René Muller

Viscoelastic properties and morphology of two-phase polypropylene/polyamide 6 blends in the melt. Interpretation of results with an emulsion model

Linear viscoelastic dynamic moduli of two‐phase PP/PA6 blends in the molten state have been measured as a function of frequency in a cone and plate rheometer. With respect to the PP and PA6 components, blends are characterized by high values of the storage modulus at low frequencies and long relaxation times. A parallel has been drawn between these results and morphological observations of sheared specimens showing that the time required for deformed dispersed domains to revert to their spherical shape is of the same order of magnitude as mechanical relaxation times. A model for undiluted emulsions of Newtonian liquids has been used to account for the variations of dynamic moduli in the terminal zone. In this frequency range, the rheological behavior is directly related to a few physically significant parameters such as zero‐shear viscosity of phases, dispersed particle size, and surface tension between phases.

Linear viscoelasticity in the melt of impact PMMA. Influence of concentration and aggregation of dispersed rubber particles

The linear viscoelastic behavior in the melt of PMMA/PS blends and various blends of PMMA containing rubbery latex particles has been characterized by dynamic shear rheometry. For the rubber‐toughened PMMA samples, the influence of rubber content, structure of the latex particles, and aggregation of the particles in the PMMA matrix have been investigated. Morphologies of the dispersed type or of the aggregated type were produced by performing the blending in the melt or in solution. The data for G’ and G‘ have been analyzed in the frame of a rheological emulsion model which is found to account for the behavior of the PMMA/PS blends and of rubber‐toughened PMMA at low rubber content. At high rubber concentrations the model does not predict the secondary plateau in G’ which arises at low frequencies for these systems. Therefore, this plateau cannot be attributed to the deformability of dispersed inclusions as in PMMA/PS blends, but is shown to depend on the extent of aggregation of the dispersed particles, ...

Droplet deformation in polymer blends during uniaxial elongational flow: Influence of viscosity ratio for large capillary numbers

The deformation in uniaxial elongational flow of dispersed droplets in immiscible molten polymer blends was studied for viscosity ratios 0.005<p=η(drop)/η(matrix)<13 and negligible interfacial tension, with an original method based on quenching elongated specimens. Although drop deformations (drop major axis over initial diameter) were in the range 1≤λd≤5, good overall agreement was found with the small deformation Newtonian theory, which predicts that the drop versus matrix deformation ranges from 5/3 to 0 when p increases from 0 to infinity. The theoretical prediction that for p lower than 1, the droplet should deform more than the faraway surrounding matrix, with a limiting ratio of 5/3 at vanishing droplet viscosity, was verified both experimentally and numerically with a finite element simulation.

Rheology/morphology/flow conditions relationships for polymethylmethacrylate/rubber blend

Viscoelastic behavior, phase morphology and flow conditions relationships in polymer/rubber blends have been investigated. The importance of such correlations is illustrated on polymethylmethacrylate (PMMA)/rubber blends subjected to different flow conditions both under small and large deformations. In small-amplitude oscillatory shear (the morphology does not change during the flow) the elastic modulus G′ of the concentrated blends shows a secondary plateau, G′p, in the low frequency region. This solid-like behavior appears for rubber particle contents beyond the percolation threshold concentration (15%). Morphological observations revealed that for concentrations higher than 15%, the particles are dispersed in a three-dimensional network-type structure.In capillary flow it was found that the network-type structure was destroyed and replaced by an alignment of particles in the flow direction. This morphological modification resulted in a decrease in both viscosity and post-extrusion swell of the blends. Morphological observations revealed that the ordered structure in the flow direction was concentrated only in the skin region of the extrudate, where the shear stress is higher than the secondary plateau, G′p. A simple kinetic mechanism is proposed to explain the observed morphology.Similarly, steady shear measurements performed in the cone-and-plate geometry revealed alignment of particles in the flow direction for shear stress values higher than G′p.

Determination of interfacial tension of polymer melts by dynamic shear measurements

Abstract The linear viscoelastic behavior of two-phase polymer blends in the melt is characterized by high values of storage modulus at low frequencies and by long relaxation times. These rheological properties depend directly on the interfacial tension α between the two polymers. Dynamic shear measurements provide, therefore, a method to determine α without perturbation of the system. The frequency dependence of dynamic moduli could be accounted for with an emulsion model of two viscoelastic liquids. Experimental data for G′ (ω) and G″ (ω) on poly(dimethylsilox (PDMS)/poly (oxyethylene-diol) (POE-DO) blends have been found to be in good accordance with the emulsion model and the value of interfacial tension found in the literature for this system.

