Dynamic rheological properties of high‐density polyethylene/polystyrene blends extruded in the presence of ultrasonic oscillations

The linear rheological properties of high‐density polyethylene (HDPE), polystyrene (PS), and HDPE/PS (80/20) blends were used to characterize their structural development during extrusion in the presence of ultrasonic oscillations. The master curves of the storage shear modulus (G′) and loss shear modulus (G″) at 200°C for HDPE, PS, and HDPE/PS (80/20) blends were constructed with time–temperature superposition, and their zero shear viscosity was determined from Cole–Cole plots of the out‐of‐phase viscous component of the dynamic complex viscosity (η″) versus the dynamic shear viscosity. The experimental results showed that ultrasonic oscillations during extrusion reduced G′ and G″ as well as the zero shear viscosity of HDPE and PS because of their mechanochemical degradation in the presence of ultrasonic oscillations; this was confirmed by molecular weight measurements. Ultrasonic oscillations increased the slopes of log G′ versus log G″ for HDPE and PS in the low‐frequency terminal zone because of the increase in their molecular weight distributions. The slopes of log G′ versus log G″ for HDPE/PS (80/20) blends and an emulsion model were used to characterize the ultrasonic enhancement of the compatibility of the blends. The results showed that ultrasonic oscillations could reduce the interfacial tension and enhance the compatibility of the blends, and this was consistent with our previous work. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3153–3158, 2004     

Rheological study of the miscibility of LLDPE/LDPE blends and the influence of Tmix

The miscibility of LLDPE and LDPE blends and the influence of mixing temperature (T_mix) are discussed. Adequate amounts of antioxidants were added during melt blending. Dynamic and steady shear measurments were carried out at 190°C in a Rheometrics Mechanical Spectrometer 800.The dependence of rheological properties on blend composition indicated that blends of LLDEPE (butene) and LDPE mixed at 190°C and 220°C are only partially miscible; immiscibilty is likely to occur around the 50/50 composition and in the LDPE‐rich blends. Blends at 190°C are likely miscible in the LLDPE‐rich range. Tncreaasing T_mix did improve the miscibility of LLDPE/LDPE blends at 190°C or influence the dynamic sher properties (η′ or G′) of the “pure” resins of blends. Suggested that the molecular order [see Hussein and Williams, J. Non‐Newt. Fluid Mech., 86 105 (1999); Hussein and Williams, Macromol. Rapid Commun., 19 , 323 (1998)] and mismatch of the molecular conformations of different polyethylene structures provide an explanation for the immiscibility of polyethylenes. Agreement was observed between themeasured dynamic properities and theortical predictions of Palierne and Bousmina‐Karner emulsion models.     

Binary blends of metallocene polyethylene with conventional polyolefins: Rheological and morphological properties

The rheology and morphology of four sets of binary blends of polyethylene synthesized with metallocene catalysis (metallocene polyethylene: MCPE) with polyolefins prepared using Ziegler‐Natta catalysts have been investigated. The blend systems are MCPE with high density polyethylene (MCPE‐HDPE), polypropylene (MCPE‐PP), poly(propylene‐co‐ethylene) (MCPE‐CoPP), and poly(propylene‐co‐ethylene‐co‐1‐butylene) (MCPE‐TerPP). Cole‐Cole plots [storage melt viscosity (η′) versus loss melt viscosity (η″)], plots of the dynamic storage modulus (G′) versus the dynamic loss modulus (G″), and plots of the log melt viscosity (η*, η′, and η″) versus blend compositions were constructed. The morphology of the blends after microtoming and etching was studied. The phase morphology of MCPE‐HDPE appeared homogeneous, whereas the other three blends were heterogeneous. Rheological and morphological investigations indicated that the MCPE‐HDPE blend was miscible, but the other three blends were immiscible in the melt as well as in the solid state. These observations can be rationalized in terms of the similarity of the chemical structures of the polyolefins.     

Rheological properties of the blends of polychloroprene with poly[ethylene(vinyl acetate)]

Blends of poly[ethylene(vinylacetate)] (EVAc-45; 45% VAc content) and polychloroprene (CR) have been studied with respect to capillary and dynamic flow. It is found that EVAc-45, CR, and their blends are shear thinning (pseudoplastic) in nature. Though shear viscosity (η_a) and dynamic out-of-phase viscosity (η′_E) obeys power law, dynamic elongational viscosity (η′_E) does not follow it due to the synchronization of molecular vibration with the applied frequency at around 11 Hz. Both η_a and η′_E of the blends show positive deviation with respect to their additive values. The relative positive deviation (RPD) in shear flow increases with increasing temperature and shear rate. In the case of dynamic flow, RPD increases with increasing temperature but exhibits a decreasing trend with increasing frequency. RPD can be fitted well into a fifth-order equation with a weight fraction of CR (W_CR) in EVAc-45—CR blends. From rheological point of view, this relative positive deviation indicates blend compatibility between EVAc-45 and CR. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1759–1765, 1997     

