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J Polym Eng 2014; aop
Youhei Kohri * , Tomoaki Takebe , Yutaka Minami , Toshitaka Kanai , Wataru Takarada
and Takeshi Kikutani
Structure and properties of low-isotacticity polypropylene elastomeric fibers prepared by sheath-core bicomponent spinning: effect of localization of high-isotacticity component near the fiber surface
Abstract: Sheath-core type bicomponent melt-spun fibers
were produced by extruding the melts of low-isotacticity
polypropylene (LPP) as the core component and the blend of
LPP and high-isotacticity PP (IPP) as the sheath component.
IPP content in the sheath was changed from 8 wt% to 40
wt% while sheath/core composition was varied from 50/50
to 10/90. Accordingly overall IPP content was kept constant
at 4 wt%. Even though the overall IPP content was intact,
bicomponent fibers with lower contraction ratio after spin-
ning, higher elastic recovery and slightly higher modulus
and strength were obtained by increasing the IPP content
in the sheath and decreasing the sheath layer composition,
i.e., localizing the IPP to the region near the surface in the
fiber cross-section. Structure analysis of the as-spun fibers
suggested the suppression of crystallization of LPP in the
sheath by blending IPP. By contrast, enhancement of molec-
ular orientation and crystallization of the sheath component
were found to occur by localizing the IPP to the region near
the fiber surface. It was speculated that this behavior was
caused by the kinematic mutual interaction of the sheath
and core components in the melt spinning process.
Keywords: bicomponent fiber; elastic recovery; elasto-
meric fiber; isotacticity; polypropylene.
DOI 10.1515/polyeng-2014-0195
Received July 16 , 2014 ; accepted August 21 , 2014
1 Introduction
Polypropylene (PP) has been widely used commercially
for the production of fibers, non-woven fabrics, films,
injection-molded products, etc. For the production of
PP, introduction of metallocene catalysts provided the
technologies for designing new types of polymers [1 – 7] ,
and recently, development of low-isotacticity PP (LPP)
with elastomeric characteristics was achieved. Structure
and properties of such PP have been investigated widely
because of its unique characteristics [8 – 13] . It was reported
that the modification high-order structure and physical
properties, as well as the improvement of processability
of conventional high-isotacticity PP (IPP), was possible by
blending a small amount of elastomeric PP [14 – 17] . By con-
trast, a technology for producing non-woven elastomeric
fabrics has been developed recently by applying the spun-
bonding process to the elastomeric PP [18] . Improvement
of the production of non-woven fabrics achieving a good
balance of processability and elastomeric recoverability of
the product has been attempted by introducing the sheath-
core bicomponent melt spinning process [19 – 22] .
In a previous paper, we investigated the effects of
sheath/core composition on the high-order structure and
mechanical properties of elastomeric bicomponent fibers
consisting of LPP as the core component and the blend of
LPP and IPP as the sheath component, in that the sheath
layer composition and the total IPP content were varied,
while keeping the IPP content in the sheath layer constant
at 10 wt% [23] . Through the analyses of the as-spun bicom-
ponent fibers, it was found that the as-spun fibers exhibit
a relatively large elastic recovery of higher than 85%, and
that the crystallization of IPP was enhanced when the
sheath layer composition was low, while the crystalliza-
tion of LPP was suppressed with the increase in the sheath
layer composition.
*Corresponding author: Youhei Kohri, Performance Materials
Laboratories, Idemitsu Kosan Co., Ltd., Chiba, Japan,
e-mail: [email protected] ; and Organic and Polymeric
Materials, Tokyo Institute of Technology, Tokyo, Japan
Tomoaki Takebe and Yutaka Minami: Performance Materials
Laboratories, Idemitsu Kosan Co., Ltd., Chiba, Japan
Toshitaka Kanai: KT Polymer, Chiba, Japan
Wataru Takarada and Takeshi Kikutani: Organic and Polymeric
Materials, Tokyo Institute of Technology, Tokyo, Japan
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2 Y. Kohri et al.: Low-isotacticity polypropylene elastomeric fibers prepared by sheath-core spinning
In this research, with the aim of producing LPP fibers
of high elastic recoverability while keeping the overall IPP
content constant, various sheath-core fibers consisting
of LPP as the core component and the blend of LPP and
IPP as the sheath component were produced, and high-
order structure and elastomeric properties of the as-spun
sheath-core bicomponent fibers were investigated.
