Presentation ID #298480: PE-CPE Blends: Morphology and Properties
A. U. Chaudhry and Vikas Mittal*
Department of Chemical Engineering,
The Petroleum Institute,
Abu Dhabi, UAE
[email protected]
Introduction
The physical polymer-reinforcement means such as blending or filler incorporation have gained
favorable position for acquiring new polymeric materials with altered properties [1,2]. The
properties of the resultant materials depend on features like interaction between the phases,
compatibilization, processing conditions, composition etc. The generation of polymer blends
specially offers advantages such as property profile combinations, aid in processing, low capital
costs as compared to development of new monomers and polymers of required properties.
Polyolefins are the largest group of industrial thermoplastics in terms of production and have
superior rank among commodity plastics owing to their use in a large number of applications.
The number of individual polyolefin members is limited and the number of applications based on
such materials is constantly increasing. Various polyolefin based blends and composites are
thus required to meet the increasing demand of materials with required properties and
processing suitable for specific applications [1,3].
Chlorinated polyethylene (CPE) blends with different polymers have been reported for many
purposes such as improvements in the toughening properties of host polymers [4], as a
compatiblization agent through enhancement of interfacial interactions between two polymers
[5,6], improved processing properties [7], ameliorated adhesion properties [8], enhanced ignition
resistance properties [9] and modified gas transport properties [10]. Based on the percentage of
chlorination of the polymer, there are many classifications of CPE ranging from plastic (0-14%),
thermo-elastoplast (15-30%), elastomer (31-46%), rigid polymer (47-61%), to friable resin (6273%) [11]. Maksimov et. al. blended CPE with 36 % chlorination content with high density
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polyethylene (HDPE) and low density polyethylene (LDPE) [12]. It was observed by using
different models that the mechanical properties depended on morphological changes occurring
at higher concentration of CPE36 in blends [12,13]. Walsh et. al showed the compatibility of
CPE with poly(methyl methacrylate) (PMMA) at around 50% chlorination content due to
favorable heat of mixing at higher percentage of chlorination [14,15]. Zhang et al. added CPE36
as an impact modifier for the blends of poly(vinyl chloride) (PVC)/poly (α-methylstyreneacrylonitrile) which led to four fold increments in the impact properties of ternary blends at 15
phr concentration [16]. However, a reduction in the modulus and strength of the blends was also
observed. In a similar work, blends of CPE25 and CPE48 with epoxidized natural rubber were
found to be miscible at higher degree of chlorination owing to the interactions involving chlorine
atoms and oxirane groups [17]. 50/50 natural rubber and CPE36 blends compatibilized with
EPDM-g-MA were also obtained for better oil and thermal aging resistance [18]. The properties
strongly depended on the natural rubber dispersed phase in CPE36 matrix. Similarly, blends of
3 wt% CPE36 with polyurethane showed improved thermal properties owing to the interactions
between the chlorinated polymer and urethane linkages strengthening the phase boundaries
[19]. Although, incorporation of CPE has already been achieved in many polymer blends but indepth morphological and rheological studies on the miscibility, structural properties and
performance of blends of different types of chlorinated polyethylene with polyolefins like
polyethylene and polypropylene is still missing.
In this work, two type of chlorinated polyethylene (with 25% and 35% chlorination content; i.e.
from the thermoplastic and elastomer range respectively) were used to generate blends with
high density polyethylene using melt blending. The content of CPE in polyethylene was varied
from 1% till 30% and the resulting impact on rheological, thermal, mechanical and
morphological properties was studied.
Experimental
Materials
Chlorinated polyethylene grades Weipren® 6025 (25% chlorine content, named as CPE25) and
CPE 135A (35% chorine content, named as CPE35) were obtained from Lianda Corporation,
USA and Weifang Xuran Chemicals, China respectively. The melt flow index (190°C, 2.16 kg)
for CPE25 and CPE35 was measured to be 1.8 and 1.9 g/10 min respectively. High density
polyethylene BB2581 was supplied by Abu Dhabi Polymers Company Limited (Borouge), UAE.
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The specifications of the polymers as received from the suppliers are also reported in Table 1
[20]. The polymer materials were used as obtained.
Generation of HDPE-CPE Blends
Polymer blends were prepared by melt mixing of CPE25 and CPE35 with HDPE using mini twin
conical screw extruder (MiniLab HAAKE Rheomex CTW5, Germany). A mixing temperature of
170°C for three minutes at 80 rpm with batch size of 5 g was used. The screw length and screw
diameter were 109.5 mm and 5/14 mm conical respectively. Blends of CPE25 and CPE35 in
weight percentages of 1%, 2%, 5%, 10%, 15%, 20% and 30% were generated .The disc and
dumbbell-shaped test samples were prepared by mini injection molding machine (HAAKE
MiniJet, Germany) at a processing temperature of 170°C. The injection pressure was 700 bar
for 6 s whereas holding pressure was 400 bar for 3 s. The temperature of the mold was kept at
55°C.
