摘要:

Experimental melt data are compared with differential constitutive equations that contain only a single adjustable parameter, besides the parameters describing the linear relaxation spectrum. These include the equations of Giesekus, Phan‐Thien and Tanner, Johnson and Segalman, White and Metzner, Larson, and Aciernoet al.The deformations are step shear, step biaxial extension, and start up of steady uniaxial extension of HDPE without long side branches and LDPE with long side branches. The Johnson‐Segalman and White‐Metzner models fail to predict the experimental data accurately. The equation of Aciernoet al.shows strong oscillations in elongation and shear. The Giesekus equation fits the uniaxial extension and shear data but fails to do so for biaxial extension regardless of the choice of the adjustable parameter. The models of Phan‐Thien and Tanner and of Larson seem to fit the data best. These two equations give a reasonably good fit to the data in all three deformations for the HDPE for a single value of the adjustable parameter. For the branched LDPE, a fit is only obtained if the parameter is separately adjusted for each of the three types of deformation.

ISSN:0148-6055    

DOI:10.1122/1.549922

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

A design for an extensional viscometer is described which is useful for studying low‐viscosity fluids at high strain rates. The configuration consists of opposing nozzles through which the liquid is either sucked in or blown out. Measurement of the force required to keep the nozzles at a fixed distance apart as a function of flow rate directly yields a determination of the extensional viscosity. Data are presented on both Newtonian and non‐Newtonian liquids. For Newtonian liquids, Trouton's rule is verified for both uniaxial extensional and compressive flows. Results are also presented on dilute solutions of polyacrylamide and Xanthan gum which indicate substantial enhancements of the extensional viscosity upon addition of these polymers. Qualitative differences were observed, however, for the extensional flow behavior of the flexible polyacrylamide chains and the more rigid and rodlike Xanthan gum chains.

ISSN:0148-6055    

DOI:10.1122/1.549923

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

An oscillating plate rheometer was devised for measuring the nonisothermal viscosity of thermoset coatings. The effects of heating rate and baking temperature on viscosity behavior were examined for acrylic‐melamine resin coatings. On heating, the viscosity decreases initially, passes through a minimum, and then increases due to advancing polymerization and crosslinking. The higher the heating rate and the baking temperature, the more rapidly the viscosity increases after passing the minimum; this resulting in the reduction of sag in practical processes. Since the viscosity behavior is intimately related to the progress of chemical reaction, the conversion of functional groups is also monitored by the use of an FT‐IR spectrometer. At low baking temperatures the transetherification is exclusively induced, whereas at temperatures above 120°C the self‐condensation occurs. The self‐condensation causes a rapid increase in viscosity and hence reduces the sag.

ISSN:0148-6055    

DOI:10.1122/1.549924

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

A nonlinear constitutive equation is advanced for cured rubber where the elastic and relaxation contributions to the overall response have separate generalized deformational dependences. Predictions of viscoelastic behavior based on this theory are then compared to transient and dynamic data acquired in two strain fields on a natural rubber gum vulcanizate. It is shown that the model successfully predicts the nonfactorizability of time and strain effects observed for the large strain and the incremental strain, stress relaxation functions, and for the incremental storage modulus. However, in the case of the incremental loss modulus, these effects are observed to be factorizable, a behavior also predicted by the model. Further, the observed deformational dependence of the incremental loss tangent is well characterized by the theory. The relaxation spectrum as defined by the linear theory of viscoelasticity is shown for this elastomer to be independent of the state of deformation in the two strain fields for strains up to 130%. This is observed despite the nonfactorizable behaviors shown by the stress relaxation and the incremental storage and relaxation modulus data. Finally, factorizability of time and strain effects in incremental loss modulus results is shown to be a necessary and sufficient condition for the relaxation spectrum to be independent of the state of strain.

ISSN:0148-6055    

DOI:10.1122/1.549925

出版商:The Society of Rheology    

年代:1987

数据来源: AIP