2 Materials and methods
2.1 Materials
A new fiber and non-woven grade LPP commercialized in
2012 (LPP; L-MODU, S901, Idemitsu Kosan Co., Ltd., Chiba,
Japan) was used in this study. The polymer was produced
through the polymerization process applying a double
cross-linked metallocene catalyst. For the improvement
of the crystallizability of LPP, isotactic PP (IPP, Y6005GM,
Prime Polymer Co., Ltd., Chiba, Japan) was blended to LPP.
Properties of the polymers used in this study are listed in
Table 1 . The melts of both polymers have similar viscos-
ity. LPP has an extremely low melting temperature of 70 ° C
because of its low isotacticity.
2.2 Melt spinning of bicomponent fibers
Sheath-core type bicomponent fibers were produced by
extruding the melts of the blend of LPP and IPP as the
sheath component and LPP as the core component using
two extrusion systems, each of which consisted of a single
screw extruder and a metering pump. The spinneret had
eight spinning holes of 0.5 mm diameter. The extrusion
temperature and throughput rate were set at 220 ° C and
1.0 g/min/hole, respectively. Fiber samples were prepared
at the take-up velocity of 2 km/min. In a previous paper,
sheath IPP content was kept constant at 10 wt% while
sheath layer composition was varied from 0% to 50% [23] .
Accordingly, total IPP content was changed from 0 wt%
to 5 wt%. By contrast, in this series of experiments, IPP
content in the sheath was set from 8 wt% to 40 wt%,
while the sheath/core composition was varied from 50/50
to 10/90. Accordingly, the overall IPP content was kept
constant at 4 wt%. Sheath layer composition, sheath IPP
content and total IPP content are summarized in Table 2 .
Since the as-spun fibers have a relatively low tensile
modulus, the spin-line tension causes the elastic stretch-
ing of the fiber in the spin-line before the fibers are wound
up on the bobbin. Therefore, when the fibers were cut
off from the bobbin after the spinning, contraction of the
fibers to the original length was observed. The contraction
ratio was calculated from the circumference length of the
bobbin, L , and the length of cut-off fiber samples, R , using
the following equation [Eq. (1)]:
-Contraction Ratio (%) 100
L RL
= ×
(1)
2.3 Evaluation of elastic recovery
Elastic recovery measurements were conducted for the
as-spun fibers using a tensile testing machine (Shimadzu
Corporation, Autograph AG-I). The gauge length L 0 was
50 mm, and the cross-head speed for extension and recov-
ery were 150 mm/min. In the measurement, the fibers were
firstly stretched to strain 100%. Secondly, the cross-head
was returned to the initial position. At this moment, the
stress was zero because of the incorporation of permanent
extension after the first stretching. Finally, the cross-head
was moved for the second stretching, and the position L
where the stress started to appear again was measured.
The elastic recovery was calculated by using the following
equation [Eq. (2)]:
Table 1 Properties of low-isotacticity polypropylene (LPP) and
high-isotacticity PP (IPP).
M w M w /M n MFR (g/10 min) T m ( ° C) H (J/g) Xc (%)
LPP 1.2 × 10 5 2.0 60 70 27 13
IPP 1.6 × 10 5 3.7 60 165 90 43
Note: Sheet sample for differential scanning calorimetry (DSC)
analysis was prepared as follows: compression molding of the
polymer at 220 ° C, quenching in water, and conditioning at room
temperature for more than 1 week.
MFR, melt flow rate.
Table 2 Sheath layer composition, sheath high-isotacticity poly-
propylene (IPP) content and overall IPP content of as-spun
IPP/low-isotacticity PP (LPP) bicomponent fibers.
