Fiber Testing

Baer Sorter
 Baer Sorter
• Instrument which enables the sample to be
fractionalized into small length groups.
• A numerical sample of fibers is arranged in
the form of an array in the descending order
of length & from a tracing of this array, the
effective length, mean length, percentage of
short fibers and dispersion are calculated.
 Baer Sorter
Steps involved:
(1) The preparation of a tuft with all fibers
aligned at one end.
(2) The withdrawal of fibers in the order of
decreasing length.
(3) The preparation of a sorter diagram by laying
the fibers on black velvet pad in decreasing
order of length, the fibers parallel & their
lowest ends aligned along a horizontal base
line.
 Baer Sorter
(4) The analysis of the diagram.
• Baer sorter consists of a bed of combs which
control & enable the sample of fibers to be
fractionalized into length groups.
• It has 12 bottom combs placed between a ‘U’
shaped metallic frame.
• All the bottom combs are hinged at one end &
are supported by a rod, extending to the
width of the frame, at the other end.
 Baer Sorter
• The rod can be moved from its position &
when it is drawn, the rod can be dropped one
by one.
• The needles of the bottom combs are
pointing upwards & in between the bottom
combs, three top combs are placed.
• The space between the two bottom combs is
¼ inch except the first two bottom combs
which will be 3/16 inch apart.
 Baer Sorter
• The top combs, when placed in between the
two bottom combs, the distance between
them will be 1/8 inch.
• Manipulation of fibers is done by a grip called
tweezer, a depressor & a blunt needle.
Sorter Diagram
 Span Length
• Distance from a line where the fibers are
randomly caught to a point where only a
certain percentage of fibers extend.
2.5% span length:
• Distance from the clamp on a fiber beard to a
point where only 2.5% of the fibers extend.
50% span length:
• Distance of the point to which 50% of the
fibers extend.
Span length
 Uniformity ratio
• Ratio between 50% span length and 2.5%
span length expressed as a percentage.
 Fiber Maturity
• Maturity of a fiber is concerned with
development of the cell wall.
• Cell wall thickening is highly sensitive to
growing conditions:
(a) Adverse weather
(b) Poor soil
(c) Plant disease
(d) Pests
 Fiber Maturity
• It will increase the proportion of immature
fibers and lead to trouble in processing.
• Major problem caused by immature fibers is
nepping.
• Immaturity also affects the shade after dyeing.
• Weft bars are seen in fabric when yarn made
up of immature fibers or yarn spun from cotton
of different maturity is used as warp & weft.
 Fiber Maturity
• Large number of breakage of yarn in ring
frame is due to the immature fibers.
• Several methods are available for determining
the maturity of cotton.
Direct method:
(a) Caustic soda swelling method
 Fiber Maturity
• Indirect method:
(a) Differential dyeing method
(b) Causticaire method
(c) Polarised light method
 Caustic soda swelling method
• Most commonly used method.
• A thin tuft of fibers is drawn by means of
tweezers from a sliver held in a comb sorter.
• The tuft is laid on a microscopic slide.
• Fibers are separated, parallelized and a cover
slip is put over the middle.
• Likewise 4 to 8 slides are prepared.
 Caustic soda swelling method
• There are two steps involved in this method:
(a) Treatment with 18% caustic soda(NaOH)
(b) Examination under a microscope to count the
mature, half mature and immature fibers.
• The fibers on the microscope slide are then
irrigated with a small amount of 18% caustic
soda solution, which has the effect of
swelling them.
 Caustic soda swelling method
• The slide is then placed on the stage of the
microscope and examined.
• The presence or absence of convolution is
observed and the fibers are classified into
three groups.
(1) Mature or normal fibers
(2) Half mature or thin walled fibers
(3) Immature or dead fibers
 Caustic soda swelling method
• The presence of caustic soda changes the
appearance of both mature and immature
fibers by swelling.
• Mature fibers, with a well developed cell wall
and pronounced convolutions in the raw
state, become rod like after swelling .
• These fibers are classed as normal or mature
fibers.
 Caustic soda swelling method
• In this case, lumen is practically absent.
• Dead or immature fibers appear ribbon like,
even after treatment.
• In dead fibers, the wall thickness is less than
1/5th of the ribbon width.
• Thin walled or half mature fibers are those
lying between the other two classes.
Caustic soda swelling method
 Caustic soda swelling method
Class Ratio of lumen width to wall
thickness(L/W)

