Presentation ID #298480: PE-CPE Blends: Morphology and ... · PDF file1 Presentation ID...

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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 (62-

73%) [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-methylstyrene-

acrylonitrile) 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 in-

depth 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 Cole-

Cole 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,

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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

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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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27. van Gurp, M.; Palmen, J. Rheol Bull, 1998, 67, 5.

28. 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.

14

Table 1. Specifications of the polymers as received from the suppliers

Property CPE25 CPE35 HDPE

Appearance white granules white powder transparent

pellets

Specific gravity,

ASTM D792

1.1-1.3 1.1-1.16 0.958

Melting point, °C,

ASTM D7138

- - 147

Heat of fusion,

J/g, ASTM

D3418

45 2 -

MFR 190°C/2.16

Kg, g/10 min,

ASTM D1238

- - 0.35

Heat deflection

temp. (0.45

N/mm2), °C,

ASTM D648

- - 80

15

Table 2. Calorimetric analysis of pure polymers and polymer blends

Code Blend ∆H

J/g

Peak

melting

temp, °C

Crystallinity, %

Peak

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

16

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

17

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 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


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.

18

60 80 100 120 140 160

hea

t flo

w,

mW

/mg

temperature [oC]

I. HDPEII. HDPE+1%.CPE25III. HDPE+2%.CPE25IV. HDPE+5%.CPE25V. HDPE+10%.CPE25VI. HDPE+15%.CPE25VII. HDPE+20%.CPE25VIII. HDPE+30%.CPE25IX. CPE25

I

IIIIIIV

VVI

VIIVIIIIX

(a)

60 80 100 120 140 160

hat

flow

, mW

/mg

temperature [oC]


III

III

IV

V

VI

VII

VIII

IX

(b)



19

60 80 100 120 140 160

hea

t flo

w,

mW

/mg

temperature[oC]


III

IIIIV

VVI

VII

VIIIIX

(a)

60 80 100 120 140 160-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

heat

flo

w,

mW

/mg

temperature [oC]


I

IIIII

IV

V

VI

VII

VIII

IX

(b)



20

100 200 300 400 500 600 700

0

20

40

60

80

100

perc

ent w

eigh

t [%

]

temperature [oC]

HDPE HDPE+10%.CPE25 HDPE+20%.CPE25 HDPE+30%.CPE25 CPE25

(a)

100 200 300 400 500 600 700

0

20

40

60

80

100

HDPE HDPE+10%.CPE35 HDPE+20%.CPE35 HDPE+30%.CPE35 CPE35

perc

ent w

eigh

t [%

]

temperature [oC]

(b)

Figure 3. TGA thermograms of (a) CPE25 containing blends and (b) CPE35 containing blends

in comparison with pure CPE and HDPE.

21

0.1 1 10 100

10000

100000

HDPE HDPE+1%.CPE25 HDPE+2%.CPE25 HDPE+5%.CPE25 HDPE+10%.CPE25 HDPE+15%.CPE25 HDPE+20%.CPE25 HDPE+30%.CPE25

G',

Pa

ang. frequency, rad/s

(a)

0.1 1 10 100

10000

100000


G',

Pa


(b)

Figure 4. Storage modulus (G’) of the (a) CPE25 and (b) CPE35 blends as a function of angular


22

0.1 1 10 100

10000

100000


G'',

Pa


(a)

0.1 1 10 100

10000

100000


G'',

Pa


(b)

Figure 5. Loss modulus (G’’) of the (a) CPE25 and (b) CPE35 blends as a function of angular


23

0.1 1 10 1000.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8 HDPE HDPE+1%.CPE25 HDPE+2%.CPE25 HDPE+5%.CPE25 HDPE+10%.CPE25 HDPE+15%.CPE25 HDPE+20%.CPE25 HDPE+30%.CPE25

tan()


(a)

0.1 1 10 1000.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8


tan()


(b)

Figure 6. tan δ vs angular frequency (ω) plots for (a) CPE25 containing blends and (b) CPE35

containing blends.

24

0.1 1 10 100

10000

100000


*,

Pa.

s


(a)

0.1 1 10 1001000

10000

100000


*,

Pa.

s


(b)

Figure 7. Complex viscosity (η*) of the (a) CPE25 and (b) CPE35 blends as a function of

angular frequency and CPE content.

25

0 20000 40000 60000 80000 100000 120000

HDPE+1%.CPE25 HDPE+2%.CPE25 HDPE+5%.CPE25 HDPE+10%.CPE25 HDPE+15%.CPE25 HDPE+20%.CPE25 HDPE+30%.CPE25

'',

Pa.

s

', Pa.s

(a)

0 20000 40000 60000 80000 100000 120000 140000

HDPE+1%.CPE35 HDPE+2%.CPE35 HDPE+5%.CPE35 HDPE+10%.CPE35 HDPE+15%.CPE35 HDPE+20%.CPE35 HDPE+30%.CPE35

'',

Pa.

s

', Pa.s

(b)

Figure 8. Cole-Cole plots of (a) CPE25 and (b) CPE35 blends.

26

10000 10000025

30

35

40

45

50

55

60

65


[d

egre

e]

G*, Pa

(a)

10000 100000

25

30

35

40

45

50

55

60


[d

egre

e]

G*, Pa

(b)

Figure 9. van Gurp plots of (a) CPE25 and (b) CPE35 blends.

27

10000 100000

10000

100000


G',

Pa

G'', Pa

(a)

10000 100000

10000

100000


G',

Pa

G'', Pa

(b)

Figure 10. Han-Chuang (G’ vs G’’) plots of (a) CPE25 and (b) CPE35 blends.

28

0 5 10 15 20 25 30

0.4

0.5

0.6

0.7

0.8

0.9

1.0

CPE35 CPE25

rela

tive

tens

ile m

odul

us

amount of CPE [%]

(a)

0 5 10 15 20 25 30

0.5

0.6

0.7

0.8

0.9

1.0

CPE35 CPE25

rela

tive

peak

str

ess

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.

29

(a) (b)

(c)

Figure 12. Transmission electron micrographs of (a) 5% CPE25 blend, (b) 5% CPE35 blend and

(c) pure HDPE.

30

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.

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