Introduction

Polymer blending is a convenient technique for improving mechanical properties including impact resistance, abrasion resistance, and fracture behavior, as well as other properties such as easy printability and dimensional stability of polymeric materials. Polymer blends have a wide range of applications, and their properties are impacted by a variety of factors including the properties of individual components, the interfacial tension between components, and the morphology of the final material. The viscoelasticity, morphology, and processing properties of polymer blends are closely related to the rheological properties, which are of fundamental importance for industrial applications and also scientific studies.

In recent years, for the toughening of thermoplastics, scientific interest was tended toward blends containing thermoplastic elastomers (TPEs) than conventional vulcanized elastomer-based ones due to the easy processability and recyclability. Thermoplastic polyurethane, styrene block copolymers, polyolefinic TPEs, thermoplastic poly (ester–ether) elastomers and thermoplastic polyether-block-polyamide elastomers are commercially available polymers. TPEs can be used in the production of shoe soles, hoses, tubes, belts, housewares, sealing rings, and coatings. The olefin block copolymers (OBCs) are relatively new type of thermoplastic elastomers, and they were developed by Dow Chemical Co. via the chain shuttling polymerization [1]. OBC consists of crystallizable ethylene/octene blocks with very low octene content alternating with amorphous ethylene/octene blocks with high octene content [2]. OBCs have low density, higher crystallization and melting temperature, better elastic recovery, compression set, and abrasion resistance than almost same-density random copolymers having the same kind of olefin comonomer [2, 3]. These superior properties lead to many potential applications in the areas of elastic films, soft injection-molded articles, and profiles. Also, OBCs are used as an effective toughening agent for isotactic polypropylene, polypropylene random copolymer, polyamide 6, poly(lactic acid), and polyethylene [4,5,6,7,8,9]. According to the reported studies, OBC is an effective impact modifier for polyethylene, polypropylene homopolymer, and polypropylene random copolymer [4, 6, 7]. OBC is shown good compatibility with polyolefins due to the similar chain architecture. Furthermore, with the object of preparing shape memory materials and improving the viscoelastic properties of polymers, OBC was blended with polycaprolactone, polycaprolactone-poly(propylene carbonate), thermoplastic polyurethane–polycaprolactone, ethylene vinyl acetate, methyl vinyl silicone rubber and silicone rubber [10,11,12,13,14,15,16]. It was declared that OBC-based blends show an outstanding shape memory performance with high values of shape fixing and recovery.

EVA copolymers are random linear copolymers produced by copolymerization of ethylene and vinyl acetate. Commercial applications of EVAs vary depending on the vinyl acetate (VA) content of the copolymers. EVAs have been blended with different elastomers to improve their poor mechanical properties such as creep, tear, and abrasion resistance. In this study, OBC, a thermoplastic elastomer with a similar molecular structure, was selected for blending to improve the performance of EVA products to be subjected to stress. To the best of our knowledge, no data on the solid-state viscoelastic properties of EVA (consisting of 18% vinyl acetate) and OBC blends have been published so far. Rheological experiments were employed to understand the compositional dependence of the miscibility of polymer blends. Additionally, scanning electron microscopy (SEM) observation was used to elucidate the phase morphology of EVA/OBC blends.

Experimental

Materials

EVA (Primeva® 1820F; vinyl acetate content = 18 wt%, density = 0.937 g/cm3, MFI at 190 °C and 2.16 kg = 2.0 g/10 min) was provided from REPSOLYPF Company, while OBC (Infuse™ 9077; density = 0.869 g/cm3, MFI at 190 °C and 2.16 kg = 0.5 g/10 min) was supplied by Dow Chemical Company. The weight percent of hard block and soft block was calculated 16 wt% and 84 wt%, respectively [2, 17].

Blend preparation

All polymers were dried in a vacuum oven overnight at 50 °C before melt processing. Polymers were manually premixed, and the mixture was melt blended in an internal mixer (RTX-M40 melt mixer, Kokbir, Turkey) at a temperature of 150 °C with a screw speed of 50 rpm for 10 min. The compositions of the samples are listed in Table 1.

