4. Testing of Fibres

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Fabric Science – ISubject Code – B FP (T) 1 09 T

National Institute of Fashion Technology, India

Unit-4

Testing of Fibres

Fabric Science-1 Unit-4



Content

4.1 Length4.2 Strength

4.3 Fineness4.4 Density4.5 Maturity

4.6 Moisture




Types of test methods


Physical tests• Includes breaking strength, abrasion resistance and pilling prosperity

Tests to determine colorfastness properties• Used to determine the resistance of dyed or printed fabrics to color

change under various conditions - sunlight, washing and crocking

Chemical tests• Solubility test, determination of anti-bacterial activity etc

Optical tests• Grading of wool fibres, inspection of textile defects etc



4.1 Length

Baer (Fibre) Sorter Method

Fibre sorter is an instrument which enables the sample to befractionalised into length groupsBasically the operation involves 4 main steps

1.preparation of a fringe or tuft with all the fibres aligned at one end2.separation or withdrawal of fibres in order of decreasing length3.preparation of a sorter diagram by laying the fibres on a blackvelvet pad in decreasing order of length, the fibres parallel and theirlower ends aligned along a horizontal base line4.analysis of the diagram




• This instrument consists of a bed of combs which control the fibres andenable the sample to be fractionalised into length groups

• Visual examination of the fibre array will provide information regarding thegeneral length characteristics of the cotton, its variability and the amount ofshort fibre










4.2 Bundle strength


Comprising the following steps:

• (a) clamping a fibre bundle at one end:

• (b) combing the fibre bundle in the direction away from the clampedend to remove fibre ends

• (c) clamping the fibre bundle at the other end;

• (d) combing the fibre bundles in the opposite direction, again to removefibre ends




(e) pre-tensioning the fibre bundle clamped(f) driving them apart from each other until fibre bundle breakage occurs.From the force required to break the fibre bundle a measurement of the

bundle strength can be made.The fibre bundle may be weighed, and the weight may be taken into

account along with any other measurements, to calculate the strength.This is commonly determined by the Pressley Tester and the data obtained

is termed as “Pressley Index” which is a ratio,= Bundle strength(lbs)

Bundle weight (mg)Other instruments used are Clemson Tester, Stelometer



4.3 Fineness


• For determining the fineness an instrument called the Micronaire is usedwhich measures the resistance of the fibre to air-flow

• This is regarded as an indication of maturity• which is nothing but the weight in micrograms of one inch (25.4

millimeters) length of the fibre in case of cotton• In the case of wool fibres and other fibres, fineness is expressed by a

parameter called 'micron value ' which is nothing but the fibre diameter inmicrometers.

• It takes into account both maturity as well as fibre fineness•

The lower the reading, the finer the fibre, which also indicate relativehumidity, a factor tending to cause neps during spinning and trouble indyeing

• MV has now become widely common in the foreign cotton trade




If the cotton is immature, it will give a lower microniare value than a

much finer but mature cotton

Coarse Indian cottons generally have a higher MV than Americancotton irrespective of maturity

Cottons with an MV less than 4, demand careful control of the process at blowroom and card

A difference of 0.5MV between two cottons is regarded asmeaningful

For a given variety of cotton higher MV shows that the cotton iscoarser while lower values indicate the fibre immaturity




Testing Procedures• A fundamental method of determining cotton fibre fineness is to cut fibres

of one inch (25.4 millimeters) length and weigh each of them

• The weight in micrograms of one inch (25.4 millimeters) of a fibre gives itsfineness in *micronaire\ A number of readings can be taken and the averagemicronaire estimated

• A basic method of determining wool fiber fineness is by preparing a crosssection of several wool fibres on a glass slide and putting the same under a

microscope with graduated markings and measuring the wool fibrediameter of each fibre and then calculating the average fibre diameter inmicrons




• A popular method of determining fineness of fibres is by using an airflow instrument which works on the method of estimating the interrelationship between the pressure of air across a plug of fibre, the flowrate of air across the plug of fibre and the fineness of the fibre when airis passed through a plug of fibre.

• In this method an external pump forces air at a constant pressurethrough a plug of fibre of unknown fineness compressed inside a

perforated chamber.

• The flow rate of air passing through the plug of fibre will depend uponits fineness since the surface area of the fibre mass offering resistanceto air flow depends upon the fibre fineness.




