European Polymer Journal 44 (2008) 1834–1842

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European Polymer Journal

journal homepage: www.elsevier .com/locate /europol j

Rheology, morphology and mechanical propertiesof polyethylene/ethylene vinyl acetate copolymer (PE/EVA) blends

M. Faker a,b,c, M.K. Razavi Aghjeh a,*, M. Ghaffari b,c, S.A. Seyyedi a

a Institute of Polymeric Materials, Chemical Engineering Department, Sahand University of Technology, Sahand New Town, Tabriz, P.O. Box 51335-1996, Iranb Yazd Radiation Processing Center, P.O. Box 89175/389, Yazd, Iranc Iran Polymer and Petrochemical Institute, P.O. Box 14965/115, Tehran, Iran

a r t i c l e i n f o a b s t r a c t

Article history:Received 26 December 2007Received in revised form 13 March 2008Accepted 2 April 2008Available online 15 April 2008

Keywords:RheologyMorphologyPE/EVA blendsInterfacial tension

0014-3057/$ - see front matter � 2008 Elsevier Ltddoi:10.1016/j.eurpolymj.2008.04.002

* Corresponding author. Tel.: +98 4123459085; faE-mail address: karimrazavi@sut.ac.ir (M.K. Raza

Rheology, morphology and mechanical properties of binary PE and EVA blends togetherwith their thermal behavior were studied. The results of rheological studies showed that,for given PE and EVA, the interfacial interaction in PE-rich blends is higher than EVA-richblends, which in turn led to finer and well-distributed morphology in PE-rich blends. Usingtwo different models, the phase inversion composition was predicted to be in 45 and47 wt% of the PE phase. This was justified by morphological studies, where a clear co-con-tinuous morphology for 50/50 blend was observed. The tensile strength for PE-rich blendsshowed positive deviation from mixing rule, whereas the 50/50 blend and EVA-rich blendsdisplayed negative deviation. These results were in a good agreement with the results ofviscoelastic behavior of the blends. The elongation at break was found to follow the sametrend as tensile strength except for 90/10 PE/EVA blend. The latter was explained in termsof the effect of higher co-crystallization in 90/10 composition, which increased the tensilestrength and decreased the elongation at break in this composition. The results of thermalbehavior of the blends indicated that the melting temperatures of PE and EVA decrease andincrease, respectively, due to the dilution effect of EVA on PE and nucleation effect of PE onEVA.

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1. Introduction

During the last few decades, increasing activities havebeen directed towards modification of existing polymersto produce new materials with desirable properties. Dueto the possibility of attaining a wide range of propertiesthrough blending of two or more polymers, it has beenknown as one of the most applicable methods for modifica-tion of polymers [1,2]. There are a few couple of polymers,the mixing of which results in a miscible blend [3].Mechanical properties of miscible blends obey linear mix-ing rules or show positive deviation from mixing rules. Be-cause of the small combinatorial entropy and positive

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x: +98 4123444355.vi Aghjeh).

enthalpy of mixing, most of the polymer blends are immis-cible and therefore they display multiphase morphology[4]. Mechanical properties of such blends can strongly beaffected by the phase morphology and interface properties[5]. Moreover, the morphology is influenced by the ther-modynamical and rheological parameters and also processconditions. Therefore, the mechanical behavior of immisci-ble blends becomes more complicated. It has clearly beenunderstood that rheological parameters such as viscosityand elasticity ratio of the blend components have aremarkable influence on the phase structure of the blends[2,3]. On the other hand, the rheological behavior of theblends is dependent on the type of morphology as wellas interfacial interaction between phases [6]. So, the infor-mation obtained from the rheological studies can be usedin the prediction of morphology and therefore mechanicalproperties of the blends.

M. Faker et al. / European Polymer Journal 44 (2008) 1834–1842 1835

PE/EVA blends are widely used in many applicationssuch as shrinkable films, multilayer packaging and wireand cable coating [7–10]. Addition of EVA onto differentgrades of PE improves their toughness, transparency, envi-ronmental stress cracking resistance (ESCR) and the capac-ity of the filler carrying.

