María Eugenia Muñoz

Influence of the processing conditions on the rheological behaviour of polymer-modified bitumen☆☆

Abstract Mixing polymers into bitumen has important consequences on the engineering properties of bituminous binders. Thus, structural and chemical changes may be observed during processing of polymer-modified bitumens. Chemical compatibility and processing conditions are crucial to obtain suitable properties. Most polymers occur to be insoluble, in some degree, in the bitumen matrix, and phase separation may result. Polymer stabilization can be achieved by mechanical dispersion of the modifier and swelling by compatible components in the maltene fraction. This paper deals with the influences that processing variables exert on the rheological properties of polymer-modified bitumens. From the experimental results obtained we may conclude that a rotor–stator mixer device enhances the rheological properties of binders prepared with high-density polyethylene, low-density polyethylene, ethylene–propylene–diene monomer, and their blends, as compared to a stirred tank device.

Chemical and Rheological Properties of the β-Glucan Produced by Pediococcus parvulus 2.6

Some physicochemical and rheological properties of the exopolysaccharide (EPS) produced by Pediococcus parvulus 2.6 were examined. Structural characterization by NMR ((1)H and 2D-COSY) showed that the same EPS, a 2-substituted (1,3)-beta-D-glucan, was synthesized irrespective of sugar source used for growth (glucose, fructose, or maltose). The molecular masses of these beta-glucans were always very high (>10(6) Da) and influenced by the culture medium or sugar source. The steady shear rheological experiments showed that all concentrations of the beta-glucan aqueous solutions exhibited a pseudoplastic behavior at high shear rates. Viscoelastic behavior of beta-glucan solutions was determined by dynamic oscillatory analysis. A critical concentration of 0.35% associated with the appearance of entanglements was calculated. The beta-glucan adopts an ordered hydrogen bond dependent helical conformation in neutral and slightly alkaline aqueous solutions, which was partly denatured under more alkaline conditions.

Ionic Supramolecular Networks Fully Based on Chemicals Coming from Renewable Sources

New supramolecular ionic networks are synthesized by proton transfer reaction between a bio-based fatty diamine molecule (Priamine 1074) and a series of naturally occurring carboxylic acids such as malonic acid, citric acid, tartaric acid, and 2,5-furandicarboxylic acid. The resulting solid soft material exhibits a thermoreversible transition becoming a viscoelastic liquid at high temperatures. All the networks show an elastic behavior at low temperatures/high frequencies, with elastic modulus values ranging from 4.5 × 10(6) to 4.5 × 10(7) Pa and soft network to liquid transitions T(nl) between -10 and 60 °C. The supramolecular ionic network based on cationic Priamine 1074 and anionic citrate shows promising self-healing properties at room temperature as well as relatively high ionic conductivity values close to 10(-6) S cm(-1).

Rheology of hydroxyethylated starch aqueous systems. Analysis of gel formation

This paper reports dynamic viscoelastic and steady shear measurements of aqueous solutions of two commercial hydroxyethyl ethers of potato starch, allowing us to define three different viscoelastic regions, depending on the polymer concentrations. The fluid-like zone (I) corresponds to a homogeneous solution, free of associations between chains, where the linear viscoelastic model can be applied; the fluid-gel transition zone (II) is associated with the rheology of complex systems which possess intermolecular specific interactions; and the gel-like zone (III) involves a network formation giving rise to a gel. The reversibility of the hydrogels was studied by means of steady/dynamic transient experiments allowing breakdown of the gel network and analysis of rehealing. Comparing the elastic moduli of the starch derivative gels leads us to assume that the functionality depends on the capacity to form hydrogen-bonding associations between polymer chains.

Basic rheological features of block polyurethane solutions : Entanglements, crystallization, and gelation

Three block polyurethane samples [differing in hard (urethane) to soft (macroglycol) segments ratio] dissolved in 2-butanone, are investigated. Rheological results obtained in the range 10–25 °C led to the hypothesis of an order-disorder transition associated with H bonds being discarded. The critical concentration and the characteristic molecular weight for entanglements, Mc, are estimated approximately from linear viscosity results. Mc decreases as the percent of hard segments in the polyurethane increases, a result which is correlated with short-distance chain parameters such as length and molecular weight per bond and characteristic ratio. Annealing clear solutions at temperatures around 0 °C causes haziness; on heating, a clearing temperature is detected at Tc≈15 °C. This transition coincides with a maximum observed in complex viscosity η* versus temperature curves. These results are probably due to incipient crystallization of soft segments domains. This hypothesis is compatible with differential sc...