Characterization Techniques
Thermal properties of the blends were recorded using Netzsch thermogravimetric analyzer
(TGA). Nitrogen was used as a carrier gas and the scans were obtained from 50 to 700°C at a
heating rate of 20°C/min. Calorimetric properties of blends were recorded on a Netzsch DSC
under nitrogen atmosphere. The scans were obtained from 50-170-50°C using heating and
cooling rates of 15°C/min and 5°C/min respectively. The heat enthalpies used to calculate the
extent of crystallinity were recorded in a narrow error range (±0.1%), which were also confirmed
by repeated runs.
AR 2000 rheometer from TA Instruments was used to characterize the rheological properties of
the blends such as storage modulus (G′), loss modulus (G″), viscosity (η’) and elasticity (η’’).
Disc shaped samples of 25 mm diameter and 2 mm thickness were measured at 185°C using a
gap opening of 1.2 mm. Strain sweep scans were recorded at ω = 1 rad/s from 0.1 to 100%
strain and the samples were observed to be shear stable up to 10% strain. For the comparison,
frequency sweep scans (dynamic testing) of all the samples were recorded at 4% strain from ω
= 0.1 to 100 rad/s.
The mechanical testing of the blends was performed on universal testing machine (Testometric,
UK). The dumbbell shaped samples with 53 mm length, 4 mm width and 2 mm thickness were
used. A loading rate of 5 mm/min was employed and the tests were carried out at room
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temperature. Win Test Analysis software was used for the calculation of tensile modulus and
yield stress properties of the blends. An average of three values is reported.
Philips CM 20 (Philips/FEI, Eindhoven) electron microscope at 120 kV and 200 kV accelerating
voltages was used for the bright field transmission electron microscopy analysis of the blend
samples. Thin sections of 70-90 nm thickness were microtomed from the sample block and
were supported on 100 mesh grids sputter coated with a 3 nm thick carbon layer. The
macroscopic features of blends were also observed under an optical microscope Olympus BX
51. The cross-section of the samples was characterized at a magnification of 20X and both
bright field and dark field reflection modes were used. Prior to the analysis, the surface of the
block face of the samples was smoothened using a knife.
Results and Discussion
In the current study, chlorinated polyethylene with two different chlorination levels (Table 1) was
blended with high density polyethylene in different weight ratios using melt mixing process. The
chlorination contents were differed in order to study their impact on miscibility with polyethylene
along with rheological, mechanical as well as thermal properties of the blends. The melt flow
indices of the chlorinated polyethylene samples were similar, however, they were higher than
that of pure HDPE indicating their lower molecular weight. The processing conditions were kept
unaltered to generate the various blends so as not to induce any variations in the material
characteristics. A lower melt mixing temperature of 170°C was chosen in order not to thermally
degrade the polymer, but it was still sufficient to have uniform polymer mixing.
Table 2 and Figures 1 and 2 demonstrate the calorimetric properties of pure HDPE, pure CPE
samples and HDPE-CPE blends. The heat of fusion of pure crystalline HDPE was taken as 293
J/g and was used to determine the extent of crystallinity in the polymer [21]. As shown in Figure
1a, CPE25 was semi-crystalline in nature as indicated by the crystalline melting peak in the
DSC thermogram and a peak melting temperature of 130°C was recorded. CPE35 polymer, on
the other hand, was amorphous in nature as no melting transition was observed in Figure 2a.
Hence, owing to the different extent of chlorination, CPE25 and CPE35 were different also in
their structural morphology. The peak melting temperatures (Tm) of the blends decreased on
adding the CPE polymers, though the magnitude of Tm reduction was less significant for blends
till 10% CPE concentration (Table 2, Figures 1a, 2a). Both the CPE polymers caused similar Tm
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reduction as compared to the pure HDPE. The crystallization transitions in the blends (Figures
1b, 2b) almost overlapped and the peak crystallization temperature also remained fairly
constant (Table 2). It confirmed that the CPE component did not act as a nucleating agent for
the polyethylene chains. In the case of blends with CPE25, the melt enthalpy remained
unchanged for blends with 1% and 2% CPE content. For a CPE concentration of 5% onwards,
the melt enthalpy started to decrease and the blend with 30% CPE25 content had a value of
119 J/g as compared to 151 J/g for pure polymer. It indicated that the CPE25 at lower
concentrations did not hinder the crystallization of HDPE. It may also indicate that the CPE25
were molecularly mixed at these low concentrations, but the higher concentrations reduced the
molecular mixing, but were still miscible as confirmed by the absence of any individual
component melting peaks in DSC thermograms. On the other hand, in the case of blends with
CPE35, the melt enthalpy gradually decreased with concentration of CPE35 due to its
amorphous nature and the 30% CPE35 blend had significantly lower melt enthalpy value of 102
J/g. The decrease was very significant at higher concentrations indicating that the higher
concentrations may have affected the crystallization ability of the HDPE chains due to
immiscibility. As compared to 52% crystallinity of pure polymer, the extent of crystallinity started
to decrease in CPE25 containing blends when CPE25 content was beyond 2% and it was
recorded to be 41% for the 30% CPE25 blend. On the other hand, the extent of crystallinity was
even lower to 35% for the 30% CPE35 blend indicating that the initial morphology of the CPE
component affected the final morphology of the blends.
