Indian Journal of Fibre & Textile Research
Vol. 28, J une 2003, pp. 1 82- 1 84
Effect of extension rate and specimen length on tenacity and breaking extension of
polyester/ viscose twin-spun air-jet yarns
Abhijit Majumdar" & Rajarshi S eng u p ta
College of Textile Technology, Berhampore 742 1 0 1 , India
Received 12 September 2001; revised received 15 January 2002; accepted 1 3 March 2002
The influence of extension rate and specimen length on tenacity and breaking extension of polyester/ viscose twin-spun
ai r-jet yarns has been studied. I t is observed that for long specimen lengths, the yarn tenacity increases steadily with the
increase in extension rate. However, for short specimen lengths, the yarn tenacity first increases with the increase in
extension rate and then decreases with the further increase in extension rate. The tenacity and breaking extension of twin­
spun air-jet yarns decrease steadi ly with the increase in specimen length.
Keywords: Air-jet yarn, Breaking extension, Extension rate, Polyester, Tenacity, Viscose
1 Introduction
Tensile properties of spun yarns are the most
important parameters for the assessment of yarn
quality. Generally, the plying of ring and rotor yarns
offers significant advantage in terms of physical and
tensile properties. During plying, the yarn strands,
consisting of bundle of fibres, wrap around each
other, resulting in better utilization of fibre
properties. Duri ng tensile loading of yarns, the
extension rate and specimen length alter the time to
break the yarn and thus influence the tensile
properties. Besides, in case of spun yarns, the tensile
behaviour depends on the characteristics and
structural arrangement of constituent fibres. The
structure of air-jet spun yarns is completely different
from those of ring and rotor yarns. Moreover, i n
plied yarns the cohesion and strength depend no
longer upon fibre migration but merely on the
wrapping of strands around each other. Therefore,
twin-spun air-jet yarns may or may not follow the
tensile behaviour of ring and rotor yarns.
Midgley and Pierce ' revealed that the breaking load
of cotton ring .yarn is inversely proportional to the
logarithm of time to break the specimen. Singh and
2
Sengupta observed an increase in yarn tenacity with
an increase in extension rate in the range of 0. 1 - 1 00
em/min. They attributed the increase in tenacity to the
increased incidence of fibre rupture. Salhotra and
Balasubramanian 3 found that for ring and rotor yarns,
a
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with the increase in extension rate the tenacity first
increases up to a certain limit and then decreases with
the further increase in extension rate. Kaushik et al.4
observed the maximum yarn tenacity at an extension
rate of 200 mm/min for 1 00 mm long specimen.
However, for 500 mm long specimen, the tenacity
shows increasing trend up to an extension rate of
1 000 mm/mi n.
7
A number of researchers5 . studied the influence of
specimen length on tenacity and breaking extension of
spun yarns. Most of these researchers are in
agreement with the Pierce' s8 classical weak link
theory which says that the yarn tenacity increases
with the decrease in specimen length since a short
specimen will have fewer weak spots than that of a
long specimen. However, no work has been reported
on the effect of extension rate and specimen length on
tenacity and breaking extension of twin-spun air-jet
yarns. In the present work, the influence of extension
rate and specimen length .o n tenacity and breaking
extension of twin-spun air-jet yarns has been
investigated.
2 Materials and Methods
Twin-spun air-jet yarns were produced from 1 .4
denier, 5 1 rum polyester fibres and 1 .5 d�nier, 5 1 mm
viscose fibres on a Murata twin spinner (MTS-88 1 ).
The tensile properties of fibres are given in Table 1 .
Three yarn counts, namely 2/40s (2x I 4. 8 tex), 2/50s
(2x 1 1 .8 tex) and 2/60s (2x9.8 tex) were spun from
65 :35 polyester/ viscose blend at a deli very speed of
MAJ UMDAR & SENGU PTA: POLYESTERIVISCOSE TWIN-SPUN AIR-JET YARNS
200 m/min. During spinning, the first and second jet
2
pressures were kept constant at 2.5 kg/cm and 4.5
2
kg/cm respectively. These yarns were then twisted on
a two-far-one twister (TFO) using 4.5 twists/ cm.
