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INTRODUCTION
In the process of texturing, the yarn is exposed to
high temperatures and tensile and torsional forces,
which affect the structure of the yarn and thus its
properties (geometric, physical-mechanical, physical-
chemical, etc.) [1, 2].
Modern technological solutions of frictional texturing
by false twisting, are characterized by short heating
zones with increased temperatures on the heaters
and with a shortening of the heating time.
Texturing parameters significantly affect the proper-
ties of textured multifilament yarn, and thus their
behaviour in subsequent processes of production of
textile materials. The tensile forces of textured multi-
filament yarn in the production processes of textile
materials significantly affect the final quality of the fin-
ished products. Poor quality of textile materials is
very often obtained, although all preconditions in the
process of preliminary design have been met. The
reasons for such shortcomings should be sought in
the irregularities in defining the tensile forces of
textured multifilament PES yarns in the production
processes of textile materials. The problem is espe-
cially pronounced in the texturing of partially oriented
PES filament (POY – Partially Oriented Yarn), about
which there is not enough data in the literature. Data
from the literature mainly refer to data from laborato-
ry conditions [3–5]. In paper [6], the influence of the
parameters of the false twisting texture process on
the structure and crimping properties of textured mul-
tifilament PES yarns produced in industrial conditions
on a machine with high-temperature heaters were
analysed.
The literature also contains information on the influ-
ence of texturing process parameters on the proper-
ties of multifilament POY PES yarns produced on tex-
turing machines with classical primary heaters
[7–10].
The literature offers a lot of information on the textur-
ing of stretched polyester filament (FOY – Fully
Oriented Yarn) which is less sensitive to changes in
the parameters of the texturing process [11]. Also,
there is information on the application of different tex-
turing processes: Fully Oriented Yarn texturing pro-
cedures [12, 13].
Investigation of deformation properties of textured multifilament PES yarns
DOI: 10.35530/IT.073.04.202167
JOVANA STEPANOVIĆ DUŠAN TRAJKOVIĆ
TATJANA ŠARAC JOVAN STEPANOVIĆ
ABSTRACT – REZUMAT
Investigation of deformation properties of textured multifilament PES yarns
In the process of texturing, smooth filaments are formed into crimpy yarns. By combining thermal and mechanical action,
thermoplastic fibres acquire a permanent wavy shape.
Since textured multifilament yarns, formed from POY PES filaments, produced on machines with high-temperature
heaters, are insufficiently studied, this paper analyses the deformation characteristics of yarns produced in industrial
conditions using different process parameters (primary heater temperature, yarn speed, yarn stretching, peripheral
speed of friction discs). Special attention is paid to the characteristics at the elastic limit, then at the creep limit, yield
and breaking of multifilament textured yarns. A method is proposed which can determine the key points of deformation
in the process of stretching textured polyester multifilament yarn, as well as the relationship between the values of force
and elongation at the limits of elasticity, creep, end of creep zone, yield and break.
Keywords: textured yarn, false twisting, elastic limit, creep limit, yield point, breaking force
Investigarea proprietăților de deformare ale firelor multifilament texturate din PES
În procesul de texturare, filamentele netede sunt transformate în fire ondulate. Prin combinarea acțiunii termice și a celei
mecanice, fibrele termoplastice capătă o formă ondulată permanentă.
Întrucât firele multifilament texturate, formate din filamente POY PES, produse pe mașini cu încălzitoare de temperatură
înaltă, sunt insuficient studiate, această lucrare analizează caracteristicile de deformare ale firelor produse în condiții
industriale folosind diferiți parametri de proces (temperatura încălzitorului primar, viteza firului, întinderea firului, viteza
periferică a discurilor de frecare). O atenție deosebită se acordă caracteristicilor la limita elastică, apoi la limita de fluaj,
deformarea și ruperea firelor texturate multifilament. Se propune o metodă prin care se pot determina punctele cheie de
deformare în procesul de întindere a firului multifilament de poliester texturat, precum și relația dintre valorile forței și
alungirii la limitele de elasticitate, fluaj, capătul zonei de fluaj, deformarea și ruperea.