Rheological and thermal properties of m-LLDPE blends with m-HDPE and LDPE

The dynamic and steady state behavior of metallocene linear low density polyethylene (m-LLDPE) blended with metallocene high density polyethylene (m-HDPE) and with low density polyethylene (LDPE) were measured in parallel plate rheometer at 160, 180, and 200 °C. The composition dependence of zero shear viscosity η₀, the characteristic relaxation time τ₀ and the characteristic frequency ω₀ of m-LLDPE/m-HDPE blends show a linear variation in the whole range of weight fraction, which indicates that m-LLDPE/m-HDPE blends are miscible blend. At the same time, m-HDPE showing a ‘dissident’ rheological behavior should possess a certain very low degree of LCB. Two calculation methods of LCB verify this point. In contrast, the composition dependence of zero shear viscosity η₀ of m-LLDPE/LDPE blends shows a positive deviation from the log-additivity rule, which can be well fitted by using the immiscible blend equation of Utracki. The characteristic relaxation time τ₀ and the characteristic frequency ω₀ have a sharp variation with the small amounts of LDPE in the blends, which also indicates a phase separation in the system. The thermal properties of m-LLDPE/m-HDPE blends are very similar to a single-component system. However, m-LLDPE/LDPE blends are immiscible in both melt and crystal states. DSC results are consistent with the rheological properties of these two series of blends.     

Rheological quantification of molecular parameters: Application to a hydrogen bond forming blend

The component dynamics and molecular parameters were investigated for miscible poly(4‐vinyl phenol)/poly(ethylene oxide) (PVPh/PEO) blends. Global values of molecular weight between entanglements (M_e) were first estimated for the blends and were compared with existing athermal model predictions. Global interchain friction coefficients (ξ) of the blends were deduced from the zero‐shear viscosity. A maximum was observed at a composition of 20–30 wt % of PEO. Chain dimensions of this phase are estimated by using a relationship between the plateau modulus and a packing length (i.e., number of individual chains present in a given small volume of the melt). A slight increase in M_e is observed at low PEO weight fraction (before 0.20), followed by a sharp decrease in M_e values after this concentration. Values of ξ in PVPh/PEO blends show a maximum value at 20–30 wt % of PEO. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1623–1630, 2004     

Rheological behavior and mechanical properties of high‐density polyethylene blends with different molecular weights

The dynamic rheological and mechanical properties of the binary blends of two conventional high‐density polyethylenes [HDPEs; low molecular weight (LMW) and high molecular weight (HMW)] with distinct different weight‐average molecular weights were studied. The rheological results show that the rheological behavior of the blends departed from classical linear viscoelastic theory because of the polydispersity of the HDPEs that we used. Plots of the logarithm of the zero shear viscosity fitted by the Cross model versus the blend composition, Cole–Cole plots, Han curves, and master curves of the storage and loss moduli indicated the LMW/HMW blends of different compositions were miscible in the melt state. The tensile yield strength of the blends generally followed the linear additivity rule, whereas the elongation at break and impact strength were lower than those predicted by linear additivity; this suggested the incompatibility of the blends in solid state. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Rheological and thermal properties of thermoplastic natural rubbers based on poly(methyl methacrylate)/epoxidized‐natural‐rubber blends

Epoxidized natural rubbers (ENRs) with epoxide levels of 10, 20, 30, 40, and 50 mol % were prepared. The ENRs were later blended with poly(methyl methacrylate) (PMMA) with various blend formulations. The mixing torque of the blends was observed. The torque increased as the PMMA contents and epoxide molar percentage increased in the ENR molecules. Furthermore, the shear stress and shear viscosity of the polymer blends in the molten state increased as the ENR content and epoxide molar percentage increased in the ENR molecules. Chemical interactions between polar groups in the ENR and PMMA molecules might be the reason for the increases in the torque, shear stress, and viscosity. All the ENR/PMMA blends exhibited shear‐thinning behavior. This was observed as a decrease in the shear viscosity with an increase in the shear rate. The power‐law index of the blends decreased as the ENR contents and epoxide molar percentage increased in the ENR molecules. However, the consistency index (or zero shear viscosity) increased as the ENR contents and epoxide molar percentage increased. A two‐phase morphology was observed with scanning electron microscopy. The small domains of the minor components were dispersed in the major phase. For the determination of blend compatibility, two distinct glass‐transition‐temperature (T_g) peaks from the tan δ/temperature curves were found. Shifts in T_g to a higher temperature for the elastomeric phase and to a lower temperature for the PMMA phase were observed. Therefore, the ENR/PMMA blends could be described as partly miscible blends. According to the thermogravimetry results, the decomposition temperatures of the blends increased as the levels of ENR and the epoxide molar percentage increased. The chemical interactions between the different phases of the blends could be the reason for the increase. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3561–3572, 2004     

