Melt rheology and morphology of physically compatibilized natural rubber–polystyrene blends by the addition of natural rubber-g-polystyrene

Blends of natural rubber (NR) and polystyrene (PS) were prepared by melt mixing in a Brabender plasticorder and by solution casting using chloroform as the casting solvent. Earlier studies have indicated that these blends are incompatible and immiscible, and their compatibility can be improved by the addition of a graft copolymer of NR and PS (NR-g-PS). The rheological behavior of these blends has been carried out in the presence and absence of the compatibilizer using a capillary rheometer and a melt flow indexer. The effects of blend ratio, processing techniques (melt mixing versus solution casting), shear stress, and temperature on the rheological behavior have been studied in detail. Both in the presence and absence of the copolymer, the blends showed a decrease in viscosity with an increase of shear stress, indicating pseudoplastic nature. Solution-cast blends showed a higher viscosity as compared to melt-mixed blends. The viscosity versus composition curve of both melt-mixed and solution-cast blends showed negative deviation from the additivity at a higher shear rate region. This is associated with the interlayer slip between the highly incompatible NR and PS phases. The effects of graft copolymer loading and temperature on solution-cast blends were studied, and it was found that as the copolymer loading increases, the shear viscosity increases. This is due to the high interfacial interaction between the two components in the presence of the copolymer. The copolymer, in fact, locates at the interface and makes the interface more broad. However, at higher loading of the copolymer, the viscosity of the blends decreases. This may be associated with the formation of micelles, which have a plasticizing action on the viscosity of the blends. Melt elasticity parameters like principal normal stress difference, recoverable elastic shear strain, and die swell were evaluated. Master curves have been generated using modified viscosity and shear rate functions that contain the melt flow index as a parameter. The extrudate morphology of the blends was studied using a scanning electron microscope. Addition of the copolymer reduces the domain size of the dispersed phase, followed by a leveling off at a higher concentration. The leveling off is an indication of interfacial saturation. The interparticle distance also decreased followed by a leveling off at a higher loading of the copolymer. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2673–2690, 1998     

Melt Rheology and Morphology of Nitrile Rubber and Ethylene-Vinyl Acetate Copolymer Blends

The melt Theological behavior of nitrile rubber (NBR)/ethylene-vinyl acetate (EVA) copolymer blends was studied with special reference to the effect of the blend ratio, cross-linking systems, and shear rate using a capillary rheometer. At a given shear stress at 90°C, the viscosities of the blends vary slightly with composition. The effect of cross-linking systems [viz., sulfur (S), peroxide (DCP) and mixed (S+DCP) systems] on the viscosity of NBR/EVA blends is negligible. The melt viscosity of the blends decreases with increasing shear rate, showing pseudoplastic behavior. The flow behavior index values also support the pseudoplastic nature of these blends. Various theoretical models were used to predict the melt viscosity of the blends. Parameters such as die swell, principal normal stress difference, recoverable shear strain, and shear modulus were calculated to characterize the melt elasticity of these blends. The melt elasticity of the system was increased by the addition of NBR to EVA. The extrudate deformation at different shear rates was also studied. It was observed that as the shear rate increases, the extrudate surface exhibits a higher degree of deformation. The morphology of the extrudates of the blends at different shear rates has been examined by a scanning electron microscope. The morphology was found to be dependent on the blend ratio and shear rate.     

Natural rubber/poly(ethylene‐co‐vinyl acetate)‐blend‐based nanocomposites

Natural rubber (NR)/poly(ethylene‐co‐vinyl acetate) (EVA) blend–clay nanocomposites were prepared and characterized. The blend nanocomposites were prepared through the melt mixing of NR/EVA in a ratio of 40/60 with various amounts of organoclay with an internal mixer followed by compression molding. X‐ray diffraction patterns revealed that the nanocomposites formed were intercalated. The formation of the intercalated nanocomposites was also indicated by transmission electron microscopy. Scanning electron microscopy, used to study the fractured surface morphology, showed that the distribution of the organoclay in the polymer matrix was homogeneous. The tensile modulus of the nanocomposites increased with an increase in the organoclay content. However, an increase in the organoclay content up to 5 phr did not affect the tensile strength, but the organoclay reduced this property when it was increased further. This study also indicated that a low silicate content dispersed in the blend matrix was capable of increasing the storage modulus of the material. The addition of the organoclay also increased the decomposition temperature of the NR/EVA blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 353–362, 2006     

