Polymer 52 (2011) 2939e2946
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Polymer
journal homepage: www.elsevier.com/locate/polymer
Modification of polymers using multilayered “smart pellet” additives: Part I
Yuxin Wang a, Henry W. Milliman a, Jack R. Johnson III a, Daniel M. Connor b, Nathan A. Mehl b,
David A. Schiraldi a, *
a
b
Department of Macromolecular Science & Engineering, Case Western Reserve University, Cleveland, OH 44106-7202, USA
Milliken Chemical, A Division of Milliken and Company, Spartanburg, SC 29304, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 February 2011
Received in revised form
12 April 2011
Accepted 16 April 2011
Available online 30 April 2011
A multilayer “smart pellet” additive composed of layered polymers, and capable of exfoliating in
a manner similar to that of smectite clays, was demonstrated to be an effective reinforcing agent for bulk
polymers processed in the melt. Polysulfone (PSF) and Ethylene-octene (PEOC-1) copolymer were chosen
as one of the model systems. PSF/PEOC-1 smart pellets were added to PEOC-1 as masterbatches during
injection-molding. This methodology allowed for high glass transition temperature PSF to function as
a reinforcing agent during injection-molding of matrix polymers processed below their glass transition
temperature. Mechanical properties of the composites were studied by performing tensile and flexural
tests. Tensile modulus was fitted to the HalpineTsai model, and this model was used to predict the
optimum tensile modulus that PSF/PEOC-1 smart pellets could achieve. The morphology of smart pellet
and polymer composites were investigated by scanning electron microscopy (SEM), atomic force
microscopy (AFM), and optical microscopy (OM). The PSF layers were observed to resemble clay platelet
morphology in PEOC-1 matrix.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Multilayer
Mechanical properties
Injection-molding
1. Introduction
Reinforcement of polymer products is well known to be
successfully accomplished using a range of inorganic fillers,
including glass fibers and flakes, smectite clays, talc and many other
minerals [1e11]. While such fillers can substantially increase the
moduli and thermal properties (heat deflection temperature, glass
transition temperature, onset of thermal degradation), these property enhancements generally come at the expense of ductility and
processability. The use of nano-scale fillers can sometime overcome
these limitations, but themselves require application of compatibilizing agents or surface modification [5,12e18]. The potential
replacement of high aspect ratio inorganic platelets with organic
platelets might offer improved phase compatibility, and potentially
could lessen their negative impact upon polymer processability.
Multilayer extrusion offers a means by which two or more
polymers can be easily arrayed in an alternating structure [19]. This
extrusion process can operate at standard polymer film line
throughputs, making use of commercial polymers and composite
materials as its constituents, subject to melt temperature/rheological match requirements [20].
* Corresponding author. Tel.: þ1 216 368 4243.
E-mail address: das44@cwru.edu (D.A. Schiraldi).
0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.04.037
Production of an alternating, micro-scale or nano-scale multilayer film comprised of a common matrix polymer with a higher
temperature/higher modulus polymer, followed by cutting this film
into discrete pieces, could potentially generate ultra-thin, high
aspect ratio platelets of the high temperature/modulus material
suitable for addition to a melt stream of the same matrix polymer
used in its extrusion. In this manner, the matrix polymer within
multilayered “pellets” would melt or flow, releasing the higher
performance platelets into the bulk. Such a process could mimic the
exfoliation of clays into polymers, albeit with an organic reinforcing
agent. The use of such multilayered pellets could also be used to
deliver inorganic fibers or platelets, either by themselves, or in the
form of a reinforced polymer composite, to matrix polymers. These
multilayered pellets with the corresponding polymer matrix form
a “smart pellet” system. One such approach described herein is the
use of polysulfone platelets as a possible reinforcing agent within
an ethylene-octene elastomer matrix.
