IJFTR 31(3) 387

I ndian Journal of Fibre & Textile Research
Vol. 3 1 , September 2006, pp. 387-393
Structural and functional characteristics of yarns manufactured by different
pneumatic spinning systems
A
R i va L Coli & M Kasem
",
I nstituto de I nvestigaci6n Textil de Terrassa CINTEXTER), U n iversidad Poli tecnica de Catalufia, Spain
Revised received 2 J April 2005; accepted R lillie 2005
The structural and functional properties of yarns manufactured by two pneumatic spinning systems, namely pneumatic
wrapping spinning by false twist and pneumatic spinning by real wrapping twist, have been studied and compared to those
of the yarns manufactured by conventional ring spinning. These properties are assessed by determining apparent diameter.
yarn deformation, yarn evenness, hairiness, neps, average apparent twist, tenacity, elongation, twist vivacity, elongation due
to untwist-backtwisting and residual shrinkage. The real wrapping twist pneumatic spinning system produces yarns that have
a less pronounced corkscrew structure than those produced by false twist pneumatic spinning. However, the yarns produced
by real twist spi nning show some characteristics of i rregularity and dynamometric characteristics that situate them in an
inferior position to yarns produced by conventional ring spinning.
Keywords: Cotton, Corkscrew structure, Pneumatic spinning, Polyester, Ring spi nning, Wrapping fibre. Yarn
IPC Code: I nl. C I . 8 00 1 H i l l i S
1 Introduction
Of the various spinning systems utilized to
manufacture yarns, pneumatic spinning allows one of
the quickest speeds of production. Nevertheless, the
yarns manufactured by pneumatic spinning are
characterised by a particular structure, i n which a core
of parallel fibres is bound by wrapping fibres. This
structure is peculiar and responsible for the difference
between the physical properties of these yarns and
those of the yarns manufactured by conventional ring
spinning or open-end spinning (rotor) systems.
The yarns manufactured by pneumatic spi nning
have a corkscrew type structure that is more or less
pronounced depending on the quantity of wrapping
fibres and on their tension around the core fibres. The
regularity and other structural characteristics of the
pneumatic yarns depend on a n umber of variables i n
the spinning process .
I n this paper, the structural and functional
properties of yarns manufactured by two pneumatic
spinning systems (pneumatic wrapping spi nning by
false twist and pneumatic spinning by real wrapping
twist) have been studied and compared to those of the
yarns manufactured by the conventional ring
spinning. I - 1 2 These properties are assessed by
"To whom all the correspondence should be addressed.
E-mail: ariva@intexter.upc.edu
determining the parameters, such as apparent
diameter, yarn deformation, yarn evenness, hairiness,
neps, average apparent twist, tenacity, elongation,
twist vivacity, elongation due to untwist-backtwisting
and residual shrinkage.
2 Materials and Methods
2.1 Materials
The yarns used in the study were of three types.
Two types of yarns were manufactured using two
different pneumatic spinning systems and the third
type was obtained using the conventional ring
spmnmg.
The two pneumatic spinning systems used were as
follows:
(i)
(ii)
Pneumatic wrapping spinning by false twist,
hereafter refened to as HZNtf.
Pneumatic spinning by real wrapping twist,
hereafter refened to as HZNtrz.
The fundamental difference between the two
systems is the manner in which they twist the
wrapping fibres. The pneumatic wrapping spinning
system (HZNtf) (Fig. I ) consists of a tandem twist­
detwist air jet. The types of air j ets which are now
used to impart transient (false) twist in the pneumatic
wrapping-spinning system have the disadvantage that
the spun yarn takes the characteristical form of a
I N D I A N J. F I B R E TEXT. RES., SEPTEMB E R 2006
388
1
2
Table I �Average fibre l e ngth a n d evenness of t h e s l ivers
Composi t ion
%
CO
1 00
75
50
25
Fig. I�Murata MJS technique ( I -draft i ng roller, 2-delivcry
roller, 3-suction nozzle, 4-false t w i st nozzle, 5-compressed air,
6-fibre and 7-yarn)
R
2
3
4
Fig. 2�New technique ( I -draft roller, 2-dc l i very roller, 3-tw isting
nozzle, 4-false twist m i n i-spindle, 5-comprcssed a i r, 6-fibre, 7yarn and 8-dust and free fibres suction)
corkscrew and shows a rough touch which negatively
influences the properties of the end product. Thi s
effect i s particularly felt i n t h e case o f high quality
woven and knitted fabrics. On trying to weigh out the
low twisting power of the spinning air jets by air
overpressure, the excess of flows degradates the
quality of the yarns . Thi s fact, together with high
hairiness more considerable in 1 00% cotton spun
yarns, negatively influences the properties of the end
product and thus the appl ication of these yarns is
Ii mited. 1 3 - 1 9 A Murata MJS 802 spinning frame was
utilized to implement this spinning system.