In Figure 3, the comparison of the TGA thermograms of blends with pure CPE and HDPE
polymers has been demonstrated. The thermograms of blends with 1%, 2% and 5% CPE were
indistinguishable from pure polymer. In the higher CPE concentration blends, the onset
degradation temperature in the first degradation step coincided with that of the pure CPE
polymers indicating that the CPE phase had independent signal. The TGA thermograms thus
confirmed the DSC indications of better mixing of CPE with HDPE at lower concentrations.
However, it has to be noted that the state of immiscibility and size of immiscible domains of two
phases can be different in both CPE25 and CPE35 containing blends as extensive immiscibility
would result in two distinct peaks in the DSC thermograms of CPE25 containing blends,
however, this was not the case (Figure 1a). Moreover, the second degradation step in the
blends was also observed to occur at higher peak temperatures (~20°C) than the pure polymer
due to the thermal stability in the presence of chlorine. In the case of CPE35 containing blends,
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the degradation temperature was observed to increase with increasing CPE 35 content probably
due to higher extents of chlorine in this system.
Network structure of the polymer blends was evaluated with shear rheology and the storage and
loss moduli of the samples as a function of angular frequency are demonstrated in Figures 4-5.
Strain sweep was conducted and samples were found to be safe up to 10% strain. Frequency
sweep of the samples was performed with controlled shear strain of 4% using frequency range
of 0.1 to 100 rad/s. All the samples exhibited good low frequency dependence followed by
gradual decline in the extent of modulus enhancement due to shear thinning effect. In the case
of CPE25 containing blends, the storage modulus increased on increasing the CPE
concentration till 2%, after which a gradual decrease in the storage modulus was observed on
increasing the CPE25 concentration. It indicated that the molecular mixing of the more stiff CPE
chains to HDPE enhanced the shear behavior of the polymer. However, the modulus values for
the blends till 15% CPE content were still higher than pure HDPE, confirming that the mixing of
the phases was still optimum. For example, the shear modulus for pure HDPE at an angular
frequency of 10 rad/s was measured to be 104000 Pa which increased to its maximum value of
127000 Pa for 2% CPE blend. The least value of modulus was observed for 30% CPE blend
where the value of 92000 Pa was observed for angular frequency of 10 rad/s due to matrix
plasticization. The curves of shear modulus were also observed to converge with each other at
higher frequency thus indicating concentration independence. In the case of CPE35 containing
blends, the modulus similarly increased initially and the maximum enhancement was observed
at 2% CPE35 blend. However, the reduction in the modulus beyond 5% CPE content was much
more significant in this case and the 30% CPE blend had a modulus value of 53470 Pa for
angular frequency of 10 rad/s. It could have resulted due to the higher extent of immiscibility of
the phases in CPE35 containing blends as compared to CPE25. The modulus vs. angular
frequency curves also did not converge at higher frequency indicating concentration dependent
morphological changes taking place in the blends. These findings were also reflected in
oscillatory torque required to maintain the same strain in the samples during the rheological
testing. The torque required to strain the samples was maximum at 2%CPE content. It remained
same as HDPE till 15% CPE content for CPE25 system and 5% CPE content for CPE35 system
followed by its decrease at higher CPE concentrations in the blends.
Similar to storage modulus, the loss modulus of the blends increased initially as compared to
pure HDPE with CPE concentration followed by decrease in its magnitude, which depended on
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the type of CPE added to HDPE. For example, the loss modulus of pure polymer at an angular
frequency of 10 rad/s was observed to be 83980 Pa which increased to 93480 Pa for 2%CPE25
blend. Blends with 5% and 10% CPE content though had higher modulus than pure polymer,
but the magnitude decreased with increasing the CPE content. 30% CPE25 blend at the same
angular frequency was measured to have a value of 78080 Pa. In the case of CPE35 containing
blends, the modulus also showed maximum increase at 2% content. Higher concentration of
CPE35, however, significantly deteriorated the polymer response as a value of 38790 Pa was
observed for blend with 30% CPE content. Similar to Figure 4, the loss modulus curves for
CPE25 blends converged with each other at higher frequency, thus, showing no dependency on
CPE concentration. However, the blends with CPE35 showed convergence only for lower CPE
concentration blends and significant concentration dependent behavior for higher CPE
concentration blends. These findings further confirmed the miscibility phenomena observed for
storage moduli of blends.