2. Experimental
2.1. Materials
Two ethylene-octene copolymers: PEOC-1 (Dow Engage 8100)
and PEOC-2 (Dow Engage 8400) with MFI values of 1 and 30
respectively and identical densities of 0.87 g/cm3, and polysulfone
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Y. Wang et al. / Polymer 52 (2011) 2939e2946
(PSF; Solvay Udel-3703) with MFI ¼ 17 g/10 min, 2.16 kg at 343 C
(ASTM D 1238) and a density of 1.24 g/cm3 were used as received.
Nanolayered films of PSF/PEOC-1, with 4096 alternating layers
and a volume ratio of 50/50 were melt extruded at 285 C on
a laboratory scale coextrusion line, employing layer-multiplying
technology [19]. The total strand thickness measured 4 mm,
including two 1.08 mm PEOC-1 skin layers. The composition of
PSF/PEOC-1 alternative layers 50/50 was by volume. The thickness
of individual PSF and PEOC-1 layers were targeted at 400 nm; later
measured by atomic force microscopy (AFM, Nanoscope IIIa, Digital
Instruments, Santa Barbara, CA). The cross sections of the strands
were microtomed perpendicular to the extrusion direction. AFM
images were obtained in air, operating in tapping mode. The
strands were cut into pellet size (about 4 mm 5 mm) using
a Flexible Plastic Blade (Model 3001EVO/13, Accu cutter Company,
Carlisle, PA).
2.2. Injection-molding conditions
All specimens used in the following tests were molded on a Boy
22-S injection-molding machine equipped with a family mold
including an ASTM D-790 flex bar and an ASTM D-638 type IV
tensile bar. The injection-molding groups were listed in Table 1; the
27:73 wt./wt. PEOC-1/PEOC-2 composited contained a total of
10 wt.% PSF.
Abbreviations used in this paper:
PSF/PEOC-1 PSF/PEOC-1 smart pellet.
PSF/PEOC-1-PEOC-1 sample from PSF/PEOC-1 smart pellet
injection molded with PEOC-1.
PSF/PEOC-1-PEOC-2 sample from PSF/PEOC-1 smart pellet
injection molded with PEOC-2.
PSF-PEOC-1 sample from PSF injection molded with PEOC-1.
PSF-PEOC-2 sample from PSF injection molded with PEOC-2.
PEOC-1-PEOC-2 sample from PEOC-1 injection molded with
PEOC-2.
The PEOC-1/PSF was melt-blended in a twin-screw extruder
(Haake Fisons Rheodrive 5000) at 280 C prior to injectionmolding; all other resins were directly injection molded. Prior to
injection-molding, PSF was dried in vacuum at 150 C overnight.
The injection-molding conditions utilized are given in Table 2.
PSF is an amorphous polymer with a Tg of 183 C and a heat
deflection temperature (HDT) of 175 C, while PEOC-1 and PEOC-2
have a Tm of 60 C. When the optimum temperature of PSF/PEOC-1
and PEOC-1 is below the Tg of PSF, it is expected that PSF would
preserve its thin layer structure as it is in the melt. PEOC-2 with
a higher MFI would allow for a lower injection-molding temperature, which would minimize the deformation of PSF layers.
Table 2
Injection-molding processing parameters.
Melt temperature ( C)
Mold temperature ( C)
Injection pressure (psi)
Cooling time (sec)
Cycle time (sec)
Screw rotation speed (rpm)
PEOC-1
PEOC-2
175
25
1800
15
60
100
130
25
1100
15
60
100
a crosshead speed of 40 mm/min. Three point static flexural tests
were carried out using 125 mm 12.7 mm 3.2 mm bars and
a 50 mm span length at a crosshead speed of 1 mm/min.
2.4. Compounding experiment
In order to investigate the effects of shear force on PSF layers
exfoliation, an experiment using a twin-screw extruder (Microcompounder, DACA instruments, Santa Barbara, CA) was performed. PSF/PEOC-1 were extruded with PEOC-1 and PEOC-2
respectively at 175 C and 130 C, 100 rpm with different time
lengths; extrudates were later compressed into 100e200 mm thick
films. Later, the cross-section morphologies were studied.