The HZNtrz system (Fig. 2) i s able to produce real
twist yarns ; it is basically composed of a false twist
miniature spindle and a special air jet, responsible for
the aspiration of slivers from the drafting roller (R),
for releasing the ends of fibres corresponding to the
group of fibres transient twisted by the false twist
mini-spindle (4) and for twisti ng them (real twist) on
the nucleus. When the yarn loses the false twi st, after
goi ng through the false twist mini-spindle, the
twisting of fibres wrapping the nucleus is reinforced.
All along the spinning zone, the fibres and the yarn
are guided by special ducts connected to a vacuum
Average fibre
length, m m
Evenness
Uster C Y %
Neps
neps/g
27.5
28 . 5
30.0
3 1 .7
34.8
3 . 84
4.46
4.49
3.57
2.95
II
9
9
7
'
PES
25
50
75
1 00
4
pump to prevent the contamination of dust and fluff in
the working envi ronment. The yarns produced with
this system have a structure almost like that of a
conventional yarns, where the fibres covering the
nucleus have real twist and only the fibres i nside
2 2
remain without torsion, as described earlier. 0. 1
A prototype studied at the I nsti tute of Textile
Research of Terrassa ( INTEXTER) was utilized to
i mplement this spinning system. The yarn obtained
using conventional ring spinning are referred to as
RS.
Cotton/polyester blend yarns ( 1 5 tex) were spun on
each of the spinning systems i n the ratios 1 00:0,
75:25, 50:50, 25:75 and 0: 1 00. The raw materials
used were extra-long Egyptian cotton (CO) and 1 .3/38
Br polyester (PES) .
The spi nning was done in a n INTEXTER pilot
plant. The slivers of all the composi tions were made
by three passes through a modified Ingolstadt
(Shubert-Salzer) drawi ng frame. From the resulting
slivers, the evenness of the sliver and the average
fibre length were determined .
The average fibre length was determined as per the
DIN Standard 53808 (ref. 22) using Afis (Uster)
equipment. 23 The evenness of the slivers was obtained
2
using an Uster Evenness Tester I I I 3 following the
ASTM Standard D 1 425 (ref. 24).
The characteristics of the resulting slivers are given
in Table I .
2.2 Methods
2.2. 1 Apparent Diameter and Yam Deformation
To determine the apparent diameter and the yarn
deformation of the wrapped yarns, a unique
methodology was developed. The yarn was taken
under constant tension over a glass slide to facilitate a
continuous observation of its s tructure. The diameters
de and d; were measured in the tested yarns by means
of optical and electronic m icroscopy, where the
hairi ness can be easily d iscarded optically (Fig. 3).
One hundred measurements were made for each
type of yarn. The average apparent diameter,
RIV A I:l al. : STRUCTURAL & FUNCTIONAL CHARACTERISTICS OF YARNS
389
Fig. 3--S tructure of the HZNtrz yarn
necessary to study the yarn deformation, was
measured in the areas of little deformation. The
coefficient of yarn deformation was determined using
the following relationship:
De
=
de - di
d
where De i s the coefficient of deformation (0 < De
> I ) ; dc, the maximu m diameter of the yarn ()..I.); di, the
minimum diameter of the yarn ()..I.); and d, the average
apparent diameter of the yarn in non-deformed areas
()..I. ) .
The closer the value of De to one, the greater i s the
deformation of the resulting yarn, which will have a
more pronounced " corkscrew" structure. On the other
hand, as this value approaches zero, the yarn shows
less deformation and is more cylindrical. Figure 4
i llustrates the meaning of the parameters indicated
above.