Use of EVA-containing mercapto groups in natural rubber–EVA blends. I. Mechanical,thermal, and morphological properties

The effect of ethylene–vinyl acetate (EVA) modified with mercaptoacetic acid on mechanical, thermal, and morphological properties of blends of natural rubber (NR) and EVA copolymers has been investigated. The introduction of EVASH promotes a crosslinking of natural rubber phase as indicated by extraction experiments and microscopy analysis. This crosslinking may be attributed to bonding between sulfhydryl groups along the EVASH backbone and double bonds in rubber phase and may be responsible for the hardness improvement of most of the studied blends. Better results on hardness and ultimate tensile strength with EVASH addition were achieved for NR–EVA (60 : 40) ratio, probably due to cocontinuous morphology of this composition. The influence of EVASH on crystallinity degree of NR–EVA blends was also studied by differential scanning calorimetry. The morphology of the blends was studied through scanning electronic microscopy. © 1995 John Wiley & Sons, Inc.     

Ethylene vinyl acetate as compatibilizer on cure characteristics and mechanical properties of (natural rubber)/(Recycled acrylonitrile‐butadiene rubber) blends

Ethylene vinyl acetate (EVA) has been used as a compatibilizer for (natural rubber)/(recycled acrylonitrile‐butadiene rubber) (NR/NBRr) blends, vulcanized by sulfur. EVA offers excellent heat, ozone, and weather resistance, whereas the vinyl acetate groups provide oil resistance to the blend. It exhibits good tear resistance and may be crosslinked. However, EVA exhibits poor low‐temperature flexibility. NBR gloves have excellent resistance to punctures, tears, and many types of chemicals, while NR has good physical and mechanical properties. NR/NBRr blends were prepared with various compositions with the EVA content fixed. Tensile properties, hardness, and swelling behavior tests were performed to determine the compatibility of NR/NBRr blends in the presence of EVA. Results indicated that incorporation of EVA into NR/NBRr blends improved tensile strength, modulus, and elongation at break compared with NR/NBRr blends without EVA. The improvement in hardness and reduction in resilience on compatibilization are due to an increase in crosslink density, which gives NR/NBRr blends better swelling resistance. Scanning electron microscopy of the fracture surfaces indicates that, with the addition of EVA in NR/NBRr blends, better adhesion between NR and NBRr was obtained, thus improving the compatibility of NR/NBRr blends. J. VINYL ADDIT. TECHNOL., 23:135–141, 2017. © 2015 Society of Plastics Engineers     

Studies on miscibility of blends of poly (ethylene acrylic acid) and ethylene‐co‐vinyl acetate by melt rheology

Rheological behavior of blends of poly (ethylene‐acrylic acid) (EAA) and ethylene vinyl acetate (EVA) copolymer have been carried out at various temperatures, namely, 100, 110, and 120°C, and different shear rates from 61.33 to 613.30 s^?1 using a Monsanto Processability Tester. The melt viscosity of the blends shows synergism during processing. The activation energy of the blends is in the range 20.7–44.6 kJ/mol. Highest activation energy was observed for the blends containing 40–60% of EVA by weight. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1947–1954, 2005     

The use of EVA-containing mercapto groups in natural rubber-EVA blends. II. The effect of curing system on mechanical and thermal properties of the blends

Natural rubber (NR)-poly(ethylene-co-vinyl acetate) (EVA) blends have been studied by incorporation of mercapto-modified EVA (EVASH) combined with dicumyl peroxide (DCP) as a curing agent. The mechanical, thermal, and morphological properties of NR-EVA blends as functions of blend composition and compatibilizer and/or curative additions were investigated. An EVASH-DCP combined system leads to the greatest improvement in tensile strength when EVA is dispersed within the NR matrix. Higher performance on Shore A hardness was also achieved with this combined system. For blends characterized by NR domains dispersed in the EVA matrix, the efficiency of pure DCP in improving the tensile strength is higher. Morphological observations and selective extraction experiments indicate the cross-linking of NR phase in both systems. A cross-linking of the EVA phase is also suggested by DCP or an EVASH-DCP combined system, based on the decreasing degree of crystallinity of this phase. © 1996 John Wiley & Sons, Inc.     

