The significance of capillary rheology testing temperature for predicting PVC extrudability

A rheological investigation of the saturated fatty acids as lubricants for PVC was made in a Sieglaff-McKelvey rheometer over a wide temperature range. Results reveal that with an increase in carbon chain, fatty acids became more effective in reducing the melt viscosity of PVC. It was also discovered that the maximum viscosity variation due to these materials was observed at 350°F. At test temperatures of 400°F and above, no major viscosity differences were observed. Furthermore, the changes in the melt viscosity were more pronounced at shear rates less than 200 sec^?1. The usefulness of the measured viscosity variations at the critical test temperature of 350°F was shown by extrusion. An excellent correlation between the apparent melt viscosity and extrusion melt temperature was found. The criticalness of the test temperature in assessing the effect of lubricants on PVC flow is discussed.     

Melt rheology of polymer blends

The rheological behavior of polymer blends is compared with that reported for emulsions, block polymers and homologous polymer blends. It has been shown that the properties of polymer alloys frequently differ from those of these “model” systems—the principal difference being the lowering of at least one rheological function below the value predicted In the log-additivity rule. Primarily, the most recent (post 1977) results are reviewed. The data obtained by the authors on the flow of poly(ethylene terephthalate)/Polyamide-6,6 are discussed in detail.     

Melt rheology of high-density polyethylene

The melt rheology of high density polyethylene was investigated. Linear viscoelasticity, capillary flow properties, and molecular weight parameter were measured with a plate relaxometer, capillary rheometer, and gel permeation chromatography, respectively. Intimate correlations among the slope of relaxation modulus curve, non-Newtonian flow behavior, Barus effect, and molecular weight parameter, M_z(M_z+1)/M_w, respectively, were found.     

Shear and elongational rheology of polyethylenes with different molecular characteristics. I. Shear rheology

Four metallocene polyethylenes (PE), one conventional low density polyethylene (LDPE), and one conventional linear low density polyethylene (LLDPE) were characterized in terms of their complex viscosity, storage and loss moduli, and phase angle at different temperatures. The effects of molecular weight, breadth of molecular weight distribution, and long‐chain branching (LCB) on the shear rheological properties of PEs are studied. For the sparsely long‐chain branched metallocene PEs, LCB increases the zero‐shear viscosity. The onsets of shear thinning are shifted to lower shear rates. There is also a plateau in the phase angle, δ, for these materials. Master curves for the complex viscosity and dynamic moduli were generated for all PE samples. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Shear and elongational rheology of polyethylenes with different molecular characteristics. II. Elongational rheology

The elongational viscosities of polyethylenes with different molecular characteristics were measured at different Hencky strains and temperatures with a capillary rheometer by the replacement of the capillary cylindrical die with a hyperbolic converging die. The hyperbolic shape of the die established a purely elongational flow field at a constant elongational strain rate throughout the die. The effects of molecular characteristics such as the molecular weight, molecular weight distribution, and long‐chain branching and processing conditions such as the temperature and Hencky strain on the elongational rheology of the polyethylene samples were studied. Good master curves were generated for temperature and Hencky strain shifting and simultaneous shifting with respect to both the temperature and Hencky strain. Both the molecular weight distribution and long‐chain branching seemed to promote strain rate thinning and reduce the elongational viscosity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1184–1194, 2007     

Melt rheology of aliphatic hyperbranched polyesters

Rheological behavior in melt of aliphatic hyperbranched polyesters (AHBP), synthesized using pseudo‐one‐step and one‐step procedure, was investigated in this work. Three commercially available AHBP were also examined. Because of the presence of relatively strong hydrogen bonds between numerous end hydroxyl groups, AHBP of lower generation number, as well as the sample of tenth pseudo generation, show non‐Newtonian behavior in the entire investigated frequency and temperature region. However, for other examined AHBP, the slope of the frequency dependence of complex viscosity (η* = f(ω)) becomes smaller with the temperature increase. Therefore, samples of fourth, fifth, and sixth pseudo generations show Newtonian behavior at temperatures higher than 70°C. Value of glass transition temperature, melt flow activation energy, fractional free volume, and thermal expansion coefficient were determined for the investigated AHBP. The influence of the type of end groups on rheological properties of AHBP was also examined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Melt rheology of some aliphatic polyamides

The melt rheology of nylon-6, nylon-6,6, nylon-6,10 and nylon-11, has been investigated by different techniques. It has been found that their behaviour is quite similar and almost Newtonian regarding both the flow curves and the elastic and instability properties. The samples show rather different viscous flow activation energies, although their values approach each other at high shear rate. The critical shear stresses of such materials are compared with those of other known polymers.     

Melt rheology of semirigid PVC compounds

This paper describes a statistical experiment on the melt behavior of semirigid PVC compounds using a capillary rheometer. Three formulating variables, viz., PVC resin inherent viscosity, internal lubricant concentration, and external lubricant concentration, and two processing variables, viz., shear rate and temperature, were examined. The dependent variables tested were melt viscosity and critical shear rate. The regression equations relating the formulating variables with dependent variables were obtained at various temperatures. Melt distortion free formulations can thus be determined from the contour plots of the dependent variables. Depending on formulation and processing conditions, a discontinuity in the flow curves is observed Melt irregularity of extrudates was observed to occur not only at very high shear rates but also at very low shear rates and at the discontinuity of flow curve.     