Cuvinte-cheie:fir texturat, torsiune falsă, limită elastică, limită de fluaj, punct de deformare, forță de rupere
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In addition, the possibility of using recycled polyethy-
lene terephthalate to make filament textured yarns
was investigated and the properties of recycled PET
filament yarns were compared with filament yarns
made of new fibre-grade PET [14].
Since the properties of textured multifilament PES
yarns produced on machines with high-temperature
heaters are insufficiently studied, in this study the
influence of texturing process parameters on the
deformation properties of textured PES multifilament
yarns produced in industrial conditions was analysed.
Experiments in industrial conditions should enable
the selection of optimal parameters of the texturing
process, with the aim of increasing productivity and
achieving energy savings. The obtained results
should contribute to the economy of production of
multifilament textured PES yarns.
MATERIALS AND METHODS
The experimental material was made in industrial
conditions. Polyester multifilament yarn is produced
on a machine for stretching friction texturing with
high-temperature heaters: FTF-15 (ICBT, France).
Technical-technological characteristics of the machine
are: maximum speed of texturing: 1500 m/min; length
of the first heater: 1.050 m; length of the second
heater: 1.60 m; cooling zone: 1.24 m; friction aggre-
gate: ICBT aggregate 1-5-1; working (5 pcs.) PU
discs; C profile.
Samples of textured PES yarns of yarn count
167f36x1 dtex and 165f36x1 dtex were produced
from POY PES multifilament of yarn count 278f36x1
dtex, manufactured by TWD Fibers (Germany). The
POY polyester filament (poly (ethylene terephtha-
late)) used in this study is partially oriented with a
very low degree of crystallinity (less than 5%), so its
structure and properties can vary greatly by changing
the parameters of the texturing process. A total of
108 industrial tests were performed, during which
the texturing speeds (v) were changed, as follows:
500 m/min, 600 m/min, 700 m/min, 900 m/min, 1000
m/min and 1100 m/min. Then, the primary heater
temperatures (T) of 350°C were applied; 400°C and
450°C, elongation coefficient (i) 1.667 and 1.687, and
peripheral disk speed ratio and yarn speed (D/Y) of
2.15; 2.20 and 2.25. The temperature of the second
heater had a constant value of 180°C.
The breaking characteristics of the experimental mate-
rial were determined on an automatic dynamometer
in accordance with the standard EN ISO 2062:2009.
The breaking speed is a constant 500 mm/min. Using
typical software, the typical force-tensile curves for
the tested textured yarn pattern are defined. Typical
curves are represented in the form of a function of a
ninth-degree polynomial, with the coefficients of the
determination being about 0.999 (figure 1).
By the analysis of the flow of the elongation force
function, are determined the elastic limit (F1, e1), the
creep limit (F2, e2), the end of the creep zone (F3, e3),
the yield after the creep zone (F4, e4) and the break
(F5, e5) of experimental material (figure 1). In the
case of textile materials, we are mainly talking about
zones in which some kind of deformation dominates.
For textured multifilament yarns, the given limits
depend on the properties of the starting multifilament,
but also on the process parameters of yarn produc-
tion.
When stretching the yarn, the crimps, which were
formed in the process of texturing, are initially
straightened. Initially, a higher slope of the curve is
noticeable i.e., a faster increase in force in relation
to the stretching of the textured yarn to the point
(F1,e1). This point simultaneously represents the end
of the elastic zone. Immediately after the elastic limit
is the creep limit (F2, e2). During further stretching,
significant changes occur in the structure and all
the way to the point (F3,e3) there is a noticeable
decrease in the slope of the force-elongation func-
tion. Then the slope increases again to the point
(F4,e4) and finally decreases until the interrupted tex-
tured yarn at the point (F5, e5).
The elastic limit defines the recommended allowable
load of textured yarns at which irreversible deforma-
tions of the material will not occur. The elastic limit of
textured multifilament yarns was determined by
analysing the flow function of tensile forces. By defin-
ing the local maximum of the first derivative of the
function, where the second derivative of the function
is equal to zero, the elastic limit is determined, as well
as the parameters of forces and elongation at the
elastic limit (F1, e1).