Melt-rheological properties of PP/EVA blend

This paper describes a study of melt-rheological properties of the binary blend of isotactic polypropylene (PP) and ethylene–vinyl acetate copolymer (EVA) at varying blending ratios (from 0 to 40 wt % EVA content) and using three samples of EVA containing different vinyl acetate contents (VA %), viz. 9, 12, and 19%. Measurements made on a capillary rheometer at three different temperatures (210, 220, and 230°C) in a shear stress range of 10⁴–10⁶ Pa (shear rate 10¹–10⁴ s^?1) are presented and discussed for the effects of blend composition and shear stress on the flow curves, melt viscosity and melt elasticity. Morphology of the blend studied through scanning electron microscopy revealed distinct differences in size and number density of dispersed EVA droplets, which are discussed in terms of the variation of average size and number density of the dispersed EVA droplets as a function of blend composition and shear stress. Melt-rheological properties and morphology of dispersion are correlated and found quite consistent.     

Three-dimensional phase morphologies in HDPE/EVA blends obtained via dynamic injection packing molding

The formation of phase morphology of injection molded HDPE/EVA blends, under the effect of shear stress, has been investigated in detail. The shear stress was induced by dynamic packing injection molding, by which a specimen is forced to move repeatedly in the model by two pistons that move reversibly with the same frequency during cooling. Two kinds of EVA with VA content 16 wt% (16EVA) and 33 wt% (33EVA) were used to investigate the effect of interfacial tension. The phase morphology was viewed both parallel and perpendicular to the shear flow direction, so one can get an overall three-dimensional phase morphology. Low shear stress provided by the pistons has a substantial effect on the phase morphology along the flow direction but is insignificant in the direction perpendicular to the flow direction. Generally, a much elongated and layer-like structure is formed along the flow direction, and spherical droplet-like morphology is formed perpendicular to the flow direction, and the degree of deformation of rubber particles also depends upon their size and elasticity as well as on the interfacial properties between matrix and dispersed phase. For static samples of HDPE/16EVA blends (without shearing), only droplet morphology is formed as 16EVA content increases from10 to 40 wt%. However, under the effect of shear stress (dynamic samples), both droplet and cylinder morphologies can be formed depending on the volume ratio. For static samples of HDPE/33EVA blends, not only droplet, but also cylinder and co-continuous morphology (perpendicular to flow direction) can be formed depending on the volume ratio. For dynamic samples of HDPE/33EVA blends, droplet, cylinder and co-continuous network (co-continuous in both parallel and perpendicular to flow direction) can be formed under the effect of shear stress. The formation of phase morphology is discussed based on interfacial interaction, viscosity ratio, shear stress, and phase inversion.     

Influence of the polarity of ethylene–vinyl acetate copolymers on the morphology and mechanical properties of their uncompatibilised blends with polystyrene

Rubber‐toughened polystyrene has been extensively studied and is a well‐established technology. However, the use of thermoplastic elastomers to toughen polystyrene (PS) is new and has the potential for further investigations. In the present study, three EVAs (ethylene–vinyl acetate copolymers) with identical melt flow indices (MFIs), of ～2.5 dgmin^?1, but different vinyl acetate (VA) contents, of 9.3 wt% (EVA760), 18.0 wt% (EVA460) and 28.0 wt% (EVA265), were melt blended with PS at 180 °C, and various ASTM test pieces were injection moulded at 200 °C. The polarity of the dispersed phase (ie EVA), has a significant effect on the mechanical properties of the blends. Both mechanical and rheological studies reveal that the uncompatibilised PS/EVA265 blends exhibit some degree of compatibility when the amount of EVA265 is lower than 30 wt%. These results indicate that EVA265 with the highest VA content is the most effective impact modifier for PS. The results clearly show that increasing the VA content in EVA increases the polarity of the dispersed phase, approaching that of the matrix (ie PS) and subsequently improving the compatibility between the two phases in terms of interfacial adhesion. © 2002 Society of Chemical Industry     

