Michel Moan

Influence of composition and morphology on rheological properties of polyethylene/ polyamide blends

Abstract The effects of composition and resulting morphology on rheology of blends of polyethylene and polyamide 12, two immiscible polymers having the same Newtonian viscosity but different elasticity, were studied in the whole range of volume fraction. The composition dependence of zero shear rate viscosity η 0 and first normal stress difference N 1 show a positive deviation from the additivity law: η 0 and N 1 increase gradually at low and moderate volume fraction of the dispersed phase, but remain almost constant in the phase inversion region. The variation of zero shear rate viscosity has been analysed, in relation to morphology observations, by an emulsion model as developed by Oldroyd in the case of droplet-type morphology and by a layer model which takes into account the simultaneous presence of droplets and fibres when the morphology is partially fibrillar. If the volume fraction of the dispersed phase is not too low, the first normal stress difference is proportional to shear rate, in agreement with the prediction of Doi-Ohta theory, as a result of morphology modifications during flow. The linear viscoelastic behaviour has been analysed using Paliernes model and the interfacial tension between the two polymers has been determined by fitting the dynamic moduli with this model.

Rheological, morphological and structural properties of PE/PA/nanoclay ternary blends: Effect of clay weight fraction

The effect of an organically modified layered silicate on the rheological, morphological, and structural properties of immiscible polyethylene/polyamide (PE/PA) blends was investigated. The blends have been prepared for PA weight fractions ranging from 10 to 90% and at clay weight fractions from 1 to 6%. Scanning electron microscopy and transmission electron microscopy have been used to study the morphology and the structure of the blends. The dispersed phase size was shown to decrease with increasing clay content up to 2% and tends to stabilize at higher fractions. For PE matrix blends, clay particles were shown to be essentially located at the interface of the two polymers, forming an interphase whose thickness grows with clay fraction. For PA matrix blends with 2% of clay, the interphase thickness is stabilized at 11 nm; further clay addition leads to dispersion of clay within PA. Oscillatory and steady shear measurements have shown that PE matrix ternary blends behaved like polymer blends and underlined the contribution of an interphase at high clay fractions. For sufficiently filled PA matrix blends, a yield behavior was observed. The behavior of PA matrix ternary blends, dominated by the organoclay dispersed in PA, is similar to that of nanocomposites.The effect of an organically modified layered silicate on the rheological, morphological, and structural properties of immiscible polyethylene/polyamide (PE/PA) blends was investigated. The blends have been prepared for PA weight fractions ranging from 10 to 90% and at clay weight fractions from 1 to 6%. Scanning electron microscopy and transmission electron microscopy have been used to study the morphology and the structure of the blends. The dispersed phase size was shown to decrease with increasing clay content up to 2% and tends to stabilize at higher fractions. For PE matrix blends, clay particles were shown to be essentially located at the interface of the two polymers, forming an interphase whose thickness grows with clay fraction. For PA matrix blends with 2% of clay, the interphase thickness is stabilized at 11 nm; further clay addition leads to dispersion of clay within PA. Oscillatory and steady shear measurements have shown that PE matrix ternary blends behaved like polymer blends and underlin...

Rheological properties of short fiber model suspensions

The rheological behavior of two series of model suspensions containing the same glass fibers in a Newtonian polybutene and in a Boger fluid has also been investigated. The steady-state shear viscosity of both supensions increased with fiber content, but the suspensions in the Boger fluid became shear thinning. Both types of suspension exhibited non-negligible normal stresses. The steady-state viscosity and normal stress difference of the supensions in the polybutene are well predicted by the Lipscomb (1987) equation coupled with the Folgar–Tucker (1984) model. Both types of fiber suspensions were shown to exhibit shear and normal stress overshoots in stress growth experiments. Under flow reversal, a shear stress overshoot was observed at a larger deformation compared to the primary overshoot. The reverse overshoot has been attributed to tumbling of fibers that are not totally aligned in the flow direction even after a very long time. When the flow was reversed, the normal stress difference took initially ...

Rheological behavior of a hydrophobically associating water soluble polymer

We have investigated experimentally the behavior of a water soluble associating polymer system, hydrophobically modified (hydroxypropyl)guar, with very few randomly distributed hydrophobic substituents along the chains. We focus mainly on the rheological effects due to the superposition of the reversible hydrophobic interaction network on the physical entanglement network in dense macromolecular systems of that kind. Both linear and nonlinear response to transient, steady, and oscillatory shear flow prove that, in the semidilute and moderately concentrated regime, the hydrophobically associating polymer behaves like a classical dense macromolecular system whose long‐time dynamics can be described using only one long relaxation time, identified as a retarded disengagement time, much larger than the association lifetime. The temporary hydrophobically associating network can be destroyed when applying a critical shear stress τc, which is studied as a function of polymer concentration.

