摘要:

It has been suggested that an extra dimensionless group such as the Weissenberg or the Deborah number is necessary to correlate the drag and heat transfer reductions of very dilute polymer solutions in turbulent flows. It is demonstrated in this study that the characteristic time necessary for these dimensionless groups may be obtained from the Carreau model B. To achieve this, rheological properties of nine concentrations (0.012–2.0% by weight) of aqueous polyacrylamide solutions (Separan AP‐273) were measured with the Weissenberg rheogoniometer (WRG). The measurements include the shear viscosity, the primary normal stress difference, the dynamic viscosity, and storage modulus. Parameters of the Carreau model B were then determined by simultaneously fitting all the experimental data. It is shown that the model adequately describes the experimental data and also that it is possible to establish the concentration dependence of these parameters. The model time constantsλ1andλ2are found to decrease with decreasing concentration. The power law slope parameters are found to be relatively constant, while α decreases as expected, with decreasing concentration. It is demonstrated that with such concentration dependence, it is possible to predict material functions that cannot be measured experimentally by determining the model parameters through extrapolation.

ISSN:0148-6055    

DOI:10.1122/1.549484

出版商:The Society of Rheology    

年代:1978

数据来源: AIP

摘要:

Nonlinear creep of a thin‐walled tube of low‐density polyethylene in torsion during increasing and decreasing temperature is reported. This material was selected after verifying that its thermal expansion was stable. Results showed that creep was dependent on temperature history for both increasing and decreasing temperature. Nonlinear creep was described reasonably well by employing the Morland‐Lee reduced time variable, together with a master creep curve. The master curve for a given stress was constructed from creep at different temperatures by horizontal shifts along the time axis. The temperature‐history independence of creep during rising temperature previously reported for polyurethane is attributed to changes in moisture content.

ISSN:0148-6055    

DOI:10.1122/1.549505

出版商:The Society of Rheology    

年代:1978

数据来源: AIP

摘要:

Rheology of aqueous solutions of xanthan gum was studied over a wide range of shear rate and concentration. At sufficient dilution and low shear rates xanthan solutions show a region of Newtonian viscosity behavior. More concentrated solutions appear to show a yield stress. These results with preliminary normal stress data and effects of salt concentration are discussed in terms of the structure of this polysaccharide in solution. Intrinsic viscosity data are modeled as a suspension of rods and found to be in agreement with existing theory. We speculate the conformation of xanthan in solution is rodlike, having some flexibility. A hydrodynamic length near 1.5 μm is estimated, assuming a diameter of 19 Å.

ISSN:0148-6055    

DOI:10.1122/1.549485

出版商:The Society of Rheology    

年代:1978

数据来源: AIP

摘要:

Shear viscosity, shear flow normal stresses, and elongational viscosity have been investigated for glass‐fiber‐filled high‐density polyethylene and polystyrene melts. Viscosity measurements are consistent in cone‐plate and capillary instruments Normal stress coefficients increase more rapidly with glass fiber content than the shear viscosity, especially at low deformation rates. Elongational viscosities are very high at low elongation rates but decrease rapidly with increasing deformation rate. Mechanisms are proposed to explain these observations.

ISSN:0148-6055    

DOI:10.1122/1.549486

出版商:The Society of Rheology    

年代:1978

数据来源: AIP

摘要:

The rheological behavior of PVC emulsion resin plastisols was investigated in steady shear flow. The shear rate dependence of the plastisol viscosity was influenced by (1) Brownian diffusion, (2) partial dissolution of the suspended resin, and (3) particle‐particle interactions. Partial dissolution of polymer from the resin particle surface resulted in a particle‐size‐dependent increase in the continuous phase viscosity. At a disperse phase volume fraction ofφ=0.02a non‐Newtonian master curve was obtained for the relative viscosity of several plastisol systems as a function of Peclet number, independent of plasticizer or particle radius. These plastisols behaved (atφ=0.20) as suspensions of rigid spheres subject to Brownian motion. The magnitude of the deviation from Newtonian behavior appeared to be influenced also by the strength of particle‐particle interactions. Viscoelastic response was observed in concentrated plastisols. Atφ=0.54relaxation time versus shear rate was found to be independent of plasticizer and of resin particle size. Large discontinuous increases in shear and normal stresses were observed in a critical shear rate range.

ISSN:0148-6055    

DOI:10.1122/1.549487

出版商:The Society of Rheology    

年代:1978

数据来源: AIP

摘要:

It is a common industrial practice to incorporate crosslinked polymer particles into raw elastomers. This results in decreased time and energy of mixing with carbon black. In the system studied, the gel is in the form of discrete particles in contrast to gels formed in bulk. Samples were butadiene‐acrylonitrile copolymer containing 33% acrylonitrile. The crosslinked particles were prepared by adding divinyl benzene in the emulsion‐polymerization recipe. With the exception of the difunctional monomer, the crosslinked particles and the noncrosslinked rubber were prepared in the same manner. The two latices were blended in different proportions. Gel contents of 100, 75, 50, 25, and 0% were examined. The flow behavior of these materials was examined with a capillary rheometer at 70, 100, and 125°C for the shear rate range of3–3000 sec−1.In the shear rate range studied, the viscosity decreased with increasing gel content. This is contrary to the cases where crosslinking is formed in the bulk, where the viscosity increases significantly with the increase of the crosslinked fraction.

ISSN:0148-6055    

DOI:10.1122/1.549488

出版商:The Society of Rheology    

年代:1978

数据来源: AIP

摘要:

The process of extracting time constants from shear‐viscosity data was investigated. Fourteen viscosity functions were fitted to 12 diverse sets of experimental data using a Gauss‐Newton optimization technique. It was found that the three‐ and four‐parameter models, while providing excellent fits to the data, did not provide time constants with as low an expected error as the better two‐parameter models. An analysis of the sensitivity of the error in the time constant to error in the viscosity data showed that regions at very low shear rate and at shear rates near the reciprocal of the time constant were critical. Time constants from shear‐viscosity data for a set of low‐density polyethylenes correlated well with Rouse times based on the weight average molecular weight.

ISSN:0148-6055    

DOI:10.1122/1.549489

出版商:The Society of Rheology    

年代:1978

数据来源: AIP