Flow Behavior of Polypropylene/Ethylene-Propylene Diene Terpolymer/Natural Rubber (PP/EPDM/NR) Blends by Torque Rheometer: The Effect of N,N-m-Phenylene Bismaleimide (HVA-2) Addition

Blends of polypropylene (PP)/ethylene-propylene diene terpolymer (EPDM)/natural rubber (NR) with different ratio were investigated using a Haake torque rheometer. The effect of N,N-m-phenylene bismaleimide (HVA-2) addition on the flow behavior of PP/EPDM/NR blends also was studied. The torque data was collected at different rotor speeds in the range of 30–60 rpm and different processing temperatures in the range of 170–190°C. The recorded data were interpreted in terms of apparent shear rate, apparent shear stress, and apparent viscosity. The shear stress–shear strain curve shows that all blends follow the power law where the pseudoplasticity behavior of melt viscosity increases with increasing NR content as well as addition of HVA-2. The apparent viscosity of the blends was found to increase with increasing NR content in the blend. The addition of HVA-2 increases the apparent viscosity due to the formation of cross-linking in rubber phase. However, blends with HVA-2 show lower flow activation energies than do similar blends without HVA-2. Scanning electron microscopy (SEM) shows good correlation with the flow properties of the blends.     

Influence of the molecular weight of ethylene vinyl acetate copolymers on the flow and mechanical properties of uncompatibilized polystyrene/ethylene–vinyl acetate copolymer blends

Rubber‐toughened polystyrene (PS) has been extensively studied and is a well‐established material. However, the use of thermoplastic elastomers to toughen PS is new and not well understood. In this study, three types of ethylene vinyl acetate (EVA) copolymers with the same vinyl acetate (VA) content (27.2–28.8 wt %) but with different melt flow indexes (MFI; g (10 min)⁻¹) of 365–440 (Elvax 210), 38.0–48.0 (Elvax 240) and 2.6–3.4 (Elvax 265) were used as impact modifiers for PS. The uncompatibilized blend systems at different compositions were prepared using a twin‐screw extruder and injection moulding to produce the required test pieces. The viscosity of the dispersed phase (EVA) has a significant effect on the mechanical properties of the blends. Rheological studies show that uncompatibilized PS/EVA265 blends exhibit some degree of compatibility when the amount of EVA265 added is below 30 wt %. These results indicate that EVA265 with the lowest melt flow index or highest molecular weight is the most effective impact modifier for PS. The mechanism for such behaviour is still unclear. © 2001 Society of Chemical Industry     

Melt rheology of HDPE/EVA blends: The effects of blend ratio,compatibilization, and dynamic vulcanization

The melt rheological behavior of high‐density polyethylene (HDPE)/ethylene vinyl acetate (EVA) blends has been examined with reference to the effect of blend ratio, shear stress, and temperature. The HDPE/EVA blends exhibit pseudoplastic behavior, and the observed rheological behavior of the blends was correlated with the extrudate morphology. The experimental values of the viscosity were compared with the theoretical models. The effect of maleic‐ and phenolic‐modified PE compatibilizers on the viscosity of H₇₀ blend was analyzed and found that compatibilization did not significantly increase the viscosity. The effect of dynamic vulcanization and temperature on the viscosity was also analyzed. The activation energy of the system decreased with increase in EVA content in the system. The phase continuity and phase inversion points of the blends were theoretically predicted and compared with the experimental values. The melt flow index (MFI) values of the blends were also determined and found that the MFI values decreased with increase in EVA content in the system. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Melt rheological properties of polypropylene–polyamide6 blends compatibilized with maleic anhydride‐grafted polypropylene