• The flow rate of air passing through the fibre is determined by using arotameter or any other flow rate measuring device

• In a rotameter the position of a float in a vertical, conical, graduated andtransparent tube will depend on the flow rate of air passing through thesame and this is initially calibrated to give the fibre fineness in microns ormicronaire value by using fibres of known fineness (estimated using othermethods)

• An alternate method based on the above mentioned interrelationship is to pass air at a constant flow rate across the fibre and measure the pressuredifference of air across the fibre.






• This pressure difference will vary depending upon the fibre fineness sincevarying fibre fineness means varying surface area of fibres

• This pressure difference of air across the fibre of unknown fineness can bemeasured by using a manometer or electronic pressure sensor and this

pressure difference is initially calibrated to directly give fibre fineness byusing fibres of known fineness

• Another known art is the use of modern electronic microscopes which willelectronically capture the image of the fibre and then measure the same

• Yet another known art is the use of a laser beam and the light scattering property of fibres to determine its fineness

• For mineral fibres - by measuring the aerodynamic pressure drop when agiven quantity of fibres, is subjected to a given pressure of a gas, generallyair or nitrogen



4.4 Density




4.5 Maturity

• Fibre maturity is another important characteristic of cotton and is an indexof the extent of development of the fibres.

• As is the case with other fibre properties, the maturity of cotton fibres

varies not only between fibres of different samples but also betweenfibres of the same seed.• The causes for the differences observed in maturity, is due to variations in

the degree of the secondary thickening or deposition of cellulose in afibre.




A cotton fibre consists of a cuticle, a primary layer and secondarylayers of cellulose surrounding the lumen or central canal.In the case of mature fibres, the secondary thickening is very high,and in some cases, the lumen is not visible.In the case of immature fibres, due to some physiological causes,the secondary deposition of cellulose has not taken sufficiently andin extreme cases the secondary thickening is practically absent,leaving a wide lumen throughout the fibre.Hence to a cotton breeder, the presence of excessive immaturefibres in a sample would indicate some defect in the plant growth.To a technologist, the presence of excessive percentage ofimmature fibres in a sample is undesirable as this causes excessivewaste losses in processing lowering of the yarn appearance gradedue to formation of neps, uneven dyeing, etc.




An immature fibre will show a lower weight per unit length than a maturefibre of the same cotton, as the former will have less deposition ofcellulose inside the fibre.This analogy can be extended in some cases to fibres belonging todifferent samples of cotton also.Hence it is essential to measure the maturity of a cotton sample inaddition to determining its fineness, to check whether the observedfineness is an inherent characteristic or is a result of the maturity.




A combined index known as maturity ratio is used to express the results.Maturity ratio = ((Normal - Dead)/200) + 0.70

where,

N - %ge of Normal fibresD - %ge of Dead fibres

MATURITY CO-EFFICIENT:Around 100 fibres from Baer sorter combs are spread across the glass

slide(maturity slide) and the overlapping fibres are again separated with thehelp of a teasing needle.The free ends of the fibres are then held in the clamp on the second strip ofthe maturity slide which is adjustable to keep the fibres stretched to thedesired extent.

The fibres are then irrigated with 18% caustic soda solution and covered with asuitable slip.The slide is then placed on the microscope and examined. Fibres are classedinto the following three categories




4.6 Regain and Moisture Content


The amount of moisture in a sample of material may be expressed in termsof Regain or Moisture Content.Regain is defined as the weight of water in a material expressed as a

percentage of the oven dry weightMoisture content is the weight of water in a material expressed as a

percentage of the total weight

Let oven dry weight – DWeight of water – WRegain – R

Moisture Content – MThen, R = 100 W and M = 100W

D D+W



• Also,

R = M and M = R1-(M/100) 1+(R/100)

• Regain depends upon the amount of moisture present in thesurrounding air

• The dampness in the atmosphere can be described in terms of„humidity either absolute humidity or relative humidity

• Absolute humidity – the weight of water present in a unit volume ofmoist air(g/m³)

• RH – ratio of the actual vapour pressure to the saturated vapour pressure at the same temperature, expressed as a percentage

• RH = actual vapour pressure x 100• saturated vapour pressure




FQI-Fibre Quality Index• This is probably the most widely used method to determine the

technological value of cotton• The main reason for its popularity may be attributed to the simplicity of the

equation used•

Several variants of the FQI model are available• In this work we have used the following form of FQI proposed by the

South Indian Textile Research AssociationFQI = L.UR.FS.M

FF• where L is 2.5% span length, UR is the uniformity ratio, FS is the fibre

bundle tenacity, M is the maturity coefficient, and FF is the fibre fineness(micronaire).


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4. Testing of Fibres