Table 1 Compositions of the samples
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Characterization

Morphological features of blend films were characterized by a field-emission scanning electron microscope (FE-SEM, FEI Quanta FEG 450) operated at 10 kV. Samples were cryo-fractured in liquid nitrogen and metallized with a thin gold layer. The particle size of the dispersed phase was measured by ImageJ 1.44p software. The number (Dn), mass (Dw) and volume (Dv) average of droplet diameter, the particle polydispersity (PD), and distance between particles (ID) of the dispersed OBC phase in the EVA matrix are calculated by Eqs. (1)–(5), respectively [18]:

$$D_{{\text{n}}} = \frac{{\sum n_{i} D_{i} }}{{\sum n_{i} }}$$
(1)
$$D_{w} = \frac{{\sum n_{i} D_{i}^{2} }}{{\sum n_{i} D_{i} }}$$
(2)
$$D_{{\text{v}}} = \frac{{\sum n_{i} D_{i}^{4} }}{{\sum n_{i} D_{i}^{3} }}$$
(3)
$${\text{PD}} = \frac{{D_{{\text{v}}} }}{{D_{{\text{n}}} }}$$
(4)
$${\text{ID}} = D_{w } \left[ {\left( {\frac{\pi }{6*\varphi }} \right)^{\frac{1}{3}} - 1} \right]$$
(5)

where ni is the number of the dispersed domains with diameter Di measured from SEM images of at least 150 droplets, \(\varphi\) is the volumetric fraction of the dispersed phase.

Rheological behaviors of polymers and blend samples were characterized by performing different test procedures in the melt state in a rotational rheometer, AR-G2 (TA Instruments). Steady-state shear flow behaviors were measured in the shear rate range of 0.1–100 s−1 at 150 °C. Linear viscoelastic (LVE) regions of samples were determined by strain sweep tests, which were performed from an initial strain value of 0.1% to a final strain value of 100% with a frequency of 1 Hz at 150 °C. Then, frequency sweep tests were carried out in a frequency range of 0.1–100 Hz with a strain value (1%) in LVE region at 150 °C. Viscoelastic moduli (G′ and G′′), dynamic (or complex) viscosity (η*) values were recorded as a function of frequency. In each rheology test, a new sample was loaded to the rheometer and equilibrated to avoid possible effects of thermomechanical conditions and deformation history on the rheological response of the sample.

Solid-state viscoelastic properties of samples were measured with creep test conducted in a dynamic mechanical analyzer (DMA, SII Nanotechnology, ExStar 6100). Creep tests were performed by applying an instantaneous stress of 1 MPa at 25 ℃ for 15 min in uniaxial tensile test mode. Then applied stress was removed from the specimen, and creep recovery was followed for 15 min. Findley and Burger's models were fitted with Nonlinear Curve Fit analysis at OriginPro 8.1 software.

Results and discussion

Morphology

Figure 1a–d shows the micrographs of the B20 and B40 blend samples with different magnifications. The B20 blend displayed an apparent droplet-matrix morphology with a narrow distribution of OBC particle size corresponding to Dn = 1.05 μm, Dw = 1.24 μm, Dv = 1.60 μm and polydispersity of 1.5 (Fig. 1a and b). On the other hand, with the increase in the concentration of OBC, the droplets obviously were expanded due to the coalescence of dispersed phase in B40 sample. It seemed that the number average droplet (Dn) size changed from 1.05 to 1.17 μm, while the Dv changed from 1.6 to 2.6 μm, and the polydispersity (Dv/Dn) of OBC particles was 2.22. The interparticle distance of OBC in the EVA matrix decreased from 0.44 to 0.122 μm as the amount of OBC increased from 20 to 40 wt%. It can be seen from the figures that the morphologies changed from uniform droplets to partially continuous droplets with an increasing OBC content in the EVA matrix. However, no significant phase separation was observed in both blend samples indicating sufficient compatibility and strong interaction between the EVA and OBC due to their olefinic structure.

Fig. 1
figure 1

SEM micrographs of EVA/OBC blends with different magnifications: a and b B20 blend, c and d B40 blend

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Rheology

The rheological characterization can provide a link between the processing properties and structural characteristics of the blends. OBC and EVA are copolymers with different architectures. The block copolymers such as OBC have relatively narrow molecular weight distribution compared to EVAs, which have relatively broader molecular weight distribution due to the random structure [1, 2, 19, 20]. The morphology and the other physical properties of blends are related to the melt viscosities of each component.

