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FIBRE TESTING

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INTRODUCTION

Testing has never been more important in textile industry

than at present, with the increasing accent and premium

on high quality products, whether it is for domestic markets

or export trade

Textile testing is carried out in fibre, yarn, fabric and

sometimes in garment stage.

There are numerous testing techniques in use throughoutthe textile industry.

For any technique selection of a sample to be tested

is very important

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SAMPLING:

The selection of small quantity of material to be testedis known as sampling. As textile testing is both

time consuming and destructive in nature in many cases,

it is necessary that we select samples for conducting

tests for various quality characteristics

Sampling Procedure:Since only a small sample from a lot is tested for estimating

the properties of the lot, it is essential that the sample

so drawn should be truly representative of the lot.In the Textile Industry, sampling of cotton has to be carried out

at three distinct stages 1. Bulk Samples

2. Basic Samples

3. Laboratory samples

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Bulk Sample: Sampling taken from the Bales

When a large no. of bales of cotton belonging to a variety

is purchased, a few bales may be chosen at random as

representing the bulk.

Bulk Size (Bales) Sample size (Bales)

Up to 50 2

51-100 4101-150 7

151-300 13

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Basic Sample:

Basic sample is prepared from the chosen bales

Draw handful of cotton from different places of the bales

so that a representative sample is drawn. These tufts of fibres

may be mixed up thoroughly to form a homogenous sample.

Finally homogenous samples prepared from all the bales

are pooled together to form one representative sample of the

Whole bulk.

The total quantity of sample prepared should be about 1 Kg.

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Laboratory sample:

The final sample on which the tests are to be carried out is

called the laboratory sample which is drawn from the

Basic sample.

The basic sample is divided in to 32 equal parts and

small tufts of fibres are drawn from each part

to form a small sample weighing 200 to 500mg.

The sample so drawn is opened and drafted several timesto form a representative sample for performing

laboratory tests like fibres length, fineness and maturity.

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Accuracy of the test data:

The accuracy of the test data depends onthe no. of tests carried out.

The no. of tests required for each property and the

Reliability of the mean so obtained in terms of

Critical Differences are calculated as given in the table:

Type of Test No. of test CD% Instrument

Effective length 2patterns/sample 4 Baer SorterMean length 2patterns/sample 4 Baer Sorter

Micronaire value 4 plugs/sample 6 Micronaire

Fibre Strength 10 breaks/sample 5 Stelometer or Pressly

Maturiry 600 fibres /sample 7 Microscope

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Example:

Data of span length of two types of cotton

Cotton A - 35mm

Cotton B - 31mm

Difference between A &B = 4mm

The CD = % of the mean of A&B

Mean of A&B = 35+31 = 33mm

2

CD % = 33 x 4 = 1.32mm100

Since the CD of Cotton A (4mm) is greater than

the CD of 1.32mm, Cotton A is longer than Cotton B.

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Testing Atmosphere:

As many of the important properties of a textile fibre are

influenced by the ambient atmospheric conditions, the

following standard atmosphere is adopted for testing

textile materials:

65% + 2% Relative Humidity and

27o C + 2o C Temperature

The sample should be conditioned at least for 18 to 24 hours

before commencing the test.

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Interpretation and application of fibre test results:

The test results need to be interpreted properly and

by applying those the properties of its products

i.e yarn or fabrics should be predicted or controlled.

The benefits of proper application of test results are:

8. The cost of the product can be minimised

9. With proper selection of fibres the yarn properties

can be engineered

11. Consistent yarn and fabric quality can be maintained

12. Proper process parameters can be selected to obtain

optimum quality of products

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FQI: Fibre Quality Index:

For cotton fibre properties an index combining

most important properties is being used frequently.

This index is termed as Fibre Quality Index (FQI),

which is given by

FQI = LSM Where L=50% span length in mm

f S= Fibre Bundle strength tested

on HVI expressed in g/tex

M = Maturity ration measured byShirley FMT

f = Fibre fineness

(maicronaire value)

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Important tests for Fibre Properties:

Fibre length Fibre Strength

Fibre Fineness Fibre Maturity Moisture content Neps

Trash Content

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FIBRE LENGTH

Length of staple fibre is one of the most important

characteristics.