The creep of textured multifilament yarns occurs by
applying a load that causes stress in the yarn above
the elastic limit. It is determined at the point of local
minimum of the second derivative of the function i.e.,
at the corresponding zero of the third derivative of the
function. At a given limit, the values of force and elon-
gation at the creep limits are determined (F2, e2). The
creep limit of textured yarns is the upper acceptable
load limit, to which the yarn can be subjected in sub-
sequent technological processes, while the proper-
ties of the yarn are still acceptable for the production
of textile products.
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Fig. 1. Curve F(e) of multifilament polyester yarn
The creep zone begins at the creep limit and lasts
until the textured yarn stops stretching faster and
begins to provide significant resistance to the tensile
force again. The end of the creep zone is determined
at the point of a minimum of the first derivative of the
function i.e., at the point where the second derivative
of the function is equal to zero (F3, e3).
Upon completion of the creep, the multifilament tex-
tured PES yarn again provides greater tensile resis-
tance and the slope of the tensile force curve increas-
es. This increase in force lasts until the moment when
significant changes in the structure of monofilaments
occur again due to stretching. The yield point after
creep is determined at the point of local maximum of
the first derivative of the elongation force function i.e.,
the zero of the second derivative of the function at a
given point. This point on the graph (F4, e4) can rep-
resent the maximum stress that the textured multifil-
ament yarn will withstand in the processes of
exploitation, to deform, but still not break.
Further stretching causes significant changes in the
structure of the textured multifilament yarn, destruc-
tion of individual monofilaments and finally breaking
of the multifilament yarn, which is marked by a dot
(F5, e5) on the graph (figure 1).
RESULTS AND DISCUSSION
In order to get the impression of changes in the val-
ues of force and elongation at the elastic limit, creep
limit, end of creep zone, yield and break limits,
graphs were chosen to show the given changes at
the same ratio of peripheral disk speed and yarn
speed (2.15) and the same stretching in the process
of texturing (1.665).
Force and elongation were registered at the elastic
limit of textured PES multifilament yarns. Based on
the obtained results, figure 2 shows graphs that indi-
cate the influence of temperature and texturing
speed of multifilament yarns on their properties at the
elastic limit.
The results show that textured multifilament yarns
produced at a primary heater temperature of 350°C
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have force values at the elastic limit generally higher
than yarns produced at a primary heater temperature
of 450°C. Also, the trend of increasing force at the
elastic limit with increasing texturing speed up to
1000 m/min is observed in yarns produced using a
primary heater temperature of 350°C, and then a
decrease in force was registered, unlike yarns pro-
duced using a texturing temperature of 450°C, where
force growth trend up to a texturing speed of 1100
m/min. Elongation values at the elastic limit are gen-
erally higher for yarns produced by applying a higher
texturing temperature.
The creep limit defines the upper allowed load limit of
textured polyester yarns in the following technologi-
cal processes of its processing.
The values of force and elongation were registered at
the creep limit of textured polyester multifilament
yarns. Based on the obtained results, Graphs are
given in figure 3 showing the influence of the speed
and temperature of texturing on the values of force
and elongation.
The results show that in the case of textured multifil-
ament yarns produced at a primary heater tempera-
ture of 350°C, the values of the force at the creep
limit are higher than the yarns produced at a textur-
ing temperature of 450°C. In addition, the trend of
increasing force at the creep limit with increasing tex-
turing speed up to 1000 m/min is observed in yarns
produced using a primary heater temperature of
350°C, and then a decrease in force was registered,
in contrast to yarns produced using a texturing tem-
perature of 450°C, where is a trend of increasing
force up to a texturing speed of 1100 m/min.
The values of force and elongation at the creep limit
and elastic limit show analogous changes at appro-
priate texturing speeds and temperatures.
The end of the creep zone of the textured multifila-
ment PES yarn ends at the moment when the tensile
force begins to increase again faster than the elon-
gation.
Figure 4 shows graphs indicating the influence of the
primary heater temperature and texturing speed of
Fig. 2. The influence of texturing speed and temperature of primary heaters on force value and elongation at elastic
limit (D/Y = 2.15, i= 1.665)
the polyester multifilament yarn on the properties at
the end of the creep zone.