Figure 2 depicts the flow curve of OBC, EVA and EVA/OBC blends as a function of shear rate at 150 °C. OBC showed Newtonian plateau at low shear rates (shear rates lower than 1 s−1) and a shear thinning behavior at high shear rates. EVA and all blend compositions have a narrower transition Newtonian to non-Newtonian region and exhibited shear thinning behavior at lower shear rates than OBC. The shear viscosity of the EVA/OBC blends increased with the increase in the OBC copolymer content, but the increase in the amount of OBC did not affect the extent of the Newtonian region of the blends. In addition, the flow properties of samples were modeled by the Williamson [21] model to a high degree of accuracy, as displayed in Fig. 2, and the model parameters are listed in Table 2. Williamson model is defined as:

$$\eta = \frac{{\eta_{0} }}{{1 + \left( {{\rm K}\dot{\gamma }} \right)^{m} }}$$
(6)

where η0 is the zero shear rate viscosity (Pa s), \(\dot{\gamma }\) is the shear rate (s−1), K is the consistency, and m is the shear-thinning index, where m < 1 indicates the shear-thinning behavior of polymers.

Fig. 2
figure 2

Steady shear viscosity as a function of shear rate for EVA, OBC and EVA/OBC blends

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Table 2 Williamson model parameters of samples
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OBC has relatively higher zero shear rate viscosity and higher critical shear rate (~ 2 s−1) than EVA copolymer. EVA exhibited shear-thinning flow behavior at relatively small shear rates, which indicated that EVA possessed relatively broader molecular weight distribution than OBC, as reported in previous results [1, 2, 19, 20]. The zero shear viscosity of blends increased gradually with OBC content into EVA matrix due to the higher viscosity of OBC, and the transition from Newtonian plateau to shear-thinning regime was shifted to lower frequencies for blend samples. The critical shear rate is defined as the point at which the break-up limit curve crosses the coalescence one [22]. As the amount of OBC content increased in the blend composition, the critical shear rate decreased with increasing coalescence of OBC droplets. The critical shear rates of blends decreased gradually (EVA; 0.83 s−1, B10; 0.51 s−1, B20; 0.46 s−1, B30; 0.42 s−1 B40; 0.38 s−1, B50; 0.36 s−1). This phenomenon can also be explained by Utracki's studies that, during blending, the viscosity of the system increased due to the formation of the entanglement of the minor phase in the major phase, and disentanglement and slippage existed at the interface that led to a deviation from the Newtonian region by increasing the shear rate [23,24,25].

Figure 3 illustrates the storage modulus (G′) and the loss modulus (G′′) of OBC, EVA, and EVA/OBC blends. The elastic and loss modulus of the blends laid between the OBC and EVA. At all frequency ranges, there was an increase in the G′ of the EVA/OBC blends with the increase of OBC content.

Fig. 3
figure 3

a Storage modulus (G′) and b loss modulus (G′′) versus angular frequency of OBC, EVA and EVA/OBC blends at 150 °C

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In phase-separated polymer blends, the dispersed droplet phase leads to a shoulder in the frequency curve versus storage modulus at the low-frequency range. Shoulder formation in the curve is due to the shape relaxation of the dispersed phase droplets driven by the interfacial tension [26, 27]. The presence of the shoulder in the low-frequency region has been reported in polystyrene/poly(vinyl methyl ether), poly(styrene-co-acrylonitrile)/poly(methylmethacrylate), and polypropylene/ethylene-propylene-diene terpolymer blends due to the occurrence of phase separation [27,28,29]. Figure 3b shows a trend of loss modulus that is similar to the storage modulus counterpart. Furthermore, it was observed that loss modulus values of OBC and EVA were higher than their storage modulus, indicating that viscous behavior was more pronounced than the elastic behavior at low frequencies. As the frequency increases (ωc > 10 rad/s), the storage modulus appeared to be higher than the loss modulus due to the elastomeric nature of both copolymers.

Figure 4 illustrates the variation of complex viscosity (η*) as a function of angular frequency (ω) for the samples. Additionally, complex viscosity as a function of the OBC content obtained through the experimental data and the calculated data employing the logarithmic additivity rule at an angular frequency of 0.1 s−1 is presented in Fig. 4. The log-additivity rule is expressed as [23]:

$$\log \eta^{*} \left( \omega \right) = \phi_{1} \log \left( {\eta^{*} \left( \omega \right)} \right)_{1} + \left( {1 - \phi_{1} } \right)\log \left( {\eta^{*} \left( \omega \right)} \right)_{2}$$
(7)
Fig. 4
figure 4

Complex viscosity of OBC, EVA and EVA/OBC blends and calculated \(\left( {\eta_{0.1}^{*} } \right)\) using log-additivity rule at angular frequency of 0.1 s−1

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It was clearly seen that the complex viscosity of the blend samples was slightly higher than that of EVA throughout the entire experimental frequency range. It could clearly be seen that EVA/OBC blends displayed a positive deviation behavior (PDB) in all compositions. PDB could be observed due to the presence of strong interfacial interaction between phases in blends [18, 23, 30, 31].