2.5. SEM micrographs
The SEM/EDX experiments were performed on microtomed
samples by a Philips XL scanning electron microscope. Prior to
imaging, all samples from both injection-molding and extrusion
were microtomed. The samples were sputter coated with palladium to provide enhanced conductivity, and were studied with the
microscope operating at 15 or 20 kV.
3. Results and discussion
3.1. Raw materials morphology investigation
Extrusion multilayered strands were produced from PSF and
PEOC-1 polymers, targeting at 4096 alternating layers with
nominal thicknesses of 400 nm. Fig. 1 shows an image of a PSF/
PEOC-1 smart pellet cut from multilayer film.
The cross-sectional structure of this multilayer film was studied
with a combination of SEM and AFM. In Fig. 2, single layer thickness
is observed to vary from 300 nm to 1.5 mm. The differences between
actual layer and designed thickness could be attributed to the
uneven flow splitting the polymer melt during the initial microlayering process; as well as layer instability and extension [21].
2.3. Mechanical properties
3.2. Injection-molding samples morphology investigation
Tensile and flexural tests were performed according to ASTM
D-638 and ASTM D-790, respectively. All the tests were carried out
at room temperature (approximately 25 C) and an average of at
least five test specimens were reported herein. Tensile tests were
conducted using an Instron 5566 Universal testing machine at
As can be seen in Fig. 3a, PSF platelets maintains their layered
structures and are dispersed when processed in the melt. The
Table 1
Polymers used in the injection-molding process.
Group
Compositions
Wt.% PSF/PEOC-1
PEOC-1 group
PEOC-1
PSF-PEOC-1
PSF/PEOC-1-PEOC-1
PEOC-1-PEOC-2
PSF/PEOC-1-PEOC-2
9:90
31:69
27:73
34:66
PEOC-2 group
Fig. 1. Images of smart pellet cut from multilayer film.
Y. Wang et al. / Polymer 52 (2011) 2939e2946
2941
Fig. 2. SEM and AFM images of the cross-section of PSF/PEOC-1 multilayer strand.
multilayer exfoliation was largely successful; a maximum stack of
only 40 single layers, derived from a 4096 layered film, was
observed. This behavior is consistent with the most exfoliated clay/
polymer composites presented in the literature to date [22,23].
Incorporation of the matrix polymer in alternating layers of the
smart pellet facilitates PSF layer exfoliation, since the PEOC-1 will
be compatible with itself, and under processing, conditions would
be expected to flow readily. Fig. 3b shows the morphology of
molded parts obtained at a higher temperature of 175 C rather
than 130 C; several single PSF layers were observed to curl slightly
but no significant aggregation of PSF occurred. Fracture of layers is
apparent, as the PSF particles are shorter than their original 5 mm
pellet length. When PSF was directly blended with PEOC-1 at
280 C then injection molded, spherical domains of PSF were
observed instead of the slightly curled platelets present at lower
processing temperature (Fig. 3c). The dramatic differences in PSF
domain morphologies results from the softening and twisting of
PSF; injection-molding temperature was crucial to PSF morphology.
SEM/EDX was employed to identify the phases in the SEM
images. Fig. 4 shows the EDX spectrum of the light-colored phase
Fig. 3. SEM images of the cross-section of injection-molding samples a: PSF/PEOC-1-PEOC-2; b: PSF/PEOC-1-PEOC-1; c: PSF-PEOC-1.
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Y. Wang et al. / Polymer 52 (2011) 2939e2946
Fig. 4. EDX of the light-colored phase in Fig. 3b.
from Fig. 3b; the presence of S and O peaks is consistent with PSF. In
Fig. 5, the EDX spectrum of the dark-colored phase from Fig. 3b
demonstrates that there are no significant peaks for elements other
than C and the Pd coating, so the darker-colored phases are
concluded to be PEOC-1.
