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Chapter-4: Fiber Dimensions (Maturity + Fineness)

Definition of Fiber Maturity:

Fibre maturity is a fibre characteristic which expresses the relative degree of thickening of the fibre wall.
In other words, it is the measure of primary and secondary wall thickness. A fiber will be matured if a
high degree of wall thickening took place into the fiber content during cotton growth.
Immature fibre, that is fibre with little or no cell wall thickening, is less rigid making it prone to nep
formation during mechanical processing.

Problems due to immature fiber:

1. Are weaker, causing more breaks and shorter fibre length,

2. Have more entanglements, causing neps and The presence of neps in a yarn will also form weak
places and therefore the average strength of the yarn will bereduced. Neps will show up as specks
in the dyed cloth.
3. Take-up less dye, producing uneven colour in the final fabric results in a variety of dye-related
appearance problems such as barre, reduced color yield, and white specks. Barre is an unwanted
striped appearance in fabric, and is often a result of using yarns containing fibres of different
maturity levels.
4. The large number of ends downs in a ring frame is due to the immature fibers.

Things upon Which the Textile Fiber Maturity Depends:

1. Weather, 2. Types of Soil, 3. Plant Diseases, 4. Pests and 5. Dead Fibers

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Chapter-4: Fiber Dimensions (Maturity + Fineness)

The Maturity Ratio is a cotton maturity parameter which, according to ASTM D-13, determines the
degree of wall thickening. To define the degree of wall thickening, the coefficient of fiber circularity was
introduced, which is defined as the ratio of the wall cell area and the area of a circle of the same perimeter
as the fiber cross-section:
Θ= (cross section area of fiber wall/ area of circle of same perimeter).

Where: P – perimeter of a given fiber cross-section,

A – Area of the cross-section of the secondary fiber wall,
A = πR2 [1 – (r/R) 2]
Where:
R – Maximum fiber radius,
r – Lumen radius.
*The circularity coefficient is equal to 1 when the fibre cross-section is a circle without a lumen.

*The IFC (Immature Fibre Content) is defined as a percentage of fibres of the circularity coefficient less
than 0.25. MR (Maturity Ratio);

The relation between the immaturity count and fibre weight

*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,
θ∞H
The maturity ratio to be derived from these conclusions is the ratio which expresses the actual fiber
weight per cm, H, in relation to a standard fiber weight per cm H s. Thus,
Maturity ratio M = H / Hs
By definition, the standard fibre weight per cm, H s, is that which the fibre would have if it were fully
matured in the arbitrary sense of having an N-D of 60.
A linear relationship found by peirce between H and N-D:
H = 0.937 (N-D) + 135.2
Hence, H/H s = [0.937 (N-D) + 135.2] / [0.937 (67 – 7) + 135.2]
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Chapter-4: Fiber Dimensions (Maturity + Fineness)

= 0.0049 (N-D) + 0.706

To round the figures, Maturity ratio M = [(N-D)/200] + 0.7
The maturity ratio is therefore directly proportional to the degree of thickening of the cell wall.

The relationship between M and θ

θ = 0.577 M

θs= standard circularity =0.59

θ
Maturity ratio= θs
The theoretical range for the value of M will be from 0.2, all dead, to 1.2, all mature or normal.

The Causticaire Method: The causticaire method for obtaining cotton fiber maturity and fineness was
developed and adopted by U.S department of Agriculture. When the cotton fibers are treated with caustic
soda, there results a swelling of the fibers with the mature fibers reacting more readily and to a greater
extent that the immature fibers. Thus the action causes an exaggeration of the original dimensions of the
fibers. Mature fibers swell quite visibly, approaching in many cases a more round section, with
obliteration of the lumen. Immature fibers swell much less, retaining their characteristics thin-walled flat
section and thus can be distinguished from the mature. Immaturity is determined by comparison of the
wall thickness with lumen diameter. To measure the maturity a sample of cotton is swelled in 18%
sodium hydroxide and then examined under microscope. The appearance of the swollen fibers depends on
its degree of thickening and fibers are classified into three groups according to their visual appearance:

1) Normal fibers (N): mature fibers with a well-developed cell wall cotton fibre become rod-like
after swelling. These fibers are classed as 'normal'.
(2) Thin-walled fibers: these category fibres lying between the other two classes.
3) Dead fibres (D): if the wall is less than one-fifth of the total width the fibre is classed as dead.
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Chapter-4: Fiber Dimensions (Maturity + Fineness)

Maturity ratio M = [(N-D)/200] + 0.7

where: N and D are, successively, the percentages of mature fibres of a circularity coefficient
θ > 0.5 and dead fibres (θ < 0.25). Fibers of a MR < 0.7 are not met in practice. Fibers of a MR in the
interval 0.7÷0.8 are immature: fibres of a MR in the interval 0.8÷1 –are mature, and fibres of a MR > 1
have been very rarely met; such fibres are too mature and can cause problems in the spinning process.