The melt compatibility of the polymer blends can be evaluated with the Han plots [32]. Han plots show a linear correlation in the plot of log G′ versus log G′′. The previous studies have shown that Han plot was independent of the temperature, and the slope of Han plot in the terminal zone was 2 for homopolymers and miscible blends in the molten state [32,33,34,35]. On the other hand, heterogeneous polymeric systems, such as mesophase and block copolymers, have slopes of less than 2. Lamnawar et al. used a Han plot to explore the miscibility of LLDPE/COC (cyclic olefin copolymer) blends [36]. They reported that the slope of Han plots had close values in pure polymers and blends, indicating the miscibility/compatibility of the blends of LLDPE/COC. The Han diagrams of OBC, EVA, and the blends with various compositions are presented in Fig. 5a.

Fig. 5
figure 5

a Han and b Cole–Cole plots of the samples

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The slope values of terminal zone were 1.27, 1.30, 1.26, 1.27, 1.27, 1.27, and 1.38 for OBC, B10, B20, B30, B40, B50, and EVA, respectively. The close slope values of the samples reflect the phase compatibility in the molten state [35,36,37].

Another method for interpreting the morphology of the blends is Cole–Cole plots, which consist of η′′\(\left( {{\raise0.7ex\hbox{${G^{\prime}}$} \!\mathord{\left/ {\vphantom {{G^{\prime}} \omega }}\right.\kern-0pt} \!\lower0.7ex\hbox{$\omega $}}} \right)\) versus η′ \(\left( {{\raise0.7ex\hbox{${G^{\prime\prime}}$} \!\mathord{\left/ {\vphantom {{G^{\prime\prime}} \omega }}\right.\kern-0pt} \!\lower0.7ex\hbox{$\omega $}}} \right)\). In Cole–Cole plots, it is assumed that miscible polymer blends show a single arc, while in multiphase blends a tail or even two circular arcs are observed [36, 38, 39]. From the findings, the EVA/OBC blends as well as OBC and EVA only present one circular arc on their Cole–Cole plots, indicating the miscibility of EVA and OBC phases in the melt state and the results consistent with the Han plots (Fig. 5b). In addition, as seen from the diagram, the radii of the arcs have increased with the increase of the OBC loading due to the high degree of entanglement of OBC [40, 41].

Several models, namely Palierne [42], Gramespacher and Meissner [43], Lee and Park [44] and Bousmina models [45], have been proposed to correlate the morphology and rheological properties of polymer blends. In this study, Palierne and Bousmina models were employed to predict the linear viscoelastic behavior of polymer blends and calculate the interfacial tension between EVA and OBC. Palierne and Bousmina emulsion models provide a constitutive equation for the complex modulus of a blend, viscoelastic property of both polymers, as a function of volume fraction of minor phase, volume average radius of dispersed phase and interfacial tension [42, 45]. The simplified Palierne model is expressed as:

$$G_{{\text{b}}}^{*} \left( \omega \right) = G_{{\text{m}}}^{*} \left( \omega \right)\frac{{1 + 3\phi_{{\text{d}}} H\left( \omega \right)}}{{1 - 2\phi_{{\text{d}}} H\left( \omega \right)}}$$
(8)

where

$$H\left( \omega \right) = \frac{{4\left( {\frac{\alpha }{R}} \right)\left[ {2G_{{\text{m}}}^{*} \left( \omega \right) + 5G_{{\text{d}}}^{*} \left( \omega \right)} \right] + \left[ {G_{{\text{d}}}^{*} \left( \omega \right) - G_{{\text{m}}}^{*} \left( \omega \right)} \right]\left[ {16G_{{\text{m}}}^{*} \left( \omega \right) + 19G_{{\text{d}}}^{*} \left( \omega \right)} \right]}}{{40\left( {\frac{\alpha }{R}} \right)\left[ {G_{{\text{m}}}^{*} \left( \omega \right) + G_{{\text{d}}}^{*} \left( \omega \right)} \right] + \left[ {2G_{{\text{d}}}^{*} \left( \omega \right) + 3G_{{\text{m}}}^{*} \left( \omega \right)} \right]\left[ {16G_{{\text{m}}}^{*} \left( \omega \right) + 19G_{{\text{d}}}^{*} \left( \omega \right)} \right]}}$$
(9)

The simplified Palierne’s model can be used assuming a narrow size distribution (Dv/Dn < 2.3).