Takidis et al. [10] studied the compatibility of PE/EVAblends and reported that the blend composition and pro-cess temperature play significant roles in determinationof the compatibility. They suggested higher than 180 �Cmixing temperature for achieving effective improvementin mechanical properties. Khonakdar et al. [11,12] appliedthe dynamic mechanical analysis (DMA) in conjunctionwith the morphological and rheological studies for clarify-ing the miscibility of both HDPE/EVA and LDPE/EVAblends. They realized that using only the DMA results can-not lead to understand the state of miscibility or immisci-bility of these blends. However, using other techniquesthey resulted that the LDPE/EVA blends are more compat-ible than HDPE/EVA blends. Ray and Khastgir [13] reportedthe existence of miscibility in amorphous regions and thepresence of individual crystalline zones, for LDPE andEVA by using DMA and differential scanning calorimetry(DSC) results. Using DSC technique Li et al. [14] observedthe depression in melting temperature of LLDPE by theaddition of EVA. These observations were related to thepartial miscibility between LLDPE and EVA, which couldin turn lead to their co-crystallization during solidificationprocess. Recently, Peon et al. [15] carried out an interestingresearch work on the viscoelastic properties of the PE/EVAblends. They evaluated the phase structure of the blendsusing linear viscoelastic data and predicted co-continuityin 60 wt% of PE.

Although a considerable number of research workshave been published on the different aspects of PE/EVAblends, there is a little work in the relationship betweenrheology, morphology and mechanical properties of theseblends. The main objective of the present work was tostudy the rheology, morphology and mechanical propertiesof PE/EVA blends and their relationship. By consideringthat the solid state morphology of semicrystalline polymerblends, such as PE/EVA blends, can be affected by theircrystallization behavior, the effect of thermal behavior onmechanical properties was also taken into account.

2. Experimental

2.1. Materials

LDPE 0030 (MFI = 0.4 g/10 min; 190 �C, 2.16 kg) fromBandar Imam Petrochemical Company, Iran, and EVA8430 (MFI = 2.2 g/10 min; 190 �C, 2.160 kg, vinyl acetatecontent = 18 wt%) from Hyundai Company, South Korea,were used as received.

2.2. Sample preparation

The melt compounding of the blends containing variousamounts of EVA was carried out in a laboratory batchinternal mixer (Brabender W350 EHT) at a temperature

of 180 �C and with a rotor speed of 60 rpm. A small amountof the prepared blend samples was rapidly quenched in li-quid nitrogen for morphological studies and the remainingwas compression molded into sheets with a thickness of2 mm in a DR Collin (25 MPa) laboratory hot press at atemperature of 165 �C for 5 min under 10 MPa pressure.Then, the sheet samples were cooled by cast under10 MPa pressure for 1.5 min.

2.3. Rheological studies

Rheological properties of the neat PE, neat EVA and PE/EVA blends were investigated by using a rheometricmechanical spectrometer (RMS) equipped with parallelplate geometry (diameter = 25 mm, gap = 1 mm). The fre-quency sweep tests were performed in the range of 0.1–500 s�1 at temperature of 180 �C and with an amplitudeof 1% in order to maintain the response of materials inthe linear viscoelastic regime.

2.4. Morphological studies

Morphology of the blends was examined using scanningelectron microscopy method (SEM LEO 440 I, UK). Only thecryofractured surfaces of the PE-rich blends and also 50/50blend were etched with xylene for 6 h at 50 �C for the re-moval of EVA phase. Then, surfaces were gold sputteredfor good conductivity of the electron beam and micropho-tographs were taken within a magnification of 5000�.

SEM images were analyzed using Image Processing soft-ware to measure the number-average diameter (Dn),weight-average diameter (Dw), volume-average diameter(Dv), polydispersity of the particles (PD) and interparticledistance (ID) in matrix-dispersed morphologies, usingEqs. (1)–(5), respectively [16–18]. At least 200 particleswere used to calculate the parameters

Dn ¼P

ni:DiPni

ð1Þ

Dw ¼P

ni:D2iP

ni:Dið2Þ

Dv ¼P

ni:D4iP

ni:D3i

ð3Þ

PD ¼ Dv

Dnð4Þ

ID ¼ Dwp

6 � /

� �1=3

� 1

" #ð5Þ

where ni is the number of particles with diameter, Di, and uis the volume fraction of the dispersed phase.