Thermorheological behavior analysis of mLLDPE and mVLDPE: Correlation with branching structure

In this article, the correlation between the thermorheological behavior and the molecular structure of two grades of metallocene polyethylene, namely linear low density and very low density polyethylene, is studied. The investigated polymers possess the same molecular weight and polydispersity index, but different levels of short branches. Increasing the number of short branches results in enhanced activation energy and delayed relaxation times of the polymers. Four methods including the time–temperature superposition (TTS), van Gurp‐Palmen and activation energy (E_a) as a function of the phase angle, E_a(δ), and the storage modulus, E_a(G′) are employed to study the thermorheological behavior of the samples. The results indicated that the thermorheologically simple behavior is dominant in the specimens. Both the E_a(δ) and E_a(G′) showed independency toward phase angle and the storage modulus. Moreover, the activation energy values obtained from the TTS principle and the E_a(δ) and E_a(G′) diagrams were in good agreement. The zero‐shear rate viscosity of the samples also followed the equation of the linear polyethylene. Regarding the simple thermorheological behavior and the agreement of the zero shear rate viscosity with the relation of the linear polyethylene, one can conclude that long branches do not exist in the investigated metallocene polyethylenes of this article. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Simplified theory for linear rheology of monodisperse linear polymers

A new version of the tube theory based on the de Gennes–Doi–Edwards reptation concept (reported in Likhtman and McLeish's work published in 2002) is evaluated, modified to allow for simplified computations, and used to study the relationship between zero‐shear viscosity and molecular weight for monodisperse entangled linear homopolymers. The Likhtman–McLeish model combines self‐consistent theories for contour length fluctuations and constraint release with reptation theory for monodisperse linear polymers. Because of the nature of the Rubinstein and Colby approach used for the treatment of constraint release, the related term is probabilistic and requires stochastic simulations for the calculation of the relaxation modulus G(t). This makes the Likhtman–McLeish model computationally difficult to use. In this work we solve this problem by generating an approximate closed‐form solution for the stochastic term. Then analytical integration of the relaxation modulus function G(t) provides an expression for the zero‐shear viscosity (η₀). Results of the computations of the zero‐shear viscosity and of the slope of η₀ versus molecular weight are compared with available experimental data for monodisperse entangled linear polystyrene and polyethylene (hydrogenated polybutadiene). The model is a major improvement over previous theoretical models, even if there is still some disagreement between the predictions and experimental data of the slope of η₀ versus molecular weight. The possibility of inferring monomer chemistry–dependent parameters from the zero‐shear viscosity remains a difficult task because of the introduction of a constraint‐release parameter. Nevertheless, the model is a useful tool for the prediction of linear viscoelasticity data. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 569–586, 2004     

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.     

HDPE/LLDPE reactor blends with bimodal microstructures—Part II: rheological properties

Reactor blends of polyethylene/poly(ethylene-co-1-octene) resins with bimodal molecular weight and bimodal short chain branching distributions were synthesized in a two-step polymerization process. The compositions of these blends range from low molecular weight (LMW) homopolymer to high molecular weight (HMW) copolymer and vice versa HMW homopolymer to LMW copolymer. The shear flow characteristics of these polymers in the typical processing range mostly depend on the molecular weight and MWD of the polymer and are independent of the short chain branch content. From oscillatory shear measurements, it was observed that the viscosity of HMW polymers was reduced with the addition of LMW material. For the polymers produced with this two-step polymerization process, the LMW homopolymer and HMW copolymer blends and HMW homopolymer and LMW copolymer blends were melt miscible, despite the large viscosity differences of the pure components.     