Bousmina’s model in the following equation for the complex modulus of blend:

$$G_{{\text{b}}}^{*} \left( \omega \right) = G_{{\text{m}}}^{*} \left( \omega \right)\frac{{2\left[ {G_{{\text{d}}}^{*} \left( \omega \right) + \left( {\frac{\alpha }{R}} \right)} \right] + 3G_{{\text{m}}}^{*} \left( \omega \right) + 3\phi_{{\text{d}}} \left[ {G_{{{\text{d}} }}^{*} \left( \omega \right) + \left( {\frac{\alpha }{R}} \right) - G_{{\text{m}}}^{*} \left( \omega \right)} \right]}}{{2\left[ {G_{{\text{d}}}^{*} \left( \omega \right) + \left( {\frac{\alpha }{R}} \right)} \right] + 3G_{{\text{m}}}^{*} \left( \omega \right) - 2\phi_{{\text{d}}} \left[ {G_{{\text{d}}}^{*} \left( \omega \right) + \left( {\frac{\alpha }{R}} \right) - G_{{\text{m}}}^{*} \left( \omega \right)} \right]}}$$
(10)

where \(G_{{\text{d}}}^{*}\), \(G_{{\text{m}}}^{*}\) and \(G_{{\text{b}}}^{*}\) are disperse, matrix and blend complex shear modulus, respectively. Parameter α is the interfacial tension between the components of the blend, \(\phi_{d}\) is the volume fraction of dispersed phase and R is the radius of the dispersed phase.

The storage modulus (G′) data for the blends of B20 and B40 were fitted using Palierne and Bousmina models, and the fitting curves were illustrated by red lines in Fig. 6a and b, respectively. It was clearly seen that the prediction accuracies of both models for B20 blend were higher than those of B40 blend. The deviation of the Palierne and Bousmina model values from the experimental data at high dispersed phase content were reported in COC/EVA, PMMA/PS, and PP/LDPE blends [31, 46,47,48]. The deviation of B40 blend could be attributed to the higher polydispersity (PD = 2.22) of the dispersed phase [46].

Fig. 6
figure 6

a Palierne model and b Bousmina model estimations of (G′) for B20 and B40 blends

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Based on the Palierne model, the calculated interfacial tensions for B20 and B40 blends were 0.0372 mN/m and 0.718 mN/m, respectively. By using the Bousmina model, the α values were found to be 0.0198 mN/m and 1.134 mN/m, respectively, for blends containing 20 and 40 wt% of OBC. These low interfacial tension values in EVA/OBC blends could be attributed to the existence of ethylene units in EVA and OBC and as a result a strong intermolecular interaction in EVA/OBC blends.

Creep and recovery of blends

Creep–recovery test is an analytical method to understand the material behavior and evaluates the service life of a product. Figure 7a and b depicts the experimental creep and creep-recovery strain curves as a function of time for OBC (Fig. 7a) and EVA/OBC blend samples (Fig. 7b) when a constant stress of 1 MPa was applied. It was clear from the plot (Fig. 7a) that an instantaneous deformation with relatively high strain rate occurs as a consequence of application of the constant stress due to the elastomeric nature of OBC. OBC displayed high instantaneous creep strain (approx. 160% at the end of 15 min.) and considerable elastic recovery (91%) where EVA showed only 4% of the initial creep strain. Compared to the previous results, it can be said that the VA content of EVA was inversely proportional to the creep resistance [15]. The recovered strain of EVA with 18 wt% of VA (86%) was lower than EVA with 12 wt% VA (92%) and higher than EVA with 28 wt% VA (84%) at the end of recovery time (15 min). In all blend samples, the creep strain values were increased continually with the increase of OBC content in compositions due to the elastomeric characteristics of OBC. In comparison with EVA, the creep strains of EVA/OBC blends increased by 11%, 51%, 66%, 89% and 168%, respectively. In the recovery region, the elastic deformation of all blends disappears instantly, and the elastic recovery of the samples (86–88%) was found approximately the same as EVA.

