fibre test method

8/11/2019 Fibre Test Method

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Length of staple fibre is one of the most important characteristics. Ingeneral a longer average fibre length is to be preferred because itconfers a number of advantages.

Firstly, longer fibres are easier to process. Secondly, more even yarns can be produced from them because there are less fiber ends in a givenlength of yarn. Thirdly, a higher strength yarn can be produced fromthem for the same level of twist.

The measurement of natural fibres is a task as there is a greatervariation in the length of different types of same material and evenwithin the same type.

The properties of cotton fibre vary; for different varieties of cotton, for

different growth areas, for different climatic conditions, from year toyear.


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After combing, the fibres are placed on avelvet pad.Then ranked into groups so that lengthrange in each group is 1/8''.Groups are then weighed on a sensitivebalance.Mean length =WL/ W

where L = Group length W = Mass of fibre in length group Upper Quartile Length ( 1/4 th of the fibres by

mass is longer than that length).


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The instruments used are 1. Baer sorter 2. Comb sorterWhere, the working principle is the same for both.

The instrument consists of a bed of 9 bottom combstand 8 top combs which control the fibres andenable the sample to be fractionalised in to lengthgroups.

The hairs are pulled down from the tufts by means ofgrip, the longest first, the combs being successivelydropped as required and combed, straightened andlaid down on velvet pad with the straight edgeagainst the marked line.


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In the diagramOQ = 1/2 OAOK = 1/4 OPKS = 1/2 KK OL = 1/4 OR


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From the comb sorter diagram, various

parameters can be analysed.

Mean length:

To determine the area of the comb sorterdiagram using the special transparent scale.Divide the area expressed in square mm bythe length of the base in mm to obtain meanfibre length.

Mean fibre length (mm) = Area of Comb sorterDiagram/ Length of the base (mm)


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Optical scanning method using Digital fibrograph: It is an optical instrument whichscans a randomly Aligned tuft of fibres and

to ensure the length of specification of thelength frequency distribution. It employs atotally new Concept of fibre length calledSpan length High Volume Instrument (HVI) : The WIRAfibre diagram machine (Wool IndustriesResearch Association)Advanced fibreinformation system


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The mass of a known length of fibre istermed as linear density and this can beexpressed as weight per unit length.

Widely used units are:-Micron Microgram /Inch

Denier Weight in grams of 9000metersTex Weight in grams of 1000 metersDecitex Weight in grams of 10,000meters.


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Fineness is one of the most important fibrecharacteristics.

Influences:Fibre fineness influences primarily : Spinning limit Yarn strength Yarn evenness

Yarn fullness Drape of the fabric product Lustre Handle Productivity of the process.


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It has been known since long that fibre finenessplays an important role in determining the qualityof resultant yarn and hence that of the resultant

fabrics. In general fiber fineness is important due tothe following factors:

1. It affects Stiffness of the Fabric As the fiber fineness increases, resistance to

bending decreases. It means the fabric made from yarn of finer fiber isless stiff in feel. It also drapes better.


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It affects Torsional Rigidity of the Yarn Torsional rigidity means ability to twist.

As fiber fineness increases, torsional rigidity ofthe yarn reduces proportionally.

Thus fibers can be twisted easily duringspinning operation.

Also there will be less snarling and kink formationin the yarn when the fine fibers are used.


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3. Reflection of Light Finer fibers also determine the luster of the fabric.

Because there are so many number of fibers per unitarea that they produce a soft sheen.

Also the apparent depth of the shade will be lighter incase of fabrics made with finer fibers than in case ofcoarser fibers.

4. Absorption of Dyes The amount of dye absorbed depends upon theamount of surface area accessible for dye out of agiven volume of fibers. Thus a finer fiber leads toquicker exhaustion of dyes than coarser fibres.


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Ease in Spinning Process A finer fiber leads to more fibre cohesion because the numbers ofsurfaces are more so cohesion due to friction is higher.

Also finer fibers lead to less amount of twist because of the sameincreased force of friction.

This means yarns can be spun finer with the same amount of twist ascompared to coarser fibers,

6. Uniformity of Yarn and Hence Uniformity in the Fabric Uniformity of yarn is directly proportional to the number of fibres inthe yarn cross section.

