摘要:

The electrical conductivity of carbon‐black‐filled composites depends on the structure of the carbon black, the morphology of the polymer, and the processing history of the composite. For identical processing conditions highly porous carbon blacks produce more conductive composites at lower filler loadings than structured blacks. Moreover, porous carbon black composites are less sensitive to processing history than structural blacks. The greater the degree of internal phase segregation produced during polymer solidification, the lower the resistivity of the resulting composite. Electrically conductive carbon‐black‐filled composites can be produced with resistivities low enough to provide 30 dB of electromagnetic interference shielding attenuation. The shielding attenuation‐volume‐resistivity relationship appears to follow predictions based on plane wave analysis when the samples are tested under plane wave radiation conditions.

ISSN:0148-6055    

DOI:10.1122/1.549758

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

As polymers are deformed anisotropically in the rubbery state, the molecules tend to become oriented there and retain varying degrees of that orientation as they are cooled into the glassy state. This frozen‐in orientation, which occurs in practically all polymer processes (intentionally or otherwise), can have significant effects on the subsequent glassy properties; also, of course, some changes may take place over time (orientation aging). While the physics of the induction and subsequent release of molecular orientation is clear enough qualitatively, we have lacked a quantitative formulation. Present viscoelastic theory is capable of “remembering” prior deformations, but little or nothing has been done with it as one passes through the glass transition. We carry out such an analysis here, dealing with both the rubbery deformation and the subsequent glassy shrinkage (or creep, if loaded) in a single theoretical formulation. A generalization of viscoelastic theory to include volume (compressible) effects is made in the following article; here we operate in the framework of existing theory, in which incompressibility is assumed.

ISSN:0148-6055    

DOI:10.1122/1.549759

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

Existing rheological equations for the rubbery state and for the glassy state are not compatible with each other, in that in the former one assumes incompressible, viscoelastic behavior (the various constitutive equations), whereas in the latter one usually presumes compressible, elastic behavior (linear elasticity theory). While it is true that nonequilibrium volume effects in the glassy state have been dealt with extensively with differential rate theories (notably those of Kovacs), these are not stated in a way which allows combination with existing viscoelastic equations, i.e., those for anisotropic deformations. We present a generalized phenomenological model which brings together these various cases in a single formulation. This allows us, at least in principle, to deal with “coupled effects,” in which volume changes induce anisotropic stresses, or vice versa; such effects occur in practically all polymer processes, in the sense that cooling causes volume changes, but with constraints from the geometry.

ISSN:0148-6055    

DOI:10.1122/1.549760

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

A promising new constitutive equation for polymer melts is herein presented, one that contains both the Lodge or upper‐convected Maxwell model and a good approximation to the Doi‐Edwards model as special cases. The upper‐convected Maxwell model is one of the most basic while the Doi‐Edwards model is the one perhaps most surely founded on molecular principles. The differential model presented here is based on molecular reasoning that should be particularly well suited to commercial, highly branched melts such as low‐density polyethylene. The idea behind the model is that long side branches can limit the extent to which a polymer strand is able to contract back within the confining tubelike region postulated by Doi and Edwards.

ISSN:0148-6055    

DOI:10.1122/1.549761

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

The behavior of an asphalt‐concrete under tensile stress has been studied using a nonlinear viscoelastic model previously proposed. Laboratory tests for the determination of mechanical properties of asphalt‐concrete have been performed at constant temperature of 20°C. For the loading range used in the tests, the constitutive equation has been found to be represented adequately by a three‐term polynomial. The inadequacy of the theory of linear viscoelasticity for characterizing asphalt‐concrete is demonstrated. A close agreement between the experimental results and the response predicted by the nonlinear model has been obtained. The similarities and differences of asphalt‐concrete behavior in tension and in compression are discussed.

ISSN:0148-6055    

DOI:10.1122/1.549762

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

The time‐dependent nonisothermal elongational flows of polymeric fluids have been modeled using the Leonov constitutive theory. The stress growth at a constant elongational strain rate or constant pulling speed and stress relaxation after elongation have been considered under various thermal histories including constant cooling rate and a sudden jump or a drop in temperature. Following the concept of thermorheological simplicity, the nonisothermal effects have been conveniently incorporated into the theory via experimentally determined temperature shift factors together with the effect of nonzero cooling rates on glass transition temperature. The predicted results have been compared with the available experimental data of Bogue and co‐workers. In general, the agreement between theory and experiment is found to be good and comparable to the available results of other theories.

ISSN:0148-6055    

DOI:10.1122/1.549763

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

Commercial HDPE, LDPE, and LLDPE resins were tested at 150, 170, and 190°C in an Instron capillary rheometer (ICR) equipped with three sets of capillaries. In addition, the resins were characterized by the gel permeation chromatography method and in the Rheometrics mechanical spectrometer under dynamic conditions. The pressure oscillation was observed for HDPEs and LLDPEs. One resin in each of these two categories showed die slip. For LDPE the slip did not occur. The capillary viscosities at low temperature and/or higher rates of deformation agreed with the complex viscosity η*while at high temperature and/or low rates with the dynamic viscosityη(ICR)→η′.

ISSN:0148-6055    

DOI:10.1122/1.549769

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

摘要:

A new method is proposed and tested for step shear strain experiments with parallel‐disk rotational rheometers. The method is applicable to large strains, i.e., outside the linear viscoelastic region. The nonhomogeneity of the strain in the parallel‐disk rheometer is accounted for by a correction term which is similar to the well‐known Rabinowitsch correction in capillary rheometry. The transient shear relaxation moduli of a low‐density polyethylene (150°C) and of a polystyrene (180°C) from this method agree very well with equivalent data from a cone‐and‐plate rheometer. The two different geometries give an overlapping set of data; small‐strain data(γ=0.1−5)from cone‐and‐plate and large‐strain data(γ=0.4−25)from parallel disk. The step strain data support the separability of the relaxation modulus into time‐ and strain‐dependent functions. The strain dependence is well approximated by a sigmoidal function. The data were obtained with a Rheometrics dynamic spectrometer having a maximum angular displacement of 0.5 rad.

ISSN:0148-6055    

DOI:10.1122/1.549770

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549771

出版商:The Society of Rheology    

年代:1984

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549782

出版商:The Society of Rheology    

年代:1984

数据来源: AIP