The co-continuity index of the EVA phase was deter-mined using selective extraction method [19,20]. Samplesof specified weight of each blend were stirred in xylenefor 72 h at a constant temperature of 50 �C to selectivelyextract the EVA phase. The co-continuity index of theEVA phase (CIEVA) was quantified using Eq. (6)

CIEVA ¼mini �mext

mini� 100% ð6Þ

where mini is the weight of the EVA phase initially presentin the blend and mext the weight of the EVA phase in the

1836 M. Faker et al. / European Polymer Journal 44 (2008) 1834–1842

blend after extraction. In the case where the sample is notdisintegrated, the PE phase is considered as continuousphase, and the continuity of PS is quantified from Eq. (6).If the sample disintegrates completely, then PE is consid-ered as fully dispersed in the EVA matrix and EVA is con-sidered as continuous phase.

2.5. Mechanical properties

An Instron 4411 was used to carry out the tensile testsfor all samples according to ASTM D-638 at crossheadspeed of 50mm/min. Five trials were performed per eachsample and the mean values were reported.

2.6. Thermal analysis

Thermal behavior of PE and EVA as well as PE/EVAblends was studied by using a differential scanning calo-rimeter (DSC-50, Ta1300, Shimadzu, Japan) in a nitrogenatmosphere at a heating rate of 10 �C/min and with scan-ning temperature range from 25 �C to 150 �C.

3. Results and discussion

3.1. Rheology

The results of complex viscosity (g*) and storage modu-lus (G0) as functions of angular frequency (x) obtained forPE and EVA are shown in Fig. 1. These results show thatPE exhibits a power-low type flow behavior similar toEVA, with a higher viscosity and elasticity in comparisonto EVA in all frequency ranges. Figs. 2 and 3 show the re-sults of complex viscosity and storage modulus versus

1.E+02

1.E+03

1.E+04

1.E+05

0.1 1 10

Angular Frequen

Co

mp

lex

Vis

cosi

ty (

Pa.

Sec

)

Fig. 1. Complex viscosity (g*) and storage modulus (G0) ver

angular frequency for blend samples having different com-positions. These results clearly indicate that all the blendsbehave as shear thinning materials similar to the blendcomponents, and show almost an intermediate behaviorbetween PE and EVA.

The results of linear viscoelastic studies, applied insmall amplitudes, can provide reliable information onmicrostructure of the blends [15]. The viscoelastic re-sponse of the blends in low frequencies (low shear rates)can be used for evaluating of the interfacial interaction be-tween phases. Because at low shear rates, the effect of flowinduced molecular orientation on viscosity and elasticitybecomes more less. The complex viscosity and storagemodulus versus blend composition together with the sameresults calculated using mixing rule at angular frequencyof 0.1 s�1 are presented in Figs. 4 and 5, respectively. Itcan clearly be seen that while the complex viscosity andin particular storage modulus show a remarkable positivedeviation from mixing rule for PE-rich blends, they shownegative deviation for EVA-rich blends. On the basis ofUtracki’s studies [21], this type of behavior (PNDB) canbe observed for the blends in which the interfacial interac-tion between phases is affected by the blend composition.In other words, from these results it can be concluded thatfor PE-rich blends the presence of strong interfacial inter-action increases the viscosity and elasticity. On the otherhand, negative deviation of the viscosity and elasticity ob-served for EVA-rich blends can be attributed to the pres-ence of weak interfacial interaction between phases inthese blends.

The reason for higher interfacial interaction for PE-richblends compared to EVA-rich blends which in turn led topositive deviation of viscosity and elasticity for PE-rich

100 1000

cy (1/sec)

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

Sto

rag

e M

od

ulu

s (P

a)PE

EVA

sus angular frequency (x) for neat PE and neat EVA.

1.E+02

1.E+03

1.E+04

1.E+05

0.1 1 10 100 1000

Angular Frequency (1/sec)

Co

mp

lex

Vis

cosi

ty (

Pa.