Fig. 7
figure 7

Experimental creep and recovery behavior of a OBC, b EVA and EVA/OBC blend samples

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In order to better understand the influence of OBC on the creep and recovery behaviors of EVA blends, two viscoelastic constitutive models, Burger’s and Findley’s power law were applied. Burger's four-element model is a series combination of the Maxwell and Kelvin–Voigt models. The total creep strain is divided into three separate parts: the instantaneous elastic deformation (Maxwell spring, εM), viscoelastic deformation (Kelvin unit, εK), and viscous deformation (Maxwell dash-pot, ε∞). The total strain as a function of time ε is given by the following equations:

$$\varepsilon \left( t \right) = \varepsilon_{{\text{M}}} + \varepsilon_{{\text{K}}} + \varepsilon_{\infty }$$
(11)
$$\varepsilon \left( t \right) = \frac{\sigma }{{E_{{\text{M}}} }} + \frac{\sigma }{{E_{{\text{K}}} }}\left[ {1 - exp\left( { - \frac{{E_{{\text{K}}} t}}{{\eta_{{\text{K}}} }}} \right)} \right] + \frac{\sigma t}{{\eta_{{\text{M}}} }}$$
(12)

where ε(t) is the creep strain, σ is the applied stress, t is the time, EM and EK are the elastic moduli of Maxwell and Kelvin springs, respectively, ηM and ηK are the viscosities of Maxwell and Kelvin dashpots, respectively [49, 50]. Retardation time (\(\tau_{0} )\) is for the Kelvin element to produce 63.21% of its total deformation and creep rate (\(\dot{\varepsilon })\) can be found using the following equations:

$$\tau_{0} = \frac{{\eta_{{\text{K}}} }}{{E_{{\text{K}}} }}$$
(13)
$$\dot{\varepsilon } = \frac{\sigma }{{\eta_{{\text{M}}} }}$$
(14)

Another analytical model, Findley’s power law model was also applied to understand structure–property relationship of the blends.

$$\varepsilon \left( t \right) = \varepsilon_{0} + At^{n}$$
(15)

where ε(t) is the creep strain, t is the time, ε0 is the time-independent strain, A is the amplitude of transient creep strain, a time-dependent term; and n is stress-independent time exponent, with values usually less than 1 [51].

The experimental data and model fittings are presented in Fig. 8, and the parameters for both models are given in Table 3. The implementation of both models provides good fits to the experimental data. The modulus of Maxwell spring (EM) represents instantaneous creep strain, which could be immediately recovered on the removal of stress. As seen in Table 3, OBC exhibited typical elastomeric behavior with low modulus values corresponding to high creep strains with very low irrecoverable creep (\(\eta_{{\text{M}}}\)). The time-dependent EK and \(\eta_{{\text{K}}}\) in the Kelvin unit can be associated with the stiffness and viscous or orientated flow of amorphous polymer chains in short term, respectively [50]. The data indicate that OBC chains promptly oriented in a short-term period once the stress loaded. EVA displayed relatively higher elastic modulus values (EM, EK) than OBC. For blends, the values of modulus and irrecoverable creep strain decreased with an increasing OBC content, these results indicated that decrease in the stiffness in blends and also an improvement in the elastic recovery of blends. The creep rate is a characteristic parameter that determines the dimensional stability of materials. In all blend compositions, these values tend to increase with the addition of OBC due to higher elasticity compared to EVA.

Fig. 8
figure 8

Creep curves of samples a OBC, b and c EVA and EVA/OBC blends (symbols represent experimental data and lines represent the model fits)

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Table 3 Burger and Findley model parameters of the samples
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The fitted results of Findley’s power law model of creep curves are also summarized in Table 3. The time-independent strain ε0 and time-dependent term A showed significant increments with the incorporation of the elastomeric phase. The exponent “n” increased with the increasing OBC content, which suggests that the blends would spend less time to achieve a certain creep level with the applied stress.

Conclusions

In this study, the effect of OBC content on the morphological and solid-state creep properties as well as the rheological behavior of EVA/OBC blends was investigated. Morphology studies of blends revealed that OBC dispersed throughout the EVA continuous matrix as droplets and the domain size became larger with increasing content of OBC; however, no phase separation was observed. From the rheological measurements, it was observed that the complex viscosity of all blends illustrated positive deviation from the log-additivity rule, which pointed out the strong interaction between EVA and OBC. Cole–Cole plots and Han plots indicated the miscibility between EVA and OBC phases; these results corroborated the morphology analysis. The Bousmina and Palierne predictions were used to obtain the interfacial tension between EVA and OBC, which was found to be 0.0198–0.0372 mN/m for 80/20 EVA/OBC blends and 1.1344 and 0.718 mN/m for 60/40 EVA/OBC blends, respectively. The solid-state creep-recovery test showed that OBC affected the creep strains of the blends without altering elastic recovery.