Sheath layer composition (wt%)
Sheath IPP content (wt%)
Overall IPP content (wt%)
10 40 4
20 20 4
30 13 4
40 10 4
50 8 4
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Y. Kohri et al.: Low-isotacticity polypropylene elastomeric fibers prepared by sheath-core spinning 3
0
Elastic Recovery (%) 1- 100LL
⎛ ⎞= ×⎜ ⎟⎝ ⎠
(2)
2.4 Tensile test
The load-elongation curves of the as-spun fibers were
obtained using the same tensile testing machine for the
elastic recovery measurement. The gauge length and
tensile speed were 50 mm and 150 mm/min, respectively.
The tensile modulus, the tensile strength and the elonga-
tion at break were obtained averaging at least 10 trials of
the tensile test for each sample.
2.5 Wide angle X-ray diffraction measurement
Wide angle X-ray diffraction (WAXD) patterns of the
as-spun fibers were obtained using an X-ray generator
and a charge-coupled device (CCD) camera (Rigaku Denki,
RTM-18HFVE, CCD Mercury). The generator was oper-
ated at 45 kV and 60 mA, and the WAXD patterns of the
fiber bundle were taken at the exposure condition of five
times/10 s.
2.6 Birefringence measurement
Birefringence of as-spun fibers was analyzed through the
measurements of fiber diameter and optical retardation
using a polarizing optical microscope (Olympus, BH-2)
equipped with a Berek compensator. Since the measure-
ment was performed at the center of the fiber, the obtained
overall birefringence represents the mean value of sheath
and core components averaged along the diameter. Thus,
in comparison with the averaging based on the weight
fractions of both components, there can be a slightly
enhanced contribution of the core component.
2.7 Differential scanning calorimetry measurement
Thermal analysis of the as-spun fibers was performed with
a differential scanning calorimeter (DSC) (Perkin Elmer,
DSC 8500) equipped with a liquid nitrogen cooling system
for the measurements from low temperature. The meas-
urement was conducted from -40 ° C to 220 ° C at a heating
rate of 10 ° C/min.
4014
12
10
8
6
Con
trac
tion
ratio
(%
)
4
2
010 20 30
Sheath layer composition (wt%)40 50
20 13
Sheath IPP content (wt%)
10 8
Figure 1 Variation of contraction of as-spun high-isotacticity
polypropylene (IPP)/low-isotacticity PP (LPP) bicomponent fibers
after spinning with sheath IPP content and sheath layer composition.
The crystallinity of pure IPP and LPP, X c-IPP
and X c-LPP
,
were calculated by using the following equations [Eqs. (3)
and (4)], where Δ H IPP
and Δ H LPP
are the heat of fusion of
IPP and LPP, and W IPP
and W LPP
are the weight fractions
of the IPP and LPP components. The heat of fusion for PP
with 100% crystallinity, Δ H *, was assumed to be 209 J/g
[24] :
-
1(%) 100
*IPP
c IPPIPP
HXH W
Δ
Δ= × ×
(3)
-
1(%) 100
*LPP
c LPPLPP
HXH W
Δ
Δ= × ×
(4)
3 Results and discussion
3.1 Melt spinning behavior
The contraction ratio of the fiber length after spinning was
plotted against the sheath layer composition in Figure 1 .
IPP content in the sheath layer is also indicated in the
figure. The contraction ratio decreased continuously from
12% to 2% with the decrease of sheath layer composition
from 50% to 10% and the increase of IPP content in the
sheath from 8% to 40%. In other words, a reduction of
the contraction ratio with the constant IPP content was
achieved by localizing the IPP to the region near the fiber
surface in the fiber cross-section.
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4 Y. Kohri et al.: Low-isotacticity polypropylene elastomeric fibers prepared by sheath-core spinning
3.2 Mechanical properties of as-spun fibers
Stress-strain hysteresis curves for the multiple cycles of
stretching and recovery of as-spun fibers with the sheath
IPP content of 40 wt% and 8 wt%, which correspond to
the sheath layer compositions of 10% and 50%, respec-
tively, are compared in Figure 2 . There was a significant
change in the stress-strain behavior between the first and
second stretchings, whereas almost identical behaviors
were observed for the second and the third stretchings.