Yarn tenacity (cN/tex) and breaking extension (%)
were measured on an Instron tensile tester (Model
430 1 ) using extension rates of 50, 1 00, 250 and 500
mm/min and specimens of 1 00, 250 and 500 mm
lengths. Samples were conditioned at 65 ± 2% RH
and 20 ± 2° C for at least 24 h before testing and all
the tests were performed in a standard atmospheric
Table I -Specifications of polyester and viscose fibres
Fibre
Fibre
length
Fibre
denier
Fibre tenacity
cN/tex
Breaking
extension
%
mm
Polyester
51
1 .4
32.42
2 1 .88
Viscose
51
1 .5
14.45
1 3.50
Table 2-Effcct of extension rate and specimen length on
tenacity of polyesterl viscose twin-spun air-jet yarns
Yarn fi neness
Tenacity
cNltex
Extension rate
mmlmin
1 00a
250a
500a
2/40s
(2 x 1 4.8 tex)
50
1 00
250
500
25.58
25.56
27.77
27.50
24.42
24.9 1
25.0 1
25 . 8 1
23.06
23.29
23.36
24.67
2/50s
(2 x 1 1 .8 tex)
50
1 00
250
500
23.9 1
24.03
25.76
25. 1 9
22.39
22.98
23.42
23.77
20.45
2 1 .38
2 1 .90
22.72
2/60s
(2 x 9.8
tex)
50
1 00
250
500
22.00
22.4 1
24.43
24.02
20.72
20.96
2 1 .43
22.06
1 9.67
1 9.74
20.02
20.07
a Specimen length in mm.
condition . The mean yarn tenacity and breaking
extension were calculated form 1 00 observations for
each yarn.
3 Results and Discussion
3.1 Yarn Tenacity
The yarn tenacity values at different extension rates
and specimen lengths are shown in Table 2 . It is
observed that the tenacity decreases with the increase
in yarn fineness. The reason is attributed to the
increase in yarn unevenness and number of thin
places with the increase in yarn fineness (Table 3).
While studying the influence of extension rate on
tenacity, it is observed that in general the tenacity
increases with the increase in extension rate. For 100
mm long specimen, the yarn tenacity becomes
maximum at an extension rate of 250 mm/min.
However, the tenacity drops when the extension rate
is further increased to 500 mm/min. These findings
are in agreement with those of other researchers3 . 4 on
ring- and rotor-spun yarns. The increase in yarn
tenacity with the increase in extension rate can be
attributed to the consequent increase in the percentage
2
of ruptured fibres . At a slow extension rate, the fibre
slippage becomes dominant and the yarn tenacity
decreases due to the non-catastrophic nature of yarn
failure. On the other hand, for 1 00 mm long
specimen, the yarn tenacity decreases at high
extension rate (500 mm/min). When a spun yarn is
strained during tensile test, the fibres are aligned in
the direction of yarn axis, depending on the packing
coefficient of yarn and relative position of fibres in
the yarn. This realignment maximizes the contribution
of individual fibres to the yarn tenacity. At shortest
specimen length ( laO mm) and maximum extension
rate (500 mm/min), the decrease in yarn tenacity is
due to the very less yarn breaking time which may not
be adequate for the alignment and orientation of fibres
in the direction of yarn axis. However, for long
Table 3-Yarn unevenness and imperfections of polyesterl viscose twin-spun air-jet yarns
Yarn
fineness
Unevenness %
Thin
placeslkm
(-50%)
1 83
Thick
places/km
(+50%)
Nepslkm
(+200%)
Total
i mperfections
7
20
28
2/40s
(2x 1 4. 8 tex)
1 1 .58
2/50s
(2x 1 1 . 8 tex)
1 2.54
2
8
33
43
2/60s
(2x9.8 tex)
1 3 .73
5
12
49
66
INDIAN J. FIBRE TEXT. RES., JUNE 2003
1 84
2/40s
(2x 14.8 tex)
50
1 00
250
500
1 3.45
14. 1 8
1 4. 1 8
1 4.0 1
1 2.27
1 2.44
1 3 .04
1 2 .45
1 1 .55
1 1 .59
1 1 .99
12. 1 0
2/50s
(2x 1 1 .8 tex)
50
1 00
250
500
1 4.70
15.3 1
1 5 .20
1 4.77
1 3.93
14.64
13.16
1 3.88
1 2.04
1 3.75
1 2.89
1 2 .44
mm long specimens, the increase in extension rate
beyond 1 00 mrnlmin shows somewhat anomalous
behaviour in breaking extension. This may be due to
the complex structural arrangement of twin-spun air­
jet yarns. These findings are not in agreement with the
results obtained by Kaushik et al.4 for rotor-spun
yarns. According to them, the breaking extension
increases conti nuously with the increase in extension
rate and tends to reach the elongation of fibre bundle.
