Blends of nylon/acrylonitrile butadiene rubber: Effects of blend ratio,dynamic vulcanization and reactive compatibilization on rheology and extrudate morphology

The melt flow behavior of thermoplastic elastomers from nylon and nitrile rubber (NBR) was studied as a function of blend ratio, dynamic crosslinking, compatibilization and temperature. The morphology of the extrudates, i.e., the size, shape and distribution of the domains, was analyzed. Uncompatibilized and compatibilized blends showed pseudoplastic behavior. The viscosity of the blends showed positive deviation from a linear rule of mixtures. Compatibilization using chlorinated polyethylene (CPE) increased the melt viscosity of the blends. The addition of the compatibilizer decreased the domain size of the dispersed phase, followed by an increase after a critical concentration of the compatibilizer, where the interface was saturated. The influence of dynamic vulcanization on the rheological behavior was also studied. The extrudate morphology depended on blend ratio, compatibilization and shear rate.     

Melt rheology of compatibilized polystyrene/low density polyethylene blends

Investigations have been made on the melt rheological behaviors of compatibilized blends composed of polystyrene, low density polyethylene and hydrogenated (styrene‐butadiene‐styrene) triblock copolymer used as a compatibilizer. The experiments were carried out on a capillary rheometer. The effects of shear stress, temperature and blending ratio on the activation energy for viscous flow and melt viscosity of the blends are described. The study shows that the viscosity of the blends exhibits a maximum or minimum value at a certain blending ratio. The activation energy for viscous flow decreases with increasing LDPE content. Furthermore, the concept of equal‐viscosity temperature is presented and its role in the processing of the blend is discussed. In addition, the morphology of the extrudate sample of the blends was observed by scanning electron microscopy and the correlation between the morphology and the rheological properties is explored. © 1999 Society of Chemical Industry     

Rheology and sheet extrusion of Novatein thermoplastic protein/polybutylene adipate-co-terephthalate blends

Novatein is a thermoplastic polymer made from blood meal proteins, but it has rheological properties very different from commodity thermoplastics. Capillary rheometry revealed an apparent time dependent shear viscosity for Novatein, evident from a decreasing pressure drop over time, measured at constant shear rate. However, blending with polybutylene adipate-co-terephthalate (PBAT) reduced the time dependence for uncompatibilized blends and virtually eliminated time dependence for compatibilized blends containing 30 wt % PBAT. Novatein's extensional viscosity is three orders of magnitude more than its shear viscosity and explained the difficulty in sheet extrusion. In contrast, 30% compatibilized blends had an extensional viscosity similar to neat PBAT and was also the only blend that could be successfully sheet extruded. Although uncompatibilized blends at the same or lower PBAT content also had a lower extensional viscosity, they could not be sheet extruded and the difference was the 30% compatibilized blends had a fine PBAT phase structure (co-continuous in this case), which was sufficiently adhered to the Novatein phase. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47977.     

Interfacial slip‐stick transition induced by reactive compatibilization in ethylene‐co‐butyl acrylate elastomer dispersed polyamide 6 blend subjected to high shear flow and extensional flow

The effect of phase interaction induced by reactive compatibilization during high shear and extensional flow in polyamide (PA6) and ethylene‐co‐butyl acrylate (EBA) blends was studied using advanced dual bore capillary rheometer. The viscosity‐composition behavior of the uncompatibilized PA6/EBA blends exhibited negative deviation behavior from log‐additivity rule. The interfacial slip mechanism, operative between the matrix PA6 and dispersed EBA during shear flow was studied by the use of Lin's and Bousmina‐Palierne‐Utracki (BPU) model for viscosity for the blends under the processing conditions. On the other hand, the compatibilized PA6/EBA‐g‐MAH^0.49/EBA blends with varying dispersed phase volume fraction show positive deviation behavior. The reactive compatibilizers EBA‐g‐MAH^0.49 and EBA‐g‐MAH^0.96 increased the phase interaction with adequate reduction in the dynamic interfacial tension, which favored the particle break‐up and stabilized the morphology in the compatibilized blends. The extensional viscosity of the blends has enhanced because of the inclusion of EBA in all the uncompatibilized and compatibilized blends. The melt elasticity and elasticity function were systematically studied from first normal stress coefficient functions (ψ₁). The variation in the recoverable shear strain (γ_R), shear rate dependent relaxation time (λ) and shear compliance (J_c) under various shear rates were thoroughly analyzed for all the blend compositions. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

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.     

