importance of fibre finess,influences of fibre finess ,effect on stiffness , effect on torsional rigidity, reflection of light , dye absoprtion, method of measurement ,gravimetric method, micronaire

1. Presented by :- NITISH SHARMA
Fibre Fineness

2. Fibre Fineness
• Importance:
• Fineness is one of the most important fibre characteristics.
• The fineness determines how many fibres are present in
the cross-section of a yarn of given thickness. Additional
fibres in the cross-section provide not only additional
strength, but also a better distribution in the yarn.
• Thirty fibres are needed at the minimum in the yarn cross-
section, but there are usually over 100.

3. .Influences
• Spinning limit
• Yarn strength
• Yarn evenness
• Yarn fullness
• Drape of the fabric product
• Lustre
• Handle
• Productivity of the process.

4. Why Fiber Fineness is so
important:
It has been known since long that
fiber fineness plays an important
role in determining the quality of
resultant yarn and hence that of the
resultant fabrics. In general fiber
fineness is important due to the
following factors:

5. 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 is
less stiff in feel.
• It also drapes better.
2. It affects Torsional Rigidity of the Yarn
• Torsional rigidity means ability to twist.
• As fiber fineness increases, torsional rigidity of the
yarn reduces proportionally.
• thus fibers can be twisted easily during spinning
operation.
• Also there will be less snarling and kink formation in
the yarn when the fine fibers are used.

6. 3. Reflection of Light
• Finer fibers also determine the luster of the fabric.
• Because there are so many number of fibers per unit
area that they produce a soft sheen.
• This is different from hard glitter produced by the
coarser fibers.
• Also the apparent depth of the shade will be lighter in
case of fabrics made with finer fibers than in case of
coarser fibers.
4. Absorption of Dyes
• The amount of dye absorbed depends upon the
amount of surface area accessible for dye out of a given
volume of fibers. Thus a finer fiber leads to quicker
exhaustion of dyes than coarser fibres.

7. 5. Ease in Spinning Process
• A finer fiber leads to more fibre cohesion because the
numbers of surfaces are more so cohesion due to friction
is higher.
• Also finer fibers lead to less amount of twist because of
the same increased force of friction.
• This means yarns can be spun finer with the same amount
of twist as compared to coarser fibers,
6. Uniformity of Yarn and Hence Uniformity in the
Fabric
• It also leads to fewer breakages in spinning and weaving.

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

9. b) Gravimetric method (for wool):
Wool has almost circular cross-section.
After completing a fibre length test the fibres are collected
and thoroughly cleared of oil, allowed to condition and then
weighed on microbalance.
The total fibre length is calculated and knowing the number
of fibres weight/unit length is derived.

10. Mean Wt/unit length = W / ∑hn
where, h = the class length (cm)
n = number of fibres in each class
W = total wt of all the classes (mg)
dgrav (microns) = √(97190×W / ∑hn)
Assuming wool cross section is circular and density of
wool is 1.31 g/cc

11. c) By microscope:
• Applicable to the fibres with
circular cross section.
• A suitable random and
representative sample is
conditioned for 24 hrs in
standard testing atmosphere.
• Fibres are cut into suitable
small length and slide is
prepared by carefully mixing
the fibres into mountant.

12. • The mounting agent should be non-swelling and have a
suitable refractive index (liquid paraffin) [should not be
equal to the fibre].
• The mixture of fibres and mount is spread thinly on the
slide and covered with a cover glass.
• The slide is traversed in zigzag fashion, to cover all the
fibres randomly.

13. d) By air-flow method:
AIR-FLOW METHOD (MICRONAIRE INSTRUMENT):
 The resistance offered to the flow of air through a plug of
fibres is dependent upon the specific surface area of the
fibres.
 Fineness tester has been evolved on this principle for determining fineness of
cotton.

14. • The resistance offered to the flow of air through a plug of
fibres is dependent upon the specific surface area of the
fibres.
• 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.
• Hence the micronaire readings have to be treated with
caution particularly when testing samples varying widely
in maturity.

16. 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

17. • Suitable for mill practice due to its speed of
measurement
• Air flow at a given pressure difference through a
uniformly distributed mass of fibres is determined by
the total surface area of the fibres (Drag on water by
river bank).
• For a constant mass of fibre ( i.e. the actual volume)
the air flow is inversely proportional to the specific
surface area

18. 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)
Two types
a) Measurement of air flow at a constant pressure drop.
b) Measurement of pressure drop at a constant air flow.

19. Thanks you