellowish brown
Dissolves & Turns yellowish brown
Burns & stops Out of flame Leaving dark hard beads
Translucent& uniform Lofty & more voluminous
Nylon
---
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---
---
---
Looses strength
---
Dissolves slowly
Burns & stops Out of flame Leaving dark hard beads
Translucent& uniform
Strong More elastic
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