The length and finess are sometimes related in natural fibreswhereas for man made fibres, length and fineness can be

controlled separately.

The cut length of manmade fibres is often influenced by theFibre length of natural fibres.

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The measurement of natural fibres is a task as there is

a greater variation in the length of different types of

same material and even within the same type.

The properties of cotton fibre varyfor different varieties of cottonfor different growth areas for different climatic conditions

from year to year

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Measurement of individual fibre length:

A representative sample is taken and the individual

fibre length is measured. These values are arranged

accordingly and the mean & coefficient of variation

are calculated.

This method is mainly used for the man made staple fibres

as the variation in length is not much.

The fibres are straightened and placed on an oil plateand the individual length of fibres (around 300-500)

is measured

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Stapling Method: (Group of fibres)

An earlier method used by classers to make a rough estimateof staple length

With the right hand a layer of fibres are drawn from

the cotton held in the left hand.

The same operation is repeated 4-5 times and the layers of

fibres are placed one on top of each other on a black velvet

board.

Block off the ends of the fibres with a cotton stapling rule

so as to indicate the length of the bulk of fibres and

distance between the blocked off ends is measured

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Combsorter Method:

This is the method in which distribution of

different length groups of fibres,

can be judged visually and numerically.

It is much less laborious than single fibre methodbut gives a fairly accurate measurement when followed

properly.

In this method, a cotton sample of around 15gm is chosento represent the bulk. Generally in 15gm of cotton there are

around 3000 hairs.

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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 combs

and 8 top combs which control the fibres and enable

the sample to be fractionalised in to length groups

The hairs are pulled down from the tufts by means of grip,

the longest first, the combs being successively dropped

as required and combed, straightened and laid downon velvet pad with the straight edge against the marked line.

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Analysis of Sorter Diagram:

From the comb sorter diagram, various parameters

can be analysed.

Mean length:

To determine the area of the comb sorter diagram using

either the special transparent scale or a planimeter.

Divide the area expressed in square mm by

the length of the base in mm to obtain mean fibre length.

Area of comb sorter diagram (mm)

Mean fibre length (mm) = -----------------------------------------

Length of the base (mm)

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Maximum length:

The length OA can be measured by scale from the tracing.

Effective length:

A geometric construction over the area of sorter diagram

will give the effective length of the fibre. It is the length which

contributes more effectively in the yarn formation.

Percent short fibres:

Percent short fibres = RB x 100, where OB is the total

length of the OB diagram.

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Other advanced test methods include:

Optical scanning method using Digital fibro graph:

It is an optical instrument which scans a randomly

Aligned tuft of fibres and to ensure the length of specification

of the length frequency distribution. It employs a totally new

Concept of fibre length called Span length

High Volume Instrument (HVI) The WIRA fibre diagram machine (Wool Industries Research

Association) Advanced fibre information system

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FIBRE STRENGTH:

Fibre strength is generally considered to be next to

fibre length and fineness in the order of importance amongst

fibre properties.

Fibre strength denotes the maximum tension thefibre is able to sustain before breaking.

It can be expressed as breaking strength or load, tenacity etc.

Elongation denotes elongation percentage of fibre at break.

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Factors affecting the strength of fibres:

Molecular structure No. and intensity of weak places Coarseness or fineness of fibre Relative humidity Elasticity

The strength or tenacity is expressed as breaking load for

unit fineness of the fibres

The tensile testing instruments can be classified in to threegroups depending on their working principle. Constant Rate of Load Constant Rate of Extension

Constant Rate of Traverse

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Fibre strength is determined by either testing individual

fibres or group of fibres

Manmade fibres are usually tested for their individual strengthas there is very less variation in length and fineness of the fibres.

Natural fibres are tested for their bundle strength due to high

variation in terms of length and fineness.