Hence finer the fiber, the more uniform is the yarn. When the yarn isuniform it leads to other desirable properties such as better tensilestrength, extensibility and luster.

It also leads to fewer breakages in spinning and weaving.


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There are different methods to assess the fineness of

the fibres:Gravimetric method: The basic principle of this method is to count the

number of fibres in a given bunch, measure themean length and weigh them. Considering thecylindrical material, the

ld can be calculated using the formula :n x l x m/9000*100

n; No. of fibres

l; avg length of fibresm; mass in gram

Mostly used for manmade fibres.


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In this method, fibres are mounted on the

microscope and the diameter is measuredafter magnification.This methods is widely used for wool fibres and

man made fibres having circular diameter.To avoid error due to swelling, the mounting

medium like Liquid paraffin can be used foreffective results.

The latest instruments can measure thediameters of 5000-10000 samples in a minuteby using micro processor.It can calculate

linear density also along with fineness.


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A sample of known weight is compressed in a cylinderof known volume and subjected to an air of known

pressure.

The rate of air that flow through this porous plug of fibresis measured. The flow meter calibrated I term of finenessinstead of volume per unit time.

The rate of air flow will depend much on the surface areaof the material. Most commonly used instruments are

Micronaire , HVI etc.

The resistance of the specimen to the flow of air is related tothe average fineness of fibre in the specimen. The rate offlow of air is indicated on a scale graduated in absoluteunitof micronaire value, a combined measure of finenessand maturity.


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Cotton fiber consists of cell wall and lumen.

The maturity index depends upon the thickness of thecell wall.

The fibers are considered ripe if they have maturity indexbetween 50-80%,unripe if they have MI between 30 to 45% and dead when

they have it less than 25%.

Unripe fibers have neither adequate strength noradequate longitudinal thickness. They lead to loss of yarnstrength, neppiness, high proportion of short fibers,varying dyeability, processing difficulties mainly at thecard.


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To measure maturity some method ofmeasurement is required. The degree of

cell wall thickening may be expressed asthe ratio of the actual cross-sectionalarea of the wall to the area of the circlewith same perimeter (see figure)


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After sorter diagram test tufts of cotton areleft on the velvet pad. Each tuft is laid on amicroscope slide. the fibres are parellel butseparated, and a cover slip put over themiddle. The fibres are then irrigated with a smallamount of 18% caustic soda solution whichhas the effect of swelling them. After thefibers should be observed under projectionmicroscope. This enables the fibers to beclassified into three groups:


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The direct method for fiber maturity is not practicable routinetest. So indirect method can be used for the same. After sorter diagram test tufts of cotton are left on the velvetpad. Each tuft is laid on a microscope slide. the fibres areparellel but separated, and a cover slip put over the middle. The fibres are then irrigated with a small amount of 18% causticsoda solution which has the effect of swelling them. After thefibers should be observed under projection microscope. Thisenables the fibers to be classified into three groups: (1) Normal fibers (N): mature fibres with a well-developed cellwall cotton fibre become rod-like after swelling. These fibres are

classed as 'normal'. (2) Thin-walled fibres: these category fibres lying between theother two classes. (3) Dead fibres (D): if the wall is less than one-fifth of the totalwidth the fibre is classed as dead (see figure


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From a sample of 100 fibres it would be abnormal to find that allthe fibres could be classed as normal fibres. The standard chosen was N D = 67 7 = 60It is also desirable that the result should be proportional to thedegree of thickening.Assuming a constant specific volume,and a perimeter, p, constant for a pure strain of cotton, then A H (hair or fibre weight per centimeter)Therefore, H

The maturity ratio to be derived from these conclusions is theratio which expresses the actual fibre weight per cm, H, inrelation to a standard fibre weight per cm H s. Thus, Maturityratio M = H / Hs By definition, the standard fibre weight per cm, H s, is that whichthe fibre would have if it were fully matured in the arbitrary senseof having an N-D of 60.