Table 3 also shows the effect of percentage of CPE25 and CPE35 on transition point from liquid
like to solid like viscoelastic behavior which is usually called gel point. At this point, polymer acts
as true viscoelastic fluid. This behavior could be referred to the lesser molecular flexibility and
mobility due to forming of viscoelastic gel or solid. It can be seen that both CPE polymers
showed opposite behavior as the percentage of CPE was increased in HDPE. For CPE35
blends, the transition point shifted to lower frequency as percentage of CPE35 was increased
and showed lowest frequency of transition point of 0.8 rad/s (pure polymer 1.9 rad/s) at 30% of
CPE35. This change could be attributed to the immiscibility of the CPE35 polymer in HDPE thus
hindering the formation of gel structures, especially at higher percentage of CPE35. On the
contrary, CPE25 addition initially decreased the transition point as compared to pure polymer
but on average the behavior shifted to higher frequency values and the highest transition
frequency of 3.4 rad/s was observed at 30% CPE content. It can also be inferred from the
transition frequency values that in both of the cases that there was gradual change in magnitude
of transition frequency point up to 15% CPE amount, but sudden changes occurred at 20% and
30%. Figure 6 shows these phenomena in relation with tan(δ) vs. angular frequency plot. For
tan(δ) > 1, G’’ > G’, whereas for tan(δ) < 1, G’’ < G’. Thus, the above mentioned transition points
can be recorded in Figure 6 at tan(δ) = 1. As observed earlier, for CPE25 blends, the transition
frequency increased with CPE25 content, whereas an opposite behavior was observed for
CPE35 containing blends. These behaviors were also reflected in linear regression between ln
G’ vs ln ω of the samples by using equation:
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′
The linear regression is a power law relationship and states that true gel is characterized by
zero slope of the power law model [22]. It can be inferred from the regression points in case of
CPE25 blends that the slope (Table 3) was constant up to 15% but significant increment in
slope could be observed when the CPE content was further increased. In the case of CPE35
blends, the slope was constant up to 10% CPE content, after which increase in the solid like
characteristic was observed as the slope decreased. The slope reduced to 0.48 for 30% blend
as compared to 0.54 for pure HDPE.
Figure 7 demonstrates complex viscosity of the blends as a function of angular velocity. The
viscosity decreased on increasing angular frequency for all the samples. Similar to shear
modulus, maximum value of complex viscosity was observed for 2% CPE blends. For CPE25
blends, the values were still higher than pure HDPE till 10% after which the viscosity decreased.
For CPE35 blends, the decrease in the viscosity at higher CPE concentrations was significant.
For example, at a frequency of 10 rad/s, the viscosity of the pure HDPE was 13400 Pa.s which
was reduced to 6606 Pa.s in the case of 30% CPE35 blend as compared to 12070 Pa.s for 30%
CPE25 blend. The transition frequency between η’ and η’’ was also followed the same pattern
as G’’ and G’. In the case of CPE25 blends, the transition frequency increased from 1.6 rad/s for
pure HDPE to 2.5 rad/s for 1% blend, which followed gradual increase till 3.9 rad/s for 30%
blend. For CPE35 blends, the transition decreased from 2.0 rad/s for 1% blend to 0.8 rad/s for
30% blend. The curves for CPE25 also converged to a single curve at higher angular frequency,
which was observed for CPE35 blends only at lower CPE concentration. Blends with higher
CPE35 content had significant concentration dependent behavior even at higher angular
frequency.
The miscibility of the blends was further studied using Cole-Cole viscosity plot which develops
relationships between real (η’) and imaginary (η’’) parts of complex viscosity [23-25]. A smooth,
semi-circular shape of the graph would suggest miscible blends with homogenous phase. The
deviation from this behavior indicates phase segregation due to immiscibility of the components
in the blends. As can be seen in Figure 8a (plots stacked vertically for clarity), 30% CPE25
blend showed deviation at higher viscosity (or lower frequency) values indicating presence of
immiscibility in this region. Insignificant deviations of blends with 15% and 20% CPE content in
the same region were also observed. All other blends followed a semi-circular shape indicating
the miscible phase morphology in the blends. In the case of CPE35 blends (Figure 8b), the
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blend with 30% CPE35 concentration showed significant deviation from the semi-circular path
indicating immiscible phase morphology. Blends with 10%, 15% and 20% CPE35 concentration
also had more straight curves indicating presence of incompatible phases in the blends. The
blends with 1%, 2% and 5% seemed to follow the semi-circular path suggesting phase
miscibility in these blends. However, it is necessary to further support the findings from ColeCole plots as these findings could sometimes be misleading [26]. Figure 9 shows the analysis of
the rheological data based on van Gurp plots representing the relationship between complex
modulus (G*) and phase angle delta (δ) [21,27]. The van Gurp plots confirmed the findings from
Cole-Cole analysis. In the case of CPE25 blends, the time-temperature superposition principle
was observed to hold (indicated by the merging of the curves into a common curve) for all the
blends except the 30% blend at lower frequency (higher delta value) thus indicating their phase
miscibility. Slight deviations at lower frequency were also observed for blends with 15 and 20%
CPE content, but it was not significant. In the case of CPE35 blends, the pure HDPE, 1%, 2%
and 5% blends were observed to merge into a common curve thus confirming their miscibility.
However, the blends with 10%, 15% and 20% CPE content had significant deviation indicating
the immiscible phases thus confirming the findings from Cole-Cole analysis. Most notable
deviation was observed for 30% CPE35 blends indicating significant morphological changes
occurring at higher concentration of CPE35.
The rheological behavior of the blends was also analyzed using criteria reported for
compatibility of polymer blends by Han and Chuang [28,29] as shown in Figure 10. When G’ is
plotted vs G’’, such analysis generated composition independent correlation for compatible
blends, whereas the correlation is composition dependent for incompatible blends. For CPE25
blends, concentration independent correlation was observed except for 30% blend at lower
frequency values indicating the miscibility of the system. However, the correlation was
concentration dependent in the case of CPE35 blends beyond a CPE concentration of 5%. It
indicated that the molecular mixing of the HDPE and CPE phases was absent when the
concentration of CPE35 was increased. These findings fully correlated with the earlier analysis
using Cole-Cole plots as well as van Gurp plots.