The melt rheological properties of binary uncompatibilized polypropylene–polyamide6 (PP–PA6) blends and ternary blends compatibilized with maleic anhydride‐grafted PP (PP–PP‐g‐MAH–PA6) were studied using a capillary rheometer. The experimental shear viscosities of blends were compared with those calculated from Utracki's relation. The deviation value δ between these two series of data was obtained. In binary PP–PA6 blends, when the compatibility between PP and PA6 was poor, the deformation recovery of dispersed PA6 particles played the dominant role during the capillary flow, the experimental values were smaller than those calculated, and δ was negative. The higher the dispersed phase content, the more deformed the droplets were and the lower the apparent shear viscosity. Also, the absolute value of δ increased with the dispersed phase composition. In ternary PP–PP‐g‐MAH–PA6 systems, when the compatibility between PP and PA6 was enhanced by PP‐g‐MAH, the elongation and break‐up of the dispersed particles played the dominant role, and the experimental values were higher than calculated. It was observed that the higher the dispersion of the PA6 phase, the higher the δ values of the ternary blends and the larger the positive deviation. Unlike uncompatibilized blends, under high shear stress with higher dispersed phase content, the PP‐g‐PA6 copolymer in compatibilized blends was pulled out from the interface and formed independent micelles in the matrix, which resulted in reduced total apparent shear viscosity. The δ value decreased with increasing shear stress. Copyright © 2006 Society of Chemical Industry     

Melt rheology and morphology of LLDPE/EVA blends: Effect of blend ratio,compatibilization, and dynamic crosslinking

The melt rheological properties of linear low‐density polyethylene (LLDPE)/ethylene vinyl acetate (EVA) blends were investigated with special reference to the effect of blend ratio, temperature, shear rate, compatibilization, and dynamic vulcanization. The melt viscosity of the blends determined with a capillary rheometer is found to decrease with an increase of shear rate, which is an indication of pseudoplastic behavior. The viscosity of the blend was found to be a nonadditive function of the viscosities of the component polymers. A negative deviation was observed because of the interlayer slip between the polar EVA and the nonpolar LLDPE phases. The melt viscosity of these blends decreases with the increased concentration of EVA. The morphology of the extrudate of the blends at different shear rates and blend ratios was studied and the size and distribution of the domains were examined by scanning electron microscopy. The morphology was found to depend on shear rate and blend ratio. Compatibilization of the blends with phenolic‐ and maleic‐modified LLDPE increased the melt viscosity at lower wt % of compatibilizer and then leveled off. Dynamic vulcanization is found to increase the melt viscosity at a lower concentration of DCP. The effect of temperature on melt viscosity of the blends was also studied. Finally, attempts were made to correlate the experimental data on melt viscosity and cocontinuity region with different theoretical models. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3210–3225, 2002     

Effect of the partially hydrolyzed EVA‐h content on the morphology,rheology, and mechanical properties of PA12/EVA blends

In this article, a hydrolyzed EVA copolymer (EVA‐h) was chosen as an interfacial agent of PA12/EVA blends. The effect of EVA‐h addition (5 and 10 wt% in relation to EVA phase) on morphological, interfacial and mechanical properties of the systems was investigated. The polymer blends were melt processed in an interpenetrating co‐rotating twin‐screen extruder. The EVA‐h practically did not change the continuity index of the blends. However, it resulted in the reduction of the size of the dispersed EVA phase in polyamide. EVA‐h contributed to the reduction of the interfacial tension (4.6 – 0.32 mN/m) and the formation of a stable morphology. The EVA‐h improved the interaction between PA12 and EVA phases, being its effect more pronounced on the elastic modulus and hardness properties. The behavior of the mechanical properties confirmed the compatibilizer effect EVA‐h in the blends. POLYM. ENG. SCI., 58:335–344, 2018. © 2017 Society of Plastics Engineers     

Dynamic properties of NR/EVA polymer blends: Model calculations and blend morphology

The dynamic mechanical properties of blends of natural rubber (NR) and the ethylene–vinyl acetate copolymer (EVA), a thermoplastic elastomer, were investigated in terms of the storage modulus and loss tangent for different compositions, using dynamic mechanical thermal analysis (DMTA) covering a wide temperature range. Mean‐field theories developed by Kerner were applied to these binary blends of different compositions. Theoretical calculations were compared with the experimental small strain dynamic mechanical properties of the blends and their morphological characterizations. Predictions based on the discrete particle model (which considers one of the components as a matrix and the other dispersed as well‐defined spherical inclusions embedded in the matrix) agreed well with the experimental data in the case of 30/70 NR/EVA but not in the case of 70/30 NR/EVA blends. A 50/50 blend, where a cocontinuous morphology was revealed by SEM studies, was found to be approximately modeled by the polyaggregate model (where no matrix phase but a cocontinuous structure of the two is postulated). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 165–174, 1999     