*Cotton classification based on maturity ratio:

Maturity Coefficient Rating

Below 0.75 Very immature

0.76 to 0.85 Immature

0.86 to 0.90 Average maturity

0.91 to 0.95 Good maturity

Above 0.95 Very high

*Polarized light method for fiber maturity:

This method has been developed taking advantages of the birefringence property of cotton fiber. In using
the polarized light method to determine maturity, the ability of the fibers to transmit light is measured.
The immature fibers will transmit the polarized light, and the lumen in this case will appear to be of the
same color as the background. The mature or thick walled fibers do not transmit light as do the immature
fibers and will appear as complementary color to the background.

In the simplest method, about two hundreds are mounted parallel to each other on a slide and observe
under a polarizing microscope. The classification for maturity is made depending upon the interference
color produced.
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Chapter-4: Fiber Dimensions (Maturity + Fineness)

Differential Dyeing method: the Goldthwaite test for maturity: The differences between dyeing
properties of mature and immature fibers is employed in the Goldthwaite test to give a visual indication of
the maturity of a sample of cotton. Two dyes are used in same bath, a red (Diphenyl fast red supra) and a
green dye (Chlorantine fast green BLL). The mature fiber take-up the red dye preferentially, while thin
walled immature fibers take-up the green dye. The red color being developed in the cellulose of
secondary wall. Hence, little or no secondary wall thickening-no red. The test samples of unknown
maturity are compared with respect to the color with masters and in that way an accurate estimate of the
maturity of the unknown is obtained.

Airflow method: As the fineness determined by airflow method is dependent both the intrinsic fineness
(perimeter of fiber) and the maturity. It may be assumed that if the intrinsic fineness is constant then the
micronaire value is the measure of the maturity. For example, if samples of the same variety are tested it
can be assumed that intrinsic fineness would be the same and hence a higher micronaire would higher
maturity.

Definition of Fiber Fineness: Fineness is normally one of the three most important fiber characteristics.
The fineness determines how many fibers are present in the cross-section of a yarn of given thickness.
Fineness denotes the size of the cross-section dimensions of the fiber. The Index of fineness which is
more commonly used is the linear density or weight per unit length of the fiber.

Measuring unit: Widely used units are:

•Micronaire – Microgram /Inch

•Denier – Weight in grams of 9000meters
•Tex – Weight in grams of 1000 meters
•Decitex – Weight in grams of 10,000meters.

The fineness scale is as below:

Micronaire Value Fineness

Below 3 Very fine.
3.1-3.9 Fine.
4.0-4.9 Average medium.
5.0-5.9 Coarse.
6.0 & above Very coarse.
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Chapter-4: Fiber Dimensions (Maturity + Fineness)

Influences of fiber fineness on yarn and fabric properties:

1. Fiber fineness↑ no. of fiber in yarn cross-section↑ Yarn irregularity↓

2. Fiber fineness↑ Yarn fineness (spinning limit)↑
3. Fiber fineness↑ surface area↑ minimum twist level required to form yarn↓
4. Fiber fineness↑ flexibility↑ (for example highly brittle glass fiber show flexibility when it is fine)
5. Fiber coarseness ↑fiber stiffness↑ resistance to bending↑ fabric stiffness↑ fabric softness↓
6. Fiber fineness↑ no. of fiber in yarn cross-section↑ yarn strength↑
7. Fiber fineness↑ yarn fullness↑
8. Fiber coarseness ↑ fabric drape ability↓
9. Fiber fineness↑ yarn torsional rigidity (resistance to twisting)↓
10. Fiber fineness↑ no. of fiber per unit area↑ fabric lusture↓ dullness↑
11. Fiber fineness↑ surface area↑ dye absorption↑
12. Fiber fineness↑ surface area↑ friction among fiber↑ cohesion↑ process ability↑ breakage↓

Methods of Fiber Fineness Measurement:

Fiber fineness can be measured by the following method:

1. Air flow method,
2. Gravimetric method,
3. Optical method,
4. Vibroscope method

AIR-FLOW METHOD (MICRONAIRE INSTRUMENT):

The resistance offered to the flow of air through a plug of fibers is dependent upon the specific surface
area of the fibers. Fineness tester has been evolved on this principle for determining fineness of cotton.
The specific surface area which determines the flow of air through a cotton plug, is dependent not only
upon the linear density of the fibres in the sample but also upon their maturity.

In the micronaire instrument, a weighed quantity of 3.24gram of well opened cotton sample is
compressed into a cylindrical container of fixed dimensions. Compressed air is forced through the sample,
at a definite pressure and the volume-rate of flow of air is measured by a rotometer type flow meter. The
sample for Micronaire test should be well opened cleaned and thoroughly mixed (by hand fluffing and
opening method). Out of the various air-flow instruments, the Micronaire is robust in construction, easy
to operate and presents little difficulty as regards its maintenance.

Two types

a) Measurement of air flow at a constant pressure drop.

b) Measurement of pressure drop at a constant air flow.