Shear rate dependence of viscosity and first normal stress difference of LCP/PET blends at solid and molten states of LCP

The liquid crystalline polymer (LCP) and polyethylene terephthalate (PET) were blended in an elastic melt extruder to make samples having 20, 40, 60, 80, and 100 wt % of LCP. Morphology of these samples was studied using scanning electron microscopy. The steady state shear viscosity (η), dynamic complex viscosity (η*) and first normal stress difference (N₁) were evaluated and compared at two temperatures: 265°C, at which LCP was in solid state, and 285°C, at which LCP was in molten state. The PET was in molten state at both the temperatures. The shear viscosity of the studied blends displayed its dependence on composition and shear rate. A maxima was observed in viscosity versus composition plot corresponding to 80/20 LCP/PET blend. The N₁ increased with LCP loading in PET and with the increased asymmetry of LCP droplets. The N₁ also varied with the shear stress in two stages; the first stage demonstrated elastic deformation, whereas second stage displayed dominant plastic deformation of LCP droplets. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2212–2218, 2007     

Elongational viscosity for miscible and immiscible polymer blends. I. PMMA and AS with similar elongational viscosity

The effects of miscibility and blend ratio on uniaxial elongational viscosity of polymer blends were studied by preparing miscible and immiscible samples at the same composition by using poly(methyl methacrylate) (PMMA) and poly(acrylonitrile-co-styrene) (AS). Miscible polymer blend samples for the elongational viscosity measurement were prepared by using three steps: solvent blends, cast film, and hot press. A phase diagram of blend samples was made by visual observation of cloudiness. Immiscible blend samples were prepared by maintaining the prepared miscible samples at 200°C, which is higher than cloud points using a LCST (lower critical solution temperature) phase diagram. The phase structure of immiscible blends was observed by an optical microscope. The elongational viscosity of all samples was measured at 145°C, which is lower than the cloud-point temperature at all blend ratios. The elongational viscosity of PMMA and AS was similar to each other. The strain-hardening property of miscible blends in the elongational viscosity was only slightly influenced by the blend ratio, and this was also the case with immiscible blends. The strain-hardening property was only slightly influenced, whether it was miscible or immiscible at each blend ratio. Polydispersity in molecular weight for blend samples was not changed by GPC (gel permeation chromatography) analysis. Almost no change in the polydispersity of the molecular weight for blends and the similarity of elongational viscosity between PMMA and AS resulted in little influence of the blend ratio and miscibility on the strain-hardening property. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 757–766, 1999     

Effect of morphology on shear viscosity for binary blends of polycarbonate and polystyrene

The structure and rheological properties of binary blends of polycarbonate (PC) and polystyrene (PS) were investigated using various PS samples with different molecular weights, namely PS1k (M_w = 1,000), PS53k (M_w = 53,000), and PS240k (M_w = 240,000). The blends with PS53k and PS240k show phase-separated structures, whereas the blend with PS1k is miscible. The shear viscosity decreases greatly on addition of PS53k and PS240k, especially at high shear rates, which would be a great advantage at processing operations. Because the nonlinear response occurs in the small strain region for multilayered films of PC and PS240k, the origin of the significant viscosity drop for the phase-separated system is interfacial slippage at the phase boundary.     

Random orientation of in situ composites based on liquid‐crystalline polymers by compression moulding

In this study, randomly oriented in situ composites based on liquid‐crystalline polymers (LCPs) were prepared by thermal compression moulding. The LCP employed was a semi‐flexible liquid‐crystalline copolyesteramide with 30 mol% of p‐aminobenzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). The matrices were poly(butylene terephthalate) (PBT) and polyamide 66 (PA66). The rheological properties, compatibility and morphological structures of these in situ composites were investigated. The results showed that PA66‐LCP and PBT–LCP component pairs of the composites are miscible in the molten state, but partially compatible in the solid state. The ratios of viscosity, λ₁ = η_LCP/η_PA66 and λ₂ = η_LCP/η_PBT, are all greater than 1.0. However, the melt viscosity of the LCP/PBT and LCP/PA66 blend is much lower than that of PBT and PA66, and it decreases markedly with increasing LCP content. When the LCP/PA66 or LCP/PBT blends are compression moulded, the LCP/PA66 or LCP/PBT melts and flows easily due to their low viscosity, and the LCP phases in the melts deform easily along the flow directions, which are random. It leads to uniformly dispersed LCP micro‐fibres randomly orientation in the thermoplastic matrix due to the compatibility between the blending components. © 2003 Society of Chemical Industry     

The role of polycarbonate molecular weight in the poly(L‐lactide) blends compatibilized with poly(butylene succinate‐co‐L‐lactate)