2.2.2 Yam Evelllless, Hairilless alld Neps
The yarn evenness was determined with an U ster
Evenness Tester I I I 23 as per the ASTM Standard
D 1 425 (ref. 24). The hairiness and neps were
analysed using the method i ncorporated i n the
evenness tester, which gives a value corresponding to
the total hairiness and the number of neps.
2.2.3 A verage Apparellt Twist
The average apparent twist of the yarns was
determined using the Zweigle 0-3 1 2 S Automatic
Digital Twist Counter, following the DIN Standard
53832 for twi st-backtwisting. 25
2.2.4 Tellacity alld Elongatioll
Uster Automatic Dynamometer was used to
determine the tenac i ty and elongation of the yarns,
fol lowing the ASTM S tandard 02256 (ref. 26). Each
yarn was tested 1 00 times and the average was taken .
2.2.5 Twist Vivacity
Twist vivacity is the tendency of a yarn to twist as
a consequence of the twist caused by the spinning
process. The method to determine the twist vivaci ty
Fig. 4-Wrapped yarns (a) with l i ttle deformation and (b) with
pronounced deformation
entai ls determining the twist produced in a thread
after it is plied and hung with a small weight and left
to twist until it stabilises. The backtwisting was
determi ned following the ISO 206 1 (ref. 27).
2.2.6 Elongatioll due to Ulltwist-Backtwisting Effect
This parameter was determined from the elongation
curve that results from the untwist-backtwisting of the
yarn. The method is based on the hypothesis that the
lesser the degree to which the thread exhibits a
corkscrew structure, the greater i s the compensation
for fibri llar twisting in the group of fibres that make
up the nucleus of the wrapped yarn. For this reason,
the elongation curve yields i nformation on the
structure of this type of yarn. The process fol lowed to
determine the elongation curve is as follows:
The average apparent twist was measured using an
automatic twist counter and following the usual
procedure. Subsequently, the elongation produced in
the yarn at the following four different moments of
backtwisting was measured:
•
When half (50%) of the apparent twist of the
yarn had unwound.
•
When all ( 1 00%) of the apparent twist of the
yarn had unwound.
•
When half (50%) of the apparent twist of the
yarn had backtwisted.
•
When all ( 1 00%) of the apparent twist of the
yarn had backtwisted and the yarn had reached
its i n i ti al length.
390
I N D I A N J. F I B R E TEXT. R E S . , SEPTE M B ER 2006
The average apparent twist of the yarns along with
the elongation curves was determined using a Zweigle
D-3 1 2 S Automatic Digital Twist Counter following
the untwist-backtwisting method as per the DIN
Standard 53832 (ref. 25).
2.2. 7 Residual Shrinkage
This parameter was observed by determining the
contraction undergone by the yarns after being boiled
i n distilled water. The testing method was based on
determining the length of a 2620 tex hank, prior to
and fol lowing hydrothermal treatment, by suspending
a 497 g weight from it for 30 s. The procedure used
was as follows :
Acclimate the hanks to a standard relative
temperature and humidity for a m i n i mum of 24
h prior to the test.
Determine the initial length of the hanks while
they sustain a weight of 479 g for 30 s.
Carry out the aforementioned shrinkage test.
To avoid the hanks becoming tangled during
the boiling process, they were introduced
longitudinally into i ndividual pouches made of
Marquisette fabric. The boiling time was 30
min. The hanks were subsequently allowed to
cool till they reached an approxi mate
temperature of 50° C .
Centrifuge the hanks for 3 m i n , dry them at 3040° C and then suspend them for 2 h under
forced ventilation.
Re-accli mate the hanks.
Re-measure the length of the hanks in the same
conditions indicated before.
Calculate the shrinkage using the following
formula:
Shri n kaae
(%) =
t:>
I n i t i al length - Final length
Initial length
x 1 00
3 Results and Discussion
3.1 Apparent Diameter and Yarn Deformation
The results obtained for these parameters are
shown i n Table 2. While i n all the cotton/polyester
blends the apparent diameters of the HZNtf yarns are
smaller than the HZNtrz yarns, the significant
differences do not exist among the different blends.
It can be clearly observed that for all the
cotton/polyester blends the deformation produced by
the HZNtrz syste m is less than that of the HZNtf
yarns. This reflects the difference that exists between
the two spinning systems; in the HZNtrz system, as a
consequence of not generating false twist, the
wrapping fibres are submitted to less tension than i n
the HZNtf which subsequently diminishes the
corkscrew effect and, therefore, yarn deformation.
