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51.
Asphalt binder was modified by low-density polyethylene (LDPE) and ethyl vinyl acetate (EVA) polymers to investigate the structure–property relationships of polymer-modified asphalt (PMA). The PMA was prepared in a high-shear blender at 160 °C. The optimum blending time (OBT) for each polymer was determined following a separate investigation. OBT was influenced by Mw, MWD, and polymer structure. The influence of Mw of LDPE and vinyl acetate (VA) content of EVA on PMAs was studied by rheological tools. Polymer modification improved the rheological properties of base asphalt. EVA–PMAs were found to be less temperature sensitive than LDPE-modified asphalts. LDPE modification increased flow activation energy (Ea) but EVA modification decreased Ea. Both VA content and Mw of LDPE have influenced the storage stability of PMAs. The low-temperature properties of PMAs and short ageing tests were not influenced by polymer type. On the other hand, the high-temperature properties of PMAs were strongly influenced by Mw of LDPE and VA content of EVA. Overall, EVA with low VA content showed the best temperature resistance to high- temperature deformations, the highest upper service temperature as well as the best storage stability. 相似文献
52.
Pierre Terech Séverine Friol Neralagatta Sangeetha Yeshayahu Talmon Uday Maitra 《Rheologica Acta》2006,45(4):435-443
We present a comparative investigation of two opposite classes of self-assembled fibrillar networks. Ribbons and tubes having cross-sectional dimensions in the nanoscale can be formed in aqueous solutions of steroids derived, respectively, from deoxycholic (DC) and lithocholic (LC) acids. Rheological features distinguish energetic networks of DC ribbons rigidly fixed in cylindrical bundles and entropic transient networks of LC tubes weakly interacting in shear-sensitive suspensions. The two classes are characterized by their frequency sweep profiles, viscoelastic linear domains, scaling laws of the elastic shear modulus vs concentration, kinetics of formation of the networks, and their optical birefringence aspects. A theoretical context for networks of rigid fibers is used to account for the scaling exponents α in the G’ (and σ*) ∝C
α
laws (α=2.0 and 1.0, respectively, for DC and LC). The evolution observed in DC gels from ribbons to cylindrical fibers with monodisperse sections made up with four ribbons is an indication of an equilibrated balance between face-to-face attractions and untwisting elastic processes of the constitutive ribbons.Paper presented at the Annual Meeting of the European Society of Rheology, Grenoble, April 2005 相似文献
53.
The stability and the rheological properties of blends of a 60/70 penetration-grade bitumen with conventional HDPEs and metallocene catalysed LLDPEs (m-LLDPE) are investigated. Considerably better stability results are obtained using m-LLDPEs instead of conventional polyethylenes, allowing one to avoid phase separation of the emulsion-like system during storage at high temperature. Thermodynamical interaction between bitumen and polyethylene is discarded as a cause of the observed difference, because the solubility parameter is practically the same for all the investigated polyethylenes. The result is explained on the basis of the lower melt elasticity of m-LLDPEs (attributed to their narrow molecular weight distribution), which facilitates the drop breakup during mixing process. The modification of bitumen with any of the m-LLDPEs considered in this work gives a new material with considerably improved viscoelastic properties. 相似文献
54.
Thomas B. Goudoulas Eleftherios G. Kastrinakis Stavros G. Nychas 《Rheologica Acta》2003,42(1-2):73-85
An investigation of the rheological properties of dense lignite-water suspensions is reported here in order to evaluate the
parameters that affect the rheology of these suspensions. Different types of particle size distributions were achieved via
wet grinding with particle sizes down to 1 μm. Polyelectrolytes and surfactants were used to improve the stability and rheology
of suspensions. The achieved solid volume fraction, φ, with acceptable rheological behavior was 0.45, while the ratio of φ/φ
m
was close to 0.85; φ
m
is the maximum solid volume fraction. Various types of flow tests were performed on lignite-water suspensions with various
preshear times and stress levels. Typical shear rates varied in the range between 10–2 to 102 s–1. The low shear behavior was found to be quite different from the high shear behavior for the most concentrated suspensions,
with a plateau value at low shear rates indicating the appearance of a yield stress. These plateau values, however, depend
on shear history, which is responsible for the development of different structures in the sample. The viscosity curves corresponding
to the ascending and descending parts of the flow curve were found to be different; these flow curve parts can be described
either by well established models or by modified ones. The non-Newtonian time dependent behavior of the lignite-water suspensions
is attributed to the high value of the ratio φ/φ
m
, the polydispersity of the particle size distribution, and the non-spherical shape of the lignite particles. 相似文献
55.
56.
57.
A class of nonlinear viscoelastic constitutive equations including the K-BKZ constitutive equations, linear viscoelasticity and the Green-Rivlin models is developed. A stored-energy functional is associated with each model in such a way that the energy dissipation rate is non-negative. The theory is developed for 1D viscoelasticity and extended to 3D viscoelastic media. 相似文献
58.
The relaxation of slightly poly-disperse linear flexible polymers has been expressed in a simplified blending rule which is presumed to be a weighted linear superposition of the relaxation spectra of mono-disperse components which constitute the blend. Discrete components are characterized by their molecular weight M
i,weight fraction w
i,and relaxation time spectrum H
i(). ). In contrast to broadly distributed blends in which the small molecules mobilize the large ones and vice versa, we introduce the term slightly polydisperse for blends with molecular weight distributions narrow enough to have very little change in the longest relaxation times of each molecular weight component. The properties of this blending rule are analyzed and dynamic data is calculated for slightly poly-disperse polystyrene. As an application, the blending rule is used to determine the characteristic mono-disperse parameters (BSW parameters) of two materials, poly (vinyl methyl ether) and polycarbonate, for which we could not determine their BSW parameters directly since they were not available in nearly monodisperse form. The proposed blending rule can only be applied to systems in which all components are above the entanglement molecular weight, i.e. M
iM
c.Dedicated to the memory of Professor Tasos C. Papanastasiou 相似文献
59.
The gelation kinetics of aqueous solutions of acrylamideacrylic acid copolymers in the presence of chromium ions was studied with different rheometers. The gel time is found to vary with the principle of the apparatus because of a low shear dependence of the elongation of the macromolecules. The variations of the gel time with the experimental conditions of the gel preparation were investigated and we conclude that the gelation is governed by the oligornerization kinetics of the chromium ions which are instantaneously, complexated by the carboxylate groups of the polymer. The variation laws of the gel time and of the elastic modulus with chromium and polymer concentrations, temperature and ionic strength are in qualitative agreement with the structure of the temporary network of the semi-dilute solutions of these copolymers. 相似文献
60.
Oscillatory rheological experiments at different temperatures and over a wide range of frequencies have been used to investigate
the gelation process and, more particularly, the sol–gel transition of various poly(vinyl chloride) (PVC) plastisols. The
sol–gel transition process was found to be universal with respect to the temperature and solid volume fraction according to
the similarity of the fractal structure in PVC plastisols. The variation of the gel time (t
gel) with temperature for any composition of PVC plastisols was predicted from the Dickinson’s model (E. Dickinson, J Chem Soc
Faraday Trans, 93:111–114, 1997). Dynamic viscoelastic properties of PVC plastisols have also been studied as a function of
temperature that allowed us to follow the gelation process of various plastisols. Thus, the influence of the type and concentration
of PVC resins in gelation process was investigated. The variation of the complex shear modulus at a constant frequency was
depicted by a master curve regarding the dependence of the moduli on PVC concentrations. 相似文献