Enhancement of the first normal stress coefficient and dynamic moduli during shear thickening of a polymer solution

Viscosity results of a solution of poly(2-hydroxyethyl methacrylamide) in glycerine, obtained from a continuous increase of shear rate and under steady state (constant shear rate) conditions, reveal the existence of a shear thickening region. The analysis of normal stresses shows that the first normal stress coefficient exhibits the same shear-thickening effect as the viscosity. The increase of the solution elasticity during shear thickening is also noticed by an enhancement of the storage modulus, measured in experiments using parallel superposition of oscillations on steady flows, as the shear stress is increased. Thermorheological simplicity, observed in dynamic measurements in absence of steady flow, is broken when shear stresses corresponding to the shear thickening region are applied. The results are explained by the presence of shear-induced hydrogen bonds, which provoke a reinforcement of the plateau modulus and an enlargement of the relaxation time spectrum.

Rheological Features of a Novel Poly(spiro phosphazene)

A study of the rheology of a new poly(2,2′-dioxybiphenyl)phosphazene is presented. The results are conditioned by a two-phase morphology and by the anisotropy of the melt, observed by microscopy in the range 200–320°C. Two temperature regions are distinguished: the range 260–320°C is characterized by the presence of a plateau zone (with G′ > G″) at intermediate frequencies, which is not detected at the range 220–260°C. The origin of this plateau is discussed. The typical rheological behavior of thermotropics, like three regions for the viscosity function and concentric “marble-like” surface texture, is observed in plate-plate flow, but not in extrusion flow.

Supramolecular structure, phase behavior and thermo-rheological properties of a poly (L-lactide-co-ε-caprolactone) statistical copolymer.

PLAcoCL samples, both unaged, termed PLAcoCLu, and aged over time, PLAcoCLa, were prepared and analyzed to study the phase structure, morphology, and their evolution under non-quiescent conditions. X- ray diffraction, Differential Scanning Calorimetry and Atomic Force Microscopy were complemented with thermo-rheological measurements to reveal that PLAcoCL evolves over time from a single amorphous metastable state to a 3 phase system, made up of two compositionally different amorphous phases and a crystalline phase. The supramolecular arrangements developed during aging lead to a rheological complex behavior in the PLAcoCLa copolymer: Around Tt=131 °C thermo-rheological complexity and a peculiar chain mobility reduction were observed, but at T>Tt the thermo-rheological response of a homogeneous system was recorded. In comparison with the latter, the PLLA/PCL 70:30 physical blend counterpart showed double amorphous phase behavior at all temperatures, supporting the hypothesis that phase separation in the PLAcoCLa copolymer is caused by the crystallization of polylactide segment blocks during aging.

Role of droplet deformation on the transient rheological response of a polypropylene/liquid-crystal-polymer blend

The transient rheological response and morphological development of 70/30 polypropylene–Rodrun 5000 liquid-crystalline emulsion-like blends have been analyzed. The droplet size distribution was broad. Our results indicate that the shear stress overshoot observed at γ=1.5 s.u. is not due to the liquid-crystalline nature of the droplets, but rather to their elongational deformation. However, quick retraction of the elongated droplets in the steady state is attributed to their nematic nature. As a consequence, the transients after resting for a short time resemble those of start-up experiments. Size polydispersity plays a significant role: shear stress undershoot and normal stress overshoot at γ=25 s.u. are only observed when droplets larger than 40 μm radius are present. Results of flow reversal experiments show that if the flow is reversed before the steady state is reached, then a delayed shear stress overshoot is produced. We relate this to the optically observed retraction of the elongated drops and sub...

The effect of pressure on the viscosity of two different nanocomposites based on a PS matrix: A case of piezorheological complexity

The pressure dependence of viscosity of two nanocomposites with a polystyrene (PS) matrix that contains, respectively, multiwalled carbon nanotubes (MWCNTs) and graphene, was investigated. Two procedures were used: (a) Pressure-volume-temperature (PVT) results to obtain the pressure coefficient β0 for Newtonian viscosity and (b) measurements in a pressure chamber in a capillary rheometer, to obtain the pressure coefficient at constant shear rate, β′ and the pressure coefficient at constant shear stress, β″. PVT results revealed that the most significant differences between the samples concerned the variation of the glass transition with pressure, dTg/dP, which was concomitant with the number of polymer chains fixed on the surface of the nanofillers. Pressure chamber results showed that the pressure coefficient β″ was similar for PS and the nanocomposites, at the shear rates involved in processing. For the first time, the piezorheological complexity of nanocomposites was analyzed, together with the thermor...