Consequently, the structure of the HZNtrz yarns is
closer to that of the yarns produced by conventional
ring spinning.
The yarns with 50:50 CO/PES blend ratio show a
slightly higher degree of deformation for both the
spinning systems. For the HZNtf system, the 1 00%
polyester thread shows the lowest degree of
deformation, while in the HZNtrz system the 75:25
CO/PES yarns show the lowest degree of
deformation.
The differences in deformation between samples of
different cotton/polyester blends can be attributed to
slight, inherent variations i n tension during the
spinning process that stem from spinning different
compositions of materials.
3 . 2 Yarn Evenness, Hairiness and Neps
Table 3 shows the results for yarn evenness and
Table 4 the results for hairiness and the number of
neps for 5 different cotton/polyester blends studied.
The yarns produced by the three spinning systems
show CY Uster values within the 25th percentile of
the Uster Standard. The HZNtf yarns yield lower
values, i.e. they have a lower percentage of
Tablc 2-Apparcnt d iameter (0) and yarn deformation (Dc)
Composi tioll, o/(J
CO
PES
0
H Z Ntrz system
CV %
�
1 00
De
�
0
HZNtf systcm
CV %
De
42. 1 4
0.63 1
�
2 1 .8
42.83
0.448
1 8.2
�
75
25
22.6
3 7.34
0.277
1 8.4
34.83
0.6 1 1
50
50
22.2
34. 1 1
0.450
1 7.4
33.94
0.745
25
75
22.0
42.92
0.352
1 8.4
33.54
0.590
1 00
22.2
4 1 .03
0.33 1
1 8.2
3 5 . 25
0.5 1 8
RIVA
1'1
{[t . : STRUCTURAL
& FUNCTION A L C H A R ACTE R I STICS OF Y A R N S
39 1
Table 3-Yarn evenness properties
CO
PES
1 00
75
SO
25
HZNtf
HZNtrz
1 2.55
1 4.6
Thick places (+50%)
1 1 1 000 III
Thin places (-50%)
1 1 1 000 III
Uster
CV %
Composition
%
RS
HZNtrz
HZNtf
RS
HZNtrz
HZNtf
RS
1 3.9
IS
4
10
44
4
34
SO
15. 1 7
1 2 .53
1 4.47
31
2
12
47
5
28
1 5 .89
1 2. 6 1
1 5 .47
59
6
12
89
14
47
75
1 5 .92
1 3.82
1 5 .76
64
8
45
47
26
67
1 00
1 7.64
1 4. 1 1
1 6. 6 1
69
20
86
89
16
80
25
Table 4-Neps and hairi ness of the yarns
Composition
%
CO
PES
1 00
75
SO
25
HZNtrz
Neps ( +200%)
1 1 1 000 III
29
Hairi ncss ( h )
(J
Hairi ness
HZNtf
RS
H ZNtrz
HZNtf
RS
HZNtrz
HZNtf
RS
IS
9
3.85
4.33
4.06
1 .07
1 .24
0.9
so
3]
13
16
3.8
4.23
3 . 89
1 .02
1.1
0.85
42
28
10
3 . 89
3 .96
3.44
0.99
1 .03
0.76
75
17
40
25
4.0 1
3.78
3 . 83
1 .04
0.94
0.85
1 00
13
\I
5
4.4 1
3.74
4.62
0.82
1 .06
25
I . 00
Table .'i-Average apparent twist and dynamometric properties of the yarns
Composition. %
CO
PES
1 00
75
so
25
25
so
75
1 00
Average apparent twist
twistS/ill
HZNtrz
HZNtf
374.2
472.9
1 92.4
1 83 . 4
1 77 . 8
1 1 2.3
392.0
4 1 4. 7
408.4
464.5
Elongation
%
Tenacity
cN/tex
HZNtrz
HZNtf
RS
HZNtrz
HZNtf
RS
1 5.04
1 6.42
26.82
3.8
3.58
4.77
(9.97 )
( 1 0. 3 7 )
( 9 . 68 )
( 1 0.05)
( 1 3.48)
( 7 .6 1 )
1 4.94
1 7 .65
24.84
4.33
3.75
5.2
( 1 0. 7 3 )
(9.34 )
(9.68)
( 1 1 .(8)
( 1 1 .54 )
( 7 .29)
1 6. 3 8
1 7 .44
2 1 . 14
6.92
4.72
5.47
( 1 2.45 )
( 1 0. 7 3 )
(9.53)
( 1 7.3 1 )
( 1 3.76)
( 1 0.54)
22.5 I
20.28
23 .99
1 0.36
7 .02
9.76
( 1 3. 1 4)
( 1 1 .9 1 )
( 1 4.92)
(9.49)
( 1 3 .94)
( 1 6.03)
24.84
23.49
3 1 .29
1 0.04
9. 1 2
1 2.35
( 1 4. 5 9 )
( 1 3 . 89 )
( 1 4.86)
(9.57)
( 1 0.89)
(7.76)
Valucs i n parentheses are C V % .