Solution and adsorption properties of hydrophobically associating water-soluble polyacrylamides

Abstract The behavior in aqueous solution and at a solid/liquid interface of an associating hydrophilic/hydrophobic copolymer of acrylamide and alkyl methacrylate has been studied. A comparison between the behavior of hydrophobically associating and of non-associating polymers termed HAPAM and PAM, respectively of the same molecular weight indicates the role played by the hydrophobic moieties. Viscosity measurements in solution show the behavior expected of HAPAM compared to PAM i.e. a smaller intrinsic viscosity measured in the dilute regime and larger viscosity in the semi-dilute regime. At the water/mineral interface, adsorption isotherms for HAPAM show an unusual shape, characterized by the absence of a plateau region and a continual increase in the adsorbed amount with polymer concentration in the bulk. The enhancement of polymer chain interactions insolution and the increase in the adsorbed amount on a mineral surface are observed within the same polymer concentration range. This particular adsorption shape can be explained by the formation of multiple layers through hydrophobic associations, the adsorbed layers being formed in part by some chains that are not directly in contact with the surface. The influence of KCl concentration has been studied. Modification of the polymer solution rheological properties and of the adsorbed amount of polymer leads to a strengthening of hydrophobic interactions in the presence of KCl.

Rheological properties and reactive compatibilization of immiscible polymer blends

The effects of addition of a reactive compatibilizer, a random terpolymer, on morphological and rheological properties of blends of polyamide dispersed in a polyethylene matrix were studied experimentally. This addition leads to smaller size and narrower size distribution of the dispersed phase. This has been related to the presence, at the interface, of copolymers, formed in situ by reaction between the polyamide and the terpolymer, which form an interphase between the nodules and the matrix. The linear viscoelasticity of these compatibilized blends reveals that, in addition to the form relaxation process (relaxation time λd) even observed in absence of compatibilizer, another relaxation process, which has been related to the dynamics of nodule-matrix interphase, is observed at a characteristic time λint higher than λd. The concentration and molecular weight dependence of this characteristic time λint, and the intensity Hint of the relaxation mechanism associated to λint has been investigated. The steady...

Nonlinear behavior of very concentrated suspensions of plate-like kaolin particles in shear flow

Steady and transient shear flows have been used to study the nonlinear behavior of aqueous, very concentrated suspensions of plate-like particles interacting mainly through excluded volume and electrostatic interactions. These interactions lead to an ordered structure corresponding to regions of aligned plates with very small interparticle gaps, as shown by cryomicroscopy. The transient shear behavior, observed at different shear rates, in terms of the shear stress τ and the first normal stress difference N1, shows that the time required to reach steady state values is relatively short, probably in relation to the high degree of packing of these highly concentrated suspensions. However, N1 changes from positive to negative values with time, and finally reaches a negative steady state value. Moreover, it is shown that the second normal stress difference N2, compared to N1, takes significant steady state values, the sign of which depends on the applied shear rate. The steady shear stress (or viscosity) vers...

Linear and nonlinear viscoelastic behavior of very concentrated plate-like kaolin suspensions

The viscoelastic behavior of very concentrated and electrostatically stabilized suspensions of kaolinite particles has been investigated in the linear and nonlinear regime as a function of volume fraction, ionic strength and in the presence of polymer at various concentrations. Material properties such as linear viscoelastic moduli and cohesive energy density are extensively enhanced by either increasing volume fraction or decreasing ionic strength. Attention has been paid to the large amplitude oscillatory shear behavior of concentrated suspensions of plate-like particles, characterized by a hump in G″ curves. Rheological investigation shows the extreme sensitivity of the intensity of the strain hardening in G″ to excluded volume, electrostatic and steric interactions. A physical interpretation of this nonlinear behavior has been proposed.

Influence of a nonionic surfactant on the rheology of a hydrophobically associating water soluble polymer

The rheological behavior of a 1% w/w commercial hydrophobically modified (hydroxypropyl)guar (HMHPG) in water solution is examined in the presence of a low molecular weight nonionic surfactant. The linear and nonlinear response to steady and oscillatory shear flow, at different surfactant concentrations around the cmc, is mainly compared with the response of a 1% w/w aqueous solution of HMHPG alone, following a rheological approach previously used by the authors. Below the cmc of the free surfactant in water, the rheological results show a reinforcement of the reversible associating network mainly due to an increase of the number of intermolecular hydrophobic associations, with hardly no modification of the average ‘‘strength’’ of the hydrophobic junctions. Above the cmc, the rheological data show that there is a progressive weakening leading to the disruption of the intermolecular hydrophobic junction network. Those results are interpreted in terms of interactions of surfactant molecules with the regions...

Study of the conformational rigidity of polyelectrolytes by elastic neutron scattering: 1. Carboxymethylcelluloses in the intermediate momentum range

Small angle elastic neutron scattered intensity l(q) by dilute solutions of a high molecular weight and low charge density carboxymethylcellulose (CMC) in D2O, without added-salt has been measured. The variation of l(q) is proportional to q−2 (q = momentum transfer) for q q∗. The dependence on q−2 shows that the distribution of the statistical units is Gaussian whereas the existence of q∗ provides the possibility of calculating the length of such a unit; according to the dependence on q−1, we conclude that these units are rigid. The length increases with dilution and charge density, which agrees with our previous results obtained by viscosity.