Prediction of high density polyethylene processing behavior from rheological measurements

In order to predict the processing behavior of a high density polyethylene resin one must know the resin flow behavior over a wide range of shear rates. Low shear properties are important in applications where melt strength, sagging, etc. are critical. On the other hand, high shear flow properties are a determining factor in applications where melt instability, melt fracture and heat generation are important. The flow behavior of a resin can be established by measuring the zero shear viscosity, η₀, the maximum relaxation time, τ₀, and the shape of the flow curve. We have measured these basic rheological parameters on a large number of high density polyethylene resins. A shear sensitivity parameter which is independent of molecular weight was derived from a correlation between η₀ and τ₀. This parameter, together with η₀, provide the vital information needed in order to predict the processing behavior of the resin. This method is applicable to other polymer systems provided that the rheological parameters η₀ and τ₀ can be experimentally obtained.     

Etude des propriétés rhéologiques de mélanges fondues de polybutène-1 et de polypropène à des cisaillements élevés

The viscoelastic behaviour of polybutene-1-polypropene blends has been studied in the molten state with respect to temperature, shear stress and shear rate. The corrections of experimental data have been carried out and the influence of the radius of capillary on these corrections was studied. The elasticity was investigated by means of Barus factor and the variation of viscosity versus composition of blends shows a minimum which might be interesting for the technology of plastic materials.     

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     

Flow behavior of concentrated solutions of an SBS block copolymer

The non-Newtonian viscosity of concentrated solutions of a styrene-butadiene-styrene, SBS, block copolymer was measured with a novel capillary viscometer. Polymer concentrations ranged from 0.165 to 0.306 g/cc. Apparent shear rates ranged from 1 to 10⁵ sec^?1. Five different solvents were employed. All of the flow curves can be reduced to a single master curve with the same shape exhibited by monodisperse polystyrenes and the Graessley theory. The shift factor for the shear rate axis, τ₀, approximately parallels the Rouse relaxation time, τ_R, but shows a residual concentration and solvent dependence not predicted by the Rouse form. For different solvents at the same concentration, better solvents show a minimum relative zero shear viscosity, η₀/η_s, and a maximum ratio τ_R/τ₀. It is concluded that all solvent effects are not adequately incorporated into the zero shear viscosity for the purposes of constructing master plots; however, the shape of the master plot is not affected by the solvent or the polymer block structure.     

Rheological behavior of semi‐aromatic transparent polyamide

The rheological behaviors of semi‐aromatic transparent polyamide (SATPA) melt are investigated using a capillary rheometer. The effects of shear rate, shear stress, and temperature on the apparent viscosity η_a of SATPA are discussed. A correlation of non‐Newtonian index with temperature is obtained. The results show the shear thinning of SATPA; meanwhile η_a decreases with increasing temperature and shear rate, and the viscous flow activation energy is further obtained from temperature dependence of the samples. It was concluded that the apparent viscosity η_a is sensitive to temperature at lower shear rate owing to the higher viscous flow activation energy; on the contrary, the influence of temperature effect on the apparent viscosity becomes minor at higher shear rate due to the lower viscous flow activation energy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1586–1589, 2005     

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.     

Rheological behavior of compatible polymer blends. I. Blends of poly(styrene-Co-acrylonitrile) and poly(ε-caprolactone)

The rheological behavior of blends of poly(styrene-co-acrylonitrile) (SAN) and poly(ε-caprolactone) (PCL) was investigated, using a cone-and-plate rheometer. For the study, blends of various compositions were prepared by melt blending using a twin-screw compounding machine. The rheological properties measured were shear stress (σ₁₂), viscosity (η), and first normal stress difference (N₁) as functions of shear rate (γ) in steady shearing flow, and dynamic storage modulus (G′) and loss modulus (G″) as functions of angular frequency (ω) in oscillatory shearing flow, at various temperatures. It has been found that logarithmic plots of N₁ versus σ₁₂, and logarithmic plots of G′ versus G″, become virtually independent of temperature but vary regularly with blend composition, and that the zero-shear viscosity of the blends, (η_o)_blend, follows the relationship, 1/log(η_o)_blend = w_A/log η_0A + w_B/log η_0B, where η_0A and η_0B are the zero-shear viscosities of components A and B, respectively, and w_A and w_B are the weight fractions of components A and B, respectively. The physical implications of the relationship found are discussed.     