Figure 11 reports the relative tensile properties of HDPE and its blends with CPE polymers. The
tensile modulus for pure polymer was observed to be 1063 Mpa, which was observed to reduce
as the CPE type and content was changed. As seen in Figure 11a, in the case of 1% and 2%
CPE25 blends, reduction in the modulus was less than 5% as compared to pure HDPE,
9
confirming good mixing between the phases. The modulus reduced more significantly beyond
these concentrations. It indicated that as CPE25 polymer was suggested to be well mixed with
the HDPE phase by the rheological results, the decrease in modulus by increasing its
concentration may have been primarily caused by matrix plasticization by the lower molecular
weight CPE chains and secondarily by reduced mixing between the phases. CPE35 blends
showed higher extent of modulus reduction and its magnitude increased with increasing CPE
concentration. As a result, the blend with 30% CPE content had a modulus reduced to 40% of
the pure HDPE. In the case of CPE35 blends, the presence of immiscibility (especially at higher
CPE concentrations) would primarily result in reduced mechanical response. These findings
further confirmed the different extent of immiscibility in the CPE25 and CE35 containing blends.
The peak stress of the blends also reduced after 5% CPE content as shown in Figure 11b.
Though CPE25 blends had lower decrease in the peak strength as compared to CPE35 blends,
the difference was less significant as compared to tensile modulus. However, similar to tensile
modulus, the difference in the magnitude of strength reduction between the CPE25 and CPE35
blends increased on increasing CPE concentration.
Morphology of the blends was also analyzed through transmission electron microscopy as
shown in Figure 12. The transmission electron micrographs represent morphological changes in
the 5% CPE blends as compared to pure HDPE. The HDPE morphology showed well defined
features due to its semi-crystalline nature. A similar but modified morphology was also observed
for 5% CPE25 blend. It also indicated that the crystalline morphology of the pure polymer may
not have been affected by the addition of CPE25. This notion is also confirmed by DSC results
which indicate that no significant change in the crystallinity of polymer was observed in this
case. The morphology in the case of 5% CPE35 blend, on the other hand, was quite different
and the nano-features observed in other two cases were observed to be diminished. These
findings were also supported by DSC results as in this case a large decrease in percent
crystallinity was measured. The miscibility of the blends could also be studied using optical
microscopy as shown in Figure 13. The miscibility of the CPE25 blends was much superior as
compared to CPE35 blends thus confirming the earlier findings. The CPE25 blends with 1%, 2%
and 5% CPE concentration (Figure 13 b,c,d) were similar to pure HDPE (Figure 13a) thus
indicating molecular mixing of the two phases. The blends with 10%, 15%, 20% and 30%
CPE25 (Figure 13 e,f,g,h respectively) were also observed to be mixed homogenously, though
uniformly dispersed small whitish regions indicating CPE25 phase were also observed. Owing
to these regions, the TGA may have shown individual response of the two phases, but in the
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rheological analysis, these phases were still proved to be miscible. In the case of CPE35
blends, the lower concentrations of CPE did lead to good mixing (Figure 13 i,j,k for 1%, 2% and
5% respectively) as confirmed earlier. However, beyond 5%, the immiscibility of the two phases
was extensive and large domains of CPE35 (as black areas in the bright field images of Figure
13 l,m,n,o for 10%,15%, 20% and 30% CPE35 content) were clearly visible.
Conclusions
In the current study, high density polyethylene was blended with chlorinated polyethylene
grades of different chlorination levels in different weight ratios. The CPE polymer with 25%
chlorination level was observed to be semi-crystalline, whereas the one with 35% chlorination
was amorphous. The melting point of the blends decreased slightly till 10% CPE concentration,
whereas at higher concentration, a decrease of 6°C was observed as compared to pure
polymer. As compared to CPE25 blends, the blends with CPE35 polymers had significant
reduction in the melt enthalpy as well as extent of crystallinity. The TGA thermograms of higher
CPE concentration exhibited individual signal of CPE component probably due to the presence
of immiscible phases. The gel point frequency in the CPE25 blends increased as the content of
CPE25 was enhanced, whereas the opposite behavior was observed for CPE35 containing
blends. The G’ and G’’ were observed to be maximum in blends with 2% CPE content followed
by decrease in these values at higher CPE concentrations, however , the CPE35 system had
much significant decrease. The regression of ln(G’) vs ln(ω) also indicated that in CPE25
blends, the slope was constant initially followed by significant increment at higher CPE
concentration. For CPE35 blends, the slope was constant up to 10% CPE content, after which
the gel behavior of CPE35 blend significantly improved as the slope decreased. Cole-Cole, van
Gurp as well as Han-Chuang analysis confirmed the miscibility in CPE25 blends (except 30%
blend at lower viscosity) whereas the CPE35 blends with only 1-5% CPE35 content were
miscible. The higher concentration blends showed significant deviations from the correlations for
miscible behavior. The tensile properties of the blends were also significantly affected by the
type as well as amount of the CPE used. The tensile modulus as well as the peak strength of
the CPE25 blends had lower decrease in magnitude as compared to CPE35 blends. The
decrease was observed only after 5% CPE content and the difference between the two systems
enhanced on enhancing the CPE content. TEM characterization of the blends also revealed the
changes in the microstructure of HDPE by the addition of amorphous CPE35, whereas the
addition of the semi-crystalline CPE25 retained the features present in the semi-crystalline
11
matrix. The optical microscopy also confirmed the earlier findings of miscibility in CPE25 blends
even at higher CPE concentration, whereas the miscibility in CPE35 blends was observed only
till 10% CPE35 content.