Melt rheology of organoclay and fumed silica nanocomposites

The objective of the present work is to investigate, from the open literature, the recent developments in the rheology of silica and organoclay nanocomposites. In particular, this paper focuses on general trends of the linear viscoelastic behaviour of such nanocomposites. Hence, the variations of the equilibrium shear modulus and critical strain (limit of linearity), which depend on power laws of the volume fraction of particles, are discussed as filler fractal structure. In the third section, the strong nonlinearity behaviour (Payne effect) of filled polymers has been discussed in terms of filler nature. Typically two mechanisms arise to depict the linear solid-like behaviour and the Payne effect: particle–particle interactions is the dominant mechanism in fumed silica nanocomposites whereas particle–polymer interaction is the dominant one in colloidal silica nanocomposites at identical filler concentrations. However, these interactions are balanced in each nanocomposite systems by the silica surface treatments (chain grafting, silane modification) and the molecular weight of the matrix. Finally, we aim to unify the main findings of the literature on this subject, at least from a qualitative point of view.We finally report on the thixotropy and modulus recovery after a large deformation in steady and dynamic shear conditions. Following this, the nonlinear rheological properties of nanocomposite materials have been discussed. The discussion is particularly focused on the effect of flow history (transient shear experiments) on the orientation–disorientation of clay platelets. Actually, the linear and nonlinear rheological properties are consistent with a network structure of a weakly agglomerated tactoids. As far as exfoliated clay nanocomposites are concerned, the inter-particle interaction is the dominant effect in the nonlinearity effect.     

Melt rheology of vinylidene chloride-vinyl chloride copolymers

A continuous extruder slit-die rheometer system determines the rheological properties of thermally sensitive copolymers of vinylidene chloride and vinyl chloride to aid the design of processing screws, melt dies, and coextrusion feed blocks for the production of barrier film. The flow of VDC-VC copolymers was dependent on molecular weight, temperature, and shear rate. Increased chain mobility causes low-melting-temperature copolymers to flow more easily. Liquid additives also reduce viscosity.     

Melt rheology of vinyl chloride-vinyl acetate copolymers

Melt flow behavior of vinylchloride-vinyl acetate copolymers is measured and expressed as melt viscosity, shear rate and shear stress—information useful to the plastics engineer in formulation, design, and processing. Copolymer of comparable I.V. to homopolymer PVC requires less energy to process. Good compounding techniques are required to realize the potential of ultra-clear profile extrudates.     

Influence of molecular structure on the rheology and thermorheology of metallocene polyethylenes

The rheology of linear and branched metallocene polyethylenes (m‐PEs) was investigated. The linear metallocenes were prepared by gas‐phase polymerization, while the branched PEs were commercial resins. Molecular parameters such as M_w, branch type, and molecular weight distribution have influenced the viscoelastic behavior of both linear and branched PEs, whereas branch content (BC) had little influence on viscoelastic properties. Plots of log G′ versus log G″ revealed the effect of comonomer type on the viscoelastic behavior of m‐PEs. Flow activation energy (E) was found to be sensitive to both M_w and BC. Also, E for ethylene‐octene copolymers was observed to be always higher than the butene counterparts, which have been caused by the increase in molar volume of the repeating unit. For the effect of BC on E, different trends were observed for octene and butene m‐LLDPEs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1717–1728, 2006     

Melt rheology of polymer blends the morphology feedback

Particular rheology compositions (PRC) so far observed for blends of polyolefins are confirmed with composition dependence of melt elasticity and viscosity functions for polypropylene/rubbers and blends of other commercial polymers. Particular morphology at PRC was indirectly ascertained from the composition dependence of specific volume, v_T–compositions for which the maximum v_T observed are those of minimum viscoelasticity. Direct evidence from scanning electron microscopy (SEM) indicates that the disperse morphology undergoes distinct change at PRC: from uniform into bimodal, with coarser core. Rubber rich mixtures display stratified texture confirming that the melt elasticity ratio (Van Oene's) criterion for disperse/stratified morphology transition is valid in case of polypropylene/rubber blends. For a set of polymers of given melt elasticity ratios and at a composition ratio, static and rotational distributive mixers generate polyblends differing significantly in the melt rheology—morphology interaction.     

Melt rheology of highly loaded ferrite-filled polymer composites

This paper presents new experimental data on the viscosity of ferrite-filled polymers at high levels of loading. The choice of matrix and the choice of filler and filler loading has direct relevance to commercially important systems of magnetic plastics and rubbers. The effect of shear rate, concentration, and temperature on the rheological behavior of such highly loaded systems has been discussed in detail. The differences in the relative viscosities between the filled and unfilled systems for various matrices have been explained on the basis of polymer filler affinity and filler-filler interaction.     

Melt rheology of polyarylate/polybutylene terephthalate blends

The viscosity, the activation energy of flow, and the exchange reactions of bisphenol A 50/50 isophthalic/terephthalic acid and poly(butylene terephthalate) blends are studied by means of an extrusion capillary rheometer, covering a range of 10 s^?1 to 300 s^?1 shear rate and 280°C to 300°C temperature. The results are interpreted in terms of compatibility and free volume additivity. The decrease in viscosity with time is explained as a result of transesterification rather than degradation.     

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     

Melt rheology of high impact polystyrenes at high shear stresses

A study of the theological properties of commercial polystyrenes, (PS), and high impact polystyrenes (HIPS), is made in the range of shear stresses of practical interest in industrial polymer processing. A general viscosity-shear rate-temperature relationship is defined for these products, with a power law exponent of n = 0.3 and an activation energy of 27 Kcal/mol. The fluid elasticity is studied in terms of steady state shear compliance. An expression relating shear compliance, viscosity and molecular weight distribution is obtained for HIPS. As in other two-phase systems, a decrease in elasticity with viscosity is observed.