Mature Less than 1

Half mature 1-2

Immature Greater than 1

 Caustic soda swelling method
• All the slides are examined as above and the
percentage of mature(N), half mature(H) and
immature(I) fibers are calculated.
• Then the maturity is expressed by any one of
the following terms:
(1) Percentage of Mature fibers, N
(2) Maturity ratio, M
(3) Maturity co-efficient, Mc
 Caustic soda swelling method
Percentage of mature fibers:
• N = (Number of mature fibers)/ (total number
of fibers examined) x 100
Maturity ratio:
• The percentage of three classes of fibers are
combined into a single index termed maturity
ratio and is approximately proportional to the
degree of cell wall thickening.
 Caustic soda swelling method
Maturity Co-efficient, Mc (Maturity count):
• The fiber maturity count is denoted by the
percentage of the mature, half mature and
immature fibers in a sample.
• Mc = (N+0.6H+0.4I)/100
where, N= Percentage of mature fibers
H= Percentage of half mature fibers
I= Percentage of immature fibers
 Caustic soda swelling method
• Based on maturity co-efficient, the fibers are
classed into different groups:
Maturity co-efficient Rating

Below 0.60 Very immature

0.60 to 0.70 Immature

0.71 to 0.80 Average

0.81 to 0.85 Good maturity

 Fiber Fineness
• If a given count is spun from a fine and coarse
fiber, a more uniform and stronger yarn can
be produced from the fine fiber.
• A fine fiber can be spun to finer counts than a
coarse fiber.
• The linear density or weight per unit length
of the fiber is the more commonly used index
of fineness.
Methods for estimating Fiber Fineness

(1) Gravimetric method

(2) Optical method
(3) Unidimensional method
(4) Bidimensional method
(5) Air flow method
 Airflow Instruments
(1) Sheffield Micronaire
(2) ATIRA Fineness tester
(3) Arealometer
Airflow Principle
 Airflow Principle
• A sample of known weight is compressed in a
cylinder to a known volume and subjected to
an air current at a known pressure.
• The rate of air flow through this porous plug
of fiber is measured.
• Let us consider two cylinders, a and b of
similar dimensions, one filled with circular
rods of large diameter (a) and the other with
circular rods of small diameter (b).
 Airflow Principle
• The number and diameter of the rods are so
chosen the total cross sectional area is equal
in both the cases.
• If air is blown through the two cylinders at the
same pressure, it will be found that the rate of
air flow through b would be less than through
a, even though the space through which air
has to pass is the same in both the cylinders.
Micronaire
 Micronaire
• Instrument based on airflow principle.
• The rate of airflow is inversely proportional to
the surface area of the fibers.
• A sample of known weight is compressed in a
cylinder to a known volume and subjected to
an air current at a known pressure.
• The rate of air flow through this porous plug
of fibers, related to the fineness of the fibers,
is measured.
 Micronaire
• Air from a compressor is supplied to this
instrument.
• To allow the air into the instrument, the foot
pedal is pressed.
• The air pressure is noted on the pressure
gauge.
• To filter the dust particles, an air filter is
incorporated in the line.
 Micronaire
• The inlet air pressure to the fibers can be
altered using the air regulator.
• This air is divided into two streams at the
point X.
• One stream passes through the flow meter to
atmosphere.
• The another steam passes through the
perforations, through the fibers in the
chamber and through the hole of the plunger
to the atmosphere.
 Micronaire
• If the fibers are fine, then the obstruction to
air flow will be more and the obstructed air
will pass along the tube Y, press the float
downwards and goes to the atmosphere.
• Hence, the micronaire value for fine fibers will
be less.
• Similarly for coarser fibers, the obstruction to
air flow will be less and micronaire value will
be more.
 Micronaire(Fiber Fineness Rating)
Micrograms per inch Rating
(Micronaire)
Below 3 Very fine