Further, the breaking extension decreases with the
increase in specimen length. This could be attributed
to the increased probability of weak spots in a longer
specimen as indicated by weak link theorl .
Table 4-Effect of extension rate and speci men length on
breaki ng extension of polyesterl viscose twi n-spun air-jet yarns
Yarn
fineness
2/60s
(2x9.8 tex)
Extension rate
mm/min
Breaking extension
%
1 00"
250"
500"
50
1 2.83
1 1 .53
1 0.30
4 Conclusions
1 00
1 4.26
12.15
1 1 .81
250
1 3.85
12.12
I l.ll
500
1 3.57
1 1 .35
1 0.97
The tenacity of twin-spun air-jet yarns decreases as
the yarn becomes finer. The maximum yarn tenacity
occurs at an extension rate of 250 mm/min for 1 00
mm long specimen and it decreases as the extension
rate is increased to 500 mm/min. However, for long
specimens (250 mm and 500 mm), a steady increase
in tenacity is observed up to an extension rate of 500
mm/min.
In general, as the extension rate increases from 50
mm/min to 1 00 mrnlmin, the breaking extension of
twin-spun air-jet yarns increases for all the specimen
lengths. Further inc rease in extension rate decreases
the breaking extension for shortest specimen length
( IOOmm) but no particular trend is observed in case of
long specimens (250 mm and 500 mm).
The tenacity and breaking extension of twin-spun air­
jet yams decrease with the increase in specimen length.
" Specimen length in mm.
specimen (250 mm and 500 mm), the fibres get
sufficient time for alignment and orientation even at
maximum extension rate. Therefore, the yarn tenacity
continues to increase with the extension rate.
It is interesting to observe that for 1 00 mm long
specimen, the maximum tenacity is obtained at an
extension rate of 250 mm/min. However, for 250 mm
and 500 mm long specimens, the maximum tenacity is
achieved at an extension rate of 500 mrnlmin. This
strengthens the perception of time dependence of yarn
failure mechanism.
While studying the effect of specimen length on
yarn tenacity, it is observed that the yarn tenacity
decreases consistently with the increase in specimen
length. The reason for this behaviour is obvious, since
there is a higher probability of including a relatively
larger number of weak spots in a longer specimen.
3.2 Breaking Extension
The breaking extension values of twin-spun air-jet
yarns at different extension rates and specimen
lengths are given in Table 4. It is observed that as the
extension rate is increased from 50 mrnlmin to 1 00
mrnlmin, the breaking extension increases. This
consistent increase in breaking extension may be due
to the increase in tenacity as the extension rate
increases. However, from the tenacity trend it may be
expected that at higher rate of extension, there should
be a drop in breaking extension for 1 00mm long
specimen. This has also happened in practice. It is
also observed from Table 4 that for 250 mm and 500
Acknowledgement
The authors are thankful to Prof. Siddhartha
Baenrjee, Mr. Swarnava B anerjee, Mr. Ritesh Neogi
and Mr. Kazi Ali Altaf of College of Textile
Technology, Berhampore, for help in carrying out the
experiments.
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