Poly(butylene succinate‐co‐L ‐lactate) (PBSL)–compatibilized poly(L ‐lactide) (PLLA) polymer blends with two commercial grades of polycarbonate (PC) were investigated. The capillary tests showed that the steady shear viscosity of high molecular weight PC (PC‐L) was 10 times higher than that of low molecular weight PC (PC‐AD) throughout the shear rate range under investigation. Morphologic examination revealed that the shape of the dispersed PC‐L phase in the as‐extruded blends was largely spherical, but the PC‐AD phase was more like a rod and elongated further during injection molding. Notched Izod impact strength (IS) of the unmodified PLLA/PC‐L blend was higher than that of PC‐AD blend. The IS of modified ternary blends increased with PBSL content because of enhanced phase interaction indicated from thermal and morphologic analysis. The PBSL modification also enhanced IS more significantly in PLLA/PC‐L than in PLLA/PC‐AD blends. On the contrary, the heat deflection temperature (HDT) of PLLA/PC‐L binary system was much lower than that of PLLA/PC‐AD. HDT of PBSL‐modified PLLA/PC‐AD blends dropped with increasing PBSL content, which is a ductile polymer. Thermal and dynamic mechanical analysis of the ternary blends showed that individual components were immiscible with distinct T_gs for PC and PLLA and distinct T_ms for PBSL and PLLA. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Compatibility,steady and dynamic rheological behaviors of polylactide/poly(ethylene glycol) blends

Understanding the rheological behavior of plasticized polylactide (PLA) contributed to the optimization of processing conditions and revealed the microstructure–property relationships. In this study, the morphological, thermal, steady and dynamic rheological properties of the PLA/poly(ethylene glycol) (PEG) blends were investigated by scanning electron microscope, differential scanning calorimeter, and capillary and dynamic rheometers, respectively. The results illuminated that the melt shear flow basically fitted the power law, whereas the temperature dependence of the apparent shear viscosity (η_a) or complex viscosity (η*) followed the Arrhenius equation. Both the neat PLA and PLA/PEG blends exhibited shear‐thinning behavior. Because the incorporation of PEG reduced the intermolecular forces and improved the mobility of the PLA chains, the η_a, η*, and storage and loss moduli of the PLA/PEG blends decreased. The PEG content (W_PEG) ranged from 0 to 10 wt %, both η_a and η* decreased significantly. However, the decrements of η_a and η* became unremarkable when W_PEG exceeded 10 wt %. The reason was attributed to the occurrence of phase separation, which resulted in the decrease in the plasticization and lubrication efficiencies. This study demonstrated that the addition of the right amount of PEG obviously improved the flow properties of PLA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42919.     

Water‐soluble polymers. LXXXIII. Correlation of experimentally determined drag reduction efficiency and extensional viscosity of high molecular weight polymers in dilute aqueous solution

The extensional viscosity for aqueous solutions of high molecular weight poly(acrylamide) copolymers and poly(ethylene oxide) homopolymers was measured using a laboratory‐designed screen extensional rheometer. A Bingham model was developed to estimate the average local polymer coil extensional viscosity (η_coil). A strong correlation was found between the measured η_coil values and the polymer extensional viscosity predicted by a bead‐spring model. The dilute aqueous solution drag reduction was measured with a rotating disk instrument under conditions minimizing the effects of shear degradation. Extensional viscosity and drag reduction measurements were performed in deionized water and in 0.514M sodium chloride. The relative drag reduction efficiency values (Δ) in both solvents were found to strongly correlate with measured η_coil values. This is the first report of the accurate prediction of drag reduction behavior for a wide range of polymer types in various solvents from the independently measured molecular parameters η_coil and [η]C. The often‐used relative drag reduction efficiency expressed as the product of [η]C and Δ can now be replaced by the absolute drag reduction efficiency [η]Cη_coil. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1222–1231, 2001     

Melt rheology of nanometre‐calcium‐carbonate‐filled acrylonitrile–butadiene–styrene (ABS) copolymer composites during capillary extrusion

The melt flow properties during capillary extrusion of nanometre‐calcium‐carbonate‐filled acrylonitrile–butadiene–styrene (ABS) copolymer composites were measured by using a Rosand rheometer to identify the effects of the filler content and operation conditions on the rheological behaviour of the sample melts. The experiments were conducted under the following test conditions: temperature varied from 220 to 240 °C and shear rate ranged from 10 to 10⁴ s^?1. The filler volume fractions were 0, 10, 20, 30, 40 and 50%. The results showed that the shear flow did not strictly obey the power law under the test conditions, and that the entry pressure drop (ΔP_en) and the extension stress (σ_e) in entry flow increased nonlinearly, while the melt shear viscosity (η_s) and extension viscosity (η_e) decreased with increasing the wall shear stress (τ_w) at constant test temperature. The dependence of the melt shear viscosity on the test temperature was approximately consistent with the Arrhenius expression at fixed τ_w. When τ_w was constant, η_s and η_e increased while ΔP_en and σ_e decreased with the addition of the filler volume fraction. © 2002 Society of Chemical Industry