3 to 3.9 Fine

4 to 4.9 Average fine

5 to 5.9 Coarse

6 and above Very coarse

 ATIRA Fiber Fineness Tester
• Developed by the Ahmadabad Textile
Industry’s Research Association (ATIRA).
• Measures the Micronaire value (Mc) and
Maturity fineness (MH-product of maturity &
fineness) on two scales.
• Works on airflow principle.
• Instrument consists of a flowmeter.
ATIRA Fiber Fineness Tester
 ATIRA Fiber Fineness Tester
• Two scales are graduated at the sides of the
flowmeter in terms of micronaire(Mc) and
maturity fineness(MH).
• The readings are indicated by a monometric
liquid, provided in a reservoir.
• Air can be supplied to the reservoir at a
constant pressure by means of a float inside
an air tank by squeezing an aspirator bulb.
 ATIRA Fiber Fineness Tester
• Fiber chamber is provided between the air
tank and the reservoir so that air can pass
through the fibers.
• Fibers can be locked inside the chamber by
means of a plunger in which small holes are
provided.
• If the pressure inside the air tank increases,
the float will descend in order to make the
outlet pressure of air uniform.
 ATIRA Fiber Fineness Tester
• If the fibers are coarse, then all the air will pass
through the holes in the plunger easily to the
atmosphere and hence a small amount of air
left will take the liquid into the bottom most
region of the flowmeter.
• Similarly for fine fibers, due to higher
obstruction to the air flow, the liquid will be
taken to the top most region of the flow meter.
 ATIRA Fiber Fineness Tester
• Hence the micronaire values will be lower for
fine fibers and higher for coarse fibers.
 Fiber Strength
• Fiber strength is generally considered to be
next to fiber length and fineness in the order
of importance amongst fiber properties.
Breaking load:
• This is the load at which the specimen breaks
due to the tension applied.
• Expressed in grams/pounds.
 Fiber Strength
• Fiber strength testing can be done in two
ways:
(a) Single fiber strength testing
(b) Bundle fiber strength testing
• Strength of fiber is expressed in terms of
either tenacity(g/denier or g/tex) or breaking
strength(km).
 Bundle strength
• Single fiber strength testing is time consuming.
• In actual practice, fibers are not used
individually but in groups, such as yarns or
fabrics.
• Testing of bundle of fibers takes less time and
involves less strain.
• Due to these reasons, determination of
bundle strength has assumed greater
importance than single fiber strength tests.
Pressley Tester
 Pressley Tester
• It is a balance type of tester and is working on
the principle of moments.
• It is an inclined plane (beam) fiber strength
tester.
• The beam is pivoted at the point O.
• The beam scale is graduated in pound units.
 Pressley Tester
• There is a free rolling weight on the beam,
which cab released or locked by the use of a
locking lever, provided with the instrument.
• The end of the beam B is attached to the top
clamp rigidly.
• In the clamping block of the instrument, two
grooves are provided.
 Pressley Tester
• The top groove is for inserting the clamps for 0
gauge length test and the bottom groove is for
1/8 inch(3mm) gauge length test.
0 Gauge length test:
• Pressley tester tests a small flat bundle of
fibers gripped between special clamps known
as Pressley clamps.
• From the bulk of the cotton fibers, small tufts
of fibers are selected at random and
manipulated into a parallel ribbon about ¼
inch wide.
 Pressley Tester
• A coarse hand comb is used initially and for
final combing, a small comb mounted on a
vice is used to remove the short fibers
present.
• Then the ribbon of fibers is placed across the
clamps which are held in the vice.
• The top jaws of the clamps are then pressed
over the fibers and tightened to a
predetermined limit using a wrench.
 Pressley Tester
• Now a fringe of fiber will protrude from each
side at the clamp.
• These fibers are trimmed-off using a knife.
• At this stage, the length of the test sample is
0.464 inch and its width is ¼ inch, the gauge
length is 0(zero) because there is no space
between the two clamps.
 Pressley Tester
1/8 inch(3mm) gauge length test:
• For this a plate called spacer, of thickness 1/8
inch(3mm) is placed between the clamps.
• Than the sample is prepared as before and the
length of the sample is 0.590 inch and its
width is ¼ inch.
 Pressley Tester
• The heavy rolling weight is initially held in
position by a catch.
• Then the prepared clamps are inserted into
the grooves in the clamping block and thje
catch is released.
• As the weight moves away from the beam
pivot, the end B of the beam rises which
moves the upper clamp upwards and away
from the fixed lower clamp.
 Pressley Tester
• Therefore, a force will be exerted on the
ribbon of fibers and breaks it.
• As soon as the ribbon breaks, the beam drops
and a breaking device causes the rolling
weight to be stopped instantly.
• The distance travelled by the rolling weight is
a measure of the load required to break the
specimen and is noted down from the scale
calibrated on the beam.
 Pressley Tester
• The clamps are then removed from the tester,
the two halves of the broken specimen are
collected and weighed on a torsion balance in
mg.
• From the breaking load of fibers in pounds
and the weight in mg, the following
calculations can be made:
 Pressley Tester
(a) 0 Gauge length test:
1. Pressley index(PI)=Breaking strength in
pounds/Bundle weight in mg
2. Tenacity in gm/tex=5.36 x PI
3. Tensile strength in 1000
pounds/sq.inch=10.8116PI-0.12
• The PI will range from 7 for weaker fibers to
11 for stronger fibers.
 Pressley Tester
(b) 1/8 inch(3mm) gauge length:
1. Pressley Index, PR=Breaking strength in
pounds/Bundle weight in mg.
2. Tenacity in g/tex= 6.8 x PR
3. Fiber strength index, FSI= (PR/3.19)x100
4. Tensile strength in 1000
pounds/sq.inch=(FSIx84)/100
 Pressley Tester
• From the values of FSI, the fibers can be
classified as follows:
FSI Category

93 & above Superior

87-92 Very strong

81-86 Strong

75-80 Average

70-74 Fair

Less than 70 Weak

 FQI
• In order to decide the quality characteristics of
fibers required for spinning different counts
with desired CSP(Count-Strength Product)
values, a single measure for the overall quality
of fibers has been established by SITRA.
• FQI=Lusm/f
 FQI
where,
• Lu=product of 2.5% span length(L) and uniformity
ratio(u) in percentage, measured by Digital
Fibrograph, divided by 100.
• s = bundle fiber strength in gm/tex measured on
Stelometer at 3mm gauge length
• m = maturity co-efficient
• f = fiber fineness, in micrograms per inch,
measured on Micronaire