Effects of extrusion conditions on rheological behavior of acrylonitrile–butadiene–styrene terpolymer melt

The influence of temperatures and flow rates on the rheological behavior during extrusion of acrylonitrile–butadiene–styrene (ABS) terpolymer melt was investigated by using a Rosand capillary rheometer. It was found that the wall shear stress (τ_w) increased nonlinearly with increasing apparent shear rates and the slope of the curves changed suddenly at a shear rate of about 10³ s^?1, whereas the melt‐shear viscosity decreased quickly at a τ_w of about 200 kPa. When the temperature was fixed, the entry‐pressure drop and extensional stress increased nonlinearly with increasing τ_w, whereas it decreased with a rise of temperature at a constant level of τ_w. The relationship between the melt‐shear viscosity and temperature was consistent with an Arrhenius expression. The results showed that the effects of extrusion operation conditions on the rheological behavior of the ABS resin melt were significant and were attributable to the change of morphology of the rubber phase over a wide range of shear rates. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 606–611, 2002     

Rheological properties of concentrated polymer solution: Polybutadiene in good and θ solvents

The zero shear viscosity, η° of three polybutadiene samples having different molecular weights over a wide range of concentration (1.0–35.0% polymer) in good and θ solvents has been studied. Superposition of viscosity data has been made to give a single composite curve for each solvent by shifting them vertically by a factor (M°/M)^3.4, where M° represents the molecular weight of the reference sample. The shift factor is found to be proportional to M^3.4 in the region of higher concentration, which indicates that the 3.4-power law is valid for the data of polybutadiene. The double-logarithmic plots of relative viscosity η°_r as a function of c⁵M^3.4 yielded a single composite curve approximating a straight line with slope of unity at the higher values of the variables. The results indicate that over a considerable range of the variables (molecular weight and concentration) at a constant temperature, the relative viscosity is a single function of c⁵M^3.4. The results for double-logarithmic plots of zero shear specific viscosity η°_csp as a function of concentration confirmed those observed in polycholoroprene samples studied earlier that the η0_sp values in θ solvents at higher concentration region are found to be higher than those found in good solvents, whereas in the moderately concentrated region the values are just opposite in θ and good solvents. The viscosity crossover in θ solvents is not as sharp as is found in case of polychloroprene samples and that crossover, too, has taken place in the range of concentration of 11.7–31.6% polymer, which is comparatively higher than that of polychloroprene samples (6.06–21.0% polymer). The results indicate some relation between viscosity crossover and polymer polarity, supporting the idea of enhanced intermolecular association in poor solvents. To correlatethe viscosity data obtained in good and poor solvents, two methods, one given by Graessley and the other given by Dreval and coworkers involving the correlating variable c[η], were considered. The plots of relative viscosity η°, versus the correlating variable c[η] in benzene (good solvent) yielded one curve, but in the case of θ solvents (dioxane and isobutyl acetate), the same plots yielded three separate curves instead of a single curve, which is rather unusual. The appropriate correction on the correlating variable for chain contraction in the concentrated region in a good solvent moved the data to a common curve, especially in lower concentration region, but at the higher concentration region a slight overestimation of data seems to have been effected. On the other hand, the plots of log η as a function of correlating variable c[η] yielded a single curve for three samples in the good solvent benzene, but in poor solvents (diozane and isobutyl acetate) the same plots yielded three separate curves for three samples instead of a single curve, the reason for which is not known at present. However, the normalization of the correlating variable c[η] with Martin constant K_M reduced all experimental data of the polymer samples to a common curve. The correlation of the viscosity data by either of the two methods seems to be possible in the case of the nonpolar flexible polymer, polybutadiene.     