A certain level of hysteresis was observed between the
stretching and recovery even after the second stretching.
By localizing the IPP to the region near the fiber surface,
the overall stress level during the first stretching increased
significantly, while reduction of the stress level from the
first to the second stretching was more significant.
Variation of elastic recovery after the first stretching
with the increase of sheath layer composition is shown in
Figure 3 . All samples showed a fairly high elastic recovery
of higher than 85%, while there was an improvement of
elastic recovery with the reduction of the sheath layer
composition and the increase of sheath IPP content.
Tensile modulus of the as-spun fibers is plotted against
the sheath layer composition in Figure 4 . The tensile
modulus decreased with the increase in the sheath layer
composition and with the decrease of sheath IPP content.
In a previous paper [23] , it was found that there was a quan-
titative accordance between the variation of contraction
ratio after spinning and the variation of tensile modulus
of the as-spun fibers with the change of sheath layer com-
position. This was because the higher tensile modulus
corresponded to the lower degree of elastic stretching in
the spin-line. In this research, however, the contraction
ratio significantly decreased from 12% to about 1% – 2%
when the sheath layer composition was decreased from
50% to 10%, while the increase in the tensile modulus of
fibers with the increase of sheath IPP content was only
about 25% (from 80 MPa to 100 MPa). The reason for
40120
100
80
60
40
20
Tens
ile m
odul
us (
MP
a)
010 20 30
Sheath layer composition (wt%)40 50
20 13
Sheath IPP content (wt%)
10 8
Figure 4 Variation of tensile modulus of as-spun high-isotacticity
polypropylene (IPP)/low-isotacticity PP (LPP) bicomponent fibers
with sheath IPP content and sheath layer composition.
40100
95
90
85Ela
stic
rec
over
y (%
)
8010 20 30
Sheath layer composition (wt%)40 50
20 13
Sheath IPP content (wt%)
10 8
Figure 3 Variation of elastic recovery of as-spun high-isotacticity
polypropylene (IPP)/low-isotacticity PP (LPP) bicomponent fibers
with sheath IPP content and sheath layer composition.
160
140
120
100
80
60
40
20
0
Str
ess
(MP
a)160
140
120
100
80
60
40
20
0
Str
ess
(MP
a)
20 40 60 80 1000
Strain (%)
20 40 60 80 1000
Strain (%)
1st stretching
2nd and 3rdstretching
1st, 2nd and 3rdrecovery
Sheath IPP content: 40 wt% Sheath IPP content: 8 wt%
Figure 2 Stress-strain hysteresis curves for the first, second and third cycles of stretching and recovery of as-spun high-isotacticity
polypropylene (IPP)/low-isotacticity PP (LPP) fibers with the sheath IPP content of 40 wt% and 8 wt%.
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Y. Kohri et al.: Low-isotacticity polypropylene elastomeric fibers prepared by sheath-core spinning 5
40800
700
600
500
400
300
200
100
Tens
ile m
odul
us o
f the
she
ath
com
posi
tion
(MP
a)
010 20 30
Sheath layer composition (wt%)40 50
20 13
Sheath IPP content (wt%)
10 8
Figure 5 Variation of the estimated tensile modulus of the sheath
component of as-spun high-isotacticity polypropylene (IPP)/low-
isotacticity PP (LPP) bicomponent fibers with sheath IPP content and
sheath layer composition.
40250
200
150
100
50
Tens
ile s
tren
gth
(MP
a)
010 20 30
Sheath layer composition (wt%)40 50
20 13
Sheath IPP content (wt%)
10 8
Figure 6 Variation of tensile strength of as-spun high-isotacticity
polypropylene (IPP)/low-isotacticity PP (LPP) bicomponent fibers
with sheath IPP content and sheath layer composition.
40250
200
150
100
50
Str
ain
at b
reak
(%
)
010 20 30
Sheath layer composition (wt%)40 50
20 13
Sheath IPP content (wt%)
10 8
Figure 7 Variation of strain at break of as-spun high-isotacticity
polypropylene (IPP)/low-isotacticity PP (LPP) bicomponent fibers
with sheath IPP content and sheath layer composition.
such a discrepancy is not clear at the moment. To explain
the extremely low contraction ratio of the fibers with the
sheath layer compositions of 10 wt% and 20 wt% in com-
parison with the tensile moduli of those fibers, progress
of structural change possibly accompanied by the crystal-
lization needs to occur either in the sheath or core compo-
nents after the fiber was wound up on the bobbin.