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Chapter-4: Fiber Dimensions (Maturity + Fineness)

*Specific surface is determined as the ratio of surface area to volume.

Let the volume V= A*l =3.1416*d2

Surface area =3.1416*dl

*Suitable for mill practice due to its speed of measurement.

*For a constant mass of fiber (i.e. the actual volume) the air flow is inversely proportional to the specific
surface area.

The ratio is equals the ratio, perimeter of cross-section/area of cross section=(3.1416*d)/3.1416*(d/2)2

for fiber of circular cross-section, specific surface area is inversely proportional to fiber diameter.

* Within a particular growth of cotton fiber the perimeter is fairly constant.

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Chapter-4: Fiber Dimensions (Maturity + Fineness)

By measuring the rate of air flow under controlled conditions, the specific surface area (s) of fibre can be
determined and consequently the fibre diameter (also the fibre weight/unit length)

**Since maturity is concerned with the development of cell wall, and the cell wall thickness of a mature
fiber is greater than that of an immature fiber, a given weight of mature fibers of a particular growth will
contain fewer fibers than a similar weight of immature fibers. Hence, for the mature sample the rate of
airflow will be higher. The relationship between specific surface area s, the maturity ratio M, and the
fiber weight per centimeter H, has the following relationship,

S= constant* [1/√ (MH)]

Measurement fiber fineness by Vibration method (Vibroscope):

An indirect method of estimating the mass/unit length of fiber, based on the theory of vibrating strings.
Used for individual fiber (one fiber at a time). The natural frequency, tension and fineness (mass/length)
of a string are corrected as follows,

*v=fλ =f*2L
𝑇
Wave velocity for a stretched string, v= √ (T/ρ) = √ (𝑀/𝑙)
F= (1/2l) ×√ (T/M)
M= T x (1/2lf)2
Where,
F = natural fundamental frequency of vibration (c/s)
T= tension
M= mass per unit length (gm/cm)
L= free length
l = wave length
It is well known that natural frequency of a tensioned string increases with tensions.
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Chapter-4: Fiber Dimensions (Maturity + Fineness)

The string is clamped at one end and led over a knife edge support loaded by ‘W’ and is induced a natural
vibration of ‘f’ frequency. The clamp and knife edge are connected to a 150 volt source so that the
specimen is electrically charged. Transverse vibrations of the specimen will therefore induce a charge in a
brass screw S situated midway between the clamp and the knife edge and spaced 1 mm from the
specimen. The screw thus acts as a transducer. If the signal from it is amplified suitably and fed back to
the vibrator, an oscillatory loop is formed, thus causing the specimen to vibrate at its resonant frequency.
The voltage across the vibrator can then be fed into frequency measuring circuit and the frequency of the
oscillation indicated on the meter. The amplitude of the vibrations is measured over a range of
frequencies. The frequency which given maximum vibration amplitude is the fiber resonance frequency.
From which the linear density is measured.

M = T /λ2 f2 = (W×g / λ2 f2) ×9×105 Denier

*Tension range = 0.3 to 0.5 cN/tex, usually applied by weighted clip on the end of the fiber.

Refinement of above equation (to allow for stiffness of fiber, since different fibers have different Young’s
modulus)

M = (W×g / λ2 f2) ×9×105 {1+ (R / l) √Eπ/T}2

Where, R = radius of fibre, E= Young’s modulus, l= length.

Vibroscope: A machine that measures vibration frequencies of fibers subjected to certain tensions.
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Chapter-4: Fiber Dimensions (Maturity + Fineness)

Model Questions:

1. What is understood by fiber fineness? Discuss the influences of fiber fineness on following: (i)
Yarn properties & (ii) Fabric properties
2. Mention the common measuring units for fiber fineness. Give the classification of fiber fineness
based on micronaire value.
3. Describe any indirect method for measuring fiber fineness with figure.
4. What is vibroscope? Explain the working principle of vibroscope for measuring fiber fineness.
5. Explain the basic mechanism of vibration method for fiber fineness measurement.
6. Explain the basic mechanism of airflow method for fiber fineness measurement. What are the
limitations of this method?
7. Explain the basic mechanism of following two methods for fiber maturity measurement:
(i) Polarized light method & (ii) Goldthwaite differential dyeing method
8. Mention the cotton classification based on maturity ratio.
9. Explain the basic mechanism of the causticaire Method for fiber maturity measurement.
10. Define the following terms: (i) Maturity fiber, (ii) Immature fiber & (iii) Dead fiber
11. Mention the problems occurred due to immature fiber. Or why study of fiber maturity is so
important?
12. Discuss the relation between the immaturity count and fiber weight.
13. What is understood by degree of thickening? Establish a relation between degree of thickening
and fiber maturity.
14. Prove that the theoretical range for the value of Maturity ratio will be from 0.2 to 1.2
15. Establish a relationship among secondary cell wall area, perimeter and degree of thickening of
cotton fiber.