i rregularity. It is also these yarns that have a smaller
i ncidence of thin and thick parts.
The HZNtrz yarns have the highest Uster
coefficients of variation, and are thus less even. They
also have the highest number of thi n and thick parts.
So, the HZNtrz yarns have less corkscrew structure but
simultaneously are more i rregular because along the
yarn length more thi n and thick places exist (Fig. 5).
The yarns obtained by pneumatic spi nning show
higher numbers of neps than the conventional yarns;
the values for the H ZNtrz yarns are slightly h igher
than those for the HZNtf yarns.
Though the values for hairi ness are generally
around 25% limit of the Uster S tandard, a few
samples sl ightly exceeded i t . Differences between the
spinning systems were not observed.
a
b
Fig . .'i-Corkscrew and evenness ( a ) yarn without corkscrew but
with bad evenness and ( b) yarn with corkscrew but w ith good
evenness
3.3 Average Apparent Twist, Tenacity and Elongation
The results obtained are shown i n Table 5. The
HZNtf yarns uniformly show h igher twist values than
the HZNtrz yarns. The yarns obtained by pneumatic
spinning have lower tenacity values than the yarns
INDIAN J. FIBRE TEXT. RES., SEPTEMB ER 2006
392
produced by conventional ring spinning, as expected.
The inferior tenacity of pneumatic yarns with respect
to conventional yarns is a well-known fact and
represents one of the main disadvantages of this type
of yarn. There were no differences worthy of mention
between the two pneumatic spinning systems.
The i ncrease in polyester fibre percentage i ncreases
the tenacity of the yarns produced on pneumatic
spinning systems . There is a slight loss in tenacity of
conventional yarn as the polyester percentage is
i ncreased to 50%; the tenacity however increases on
further i ncrease i n polyester content.
For the yarns obtained by pneumatic spinning, the
elongation values are lower than those obtained by
conventional yarns; the HZNtf yarns have the lowest
values . Thi s behaviour can be explained by their yarn
structure; i n the case of the HZNtf yarns, there exists
a smaller chance of sliding of fibres i n the nucleus of
the yarn .
blends, which indicates that these kind of yarns have a
more pronounced corkscrew structure than the
HZNtrz yarns.
Coherent elongation values were obtained for the
1 00% polyester and 25 :75 cotton/polyester yarns . The
values i ncrease when the yarn approach the total
unwound and then decrease to zero once the yarn had
completely backtwisted. In other cases, the behaviour
was somewhat anomalous. One should take note that
as the yarns did not show a uniform twist, the moment
at which the yarn was completely u ntwisted cannot be
determined with exactitude (even if the apparent twist
had been determi ned previously). Thus, it i s possible
for the yarns to begin to twist again w ithout reaching
zero twist, and for this reason they have a smaller
length at the end of the test than at the beginning; thi s
explains w h y i n some cases negative elongation
values are obtained.
3.4 Twist Vivacity of Threads
The values for residual shrinkage are shown i n
Table 8. I t can be observed that the HZNtrz yarns
show less shrinkage than the conventional yarns and
that the HZNtf yarns exhibit more shrinkage. The
reason behind thi s behaviour is again the HZNtf
yarns' thread composition, which is characterised by a
strong wrapping configuration.
This behaviour is explained by the fact that inside a
hank the areas of HZNtf yarns that have a corkscrew
structure are more likely to be compacted.