By contrast, to clarify the origin of the different
characteristics between the fibers with different sheath
layer compositions, the tensile modulus of the sheath
component was estimated based on a simple parallel
model, assuming the constant tensile modulus of 38 MPa
for the core component, which corresponds to that of the
pure LPP single component fiber. The estimated tensile
modulus of the sheath component increased from 113 MPa
to 667 MPa with the decrease of sheath layer composition
as shown in Figure 5 .
Increasing tendency of the tensile modulus with the
decrease of sheath layer composition can be regarded as
a normal behavior, since the IPP content increases at the
same time, however it should be noted that there can be
another mechanism for the increase in the tensile modulus
of sheath component. As described in a previous paper
[25, 26] , when the sheath layer composition is decreased,
its structure development behavior can be altered signifi-
cantly in comparison with its single component spinning,
because of the kinetic mutual interaction of the sheath
and core components in the melt spinning process of
bicomponent fibers. In the bicomponent melt spinning of
the LPP and the blend of IPP and LPP, enhancement of the
structure formation of the blend can be expected because
of its higher crystallizability. Such an effect becomes more
significant for the sheath or core component with lower
composition [23] .
Tenacity and elongation at break of the as-spun fibers
are plotted against sheath layer composition in Figures 6
and 7 . The tensile strength increased, whereas the elonga-
tion at break decreased with the decrease of sheath layer
composition, that is, by localizing the IPP to the region
near the fiber surface.
Summarizing the above, it was found that even though
the total IPP content was kept constant, the contraction
ratio after spinning became lower, and the as-spun fibers
with higher elastic recovery, slightly higher modulus and
strength, and lower elongation were obtained by the
enhanced localization of IPP component in the cross-sec-
tion of LPP fiber.
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6 Y. Kohri et al.: Low-isotacticity polypropylene elastomeric fibers prepared by sheath-core spinning
3.3 Fiber structure
WAXD patterns of the as-spun fibers of various sheath
layer compositions are shown in Figure 8 . All as-spun
fibers showed similar WAXD patterns with highly oriented
α form crystals. Effects of sheath/core composition and
IPP content in the sheath were not clear.
In our previous study on the sheath-core bicompo-
nent spinning of IPP and LPP, the IPP component showed
highly oriented α form crystals, whereas the LPP com-
ponent showed α form crystals of virtually no orienta-
tion [27] . The mechanism for the development of such
structure was speculated as follows. In the bicomponent
spin-line, crystallization of the IPP component proceeded
at a relatively high temperature before the stating of the
crystallization of LPP. This caused the termination of the
spin-line thinning and thus the orientation relaxation of
the LPP component. In this study, however, by changing
the sheath layer component from pure IPP to the blend of
IPP and LPP, both sheath and core components showed
high crystalline orientation.
By contrast, in our previous paper on the sheath-core
bicomponent melt spinning of the blend of IPP and LPP
with the constant IPP content of 10 wt% as the sheath
and the pure LPP as the core [23] , it was speculated for
the mechanism of the formation of highly oriented α form
crystals in the core that even though crystallization of the
IPP component in the blend started to occur at higher
temperatures, deformability of the blend could be main-
tained because the content of IPP was only 10 wt%, and
accordingly orientation of the core component, LPP, could
proceed in the spin-line. In this research, highly oriented
α form crystals were formed in the core even when the IPP
content in the blend was increased up to 40 wt%, sug-
gesting that the deformability of the blend of IPP and LPP
was maintained after starting the crystallization of the
IPP component in the spin-line, even at such a high IPP
content.
Variation of overall birefringence of as-spun fibers
with sheath layer composition and the sheath IPP content
is shown in Figure 9 . All as-spun fibers exhibited similar
levels of birefringence. This is partly because the meas-
ured birefringence in this research represents the aver-
aged birefringence of the sheath and core components.