Rheological behavior of noncompatibilized and compatibilized PP/PET blends with SEBS‐g‐MA

The rheological behaviors of noncompatibilized and compatibilized polypropylene/polyethylene terephthalate blends (80/20) in relation with their morphology were studied at two constant levels using maleic anhydride‐modified styrene‐ethylene‐butylene‐styrene polymer. By scanning electron microscopy of cryofractured surfaces, the morphology of the blends was examined after etching. The frequency sweep and step strain experiments were carried out for the blends. The frequency sweep results indicated that increasing the compatibilizer causes behavioral changes of the rheological properties, which could be related to the aggregation of the dispersed particles with rubbery shell. Also, the frequency sweep and step strain experiments in linear region, after cessation of simple steady shear flow with various preshear rates (higher shear stress values than G′_p), were done on compatibilized blend. The results showed that the morphology characteristics, defined by the aggregation of the dispersed particles based on rheological experimental data, were destroyed and replaced by an alignment in the flow direction for present imposed shear rates. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of coalescence and interfacial tension on the morphology of PP/HDPE compatibilized blends

In this paper, the compatibilization of polypropylene (PP)/high-density polyethylene (HDPE) blend was studied through morphological and interfacial tension analysis. Three types of compatibilizers were tested: ethylene-propylene-diene copolymer (EPDM), ethylene-vinylacetate copolymer (EVA) and styrene-ethylene/butylene-styrene triblock copolymer (SEBS). The morphology of the blends was studied by scanning electron microscopy. The interfacial tension between the components of the blends was evaluated using small amplitude oscillatory shear analysis. Emulsion curves relating the average radius of the dispersed phase and the interfacial tension to the compatibilizer concentration added to the blend were obtained. It was shown that EPDM was more efficient as an emulsifier for PP/HDPE blend than EVA or SEBS. The relative role of interfacial tension reduction and coalescence reduction to particle size reduction was also addressed. It was observed that the role of coalescence reduction is small, mainly for PP/HDPE (90/10) blends compatibilized by EPDM, EVA or SEBS. The results indicated that the role of coalescence reduction to particle size reduction is lower for blends for which interfacial tension between its components is low at compatibilizer saturation.     

Morphological and rheological responses to the transient and steady shear flow for a phase-separated polybutadiene/polyisoprene blend

The morphological and rheological responses to the transient and steady shear flow for a phase-separated polybutadiene (PB)/low vinyl content polyisoprene (LPI) blend have been investigated. Under steady shear flow where the applied shear rate is not too large, the steady sheared structures become increasingly anisotropic and interconnected with an “en route” to the formation of string phases as shear rate increases. After that, the further increase of shear rate leads to a blurred domain interface. These shear-induced complex structures in turn affect the rheological response greatly and both the shear thinning and shear thickening were observed in the steady shear behavior of the phase-separated PB/LPI blend. Under transient shear flow, the time (or strain) dependence of viscosity and morphology after a shear rate jump were extensively studied in order to obtain the insight into the steady state formation and found to be mainly determined by the final shear rates. Depending on whether the transient string phases which were formed by the transient shear flow can be stabilized and with clear domain interface, three kinds of transient shear viscosity changes have been observed. Some of the observations are quite different from the model immiscible blend and believed to be closely related to the significant shear-induced mixing effect happened in the PB/LPI blend.     

Melt blending of linear low-density polyethylene and polystyrene in a Haake internal mixer. II. Morphology-processing relationships

A measure of the effective shear rate range for dispersive mixing in the Haake mixer has been developed, which is more representative of shearing conditions than that currently used. In addition, the effects of processing conditions, composition, and compatibilizer on linear low-density polyethylene and polystyrene (LLDPE/PS) blend morphology were studied. Fiber/stratified morphologies form with blends when the minor phase has low viscosity and is present at its higher concentration. The influence of the viscosity ratio on phase size was found to be a minor effect for mixtures having a low fraction of the dispersed phase (20% PS). The effect of shear intensity, however, was found to be more important at a low composition of the dispersed phase or in compatibilized blends. During Haake blending, an optimal time for adding compatibilizer to stabilize phase morphology was found to be when the final morphology of an incompatible blend had developed. Further studies have concluded that the addition of styrene–ethylene/butylene–styrene (SEBS) stabilized the blend morphology of LLDPE/PS more efficiently than styrene–ethylene/propylene (SEP) on different blending conditions and compositions. At high temperatures, the addition of SEP to a LLDPE/PS blend did not modify the dispersed phase size. On the other hand, SEBS stabilized the dispersion so that the final domain size is independent of composition. © 1995 John Wiley & Sons, Inc.     