Studies on preparation of immersion‐type polypropylene fragrant fiber. I. Formation of matrix fiber in the melt‐spinning process and its technique of immersion essential oil

Polypropylene/ethylene vinyl acetate (PP/EVA) blends were prepared in a plastic extruder with a static mixer. The thermodynamic compatibility, morphology, crystal form, and rheological behavior of PP/EVA blends were investigated by SEM, DSC, and rheology instruments. The results showed that PP and EVA were thermodynamically incompatible, the viscosity of the PP/EVA blends decreased with increase of shear rate in a range of temperature, the PP/EVA blends had a sea‐islands structure, and the crystalline zones remained in their original state and could not form mixed crystals in the PP/EVA blends. The PP/EVA blends were melt spun to prepare matrix fibers and the spinning conditions such as EVA content, the matching factor between pump delivery and winding velocity, and the melt‐spinning temperature were also determined. The sorption process of a matrix fiber for essential oils, adsorbed under various sorption conditions such as sorption time, sorption temperature, and EVA content, was also studied. The results revealed that the composite isotherm of the adsorption of matrix fiber for essential oil was characteristic of a U model. Through adsorbing essential oil, the immersion‐type PP fragrant fibers could be prepared with the matrix fiber. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1970–1979, 2003     

Toughening and compatibilization of polypropylene/polyamide‐6 blends with a maleated–grafted ethylene‐co‐vinyl acetate

In this article, maleated–grafted ethylene‐co‐vinyl acetate (EVA‐g‐MA) was used as the interfacial modifier for polypropylene/polyamide‐6 (PP/PA6) blends, and effects of its concentration on the mechanical properties and the morphology of blends were investigated. It was found that the addition of EVA‐g‐MA improved the compatibility between PP and PA6 and resulted in a finer dispersion of dispersed PA6 phase. In comparison with uncompatibilized PP/PA6 blend, a significant reduction in the size of dispersed PA6 domain was observed. Toluene‐etched micrographs confirmed the formation of interfacial copolymers. Mechanical measurement revealed that the addition of EVA‐g‐MA markedly improved the impact toughness of PP/PA6 blend. Fractograph micrographs revealed that matrix shear yielding began to occur when EVA‐g‐MA concentration was increased upto 18 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99:3300–3307, 2006     

Correlation of rheology and morphology and estimation of interfacial tension of immiscible COC/EVA blends

Rheology and morphology of cyclic olefin copolymer (COC) / ethylene vinyl acetate copolymer (EVA) immiscible blends with droplet and co-continuous morphologies were experimentally examined and theoretically analyzed using emulsion and micromechanical models. The blends showed an asymmetric phase diagram in which the EVA-rich blends had smaller dispersed size domains as compared to the COC-rich blends. This could be explained based on the higher melt elasticity and viscosity of COC as compared to EVA determined by the rheological investigations. The rheological tools were used to investigate the miscibility of the blends. From the melt viscosity data it is found that the COC/EVA blends show a positive deviation behavior at all compositions which is a hint for strong interaction between the COC and EVA. Analysis of Cole-Cole and Han diagrams revealed that COC/EVA blends, at high EVA contents, were more compatible than COC-rich blends. For the droplet morphology, Palierne model was more successful but, by increasing the dispersed phase content some deviation was observed. In the co-continuous region, the Coran model was in good correspondence with the experimental data as compared to the Veenstra’s model. The storage and loss modulus of EVA-rich blends had a better correspondence with the Palierne model than the COC-rich blends which further confirmed the morphological findings. Interfacial tension calculated for the COC/EVA blends using the Palierne model, were about 1.2 and 15 mN/m² for EVA-rich (10/90) and COC-rich blends (90/10), respectively. In both EVA-rich and COC-rich systems the interfacial tension increased with increasing the dispersed phase content.