3.3. PSF layer exfoliation process investigation
The PSF layered structure shown in Fig. 3c raised questions
concerning morphological changes which occur during the process
of injection-molding. The key parameters involved are mixing
temperature, screw speed and time [24]. To study the effects of
these separate parameters, a series of experiments using a twin
extruder were carried out. PSF/PEOC-1 multilayer pellets were cut
into thin slices and studied by optical microscopy before and after
heating to 175 C for 4 min. After heating, a wider gap, but little
exfoliation between layers was observed.
Fig. 6 shows the morphology of PSF/PEOC-1 polymer mixing at
a speed of 100 rpm and 175 C melt temperature (chosen to be
more representative of the conditions used in an injection-molding
machine) as a function of mixing time. Fig. 7 illustrates PSF/PEOC-2
mixing at 130 C. PSF layers were uniformly dispersed in both
PEOC-1 and PEOC-2 matrix; this could be attributed to the intermolecular repulsion between PEOC-1 and PSF.
As mixing time increased, more PSF layers were exfoliated until
exfoliation was fully achieved. PSF platelets are oriented mostly in
the parallel direction after 4 min, and later to a more random
dispersion after 16 min as seen in Fig. 7. The same behaviors
reappeared in the vertical direction in Fig. 8 where PSF layers lost
their alignment after 16 min mixing. Melt flow of PEOC-1 in both
the multilayer structure and the bulk PEOC-1 matrix accelerated
the release of PSF layers into the PEOC-1 matrix. The continuous
shear forces resulted in the penetration of PEOC-1 into the interlayers of multilayer structure as well. Simultaneously, as heat
accumulated in the interaction between PSF layers and PEOC-1
matrix, it caused the curling structures of PSF layers observed
also in the injection-molding experiments. Thus, melt flow of
PEOC-1 spacer layers appears to be the main cause of PSF layer
exfoliation in PSF/PEOC-1 smart pellet composite.
3.4. Mechanical properties
3.4.1. Tensile tests
Improvement of mechanical properties is the main purpose for
introducing smart pellet additives. Fig. 8 shows representative
Fig. 5. EDX of the dark-colored phase in Fig. 3b.
Y. Wang et al. / Polymer 52 (2011) 2939e2946
2943
Fig. 6. SEM images of compression molded PSF/PEOC-1-PEOC-1 films, processed at 175 C.
stress-strain curves of injection molded PEOC-1, PSF/PEOC-1 blend
and PSF/PEOC-1 smart pellet blend samples. It is clear that
PSF-PEOC-1/PEOC-1 exhibits enhanced modulus compared to the
matrix polymer or a simple blend of PEOC-1 and PSF. The tensile
modulus of PEOC-1 was increased by 28% with the addition of 10%
PSF via simple melt blending, while the same amount of PSF
delivered in the form of a PSF/PEOC-1 smart pellet resulted in an
increase of the tensile modulus by 130%.
Fig. 7. SEM images of compression molded PSF/PEOC-1 - PEOC-2 films, processed at 130 C.
2944
Y. Wang et al. / Polymer 52 (2011) 2939e2946
9
Table 3
Tensile test results of PSF and PEOC-1 injection-molding samples.
PEOC-1
PSF-PEOC-1
PSF/PEOC-1-- PEOC-1
8
7
Stress/ MPa
6
Compositions
5% secant
modulus/MPa
Ultimate
strength/MPa
Elongation at
break/100%
PEOC-1
PSF-PEOC-1
PSF/PEOC-1-PEOC-1
9.4 0.4
12 1
22 2
4.9 1.4
7.6 1.0
6.5 1.4
230 10
430 30
140 20
5
4
3
2
1
0
0
50
100
150
200
250
300
350
400
450
Strain%
3.4.2. Three-point flexural tests
Flexural properties are also crucial for polymer composites. The
flexural modulus of PEOC-1 was increased by 77% with addition of
10% PSF; it was increased by 110% with same amount of PSF added
via PSF/PEOC-1 (Table 5). Hence, smart pellet addition has shown
an advantage in improving both tensile and flexural moduli when
properly designed.