Sec

)

PE

PE/EVA = 90/10

PE/EVA = 75/25

PE/EVA = 50/50

PE/EVA = 25/75

PE/EVA = 10/90

EVA

Fig. 2. Complex viscosity versus angular frequency for different blend compositions.

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

0.1 1 10 100 1000

Angular Frequency (1/sec)

Sto

rag

e M

od

ulu

s (P

a)

PE

PE/EVA = 90/10

PE/EVA = 75/25

PE/EVA = 50/50

PE/EVA = 25/75

PE/EVA = 10/90

EVA

Fig. 3. Storage modulus versus angular frequency for different blend compositions.

M. Faker et al. / European Polymer Journal 44 (2008) 1834–1842 1837

blends and negative deviation of viscosity and elasticity forEVA-rich blends can be discussed as follows.

As it can be seen from the results of rheological studies,the used PE exhibits higher elasticity than the used EVA.Therefore, according to Van Oene [22] equation (Eq. (7)),during the mixing process, the induced second normalstress difference of PE phase will be higher than that ofEVA phase, resulting to lower dynamic interfacial tension

of PE-rich blends (EVA dispersed blends) compared toEVA-rich blends (PE dispersed blends)

c12 ¼ co

12þ D

12ðN2:d � N2:mÞ ð7Þ

In this equation c12 and c12o

are the dynamic and staticinterfacial tensions, respectively. D is the particle diameter,N2.d and N2.m are the second normal stress differences for

6.E+03

2.E+04

3.E+04

3.E+04

4.E+04

0 25 50 75 100

EVA (wt.%)

Co

mp

lex

Vis

cosi

ty (

Pa.

Sec

)

Experimental

Mixing Rule

Fig. 4. Complex viscosity versus blend composition obtained from exper-imental and calculated using mixing rule at angular frequency of 0.1 s�1.

1.E+02

8.E+02

2.E+03

2.E+03

0 25 50 75 100

EVA (Wt.%)

Str

ora

ge

Mo

du

lus

(Pa)

ExperimentalMixing Rule

Fig. 5. Storage modulus versus blend composition obtained from exper-imental and calculated using mixing rule at angular frequency of 0.1 s�1.

Fig. 6. SEM micrograph of the PE/EVA 90/10 blend.

Fig. 7. SEM micrograph of the PE/EVA 75/25 blend.

Fig. 8. SEM micrograph of the PE/EVA 50/50 blend.

1838 M. Faker et al. / European Polymer Journal 44 (2008) 1834–1842

dispersed and matrix phases, respectively. The secondterm of the right-hand side of the equation is negativefor PE-rich blends and positive for EVA-rich blends. Thismeans that the dynamic interfacial tension of PE-richblends is lower than static interfacial tension, and dynamicinterfacial tension of EVA-rich blends is higher than staticinterfacial tension.

3.2. Morphology

By knowing that there is no selective extraction methodfor PE phase near the EVA phase from one side, and in or-der to be able to observe the real morphology of EVA-richblends, the SEM micrographs for EVA-rich blends were ta-ken from cryofructured surfaces without any extraction.Selective extraction of EVA phase was applied only forPE-rich blends and 50/50 blend.

Figs. 6–10 show the obtained SEM micrographs forblends containing various amounts of EVA. The values ofthe number-average diameter, weight-average diameter,volume-average diameter, polydispersity and interparticle

distance of the dispersed particles in matrix-dispersedmorphologies are taken in Table 1.

SEM micrographs clearly indicate that all the blendswith different compositions have a two-phase morphol-

Table 1The number-average diameter, weight-average diameter, volume-average diameter, polydispersity, interparticle distance and interfacial tension values fordifferent blend compositions

Blend Dn (lm) Dw (lm) Dv (lm) PD (lm) ID (lm) Interfacial tension (mN/m)

PE/EVA = 90/10 0.223 0.224 0.253 1.134 0.186 0.6–0.7PE/EVA = 75/25 0.524 0.546 0.624 1.190 0.174 0.6–0.7PE/EVA = 25/75 0.609 0.726 0.921 1.512 0.279 1.4–1.5PE/EVA = 10/90 0.514 0.602 0.785 1.527 0.736 1.4–1.5

Fig. 10. SEM micrograph of the PE/EVA 10/90 blend.