Bundle fibre strength testing:

A bunch of fibres are put in to two jaws. The jaws are moved

until the fibres break. The breaking load and elongation at break

are noted

Tensile strength/ Breaking load in kg x Length of sample

tenasity of the fibre = ------------------------------------------------

in g/tex mass of the fibres in mg

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Bundle strength of cotton:

The Stelometer the name coined from strength and elongationwhich functions on pendulum lever principle.

Pressley fibre strength tester - functions on pivoted beam balance

principle.

Uster spinlab High Volume Instrument:

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FIBRE FINENESS:

The mass of a known length of fibre is termed as

linear density and this can be expressed as weight per

unit length.

Widely used units are:

Micron Microgram /Inch Denier Weight in grams of 9000meters Tex Weight in grams of 1000 meters Decitex Weight in grams of 10,000meters.

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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 the length and weigh them.

Considering the cylindrical material, the ld can be calculatedusing the formula:

n x l x m Where, F linear densityF Denier = ----------- n Number of fibres

9000 x100 l Average length of fibres

m mass in grams

*: Mostly used for man made fibres.

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Microscopic method:

In this method, fibres are mounted on the microscope and the

diameter is measured after magnification. This methos 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 for effective results.

The latest instruments can measure the diameters of5000-10000 samples in a minute by using micro processor.

It can calculate linear density also along with fineness.

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Air flow method: based on air flow principle.

A sample of known weight is compressed in a cylinder ofknown volume and subjected to an air of known pressure.

The rate of air flow through the compressed fibres is measured.

The rate of air flow will depend much on thesurface area of the material.

Most commonly used instruments are Micronaire, HVI etc.

The resistance of the specimen to the flow of air is related to

The average fineness of fibre in the specimen. The rate of flow

of air is indicated on a scale graduated in absolute units of

micronaire value, a combined measure of fineness and maturity.

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FIBRE MATURITY:

A measure to express the development of cotton fibres.The maturity can vary within fibres of the same seed.

A cotton fibre consists of a cuticle, a primary wall and

secondary wall surrounding the lumen or central canal.

The growth of secondary cell wall i.e., deposition of

cellulose in a fibre is the reason for variation in maturity.

This growth is dependent on the fertilizer used in cotton plant,

weather etc.

The material with higher number of immature fibres causes

fibre damages during processing causing

higher number of neps and irregular absorption of dyes.

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There are several methods for determining the maturity

of fibres. They are classified in to direct and indirect methods.

Direct methods:

Microscopic analysis by caustic soda swelling

Maturity Coefficient: Mostly used in India.

The fibres are classified in to three groups.

11. Mature lumen width/ wall thickness < 1

12. Half-mature 1< lumen width/ wall thickness < 2

13. Immature- lumen width/ wall thickness >2(M + 0.6 H + 0.4 i)

Mc = ----------------------------100

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Percentage of Mature fibres is calculated byM

Pm = ------ x 100 M- matured fibresT T- total fibres

Normal (N)- Dead (D)Maturity ratio (Mr) = ------------------------------ + 0.7

200

Indirect methods:

Polarised light methodDifferential dyeing testAir Flow Method (Micronaire / Shirley fineness & maturity

tester Digital Fibrograph Advanced Fibre Information System

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MOISTURE TESTING:

Some properties of the textile fibres like strength,Extension and electric conductivity are being affected

by the presence of moisture in the material

Most of the textile fibres are hygroscopic in nature.

They have the capacity to absorb moisture from the

atmosphere.

The amount of moisture present in a cotton sample

can be expressed in two ways.13. Moisture content (M)

14. Moisture regain (R)

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Moisture Content = 100W / (D+W)

Moisture regain = 100W/ D

D= Oven dry whight

W= Weight of water

R= Regain

Instrument used:Automatic moisture oven

Relative Humidity:

If two samples of the same material are taken in to a

given atmosphere, one completely wet and the other dry,

the regain values will be different. The sample which wasOriginally wet will have more regain value.

At higher relative humidity the moisture regain of the

Material will be higher than that of lower relative humidity.

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