With the PSF and PEOC-2 system shown in Table 6, 10% PSF
added via the PSF/PEOC-1 further increased the flexural modulus of
PEOC-1-PEOC-2 by more than 100%.
Fig. 8. Tensile test of PSF and PEOC-1 injection-molding samples.
Mechanical properties of the three compositions are detailed in
Table 3, which shows that with increased reinforcement by smart
pellet-derived rigid platelets, modulus and strength of the matrix
resin are increased at the cost of reduced ductility, similar to the
trend normally associated with fiber and platelet fillers in polymers. The simple blend of PEOC-1 and PSF produced rule-of-mixing
properties.
The decrease of elongation at break in PSF/PEOC-1-PEOC-1
compared with PSF-PEOC-1 likely resulted from PSF and PEOC-1
interactions. Rigid PSF would carry more load than the elastomeric PEOC-1 matrix. PSF spheres have less surface area compared
with PSF platelets which translates to fewer interactions with the
PEOC-1 matrix. Thus, the elastomeric PEOC-1 matrix can stretch
more in PSF-PEOC-1.
The representative stress-strain curves of PSF and PEOC-2
injection molded samples are shown in Fig. 9. It is apparent that
when 10% PSF is added to PEOC-1-PEOC-2 via PSF/PEOC-1, the
tensile modulus is considerably higher (65%) than that of PEOC-1PEOC-2 blend. As indicated in Table 4, the elongation at break
decreased from 810% to 160%, which is due to the inextensibility of
rigid PSF interacting with the elastomeric PEOC-1 matrix.
6
Stress/ MPa
5
4
3
2
1
0
A mathematical model using the HalpineTsai equations was
employed to study the reinforcement of PEOC-1 using PSF/PEOC-1
and simple blends with PSF. The HalpineTsai approach is a classic
method used in predicting reinforcement with nano particles of
clay, micro-scale glass fibers and other systems [25e28]. In our
study, the reinforcing agent was PSF either in form of PSF/PEOC-1
multilayer smart pellet or PSF pellet. The weight fraction of PSF
was 0.1 in PSF/PEOC-1 composites studied herein.
mf
Vf
rf
fp ¼
¼ 0:072 ¼ constant
¼
mf mm
Vf þ Vm
þ
rf
rm
(1.1)
Ef
1
285
Em
h¼
¼
Ef
286 þ 2AS
þ 2As
Em
(1.2)
Ec
1 þ 2As h fp
¼
Em
1 h fp
(1.3)
where fp ¼ fiber volume fraction; As ¼ fiber aspect ratio ¼ length/
thickness; Ec ¼ tensile modulus of composite; Em ¼ tensile
modulus of matrix ¼ 9.4 MPa, tested in our lab; Ef ¼ tensile
modulus of PSF ¼ 2690 MPa, literature value.
Based on different As values, values for Ec/Em vs As were
calculated and plotted (Table 7 and Fig. 10). Ec/Em increased with
As, consistent with PSF platelets serving as reinforcing structure.
The theoretical Ec values in Table 8 can be calculated based on
the theoretical As and equation 1.3; for PSF-PEOC-1, the As is 1
according to PSF spherical geometry. However, theoretical As for
PSF/PEOC-1-PEOC-1 is the optimum As. Assuming all 4096 layers
are fully exfoliated, the layer thickness equals 4 nm. As is length
PEOC-1-- PEOC-2
PSF/PEOC-1-- PEOC-2
7
3.5. HalpineTsai equation to model the PSF/PEOC-1 behavior in
PEOC-1 composite
Table 4
Tensile test results of PSF and PEOC-2 injection-molding samples.
0
100
200
300
400
500
600
700
800
Strain %
Fig. 9. Tensile test of PSF and PEOC-2 injection-molding samples.
900
Compositions
5% secant
modulus/MPa
Ultimate
strength/MPa
Elongation at
break/100%
PEOC-1-PEOC-2
PSF/PEOC-1-PEOC-2
5.5 0.3
9.1 0.7
6.7 0.4
2.0 0.2
810 60
160 70
Y. Wang et al. / Polymer 52 (2011) 2939e2946
Table 5
Flexural test results of PSF and PEOC-1 injection-molding samples.