The HZNtrz yarns have a higher apparent diameter
than the HZNtf yarns, though they have an identical
count (number of fibres per section). Thus, the
porosity of the HZNtrz yarns is greater than that of
the HZNtf yarns.
Furthermore, there i s a greater incidence of yarn
deformation in the HZNtf yarns than i n the HZNtrz
yarns, which causes the former to be more liable to
suffer shrinkage.
The 1 00% cotton yarns had the least shrinkage
throughout. Bearing in mind the fact that the polyester
3.6 Residual Shrinkage
The values of twist vivacity (Table 6), somewhat
higher in the HZNtf yarns, indicate that these yarns
have a greater tendency to backtwist than the HZNtrz
yarns . Once again, the values for this parameter
i ndicate that the structure of the HZNtf yarns has
areas where the wrapping is very pronounced.
3.5 Elongation due to Ulltwist-Backtwistillg Effect
Table 7 shows that the values obtai ned for
elongation due to the untwist-backtwisting effect are
greater in the HZNtf yarns for all the cotton/polyester
Table 6-Average twist vivacity of the yarn
Twist vi vacity, twistS/ill
Composition, %
CO
PES
HZNtrz
HZNtf
25
50
75
1 00
20.7
25.0
1 9. 1
1 8.2
29.4
30.6
39.6
49.8
49.9
49.8
1 00
75
50
25
Table 7-Elongation due to the untwi st-backtwisting effect
Untwistbacktwisting
%
0
-50
- 1 00
50
1 00
Elongation, %
1 00% CO
75:25 CO/PES
50:50 CO/PES
25:75 CO/PES
HZNtrz
HZNtf
HZNtrz
HZNtf
HZNtrz
HZNtf
HZNtrz
0
0.24
0.36
0.2 1
-0.50
0
0.27
0.39
0.36
0.02
0
0.08
0. 1 0
-0.02
-0.48
0
0.2 1
0.32
0. 1 1
-0.39
0
0.08
0.08
-0.07
-0.44
0
0.82
0.45
0.32
-0.36
0
0. 1 1
0.22
0.2 1
0.00
HZNtf
0
0.32
0.56
0.52
0.00
1 00% PES
HZNtrz
0
0.08
0. 1 2
0. 10
0.00
HZNtf
0
0.47
0.80
0.74
0.05
RIV A et al. : STRUCTURAL & FUNCTIONAL CHARACTERISTICS OF YARNS
Table 8--Residual shrinkage
Composition, %
PES
CO
1 00
25
75
50
50
25
75
1 00
Residual shrinkage, %
RS
HZNtf
2.30
2.07
3.03
4.4 1
3.60
4.89
3.20
4.96
2 .54
4.33
HZNtrz
1 .73
1 .93
2.34
2.27
2.4 1
yarns had not been thermofixed beforehand, it stands
to reason that the polyester and the cotton/polyester
blend yarns should exhibit a greater degree of
shrinkage.
4 Conclusions
4.1 The real wrapping twist pneumatic spinning
system gives rise to yarns that exhibit less yarn
deformation and have a slightly greater apparent
diameter than the yarns produced by the false twist
spinning system.
4.2 The yarns obtained by the real twist pneumatic
system ( HZNtrz) exhibit less evenness although have
a greater number of thi n and thick places which
exceed in both measures the corresponding values for
the HZNtf yarns. The HZNtrz yarns also have a
higher number of neps.
4.3 The average apparent twist is greater i n the
HZNtf yarns than in the HZNtrz yarns for all the
blends studied.
4.4 The dynamometric behaviour of the yarns
produced by both pneumatic spinning systems is very
similar and logically worse than that of the yarns
produced by conventional ring spinning.
4.5 The HZNtrz yarns have less twist v ivacity than
the HZNtf yarns.
4.6 The elongation due to untwist-backtwisting is
greater i n HZNtf yarns than that in HZNtrz yarns.
4.7 The shrinkage produced by hydrothermal
treatment is less in HZNtrz yarns than in HZNtf
yarns.
It can be concluded that the real wrapping twist
pneumatic spinning system produces yarns that have a
less pronounced corkscrew structure than those
produced by false twist pneumatic spinning.
However, the yarns produced by real twist spinning
show some characteristics of irregularity and
dynamometric characteri stics that situate them in an
393
inferior position to yarns produced by conventional
ring spinning.
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