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Fibre fineness is another important quality characteristic which plays aprominent part in determining the spinning value of cottons. If the same count of yarn is spun from two varieties of cotton, the yarnspun from the variety having finer fibres will have a larger number offibres in its cross section and hence it will be more even and strong thanthat spun from the sample with coarser fibres. Fineness denotes the size of the cross-section dimensions of the fibre. As the cross-sectional features of cotton fibres are irregular, directdetermination of the area of cross-section is difficult and laborious. The Index of fineness which is more commonly used is the linear densityor weight per unit length of the fibre. The unit in which this quantity is expressed varies in different parts of the

world. The common unit used by many countries for cotton is micro grams perinch and the various air-flow instruments developed for measuring fibrefineness are calibrated in this unit.


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Following are some methods of determining fibre fineness Gravimetric or dimensional measurements. Air-flow method. Vibrating string method. Some of the above methods are applicable to singlefibres while the majority of them deal with a mass of fibres. As there is considerable variation in the linear density fromfibre to fibre, even amongst fibres of the same seed, singlefibre methods are time-consuming and laborious as alarge number of fibres have to be tested to get a fairlyreliable average value.It should be pointed out here that most of the finenessdeterminations are likely to be affected by fibre maturity,which is another important characteristic of cotton fibres.


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Measurement of fibre fineness cannot be done by measuring thediameter (except for some fibres) because Cross sections of most of the fibres are not circular. Variation in the diameter along the length is very high (for naturalfibres).

The cross section shape of the fibres within a sample may not beuniform.So, the most convenient way of expressing fibre fineness is by measuringthe weight of a known length of fibre, i.e. linear density.Mass = Volume Density = Cross-sectional area length Density

So, Mass/length a Cross sectional area Tex = mass in gms of 1000 mts of yarn Decitex = mass in gms of 10000 mts of fibre/yarn Denier = mass in gms of 9000 mts of fibre/yarn Micronaire = mass in gms of 1 inch of fibre (for cotton)Decitex = 10 -2 ( ( d 2)/4) = 7.85 10 -3 d 2 = density in gm/cc, d = diameter in m


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) Gravimetric method (Cotton): From comb sorter diagram, fibre tufts are taken and at spacing of 1 cmtufts sections are sliced out with the help of razor. 100 fibres are counted and weighed on a sensitive micro-balance. Convert into mass/length.

b) Gravimetric method (for wool): Wool has almost circular cross-section. After completing a fibre length test the fibres are collected andthoroughly cleared of oil, allowed to condition and then weighed onmicrobalance. The total fibre length is calculated and knowing the number of fibresweight/unit length is derived.Mean Wt/unit length = W / hn where, h = the class length (cm)n = number of fibres in each classW = total wt of all the classes (mg)dgrav (microns) = (97190W / hn)Assuming wool cross section is circular and density of wool is 1.31 g/cc


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c) By microscope: Applicable to the fibres with circular

cross section. A suitable random and representativesample is conditioned for 24 hrs instandard testing atmosphere. Fibres are cut into suitable small lengthand slide is prepared by carefully mixingthe fibres into mountant.


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By air-flow method: AIR-FLOW METHOD(MICRONAIRE INSTRUMENT):

The resistance offered to the flow of airthrough a plug of fibres is dependentupon the specific surface area of thefibres. Fineness tester has been evolved on thisprinciple for determining fineness ofcotton.


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The specific surface area which determines the flow of airthrough a cotton plug, is dependent not only upon the lineardensity of the fibres in the sample but also upon their maturity. Hence the micronaire readings have to be treated with cautionparticularly when testing samples varying widely in maturity. In the micronaire instrument, a weighed quantity of 3.24gram ofwell opened cotton sample is compressed into a cylindricalcontainer of fixed dimensions. Compressed air is forced throughthe sample, at a definite pressure and the volume-rate of flow ofair is measured by a rotometer type flow meter. The sample forMicronaire test should be well opened cleaned and thoroughlymixed (by hand fluffing and opening method). Out of thevarious air-flow instruments, the Micronaire is robust inconstruction, easy to operate and presents little difficulty asregards its maintenance.


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For a constant mass of fibre ( i.e. theactual volume) the air flow is inversely

proportional to the specific surface area By measuring the rate of air flow undercontrolled conditions, the specificsurface area (s) of fibre can bedetermined and consequently the fibrediameter (also the fibre weight/unitlength)


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fibre test method

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