Compositions
Flexural Modulus/MPa
PEOC-1
PSF-PEOC-1
PSF/PEOC-1-PEOC-1
13 2
23 7
27 5
Table 6
Flexural test results of PSF and PEOC-2 injection-molding samples.
2945
Table 8
Comparison of actual results and modeling results of PSF and PEOC-1 injectionmolding samples.
ompositions
Actual Ec/MPa
Theoretical As
Theoretical Ec/MPa
PEOC-1
PSF-PEOC-1
PSF/PEOC-1-PEOC-1
9.4 0.4
12.0 1.2
21.8 2.4
e
1
12500
e
11.5
196
4. Conclusions
Compositions
Flexural Modulus/MPa
PEOC-1/PEOC-2
PSF/pEOC-2smart pellet system
10 1
29 6
Table 7
Ec/Em vs As.
As
h
Ec/Em
1
2
3
4
5
6
7
8
9
10
0.98
0.97
0.96
0.95
0.94
0.93
0.92
0.91
0.9
0.89
1.23
1.38
1.52
1.66
1.8
1.93
2.06
2.19
2.31
2.43
divided by thickness, which is 5 mm/4 nm ¼ 12500. Compared with
actual Ec, theoretical Ec/Em ¼ 21, which is a 2000% increase
compared with the actual 130% measured in the experiments.
As can also be back calculated, employing equation 1.3 where
the actual Ec values were taken from the tensile tests.
PSF-PEOC-1: Ec/Em ¼ 12.0/9.4 ¼ 1.3 measured; estimated As ¼ 1
from Table 7.
PSF/PEOC-1-PEOC-1: Ec/Em ¼ 21.8/9.4 ¼ 2.3 measured; estimated As ¼ 9 from Table 7.
The As values can also be compared with the images in Fig. 3.
From the PSF layered structure in Fig. 3a, As is estimated to be
length/layer thickness ¼ 60mm/2 mm ¼ 30, which translates to a Ec/
Em value of 4.4 according to equation 1.3, twice of the actual Ec/Em
value of PSF/PEOC-1-PEOC-1. The difference in results is attributable to lack of achieving the HalpineTsai assumption of perfect PSF
platelet structure.
Smart pellets of PSF/PEOC-1 were prepared via multilayer
coextrusion. Injection-molding of PSF/PEOC-1 with PEOC-1 resulted in a composite with superior mechanical properties compared
to those obtained via simple PSF and PEOC-1 blends. Addition of
10 wt.% PSF via the smart pellet system increases the tensile
modulus of PEOC-1 by 130% and flexural modulus by 110%. By
comparison, conventional injection-molding can only bring those
values up by 28% and 77% respectively. The enhanced reinforcement obtained using smart pellet additives of PSF/PEOC-1 is
attributed to the unique PSF structure in the composite. SEM
images of PSF/PEOC-1-PEOC-1 indicated that PSF in smart pellet
composites resembled clay platelet morphology, as was the original
objective of this work. When injection molded below the Tg of PSF,
PSF preserves its layer structure from multilayered films and
exfoliation helped layer dispersion in the PEOC-1 matrix. Deformation and breakage of PSF were inevitable due to the shear forces
during processing.
The HalpineTsai equation was successfully applied to model the
tensile modulus of this new composite. The analysis assumed that
the PSF layers achieved a perfect platelet structure with full exfoliation and no shape distortion and breakage, to a 2000% increase in
modulus, compared to the observed increase of 130%. Though this
theoretical value is far from achievable, the modeling approach
suggest that superior reinforced composites should be attainable
using smart pellet additives, either by optimizing our current
PSF/PEOC-1 or exploring new components for smart pellets.
Acknowledgment
This research was supported by the National Science Foundation
under Grant No. DMR 0423914.
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