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• 1985-1989  (7)
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Year
• 1
Electronic Resource
Hoboken, NJ : Wiley-Blackwell
Advances in Polymer Technology 6 (1986), S. 407-407
ISSN: 0730-6679
Keywords: Chemistry ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Type of Medium: Electronic Resource
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• 2
Electronic Resource
Bognor Regis [u.a.] : Wiley-Blackwell
ISSN: 0887-6266
Keywords: Chemistry ; Polymer and Materials Science
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Linear low-density polyethylenes (LLDPES) and polypropylene (PP) have been recovered from solutions of varying initial polymer concentration. Melts of these polymers show significant reductions in viscosity and elasticity, and the effects are attributed to changes in the entanglement density of the polymer. Measurements of entanglement densities have been attempted from experimental values of the apparent zero-shear melt viscosity. These indicate that solution treatments in trichlorobenzene at 135°C reduce the entanglement density more effectively in PP than in LLDPE. In all cases the observed effects are reversible by annealing at elevated temperatures. Analytic data point to entanglement changes as the true origin of changes in viscoelastic properties, since solution treatments produce no changes in molecular weights and weight distributions, and the samples tested are free of solvent residues.
Type of Medium: Electronic Resource
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• 3
Electronic Resource
Springer
Rheologica acta 25 (1986), S. 95-101
ISSN: 1435-1528
Keywords: End effect ; elastic-constant viscosity fluid ; Boger fluid ; primary normalstress difference ; shear-thinning properties
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Abstract In the light of a new interpretation, we have studied the end effects for highly elastic-constant viscosity fluids commonly called Boger fluids. In terms of entrance effect only, the presence of primary normal-stress differences in absence of shear-thinning properties results in a decrease of the entrance correction below the Couette (Newtonian) value, whereas the total end correction can be substantially increased by an amount which is strongly dependent on the Weissenberg number or recoverable shear.
Type of Medium: Electronic Resource
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• 4
Electronic Resource
Springer
Rheologica acta 27 (1988), S. 241-254
ISSN: 1435-1528
Keywords: Rheological equation ; dilute polymersolution ; polyelectrolyte ; shear thickening ; polyacrylamide solution
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Abstract A mathematical model based on the diffusion-convection equations is used to describe the rheological properties of dilute polymer solutions. The model uses a second-order conformation tensor as a measure of the internal strain; this avoids the mathematical complexity resulting from the use of a more detailed description of the macromolecules and also avoids the necessity of introducing additional ad-hoc assumptions (closure approximations) commonly used in other molecular theories. The rheological equation is obtained in terms of the rate-of-deformation tensor $$\dot \gamma$$ and a scalar functionf(σ) relating the extra stress tensorσ to the internal strain tensorc. The functionf(σ) depends on the physical insight introduced in the Helmholtz free energyA(c) of the solvent-polymer system. This approach is illustrated for an intra-molecular potential of a “FENE-charged” type. The concept of an isotropic, but conformation-dependent, friction coefficient, is also introduced to account for the “coil-stretch” transformation of macromolecules in solution. Viscosity and first normal-stress data, of partially hydrolyzed polyacrylamide solutions, (polyelectrolytes) are analyzed and compared to the model predictions in steady shear and elongational flows.
Type of Medium: Electronic Resource
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• 5
Electronic Resource
Springer
Rheologica acta 25 (1986), S. 214-224
ISSN: 1435-1528
Keywords: Constitutive equation ; viscoelastic fluid ; kernel function ; simple shear flow ; uniaxial extension
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology , Physics
Notes: Abstract A selection of kernel functions is given to be used in a new integral constitutive equation proposed by Piau whereby the deviatoric stress is calculated from the integral of the history of the past intrinsic rate of rotation and rate of deformation tensors through a representation theorem. Piau has demonstrated the objectivity of a frame moving with a given particle whose axis are directed along the eigenvectors of the rate of deformation tensor. The use of such a framework provides a new approach in the attempt to reduce the computational difficulties associated with conventional constitutive equations written in co-deformational or co-rotational reference frames. The shear and primary normal-stress material functions and the extensional (elongational) stress growth function are defined for the proposed integral constitutive equation. These material functions are used to calculate the kernel functions using steady state, stress relaxation and stress growth data of Attané in simple shear flow for monodisperse polystyrene solutions. The shear and extensional stress growth data of Meissner for a polyethylene melt are also used to show the flexibility of the rheological model. The material functions are first written in terms of five monotonically decreasing functions of the time lag between the past and the present time. Then kernel functions are chosen such that when substituted in the new integral constitutive equation they yield the functions used to describe the data. A further condition imposed on the normalized kernel functions is that they be decreasing functions of time lag.
Type of Medium: Electronic Resource
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• 6
Electronic Resource
Stamford, Conn. [u.a.] : Wiley-Blackwell
Polymer Engineering and Science 27 (1987), S. 1627-1633
ISSN: 0032-3888
Keywords: Chemistry ; Chemical Engineering
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
Notes: This second paper of a series continues the examination of the tensile properties of two series of linear low density polyethylene/polypropylene, (LLDPE/PP) blends. The blends were prepared using a twin-screw extruder and cover the whole concentration range, An Instron Universal Tensile Tester was used to measure the tensile properties of the blends between 10 and 70°C, and the temperature and composition dependences of the modulus were examined. A comparison is established between the solid state and melt properties to underline the behavior in the PP rich region. Results of dynamic mechanical experiments and differential scanning calorimetry on the same materials are also given, and the mechanical behavior is discussed in terms of the variation of the system's crystallinity.
Type of Medium: Electronic Resource
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• 7
Electronic Resource
Stamford, Conn. [u.a.] : Wiley-Blackwell
Polymer Engineering and Science 29 (1989), S. 1265-1272
ISSN: 0032-3888
Keywords: Chemistry ; Chemical Engineering
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
Notes: Primary normal stress difference data of some 32 different polymer solutions have been examined and correlated to the shear stress by a simple power-law model. The normal stress at constant shear stress is shown to increase with the molecular weight of the polymer, but decreases with the polymer concentration. The method proposed by Abdel-Khalik, et al., for predicting the primary normal stress difference from viscosity data for these polymer solutions is inadequate. The FENE-P dumbbell model is used to obtain master curves combining normal stress and viscosity data as a function of a dimensionless shear rate. It is found that this presents several drawbacks. It predicts shear-thinning effects with a power-law slope of -2/3, which is found to be too restrictive. The model fails to predict shear-thinning effects for dimensionless shear rates λEγ lower than approximately 0.5. It also fails to predict satisfactorily the low shear rate value of the dimensionless combination of viscosity and first normal stress coefficient Ψ1/λE(η - ηs). An empirically modified correlation is proposed. The fit for a series of polyacrylamide (Dow Separan AP-30) solutions is very good. In the case of a series of monodisperse polystyrene solutions, the fit is not as good, as the data show a more pronounced effect of polymer concentration at high shear rates.