Analysis of the force value at the end of the creep
zone at texturing temperatures of 350°C and 450°C
shows that the force values are higher at a lower tem-
perature, while the textured PES multifilament yarn
elongates more at the end of the creep zone if pro-
duced at a higher primary heater temperature. Also,
based on the obtained results, a significant decrease
in elongation at the end of the creep zone can be
stated in yarns produced at speeds higher than 900
m/min. The changes in the values of the forces in the
creep zone are precisely the consequence of the
uneven heat reception of the multifilament yarn,
observed from the yarn surface towards the core. In
his research, Eskin [15] showed that the difference in
temperature of surface and core of yarn increases
with increasing heater temperature, texture speed
and decreases with yarn count, while the difference
in temperature of yarn surface and core decreases
with increasing heater length, which in this case is not
a reason since these are HT heaters 1.050 m long.
Figure 5 shows graphs showing the influence of the
temperature of the primary heater and the texturing
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speed of the polyester multifilament yarn on its prop-
erties at the yield point after creep.
The results show that textured yarns produced at a
texturing speed of up to 900 m/min, at a primary
heater temperature of 450°C have higher values of
the force at the yield point compared to yarns pro-
duced at a primary heater temperature of 350°C.
Elongations of textured yarns at the yield point have
approximate values. Also, a trend of decreasing the
value of force and elongation of the yarn at the yield
point with increasing texturing speed was observed.
There is a significant decrease in elongation at the
yield point in yarns produced with texturing speeds
above 900 m/min.
Figure 6 shows graphs showing the influence of pri-
mary heater temperature and texturing speed of
polyester multifilament yarn on its breaking properties.
Based on the obtained results, it can be noticed that
the textured yarns produced at the temperature of the
primary heater of 450°C have higher values of break-
ing force in relation to the yarns produced at the tem-
perature of the primary heater 350°C. Textured multi-
filament PES yarns produced at a primary heater
temperature of 400°C have higher breaking strength
Fig. 3. The influence of texturing speed and temperature of primary heater on force value and elongation at creep
limit (D/Y = 2.15, i= 1.665)
Fig. 4. The influence of texturing speed and temperature of the primary heater on the force value and elongation at the
end of the creep zone (D/Y = 2.15, i= 1.665)
values compared to yarns produced at a primary
heater temperature of 350°C, and less than yarns
produced at a primary heater temperature of 450°C.
Also, a decrease in the breaking force of the yarn is
observed with an increase in the texturing speed.
Yarns produced at a texturing speed of 1100 m/min,
at a primary heater temperature of 400°C, have
approximate values of breaking force as yarns pro-
duced at a texturing temperature of 350°C, at the
same other production process parameters. The
breaking elongations of textured yarns have approxi-
mate values, with slightly higher values for yarns pro-
duced by a texturing temperature of 450°C at speeds
of 1000 m/min and 1100 m/min. Also, there is a trend
of decreasing the value of breaking force and break-
ing elongation with increasing texture speed above
900 m/min.
The higher temperature of the primary heater and
longer exposure to temperature contribute to stress
relaxation within the molecular chains of filament
yarns, which affects the elasticity of the yarn.
Simultaneous action of friction discs causes disorien-
tation of macromolecular chains in the sense of twist-
ing and bending in the process of false twisting, and
higher temperature and longer retention of yarn in the
heater contribute to greater disorientation of macro-
molecules in the process of false twisting and slight-
ly lower value of force at the elastic and creep limit.
Relaxation of internal stresses in the yarn due to a
higher temperature and longer temperature exposure
is expressed in the values of yarn parameters at the
yield point after the creep zone. Namely, during
stretching, in the process of breaking on the
dynamometer, the macromolecules are oriented in
the direction of the yarn axis. It is expected that mul-
tifilament textured yarns produced by applying a
higher texturing temperature have a better orientation
of the macromolecular chains at the yield point, due
to the lower internal stress of the yarns thus formed.
This may be the reason mainly for slightly higher val-
ues of forces at the yield point and higher values of
breaking forces of textured multifilament PES yarns,
produced by applying higher texturing temperatures.