Melt rheological properties of reactive compatibilized HDPE/PET blends

Melt rheological properties of high density polyethylene and poly(ethylene terephthalate) (HDPE/PET) blends compatibilized by an ethylene–butyl acrylate–glycidyl methacrylate terpolymer (EBAGMA) were studied by means of a HAAKE torque rheometer and a capillary rheometer. The phase morphology of the blends was evaluated by a scanning electron microscope (SEM). The results showed that the melts of blends behave pseudoplasticity. The addition of EBAGMA strengthens the interfacial adhesion between HDPE and PET and improves the phase dispersion due to reactive compatibilization. It was observed that the balance torque, melt viscosity, and sensitivity of melt viscosity to shear rate of the melts increase with increasing content of EBAGMA, but the melt flow index and activation energy decrease. At the same time, the plasticizing time is shortened indicating that the processability of the compatibilized blends has been improved. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The effect of viscosity ratio on the phase inversion of polyamide 66/polypropylene blends

The rheological properties of the blend components are an important parameter in the formation of a blend morphology. The effect of viscosity ratio on the morphology of polyamide 66/polypropylene blends was studied, with primary attention to the phase-inversion behavior and the average particle size of the dispersed phase. The relationship between the mechanical properties and the phase-inversion composition was investigated as well. Noncompatibilized and compatibilized blends having five different viscosity ratios were prepared by twin-screw extrusion. Maleic anhydride-grafted polypropylene was used as the compatibilizer to increase the adhesion between the two polymers and to stabilize the blend morphology. Investigation of the morphology of the blends by microscopy (SEM and TEM) showed that the smaller the viscosity ration (η_PA/η_PP) the smaller was the polyamide 66 concentration at which the phase inversion took place and that polyamide 66 became the continuous phase. The results are in accord with the model of Jordhamo. The compatibilizer induced a sharp reduction of particle size, but did not have a major effect on the phaseinversion point. The tensile and impact properties of the compatibilized blends were found to correlate with the phase inversion. An improvement in the mechanical properties was observed when polyamide 66 provided the matrix phase. © 1994 John Wiley & Sons, Inc.     

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     

Rheology‐morphology correlation in PET/PP blends: Influence of type of compatibilizer

Rheological and morphological properties of melt processed poly(ethylene terephthalate) (PET)/polypropylene (PP) blends are presented. Two types of compatibilizer namely, PP‐g‐MA <MA= maleic anhydtide> and Elvaloy PTW, an n‐butyl acrylate glycidyl methacrylate ethylene terpolymers, were incorporated at different levels to the PET/PP blend system. Scanning electron microscopy revealed that the dispersed particle sizes were smaller in PET‐rich blends than PP‐rich blends. With increasing compatibilizer level, the refinement of morphology was observed in both the systems. However, the blends compatibilized with PTW showed a more refined (smaller) particle size, and at high PTW content (10 wt%), the morphology changed towards monophasic. The significant changes in morphology were attributed to the highly reactive nature of PTW. Investigation of rheological properties revealed that the viscosity of the PET/PP blends followed typical trends based on mixing rule, which calculates the properties of blends based on a linear average. Incorporation of PP‐g‐MA into the blends resulted in a negative deviation in the viscosity of the system with respect to that of the neat blend. With increasing PP‐g‐MA level, the deviation became more pronounced. Although incorporation of the compatibilizer into the PET/PP blends refined the morphology, it led to a drastic drop of viscosity, which could be attributed to inherently lower molecular weight of the compatibilizer. In the case of the blends compatibilized by PTW, a strong positive deviation in rheological properties was observed that confirmed the stronger interaction between the blend components due to reactive compatibilization process, which led to the more refined morphology in this series of blends. J. VINYL ADDIT. TECHNOL., 19:25–30, 2013. © 2013 Society of Plastics Engineers     

Rheology and morphology of polytrimethylene terephthalate/ethylene propylene diene monomer blends in the presence and absence of a reactive compatibilizer

The dynamic rheological behavior and phase morphology of Polytrimethylene terephthalate (PTT) and ethylene propylene diene monomer (EPDM) uncompatibilized blends and those compatibilized with maleic anhydride grafted EPM (EPM‐g‐MA) were investigated. Effects of blend ratio and reactive compatibilization on the morphology and rheological properties of compatibilized and uncompatibilized blends have been analyzed. The viscosity ratio between the polymers was found to be sensitive to frequency which gave an indirect idea about the unstable morphology. The complex viscosity and dynamic modulus increased with increase in compatibilizer addition up to critical micelle concentration. Palierne and Choi‐Schowalter models were used to calculate the interfacial tension between the polymers. The interfacial tension decreased with the addition of compatibilizer up to CMC. It was also found that the minimum value of interfacial tension was found at CMC beyond that a levelling off is observed. The rheological properties of both compatibilized and uncompatibilized blends are found to be closely related to their phase morphology. POLYM. ENG. SCI., 50:1945–1955, 2010. © 2010 Society of Plastics Engineers     

Studies on the melt flow behavior of thermoplastic elastomers from polypropylene—Natural rubber blends

The melt flow behavior of thermoplastic polypropylenenatural rubber blends has been evaluated with specific reference to the effects of blend ratio, extent of dynamic crosslinking of the rubber phase and temperature, on viscosity, flow behavior index, and deformation of the extrudate. The proportion of rubber in the blend and the extent of dynamic crosslinking of the rubber phase were found to have profound influence on the viscosity of the blends at lower shear stresses. But at higher shear stresses, the effect of blend ratio on viscosity was comparatively less for the uncrosslinked blends than that for the crosslinked blends. At lower shear stress, the viscosity of the blend increased with increase in degree of crosslinking but at higher shear stress, the effect of crosslinking on viscosity was found to vary depending on the ratio of the plastic and rubber components in the blend. The deformation of the extrudates was also very much dependent on both blend ratio and degree of crosslinking.     