Shear stress at polymer/metal interface during melting in extrusion

Prediction of the screw horsepower requirement involves, among many others, the calculation of the shear stress (τ_s) between the solid polymer and the barrel surface during melting. Prediction of the solid bed down-channel velocity also requires the calculation of τ_s. However, the pseudoplastic nature and strong temperature dependence of melt viscosity make the mathematics of calculating τ_s extremely difficult. As a first step of developing a reasonable mathematical model for calculating τ_s, experimental measurements of τ_s were made over a wide range of metal temperature and sliding speed for five commercial polymers using molded, block samples. Although dependences of τ_s on metal temperature and sliding speed were found to have similar functionality to those of the dependences of melt viscosity on melt temperature and shear rate, this study showed that τ_s could not be expressed as a sole function of the melt rheological properties. Our subsequent study, to be reported in a follow up paper, will show that τ_s must be expressed as a function of the thermodynamic properties and melt density of the polymer as well as the melt rheological properties and the melting conditions.     

Shear creep resistance of styrene–isoprene–styrene (SIS)‐based hot‐melt pressure‐sensitive adhesives

The effects of the properties of substrates and tackifier on the shear creep of SIS‐based HMPSAs were investigated. The holding power (t_b) and shear adhesion failure temperature (SAFT) were measured. The relationship between the complex viscosity and the holding power was examined. The holding power and SAFT values of the triblock SIS blends were higher than those of the diblock‐containing SIS blends, perhaps because blends using triblock SIS have higher crossover temperature and complex viscosity than those using diblock‐containing SIS. Higher levels of aromatic resin‐modified aliphatic tackifier and rosin ester were found to decrease the holding power of the HMPSAs. This maybe due to the fact that rosin ester and aromatic‐modified aliphatic resin are compatible with both the ends and midblocks of SIS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 825–831, 2006     

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.     

Effect of concentration on apparent viscosity of a globular protein solution

The viscosity of a globular protein solution as a function of concentration was studied with a cone and plate viscometef (Ferranti-Shirley Viscometer System) using, β-lactoglobulin as a model. An aqueous buffer solution (pH 7, ionic strength 0.04) containing up to 40 percent protein was subjected to rates of shear between 800 and 17,000 sec^?1. Specific viscosity of β-lactoglobulin up to 10 weight percent was proportional to the weight concentration of protein in solution such that: η_s = η₀ [ 1+0.8 (weight percent concentration)] where η₀ and η_s are viscosity coefficients for the pure solvent and the solution, respectively. For 3-40 weight percent, a linear relation of shear rate and shear stress was observed at high shear rates. Linearity began at 3500, 4300, 6800, and 7000 see^?1 for 10, 20, 30 and 40 weight percent concentrations respectively. The apparent viscosity was lower below these critical shear rates.     

Morphology control of polyoxy‐methylene/thermoplastic polyurethane blends by adjusting their viscosity ratio

Polyoxymethylene (POM) is an important plastic with very good properties. However, its poor impact strength limits its applications. Theoretical and experimental studies have confirmed that thermoplastic polyurethane (TPU) can effectively enhance the notched impact strength of POM. This paper reports that the notched impact strength of POM/TPU blends can be further improved when these blends are endowed with a fine morphology by changing the viscosity ratio of TPU to POM (P = η_TPU/η_POM) during processing. The experimental results show that the viscosity of TPU is more sensitive to temperature than that of POM, and that the viscosity ratio P decreases with increasing temperature; also for quite a wide range of shear rate, P is close to 1 when the processing temperature (T_p) is around 190 °C. Accordingly, the phase structure of POM/TPU blends changes with P. The dispersed phase of TPU shows ellipsoidal morphology when P > 1 at T_p < 190 °C, filamental morphology when P ≈ 1 at T_p ≈ 190 °C and spheroidal morphology when P < 1 at T_p > 190 °C. The results suggest that the filamental morphology endows POM/TPU (90/10) blends with the highest notched impact strength (～14 kJ m^?2). Copyright © 2006 Society of Chemical Industry     

Effect of rheological parameters on the miscibility and polymer–filler interactions of the black-filled blends of polyethylene–vinyl acetate and polychloroprene