Acknowledgements
The authors are grateful to Dr. N. B. Matsko at Graz University of Technology for the
transmission electron microscopy analysis.
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Chuang, H. K.; Han, C. D. J Appl Polym Sci, 1984, 29, 2205.
29.
Han, C. D.; Chuang, H. K. J Appl Polym Sci, 1985, 30, 4431.
13
Table 1. Specifications of the polymers as received from the suppliers
Property
CPE25
CPE35
HDPE
Appearance
white granules
white powder
transparent
pellets
Specific gravity,
1.1-1.3
1.1-1.16
0.958
-
-
147
45
2
-
-
-
0.35
-
-
80
ASTM D792
Melting point, °C,
ASTM D7138
Heat of fusion,
J/g, ASTM
D3418
MFR 190°C/2.16
Kg, g/10 min,
ASTM D1238
Heat deflection
temp. (0.45
N/mm2), °C,
ASTM D648
14
Table 2. Calorimetric analysis of pure polymers and polymer blends
Code
Blend
∆H
J/g
Peak
melting
Peak
Crystallinity, %
temp, °C
crystallization
temp, °C
1
HDPE
151
140
52
115
2
CPE 25%
47
130
-
-
3
CPE 35%
-
-
-
-
4
HDPE/1%CPE25
153
137
52
116
5
HDPE/2%CPE25
149
137
51
115
6
HDPE/5%CPE25
140
137
48
115
7
HDPE/10%CPE25
134
137
46
115
8
HDPE/15%CPE25
130
134
44
115
9
HDPE/20%CPE25
128
134
44
116
10
HDPE/30%CPE25
119
134
41
116
11
HDPE/1%CPE35
138
138
47
114
12
HDPE/2%CPE35
137
138
47
115
13
HDPE/5%CPE35
130
137
44
115
14
HDPE/10%CPE35
132
136
45
115
15
HDPE/15%CPE35
115
134
39
115
16
HDPE/20%CPE35
103
134
35
114
17
HDPE/30%CPE35
102
134
35
115
15
Table 3. Angular frequency at gel point as well as slope of the ln(G’) vs ln(ω) plots in various
HDPE-CPE blends
% of CPE in
blend
angular frequency rad/s at G’=G”
slope of the ln(G’) vs ln(ω) plot
CPE25
CPE35
CPE25
CPE35
0 (pure polymer)
1.910
1.910
0.54
0.54
1
2.059
1.703
0.55
0.54
2
1.645
1.700
0.54
0.54
5
1.798
1.556
0.54
0.53
10
1.999
1.479
0.55
0.55
15
2.216
1.405
0.55
0.50
20
3.358
1.077
0.59
0.48
30
3.400
0.773
0.57
0.46
16
Figure Captions
Figure 1. DSC thermograms of (a) melting behavior and (b) crystallization behavior of CPE25
blends as a function of CPE25 concentration in comparison with pure HDPE. Figure 2. DSC thermograms of (a) melting behavior and (b) crystallization behavior of CPE35
blends as a function of CPE35 concentration in comparison with pure HDPE.
Figure 3. TGA thermograms of (a) CPE25 containing blends and (b) CPE35 containing blends
in comparison with pure CPE and HDPE.
Figure 4. Storage modulus (G’) of the (a) CPE25 and (b) CPE35 blends as a function of angular
frequency as well as CPE concentration in the blends.
Figure 5. Loss modulus (G’’) of the (a) CPE25 and (b) CPE35 blends as a function of angular
frequency as well as CPE concentration in the blends.
Figure 6. tan δ vs angular frequency (ω) plots for (a) CPE25 containing blends and (b) CPE35
containing blends.
Figure 7. Complex viscosity (η*) of the (a) CPE25 and (b) CPE35 blends as a function of
angular frequency and CPE content. Figure 8. Cole-Cole plots of (a) CPE25 and (b) CPE35 blends.
Figure 9. van Gurp plots of (a) CPE25 and (b) CPE35 blends.
Figure 10. Han-Chuang (G’ vs G’’) plots of (a) CPE25 and (b) CPE35 blends.
Figure 11. (a) Relative tensile modulus and (b) relative peak stress of the HDPE-CPE blends as
a function of amount of CPE in the polymer blends.