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     

Rheological properties,crystallization, and morphology of compatibilized blends of isotactic polypropylene and polyamide

Blends of isotactic polypropylene (iPP) with the polyamide nylon-6 (N6), prepared by extrusion, were studied with a composition of up to 30% by weight polyamide. In the case of a 70/30 iPP/N6 blend, the influence of a compatibilizing agent based on polypropylene functionalized with maleic anhydride (PP-g-MA), with compositions of 1, 3, 5, and 10% by weight in polypropylene, was followed. The influence of the concentration of N6 and the compatibilizing agent on the rheological and thermal properties, and the morphology of the blends, was analyzed by monitoring the melt viscosity at different shear rates, differential scanning calorimetry, and polarized light microscopy. Vibrational spectroscopy was used to characterize the blends and to study the effect of the compatibilizing agent. The viscosity—composition curves for the iPP/N6 blends, in the composition and shear rate ranges analyzed, show a negative deviation from the additive rule, while the opposite trend is observed for the blends compatibilized with PP-g-MA. Important variations in the spectroscopic behavior was observed between compatibilized and noncompatibilized blends, which varied as a function of the compatibilizing agent concentration. The crystallization rates of iPP in the iPP/N6 blends, under both dynamic and isothermal conditions, are much greater than are those observed for pure iPP and are directly related to the nucleating activity of the polyamide. This effect is much smaller in the presence of the compatibilizing agent. The isothermal crystallization of the polyamide N6 in compatibilized blends is affected by the presence of iPP, reducing the crystallization rate due to the diluent effect of the polypropylene. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2665–2677, 1997     

Effect of dynamic cross‐linking on melt rheological properties of polypropylene/ethylene‐propylene‐diene rubber blends

Study of melts rheological properties of unvulcanized and dynamically vulcanized polypropylene (PP)/ethylene‐propylene‐diene rubber (EPDM) blends, at blending ratios 10–40 wt %, EPDM, are reported. Blends were prepared by melt mixing in an internal mixer at 190°C and rheological parameters have been evaluated at 220°C by single screw capillary rheometer. Vulcanization was performed with dimethylol phenolic resin. The effects of (i) blend composition; (ii) shear rate or shear stress on melt viscosity; (iii) shear sensitivity and flow characteristics at processing shear; (iv) melt elasticity of the extrudate; and (v) dynamic cross‐linking effect on the processing characteristics of the blends were studied. The melt viscosity increases with increasing EPDM concentration and decreased with increasing intensity of the shear mixing for all compositions. In comparison to the unvulcanized blends, dynamically vulcanized blends display highly pseudoplastic behavior provides unique processing characteristics that enable to perform well in both injection molding and extusion. The high viscosity at low shear rate provides the integrity of the extrudate during extrusion, and the low viscosity at high shear rate enables low injection pressure and less injection time. The low die‐swell characteristics of vulcanizate blends also give high precision for dimensional control during extrusion. The property differences for vulcanizate blends have also been explained in the light of differences in the morphology developed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1488–1505, 2000     

Structure‐property relationships of blends of polycarbonate

Three grades of bisphenol‐A polycarbonate—high molecular weight linear, high molecular weight branched and low molecular weight linear—and their blends have been studied by GPC, DMTA, DSC, rheometry and impact measurements. The molecular weight distribution of the blends agred with that predicted from the component's distributions, indicating that no transesterification reactions had occurred during melt blending. The T_g of the blends varied with blend composition according to the Fox equation and was related to the reciprocal molecular weight predicted by the Flory‐Fox equation. The low shear rate viscosity of the blends agreed with a logarithmic rule of mixtures and showed power‐law dependence on the weight average molecular weight. At higher shear rates, shear thinning was observed. The steady shear viscosity correlated well with the dynamic viscosity, as suggested by the Cox‐Merz relation. The stress relaxation behavior of the melt was very sensitive to the blend composition and molecular weight and correlated well with the real modulus. Temperature studies of the dart impact energy showed that only the low molecular weight polymer underwent a brittle‐duetile transition at ea ?30°C and that all the blends were tough at room temperature. The enhanced stress triaxiality inherent in the notched lzod test caused the impact strenght at room temperature to decrease almost linealy with blend composition.