Miscibility of 30 phr loaded black-filled (N110) blends of polyethylene-vinyl acetate (EVAc, VAc content 28%) and polychloroprene (CR) are investigated through shear and dynamic deformations. Both shear (η_a) and dynamic elongational (η′_E) viscosities are conducive to their miscibility as both show positive deviation for all blends, though dynamic out-of-phase (η″_E) viscosity shows negative-positive deviation. Both η_a and η′_E follow the power law relationship with shear rate (γ˙_wa) and frequency (ω), respectively. Both storage (E′) and loss (E″) modulii increases with frequency. The higher dissipative energy at around 11 Hz may be due to its syncronization with molecular vibrations of the polymer segments. The effect of rheological parameters like strain rate and temperature on the relative change in shear (RV_S) and dynamic elongational (RV_D) viscosities is reported for the variation of blend composition with 30 phr loaded black-filled compounds. The variation of both RV_S and RV_D follows a third order polynomial equation with carbon black loading in 50/50 EVAc/CR blend; all the polynomial constants are function of temperature and strain rate. © 1996 John Wiley & Sons, Inc.     

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     

A phenomenological master curve for viscosity—structure data for two phase polymer systems in simple shear flow

A master curve hypothesis is established based on a mass balance and an assumption of continuous stress through interfaces for well dispersed two phase systems with “defined” zero shear viscosity. The master curve, which is in reasonable accordance with experimental data is represented in a double logarithmic plot of log (η_T/_T,0) against log \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{\eta _{T,0} M_C H\rho}}{{c^2 RT}}\dot \gamma _T} \right) $\end{document}. M_c is the molecular weight between entanglements, H = M?_w/M?_n, ρ is the density, c is the polymer concentration, all defined for the continuous phase. η_T and η_T,0 are the viscosity and zero shear viscosity of the blend, η_T is the apparent shear rate, R the gas constant, and T is absolute temperature.     

Physical Characterization of a Commercial Suspoemulsion as a Reference for the Development of Suspoemulsions

Viscoelasticity, low shear flow, microstructure, and physical stability of a commercial suspoemulsion pesticide are studied to serve as a point of reference for the development of new suspoemulsions. Creep compliance tests allow the zero‐shear rate viscosity, η₀, to be calculated. As expected, the values of η₀ decrease with temperature. The storage modulus is higher than the loss modulus until a crossover frequency, ω*, which is located at the lower frequencies studied. The dynamic parameters decrease with higher temperature and ω* increases in agreement with a faster relaxation mechanism. Multiple light scattering predicts the occurrence of a creaming destabilization process, whose kinetics depends on temperature. Rheological measurements are demonstrated to be a powerful tool to assist in the prediction of destabilization processes together with the multiple light scattering technique.     

Influence des copolymères greffés sur les propriétés mécaniques des alliages de polyéthylène avec polystyrène

The use of graft copolymers polyethylene-graft-polystyrene (P(E-g-S)) in blends of low-density polyethylene and polystyrene is studied. The copolymers P(E-g-S) are prepared by polymerisation of styrene in the presence of hydroperoxylated polyethylene. Addition of 2,5 wt.-% P(E-g-S) to polyethylene-polystyrene blends considerably increases its breaking strength σ_R but much less so its elongation at break ε_R. A comparison of graft and block copolymers used as emulsifiers in polyethylene-poly-styrene blends at present shows that P(E-g-S) is intermediate between the former graft and block copolymers with regard to their influence on the mechanical properties of blends. Photographs of fractures in the blends show a tenfold smaller phase size upon adding P(E-g-S) to the blends.     

Rheological properties of glass bead-filled low-density polyethylene composite melts in capillary extrusion

The melt flow of glass bead-filled low-density polyethylene composites in extrusion have been observed by using a capillary rheometer to investigate the effects of temperature, shear rate, and filler content on the rheological properties of the melts. The results show that the melt shear flow obeys a power law, and the dependence of the apparent shear viscosity, η_app, on temperature is in accord with an Arrhenius equation. At the same temperature and shear rate, η_app increases slightly with increasing the volume fraction of glass beads, but the flow behavior index decreases with increasing filler content. In addition, the first normal stress difference of the melts linearly increases with increasing wall shear stress. Good agreement is shown with the N₁ calculated with the equation presented in this article and the pressured data from the sample melts. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1451–1456, 1999