Considering the above, birefringence of the sheath
component was estimated assuming the birefringence
of the core component LPP to be 9.9 × 10 -3 , which corre-
sponds to the birefringence of the as-spun single compo-
nent LPP fiber prepared at the same take-up velocity. The
detailed calculation method was reported in a previous
paper [23] .
Birefringence of the sheath component estimated
through the method stated above is plotted against the
sheath layer composition and the sheath IPP content as
shown in Figure 10 . When the sheath layer composition
was 50 wt%, no boundary between the sheath and the
core could be observed under the polarizing microscope.
This fact is consistent with the result in Figure 10 that the
sheath and core have a similar level of birefringence at
this composition.
Sheath layercomposition=10%
Sheath layercomposition=30%
Sheath layercomposition=20%
Sheath layercomposition=40%
Sheath layercomposition=50%
Figure 8 Wide-angle X-ray diffraction patterns of as-spun high-isotacticity polypropylene (IPP)/low-isotacticity PP (LPP) bicomponent fibers
of five different sheath layer compositions.
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Y. Kohri et al.: Low-isotacticity polypropylene elastomeric fibers prepared by sheath-core spinning 7
By contrast, birefringence of the sheath component
increased with the increase in IPP content in the sheath
layer and also with the decrease in the sheath layer com-
position. Increase of birefringence in the sheath layer with
the increase of IPP content can be expected, however, esti-
mated birefringence of 40 × 10 -3 is significantly higher than
that of single-component IPP fiber prepared at the same
take-up velocity. This result is further evidence for the
enhanced structure formation in the sheath component
when the sheath layer composition was as low as 10%,
which was discussed for the estimated tensile modulus of
the sheath component in Figure 5.
4045
40
35
30
25
20
5
15
10
Bire
frin
genc
e of
she
ath
com
pone
nt×1
000
010 20 30
Sheath layer composition (wt%)40 50
20 13
Sheath IPP content (wt%)
10 8
Figure 10 Variation of birefringence of sheath layer of as-spun
high-isotacticity polypropylene (IPP)/low-isotacticity PP (LPP)
bicomponent fibers with sheath IPP content and sheath layer
composition. Birefringence of the sheath layer was estimated
assuming the constant birefringence in the core.
End
othe
rmal
dow
n
Temperature (°C)
-50 50 100 150 200 250
5 wt%
4 wt%
3 wt%
2 wt%
1 wt%
Sheath layercomposition
0
Figure 11 Differential scanning calorimetry (DSC) thermograms of
as-spun high-isotacticity polypropylene (IPP)/low-isotacticity PP
(LPP) bicomponent fibers of six different sheath IPP contents.
4014
13
12
11
9
10
Bire
frin
genc
e ×1
000
810 20 30
Sheath layer composition (wt%)40 50
20 13
Sheath IPP content (wt%)
10 8
Figure 9 Variation of overall birefringence of as-spun high-isotacticity
polypropylene (IPP)/low-isotacticity PP (LPP) bicomponent fibers with
sheath IPP content and sheath layer composition measured under
polarizing microscope at the center of individual fiber.
It should be noted that assumption of the birefrin-
gence of the core to be similar to that for the single com-
ponent LPP fiber is reasonable because: (1) if the sheath
composition is only 10%, melt spinning behavior is gov-
erned by the core component; and (2) even if there is an
effect of the kinematic mutual interaction between the
sheath and core components, it leads to the reduction
of the birefringence of the core component, which yields
further increase of the estimated birefringence of the
sheath component.
DSC curves of as-spun fibers are shown in Figure 11 .
Melting peaks of the LPP and IPP components were
detected at 50 ° C – 80 ° C and at around 165 ° C, respectively.
The melting peak of LPP consisted of two peaks, a rela-
tively sharp peak at a lower temperature of around 50 ° C
and a relatively broad peak at a higher temperature of
around 75 ° C. Even though total IPP content was constant,
different behaviors were observed for the melting of LPP
depending on the LPP composition in the sheath. Particu-
larly, with the decrease of sheath layer composition, peak
height of the lower temperature peak tended to decrease
in comparison with the peak area of the higher tempera-
ture peak of 75 ° C.