Figure 12. Transmission electron micrographs of (a) 5% CPE25 blend, (b) 5% CPE35 blend and
(c) pure HDPE. Figure 13. Optical micrographs of (a) pure HDPE, (b) 1% CPE25, (c) 2% CPE25, (d) 5%
CPE25, (e) 10% CPE25, (f) 15% CPE25, (g) 20% CPE25, (h) 30% CPE25, (i) 1% CPE35, (j)
2% CPE35, (k) 5% CPE35, (l) 10% CPE35, (m) 15% CPE35, (n) 20% CPE35 and (o) 30%
CPE35 blends. The width of the images reads 500 µm.
17
heat flow, mW/mg
I
II
III
IV
I. HDPE
II. HDPE+1%.CPE25
III. HDPE+2%.CPE25
IV. HDPE+5%.CPE25
V. HDPE+10%.CPE25
VI. HDPE+15%.CPE25
VII. HDPE+20%.CPE25
VIII. HDPE+30%.CPE25
IX. CPE25
60
80
V
VI
VII
VIII
IX
100
120
140
160
temperature [oC]
(a)
I
II
hat flow, mW/mg
III
IV
V
VI
I. HDPE
II. HDPE+1%.CPE25
III. HDPE+2%.CPE25
IV. HDPE+5%.CPE25
V. HDPE+10%.CPE25
VI. HDPE+15%.CPE25
VII. HDPE+20%.CPE25
VIII. HDPE+30%.CPE25
IX. CPE25
60
80
VII
VIII
IX
100
120
140
160
temperature [oC]
(b)
Figure 1. DSC thermograms of (a) melting behavior and (b) crystallization behavior of CPE25
blends as a function of CPE25 concentration in comparison with pure HDPE.
18
heat flow, mW/mg
I
II
III
IV
I. HDPE
II. HDPE+1%.CPE35
III. HDPE+2%.CPE35
IV. HDPE+5%.CPE35
V. HDPE+10%.CPE35
VI. HDPE+15%.CPE35
VII. HDPE+20%.CPE35
VIII. HDPE+30%.CPE35
IX. CPE35
60
80
VI
V
VII
VIII
IX
100
120
140
160
temperature[oC]
(a)
2.0
I
heat flow, mW/mg
1.5
II
III
1.0
IV
V
0.5
0.0
-0.5
-1.0
-1.5
-2.0
I. HDPE
II. HDPE+1%.CPE35
III. HDPE+2%.CPE35
IV. HDPE+5%.CPE35
V. HDPE+10%.CPE35
VI. HDPE+15%.CPE35
VII. HDPE+20%.CPE35
VIII. HDPE+30%.CPE35
IX. CPE35
60
80
VI
VII
VIII
IX
100
120
140
160
temperature [oC]
(b)
Figure 2. DSC thermograms of (a) melting behavior and (b) crystallization behavior of CPE35
blends as a function of CPE35 concentration in comparison with pure HDPE.
19
100
percent weight [%]
80
60
40
20
0
100
HDPE
HDPE+10%.CPE25
HDPE+20%.CPE25
HDPE+30%.CPE25
CPE25
200
300
400
500
600
700
600
700
temperature [oC]
(a)
100
percent weight [%]
80
60
40
20
HDPE
HDPE+10%.CPE35
HDPE+20%.CPE35
HDPE+30%.CPE35
CPE35
0
100
200
300
400
500
temperature [oC]
(b)
Figure 3. TGA thermograms of (a) CPE25 containing blends and (b) CPE35 containing blends
in comparison with pure CPE and HDPE.
20
G', Pa
100000
HDPE
HDPE+1%.CPE25
HDPE+2%.CPE25
HDPE+5%.CPE25
HDPE+10%.CPE25
HDPE+15%.CPE25
HDPE+20%.CPE25
HDPE+30%.CPE25
10000
0.1
1
10
100
ang. frequency, rad/s
(a)
G', Pa
100000
HDPE
HDPE+1%.CPE35
HDPE+2%.CPE35
HDPE+5%.CPE35
HDPE+10%.CPE35
HDPE+15%.CPE35
HDPE+20%.CPE35
HDPE+30%.CPE35
10000
0.1
1
10
100
ang. frequency, rad/s
(b)
Figure 4. Storage modulus (G’) of the (a) CPE25 and (b) CPE35 blends as a function of angular
frequency as well as CPE concentration in the blends.
21
G'', Pa
100000
HDPE
HDPE+1%.CPE25
HDPE+2%.CPE25
HDPE+5%.CPE25
HDPE+10%.CPE25
HDPE+15%.CPE25
HDPE+20%.CPE25
HDPE+30%.CPE25
10000
0.1
1
10
100
ang. frequency, rad/s
(a)
G'', Pa
100000
HDPE
HDPE+1%.CPE35
HDPE+2%.CPE35
HDPE+5%.CPE35
HDPE+10%.CPE35
HDPE+15%.CPE35
HDPE+20%.CPE35
HDPE+30%.CPE35
10000
0.1
1
10
100
ang. frequency, rad/s
(b)
Figure 5. Loss modulus (G’’) of the (a) CPE25 and (b) CPE35 blends as a function of angular
frequency as well as CPE concentration in the blends.