1.E+06

Experimental data

M. Faker et al. / European Polymer Journal 44 (2008) 1834–1842 1839

ogy, showing the immiscibility of the used PE and EVA, inwhole composition ranges. SEM micrograph of PE/EVA 90/10 blend shows the uniform distribution of submicron EVAparticles in the PE matrix (Fig. 6). Increasing EVA contentfrom 10% to 25% increases the average diameter of the dis-persed EVA domains from 0.22 to 0.52 lm (Figs. 6 and 7).

The matrix-dispersed morphology can also be observedfor EVA-rich blends similar to PE-rich blends (Figs. 9 and10). Comparison made between the SEM micrographs ofPE-rich and EVA-rich blends reveals that, in the same dis-persed phase content, the dispersed particle size for EVA-rich blends is larger with broad size distribution than thoseobserved for PE-rich blends. These differences can also beconcluded by comparing the determined average diameterand polydispersity of the dispersed particles in differentblend compositions (Table 1). These results evidence theresults of rheological studies, where it was shown that, inaddition to higher viscosity and elasticity of PE than EVA,the interfacial interaction for PE-rich blends is strongerthan EVA-rich blends. This can lead to better interfacialadhesion and effective stress transmits from matrix to dis-persed phase and therefore finer and well-distributed mor-phology in PE-rich blends.

Using Palierne’s emulsion model [23], the complexmodulus of a blend can be predicted as a function of dis-persed particle size, the interfacial tension and the com-plex modulus of the blend components. Using the curvefitting method, Palierne’s model can also be used for esti-mation of the interfacial tension, if the viscoelastic proper-ties of the blend and its components as well as the blendmorphology are accessible. Although application of Pali-erne’s model is more reliable for the blends in which the

Fig. 9. SEM micrograph of the PE/EVA 25/75 blend.

viscosity ratio (viscosity of dispersed phase/viscosity ofmatrix phase) is below the unity, in some experiments[24–26] it has been applied for a wide range of viscosityratios.

The interfacial tension values for different blend com-positions estimated using Palierne’s model are summa-rized in Table 1. Also the experimental complex modulusfor 90/10 and 10/90 blends together with the same resultsobtained using Palierne’s model and curve fitting methodis shown in Fig. 11. These results show that the interfacial

1.E+03

1.E+04

1.E+05

0.1 1 10 100 1000

Angular Frequency (1/sec)

Co

mp

lex

Mo

du

lus

(Pa)

Palierne model

PE/EVA=90/10

PE/EVA=10/90

Fig. 11. Experimental complex modulus for PE/EVA 90/10 and PE/EVA 10/90 blends together with the same results obtained using Palierne’s modeland curve fitting method.

0

25

50

75

100

0 25 50 75 100

EVA Content (wt%)

EVA

Co-

cont

inui

ty In

dex

(%)

Fig. 12. The co-continuity index of EVA phase versus EVA content,determined using solvent extraction method.

-4

-1.5

1

3.5

6

60 80 100 120 140

T(ºC)

Hea

t F

low

(m

W)

PE/EVA = 90/10

PE/EVA = 75/25

PE/EVA = 50/50

PE/EVA = 25/75

PE/EVA = 10/90

EVA

PE

Fig. 13. DSC endotherms for PE, EVA and PE/EVA blends.

1840 M. Faker et al. / European Polymer Journal 44 (2008) 1834–1842

tension of PE-rich blends is lower than EVA-rich blends.These results are in a good agreement with the results ob-tained from rheological and morphological studies. Re-cently, Kontopoulou et al. [24,25] have studied theinterrelationship between rheology and morphology ofEVA and polyolefin plastomer blends, and showed the ef-fect of viscosity and elasticity ratios on the blend morphol-ogy development. They reported the positive deviation forviscosity and elasticity at low frequency ranges in someblend compositions. Also they showed that the interfacialtension values for polyolefin plastomer-rich blends arelower than that of EVA-rich blends. Our results are in agood agreement with their results.