The melting behavior of the as-spun fibers was ana-
lyzed through DSC. Figure 12 shows the variations of the
melting enthalpies of IPP and LPP as well as the total
melting enthalpy with the changes in the sheath layer
composition and the sheath IPP content. Even though
the total IPP content was kept constant, total melting
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8 Y. Kohri et al.: Low-isotacticity polypropylene elastomeric fibers prepared by sheath-core spinning
enthalpy for IPP increased by localizing the IPP near to
the fiber surface. By contrast, the melting enthalpy for LPP
decreased with the increase of sheath layer composition.
If constant crystallinity of pure LPP in the core is
assumed, this result indicates that the crystallization of
LPP was suppressed by blending IPP. This behavior is
similar to the one observed in a previous paper [23] . By
contrast, a slight increase of the IPP melting peak area
may indicate that a small amount of LPP molecules are
incorporated into the IPP crystals.
3.4 Mechanism of structure formation in sheath-core fibers
Gathering the experimental results stated above, the mech-
anism of fiber structure development in the bicomponent
melt spinning of the LPP and the blend of IPP and LPP
can be summarized as follows. Firstly, when the sheath
layer composition is 50 wt%, the spinning behavior and
structure formation in both sheath and core components
were considered to be similar to those for the single com-
ponent fiber of pure LPP. With the decrease of the sheath
layer composition, crystallinity and molecular orientation
in the sheath were expected to increase because of the
increased content of IPP. In addition, from the view point
of the kinematic mutual interaction of the sheath and
core components in the melt spinning process, structure
development of the sheath was expected to be enhanced
with the decrease in the sheath layer composition. The
reasons for such prediction are that: (1) the kinematic
mutual interaction of the sheath and core components
in the spinning process on the structure development is
more effective to the component with lower composition;
Sheath layer composition (wt%)
0
5
10
15
20
25
30
3540 20 13
Sheath IPP content (wt%)
Total melting enthalpy
IPP melting enthalpy
LPP melting enthalpy
10 8
10 20 30 40 50
Mel
ting
enth
alpy
H (
J/g)
Figure 12 Variations of heat of fusion of low-isotacticity polypro-
pylene (LPP), high-isotacticity PP (IPP) and total components of
as-spun IPP/LPP bicomponent fibers with sheath IPP content and
sheath layer composition.
and (2) the structure development of the component with
higher IPP content should be enhanced more effectively
because a larger difference in thinning behavior in the
single component melt spinning process in comparison
with that for the pure LPP can be expected because of its
higher crystallizability.
4 Conclusions In the bicomponent melt-spinning of sheath-core fibers,
LPP and the blend of LPP and IPP were used as the core and
sheath components, where IPP content in the sheath was
changed from 8 wt% to 40 wt% and the sheath/core com-
position was varied from 50/50 to 10/90. Even though the
total IPP content was kept constant at 4 wt%, the bicom-
ponent fibers with lower contraction ratio after spinning,
higher elastic recovery and slightly higher modulus and
strength were obtained by localizing IPP to the region near
the surface in the fiber cross-section. Structure analysis of
the as-spun fibers suggested that there was a suppression
of the crystallization of LPP by blending IPP, whereas the
molecular orientation and crystallization of the sheath
component was enhanced by localizing the IPP near to the
fiber surface because of the kinematic mutual interaction
of the sheath and core components in the bicomponent
melt spinning process.
References [1] De Rosa C, Auriemma F, Di Capua A, Resconi L, Guidotti S,
Camurati I, Nifant ’ ev IE, Laishevtsev IP. J. Am. Chem. Soc. 2004,
126, 17040 – 17049.
[2] De Rosa C, Auriemma F. Polym. Chem. 2011, 2, 2155 – 2168.
[3] Stephens CH, Poon BC, Ansems P, Chum SP, Hiltner A, Baer E.