22
1.8
HDPE
HDPE+1%.CPE25
HDPE+2%.CPE25
HDPE+5%.CPE25
HDPE+10%.CPE25
HDPE+15%.CPE25
HDPE+20%.CPE25
HDPE+30%.CPE25
1.6
tan()
1.4
1.2
1.0
0.8
0.6
0.4
0.1
1
10
100
ang. frequency, rad/s
(a)
1.8
HDPE
HDPE+1%.CPE35
HDPE+2%.CPE35
HDPE+5%.CPE35
HDPE+10%.CPE35
HDPE+15%.CPE35
HDPE+20%.CPE35
HDPE+30%.CPE35
1.6
1.4
tan()
1.2
1.0
0.8
0.6
0.4
0.1
1
10
100
ang. frequency, rad/s
(b)
Figure 6. tan δ vs angular frequency (ω) plots for (a) CPE25 containing blends and (b) CPE35
containing blends.
23
*, Pa.s
100000
10000
HDPE
HDPE+1%.CPE25
HDPE+2%.CPE25
HDPE+5%.CPE25
HDPE+10%.CPE25
HDPE+15%.CPE25
HDPE+20%.CPE25
HDPE+30%.CPE25
0.1
1
10
100
ang. frequency, rad/s
(a)
*, Pa.s
100000
10000
HDPE
HDPE+1%.CPE35
HDPE+2%.CPE35
HDPE+5%.CPE35
HDPE+10%.CPE35
HDPE+15%.CPE35
HDPE+20%.CPE35
HDPE+30%.CPE35
1000
0.1
1
10
100
ang. frequency, rad/s
(b)
Figure 7. Complex viscosity (η*) of the (a) CPE25 and (b) CPE35 blends as a function of
angular frequency and CPE content.
24
'', Pa.s
HDPE+1%.CPE25
HDPE+2%.CPE25
HDPE+5%.CPE25
HDPE+10%.CPE25
HDPE+15%.CPE25
HDPE+20%.CPE25
HDPE+30%.CPE25
0
20000
40000
60000
80000
100000 120000
', Pa.s
'', Pa.s
(a)
HDPE+1%.CPE35
HDPE+2%.CPE35
HDPE+5%.CPE35
HDPE+10%.CPE35
HDPE+15%.CPE35
HDPE+20%.CPE35
HDPE+30%.CPE35
0
20000 40000 60000 80000 100000 120000 140000
', Pa.s
(b)
Figure 8. Cole-Cole plots of (a) CPE25 and (b) CPE35 blends.
25
65
60
55
 [degree]
50
45
HDPE
HDPE+1%.CPE25
HDPE+2%.CPE25
HDPE+5%.CPE25
HDPE+10%.CPE25
HDPE+15%.CPE25
HDPE+20%.CPE25
HDPE+30%.CPE25
40
35
30
25
10000
100000
G*, Pa
(a)
60
55
 [degree]
50
45
40
35
30
25
HDPE
HDPE+1%.CPE35
HDPE+2%.CPE35
HDPE+5%.CPE35
HDPE+10%.CPE35
HDPE+15%.CPE35
HDPE+20%.CPE35
HDPE+30%.CPE35
10000
100000
G*, Pa
(b)
Figure 9. van Gurp plots of (a) CPE25 and (b) CPE35 blends.
26
G', Pa
100000
HDPE
HDPE+1%.CPE25
HDPE+2%.CPE25
HDPE+5%.CPE25
HDPE+10%.CPE25
HDPE+15%.CPE25
HDPE+20%.CPE25
HDPE+30%.CPE25
10000
10000
100000
G'', Pa
(a)
G', Pa
100000
HDPE
HDPE+1%.CPE35
HDPE+2%.CPE35
HDPE+5%.CPE35
HDPE+10%.CPE35
HDPE+15%.CPE35
HDPE+20%.CPE35
HDPE+30%.CPE35
10000
10000
100000
G'', Pa
(b)
Figure 10. Han-Chuang (G’ vs G’’) plots of (a) CPE25 and (b) CPE35 blends.
27
1.0
CPE35
CPE25
relative tensile modulus
0.9
0.8
0.7
0.6
0.5
0.4
0
5
10
15
20
25
30
amount of CPE [%]
(a)
1.0
CPE35
CPE25
relative peak stress
0.9
0.8
0.7
0.6
0.5
0
5
10
15
20
25
30
amount of CPE [%]
(b)
Figure 11. (a) Relative tensile modulus and (b) relative peak stress of the HDPE-CPE blends as
a function of amount of CPE in the polymer blends.
28
(a)
(b)
(c)
Figure 12. Transmission electron micrographs of (a) 5% CPE25 blend, (b) 5% CPE35 blend and
(c) pure HDPE. 29
Left to right: (a)-(e)
Left to right: (f)-(j)
Left to right: (k)-(o)
Figure 13. Optical micrographs of (a) pure HDPE, (b) 1% CPE25, (c) 2% CPE25, (d) 5%
CPE25, (e) 10% CPE25, (f) 15% CPE25, (g) 20% CPE25, (h) 30% CPE25, (i) 1% CPE35, (j)
2% CPE35, (k) 5% CPE35, (l) 10% CPE35, (m) 15% CPE35, (n) 20% CPE35 and (o) 30%
CPE35 blends. The width of the images reads 500 µm.
30