Drop deformation during elongational flow in blends of viscoelastic fluids. Small deformation theory and comparison with experimental results

The deformation of dispersed droplets in immiscible polymer blends was studied in elongational flow, with an original method based on quenching specimens elongated in the melt. Results for high capillary numbers and different viscosity ratios were compared to the linear theory of viscoelastic emulsions of Palierne. Simple expressions for the drop deformation could be obtained for Maxwell fluids, and the influence of viscoelasticity of matrix and inclusions on the drop deformation process was discussed. With respect to the Newtonian approximation, the description of some experimental data could be improved. However, the predictions of the viscoelastic model appeared to be very sensitive to the choice of relaxation times.

Rheological and morphological study of the phase inversion in reactive polymer blends

Abstract The morphology and melt rheological properties were characterized for a polymer blend where the viscosity ratio was changing with time. The reactive phase, an ethylene methyl acrylate (EMA) copolymer containing a diol, was blended in the melt with linear low density polyethylene (LLDPE). Dual continuity was found for the initial morphology of the reactive blends over a broad range of composition in contradiction with the phase inversion rule: ΦAηB = ΦBηA. The influence of blending conditions and annealing on the initial morphology was studied. For a blend where the LLDPE phase is initially dispersed in EMA, the torque and normal force measured in the parallel plate geometry go through a maximum when the morphology becomes co-continuous.

Viscoelastic Properties of Polydimethylsiloxane‐Polyoxyethylene Blends in the Melt. Emulsion Model

Linear viscoelastic dynamic moduli of two‐phase polymer blends in the molten state have been measured as a function of frequency in a conicylinder rheometer. The polymer blends are characterized by high values of the storage modulus at low frequencies and by long relaxation times. The model developed by Choi and Schowalter for semidilute emulsions of Newtonian liquids has been used to account for the variations of dynamic moduli in the terminal zone. In this frequency range, the rheological behavior is directly related to a few physically significant parameters such as zero‐shear viscosity of phases, dispersed particle size, and interfacial tension between phases. The experimental results obtained for the polydimethylsiloxane‐polyoxyethylene blends show that the variation of matrix viscosity and volume fraction of inclusions is in accordance with the semidilute emulsion law.

Influence of molecular weight distribution on viscoelastic constants of polymer melts in the terminal zone. New blending law and comparison with experimental data

Abstract A new blending law for the viscoelastic constants of polymer melts in the terminal zone is proposed on the basis of the well known power law for viscosity (η0 ∼ Maw) and a simple assumption of the dependence of the weight-average relaxation time on molecular weight distribution. This blending law reduces to the modified Rouse model if the exponent a takes the value of 3. The recoverable compliance of binary blends can be calculated as a function of zero-shear viscosities and recoverable compliances of their components and of parameter a. Measurements have been carried out on binary blends of nearly monodisperse PS melts. For these results as well as for various experimental data from the literature, satisfactory agreement between calculated and experimental values of the recoverable compliance has been observed. The blending law is extended to polymer melts with continuous molecular weight distribution.

Dynamic Compressive Behavior of a Melt Mixed Polypropylene/Organoclay Nanocomposites

This work aims to investigate the dynamic behavior of polypropylene organoclay nanocomposites. The nanocomposite was obtained by mixing the polypropylene matrix with a masterbatch of polypropylene modified anhydride maleic and montmorillonite organoclay (pp-nanocor). The dynamic behavior was investigated by using split Hopkinson pressure bars, at different strain rates and different temperatures. The obtained nanocomposite exhibits a good dispersion and a partially exfoliated morphology. To study the effect of nanocomposite dispersion and morphology on the dynamic behavior, another nanocomposite was prepared by melt mixing of polypropylene and a modified montmorillonite (dellite) (PP dellite). The dynamic property results for PP-nanocor show an increase of both Young’s modulus and yield stress with the increasing organoclay concentration. However, PP-dellite nanocomposites present poor mechanical properties compared with those of PP-nanocor. [DOI: 10.1115/1.4005420]