J. Appl. Polym. Sci. 2006, 100, 1651 – 1658.
[4] Chum PS, Swogger KW. Prog. Polym. Sci. 2008, 33, 797 – 819.
[5] Wang HP, Khariwala W, Cheung S, Chum P, Hiltner A, Baer E.
Macromolecules 2007, 40, 2852 – 2862.
[6] De Rosa C, Auriemma F, de Ballesteros OR, Resconi L,
Camurati I. Macromolecules 2007, 40, 6600 – 6616.
[7] Jeon K, Chiari YL, Alamo RG. Macromolecules 2008, 41,
95 – 108.
[8] Liu L-Z, Hsiao BS, Fu BX, Ran S, Toki S, Chu B, Tsou AH, Agarwal
PK. Macromolecules 2003, 36, 1920 – 1929.
[9] Toki S, Sics I, Burger C, Fang D, Liu L, Hsiao BS, Datta S,
Tsou AH. Macromolecules 2006, 39, 3588 – 3597.
[10] Poon BC, Dias P, Ansems P, Chum SP, Hiltner A, Baer E. J. Appl. Polym. Sci. 2007, 104, 489 – 499.
[11] Deplace F, Wang Z, Lynd NA, Hotta A, Rose JM, Hustad PD,
Tian J, Ohtaki H, Coates GW, Shimizu F, Hirokane K, Yamada F,
Shin Y-W, Rong L, Zhu J, Toki S, Hsiao BS, Fredrickson GH,
Authenticated | [email protected] author's copyDownload Date | 2/25/15 2:16 AM
Y. Kohri et al.: Low-isotacticity polypropylene elastomeric fibers prepared by sheath-core spinning 9
Kramer EJ. J. Polym. Sci., Part B: Polym. Phys. 2010, 48,
1428 – 1437.
[12] Bensason S, Stepanov EV, Chum S, Hiltner A, Baer E.
Macromolecules 1997, 30, 2436 – 2444.
[13] Zuo F, Mao Y, Li X, Burger C, Hsiao BS, Chen H, Marchand GR.
Macromolecules 2011, 44, 3670 – 3673.
[14] Wang Z-G, Phillips RA, Hsiao BS. J. Polym. Sci., Part B: Polym. Phys. 2000, 38, 2580 – 2590.
[15] Wang Z-G, Phillips RA, Hsiao BS. J. Polym. Sci., Part B: Polym. Phys. 2001, 39, 1876 – 1888.
[16] Auriemma F, de Ballesteros OR, De Rosa C, Invigorito C.
Macromolecules 2011, 44, 6026 – 6038.
[17] Rana S, Hsiaoa BS, Agarwalb PK, Varma-Nairc M. Polymer
2003, 44, 2385 – 2392.
[18] Tajima T, Kanai T, Takebe T, Minami Y. WO2006/051708 A1.
[19] Takebe T, Minami Y. Polymers 2010, 59, 853 – 856.
[20] Takebe T, Minami Y, Kanai T. Seikei-Kakou 2009, 21, 202 – 207.
[21] Takebe T, Minami Y, Kanai T. JP2009-209506A.
[22] Takebe T, Minami Y, Kanai T. JP2009-62667A.
[23] Kohri Y, Takebe T, Minami Y, Kanai T, Takarada W, Kikutani T.
Sen ’ i Gakkaishi 2014, 70, 9, 203 – 212.
[24] Brandrup J, Immergut EH. Polymer Handbook , 2nd Ed., John
Wiley & Sons: New York, 1975, V-24.
[25] Kikutani T, Arikawa S, Takaku A, Okui N. Sen ’ i Gakkaishi 1995,
51, 408 – 415.
[26] Kikutani T, Radhakrishnan J, Arikawa S, Takaku A, Okui N, Jin X,
Niwa F, Kudo Y. J. Appl. Polym. Sci . 1996, 62, 1913 – 1024.
[27] Okamoto K, Takarada W, Kikutani T, Takebe T, Minami Y,
Koori Y, Kanai T. Preprints of Seikei-kakou Annual Meeting ,
2012, 259–260.
Authenticated | [email protected] author's copyDownload Date | 2/25/15 2:16 AM