The blend with the same amount of PE and EVA (50/50blend) has a clear co-continuous morphology and it seamsto be near the phase inversion composition range (Fig. 8).In this composition both PE and EVA phases create athree-dimensional canales, running through each otherand form IPN-like morphology. This type of morphology(co-continuous morphology) has previously been reportedby Ray and Khastgir [13] and Khonakdar et al. [11,12], butin the different blend compositions compared to our re-sults. These differences are due to the use of differentgrades of PE and EVA in different experiments.

Using Krieger and Dougherty’s model [27], Utracki [21]proposed a criterion for prediction of the phase inversioncomposition (Eq. (8))

/2 ¼1� log g1

g2

� �� .½g��

2; ½g� ¼ 1:9 ð8Þ

Steinman et al. [28] have introduced another equation (Eq.(9)) for phase inversion prediction

/2 ¼ �0:12 logg1

g2

� �þ 0:48 ð9Þ

In our experiments, using Utracki’s and Steinman’sequations and considering the viscosity ratio in the pro-cessing conditions (60 rpm and 180 �C) the phase inversioncomposition was found to be in 45 and 47 wt% of EVA,respectively. These results show one more time the realityof the observed co-continuity in 50/50 composition.

The co-continuity index of EVA phase versus EVA con-tent, determined using solvent extraction experiments, ispresented in Fig. 12. It is clear from the results that thecompositions at which the different blends exhibit fullco-continuous phase morphology cover the range approx-imately between 40 and 80 wt% of EVA. The reason behindthe fact that the co-continuous morphology is not ob-served for PE/EVA 25/75 blend (Fig. 9) in contrary the ob-tained results using solvent extraction method may bedue to the two-dimensional scanning in SEM experiment,whereas solvent extraction already acts in differentdirections.

3.3. Thermal properties

DSC heating curves obtained for PE, EVA and theirblends are presented in Fig. 13. PE shows a single endo-thermic peak (Tm = 118 �C), as well as EVA (Tm = 97 �C) rep-resentative of the melting temperature of their crystalline

phase. The presence of two peaks for all the blends, except90/10 PE/EVA blend, corresponding to the melting point ofdifferent crystalline type, verifies the immiscibility of thePE and EVA crystalline phases. For all the blends, thedepression of melting temperature for PE crystalline phaseto lower temperatures is due to the dilution effect of EVAand/or co-crystallization of PE with part of EVA. On theother hand, nucleation effect of PE crystallites and somepart of PE chains in the amorphous phase can be responsi-ble for increasing the crystallization temperature andtherefore melting temperature of EVA crystalline phase.These results show that PE/EVA blends are not completelyimmiscible and there is a partial miscibility between PEand EVA in the melt state, which could in turn lead to par-tial miscibility in the amorphous region in the solid state.On the other hand, partial miscibility in the melt state fromone side and nearness of PE and EVA melting temperaturesand also their structural similarity from the other side canlead to their co-crystallization. A single peak near the PEphase melting temperature and a week shoulder near theEVA melting temperature, observed for 90/10 blend, verifythe high extent of co-crystallization in this blend composi-

600

750

900

0 25 50 75 100

EVA (Wt.%)

Elo

ng

atio

n a

t B

reak

(%

)

Experimental

Mixing Rule

Fig. 15. The results of elongation at break for different blend samplestogether with the same results calculated using mixing rule.

M. Faker et al. / European Polymer Journal 44 (2008) 1834–1842 1841

tion with respect to EVA content. As mentioned before inrheological section, there is a high compatibility betweenPE and EVA in this blend composition at the melt state.This allows the PE and EVA chains to diffuse to each other,in particular, near the interface and causes a higher degreeof co-crystallization during solidification process.