In order to preserve the mechanical characteristics of
multifilament textured PES yarns, it is very important
to define the allowable yarn loads in the following
technological processes. Especially since all monofil-
aments of multifilament yarn could not absorb the
same amount of heat, due to their position in the
yarn, so their properties will differ enough that we
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Fig. 5. The influence of texturing speed and temperature of the primary heater on the force value and elongation
at the yield point (D/Y = 2.15, i= 1.665)
Fig. 6. The influence of texturing speed and primary heater temperature on breaking force and breaking elongation
(D/Y = 2.15, i= 1.665)
cannot talk about the homogeneity of multifilament
textured PES yarn. This inhomogeneity of the struc-
ture will in any case lead to variation in the quality of
the multifilament yarn, to which special attention
must be paid when predicting the properties of these
yarns. A responsible approach to the analysis of the
properties of textured multifilament yarns can
achieve energy savings in the texturing process and
contribute to the optimization of the production of
yarns produced on machines with HT heaters.
In industry, a conclusion is often made about the
quality of yarn, in terms of mechanical characteris-
tics, only on the basis of its breaking characteristics.
That is not a good solution. Knowing the values of
forces and elongation at the limits of elasticity and
creep of textured multifilament PES yarns gives a
true picture of the values of forces that the yarn can
be loaded in the technological processes of process-
ing into textile materials. In that way, the properties of
the yarn will be preserved and thus the good quality
of the finished product will be ensured in accordance
with the design of the textile material and the require-
ments of the standard.
Taking into account all the above, the optimal param-
eters of the texturing process must be chosen as a
compromise solution having in mind the texturing
temperature, texturing speed, stretching of multifila-
ment yarn in the manufacturing process, the ratio of
peripheral disk speed and yarn speed, POY PES
multifilament quality, machine condition and crimp
characteristics of the textured yarn. The obtained
results showed that the partially oriented polyester
yarn used in this paper can be textured at significantly
higher texturing speeds compared to the standard
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texturing speeds (up to 700 m/min) used for process-
ing the yarns of tested yarn count.
Figures 7, a–f show the relationship of parameters at
the limits of elasticity, creep, end of creep zone, yield
and break. Therefore, only images showing the cor-
relation of the analysed parameters in textured multi-
filament yarns produced at a temperature of 400°C
are presented. The values of force (cN) and corre-
sponding elongations (%) at given points are
described by equations:
F = a eb (cN) (1)
Table 1 gives the parameters of function a, bfor
determining the value of force in points 1 to 5 (fig-
ure 1), at texturing temperatures of 350°C, 400°C
and 450°C and speeds of 500 m/min, 600 m/min, 700
m/min, 900 m/min, 1000 m/min and 1100 m/min i.e.,
for all 108 samples made in industrial conditions. The
obtained results (at different texturing speeds and
temperatures) include all samples where the values
of D/Y are 2.15, 2.20 and 2.25, as well as stretching
1.665 and 1.685, since this range of changes did not
have a significant effect on the deformation proper-
ties of the textured multifilament yarns analysed in
this study.