3.4. Mechanical properties

The tensile strength for different blend compositions to-gether with the same results calculated using mixing ruleis depicted in Fig. 14. The results show that while for PE-rich blends the tensile strength shows positive deviationfrom mixing rule (synergistic effect), it shows negativedeviation for 50/50 and EVA-rich blends. As discussed inSection 1, the mechanical behavior of polymer blends canstrongly be affected by the extent of interfacial interactionbetween phases. It is well known that, for incompatiblepolymer blends such as PE/PS blends, due to the presenceof high interfacial tension, the mechanical behavior followsa negative deviation from the mixing rule in all blend com-positions [29,30]. But for compatible polymer blends, thevariation trend of mechanical properties can influentiallybe affected by the degree of compatibility and thereforethe variation of the blend composition. Higher compatibil-ity can lead to enhanced mechanical properties even posi-tive deviation (synergistic effect) and vice versa. As it wasconcluded from the rheological and morphological studies,the extent of compatibility and interfacial interaction forPE-rich blends is higher than EVA-rich blends. Also the re-sults of particle size distribution measurements (Table 1)showed that PE-rich blends contain smaller and well-dis-tributed particles compared to EVA-rich blends. Thesecan be responsible for the observed mechanical behavior.

An appreciable negative deviation has been appeared in50/50 blend. It should be noted that the blends with co-continuous morphology show almost near iso-strainbehavior whereas the blends having matrix-dispersedmorphology obey near iso-stress behavior in tensile test.For these morphologies (co-continuous morphologies) themechanical behavior is critically controlled by the interfaceproperties. Using rheological studies it can be concluded

15

17.5

20

0 25 50 75 100

EVA (Wt.%)

Ten

sile

Str

eng

th (

MP

a)

Tensile(Exp)Mixing Rule

Fig. 14. The results of tensile strength for different blend samples toge-ther with the same results calculated using mixing rule.

that the interfacial interaction in 50/50 blend is low. Iso-strain behavior in tensile test from one side, and low inter-facial interaction from the other side, can be reasonable forthe inferior mechanical properties of this blend composi-tion. For PE/EVA blends, this minimum in mechanicalproperties has been reported in different blend composi-tions [10,13]. These differences are due to the use of differ-ent PE and EVA grades (MFI values and vinyl acetatecontent of EVA) in different experiments.

Fig. 15 shows the results of elongation at break for dif-ferent blend compositions together with the same resultscalculated using mixing rule. The elongation at break fol-lows near the same trend as tensile strength, except in90/10 composition. This complication can be explained interms of the effect of co-crystallization on mechanicalproperties. With reference to the results of thermal proper-ties, co-crystallization can widely occur in 90/10 blendwith respect to EVA content. Although the co-crystalliza-tion can increase the interlocking between phases andtherefore increase the interfacial adhesion between phasesin the solid state, which results in an increase in tensilestrength and elastic modulus, it reduces the mobility ofthe chains in particular at the blend interface and thereforereduces the elongation at break in tensile test.

4. Conclusion

Rheology, morphology and thermo-mechanical prop-erties of PE/EVA blends were studied. From the resultsof flow behavior and melt linear viscoelastic propertiesof the blends, it was found that PE- rich blends had agood compatibility compared to EVA-rich blends, whichin turn led to strong interfacial interaction betweenphases and therefore to the formation of a finer dis-persed phase consisting of narrow size distribution forPE-rich blends. These results were justified by estimationof the interfacial tension values for PE-rich and EVA-richblends using Palierne model. It was also found thatalthough the interfacial interaction in the melt state havean influential effect on the mechanical properties of theblends, the mechanical behavior of the semicrystalline

1842 M. Faker et al. / European Polymer Journal 44 (2008) 1834–1842

polymer blends such as PE/EVA blends can also be af-fected by the crystallization process. From the resultsof thermal properties it was concluded that the blendingof PE and EVA decreases the PE phase melting tempera-ture and increases the EVA phase melting temperature.These results were explained in terms of the dilution ef-fect of EVA chains for PE phase and nucleation effect ofPE chains and PE crystallites for EVA phase. It was dem-onstrated that the rheological behavior and viscoelasticproperties have a reliable sensitivity for evaluating theinterfacial interaction between phases in the blends. So,the information obtained from these studies in conjunc-tion with the behavior of the blend components duringthe solidification process can be used for prediction ofthe morphology and therefore mechanical properties ofthe blends.

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