The results are presented for textured multifilament
polyester yarns produced using the appropriate pri-
mary heater temperature and texturing speed with a
defined ratio of peripheral disc speed and yarn and
elongation speed in the production process. The
results can be applied to predict the properties of tex-
tured PES multifilament yarns at appropriate produc-
tion process parameters. In addition, the obtained
results can be used to predict the properties of
PARAMETERS OF FUNCTION a, bFOR DETERMINING THE VALUE OF FORCE IN POINTS 1 TO 5
Function F = a × e
b (cN)
Parameters a St.error b St.error r2
v = 500 m/min; T = 350°C94.99763 2.42722 0.60357 0.00889 0.99662
v = 500 m/min; T = 400°C81.65465 2.32775 0.6616 0.00987 0.99652
v = 500 m/min; T = 450°C88.03712 2.12453 0.64778 0.00832 0.99735
v = 600 m/min; T = 350°C101.49837 3.02126 0.56914 0.01032 0.99444
v = 600 m/min; T = 400°C94.26997 2.29022 0.60384 0.00835 0.99698
v = 600 m/min; T = 450°C80.33149 1.77259 0.66029 0.00749 0.99811
v = 700 m/min; T = 350°C99.92983 3.32977 0.57814 0.01173 0.99319
v = 700 m/min; T = 400°C85.48915 2.00175 0.64161 0.00802 0.99768
v = 700 m/min; T = 450°C88.13831 1.81877 0.63819 0.00707 0.99815
v = 900 m/min; T = 350°C115.62203 3.14297 0.51605 0.00951 0.99358
v = 900 m/min; T = 400°C109.67339 2.75136 0.54877 0.00882 0.99524
v = 900 m/min; T = 450°C96.22174 2.64515 0.59987 0.00956 0.99558
v = 1000 m/min; T = 350°C127.07795 2.19324 0.52338 0.00657 0.99676
v = 1000 m/min; T = 400°C120.38161 2.14329 0.54593 0.00666 0.99702
v = 1000 m/min; T = 450°C107.32115 3.00239 0.58121 0.01018 0.99416
v = 1100 m/min; T = 350°C124.46485 1.87702 0.53296 0.00586 0.99755
v = 1100 m/min; T = 400°C119.72414 1.50149 0.55417 0.00483 0.99849
v = 1100 m/min; T = 450°C121.07555 2.22649 0.54629 0.00689 0.99687
Table 1
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textured multifilament PES yarns in subsequent pro-
duction processes into textile products.
CO N C LU S I ON
Knowledge of the deformation characteristics of tex-
tured multifilament PES yarn is very important from
the aspect of predicting its behaviour in the process-
es of production into textile materials and products,
as well as predicting the behaviour of textile products
during exploitation.
The key points of deformation of textured multifilament
PES yarn in the stretching process are defined and a
Fig. 7. Relationship of parameters at the limits of elasticity, creep, end of creep zone, yield and break: a– relationship
of parameters (v= 500 m/min, T= 400°C); b– relationship of parameters (v= 600 m/min, T= 400°C); c– relationship
of parameters (v= 700 m/min, T= 400°C); d– relationship of parameters (v= 900 m/min, T= 400°C); e– relationship
of parameters (v= 1000 m/min, T= 400°C); f– relationship of parameters (v= 1100 m/min, T= 400°C)
ef
cd
ab
method for determining the elastic limit, creep limit, end
of creep zone and yield point after creep is proposed.
In addition, the results showed that the texturing tem-
perature has an analogous influence on the values of
the forces at the elastic and creep limits. It was found
that lower texturing temperatures have a more
favourable effect on the values of force at the elastic
limit and force at the creep limit, while higher temper-
ature values generally have a more favourable effect
on elongation at the elastic limit and creep limit.
The influence of temperature on the value of the
force at the yield point and on the breaking force of
the yarn is opposite in relation to the changes in the
value of the force at the elastic limit and at the creep
limit. Namely, higher texturing temperatures generally
give slightly higher values of the force at the yield
point and higher values of the breaking force.
In order to contribute to the development of a method
for predicting the behaviour of textured multifilament
PES yarn in the next phases of processing, an equa-
tion is proposed that correctly connects the key
points (force-elongation at the elastic limit, at the
creep limit, at the end of the creep zone, at the yield
point and yarn break) in the process of stretching the
yarn, until it breaks.
The purpose of textured multifilament PES yarn and
the tensile force of yarn in technological processes of
production into textile materials must be observed
simultaneously and the technological parameters of
yarn texturing adjusted accordingly. In this way, ener-
gy savings in the texturing process can be achieved
and contribute to the optimization of the production of
textured multifilament PES yarn on machines with
high-temperature heaters.
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Authors:
JOVANA STEPANOVIĆ, TATJANA ŠARAC, DUŠAN TRAJKOVIĆ, JOVAN STEPANOVIĆ
University of Niš, Faculty of Technology, Bulevar oslobođenja, 124, Leskovac, Serbia
Corresponding author:
JOVAN STEPANOVIĆ
e-mail: jovan.stepanovic@ni.ac.rs
