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A method has been developed for measuring three orthogonal forces in a polymer melt subjected to shear. Data are presented showing the relationship of these forces to shear rate for linear polyethylene. It has been found possible to measure the elastic and viscous forces while varying the shear rate in two different independent manners: (1) by varying the time scale of applying a given magnitude of shear deformation; (2) by varying the magnitude of shear deformation for a given time scale of application. Method number one results in the usual nonlinear relationship between shear stress and shear rate for polymer melts. Method number two results in a linear relationship between shear stress and shear rate thus making it possible to determine a single value of the coefficient of viscosity for any given time scale of application of shear strain. By varying the time scale of strain application, it has been found possible to measure polymer melt viscosities from essentially the zero shear rate viscosity to the disentangled viscosity.
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Maxwell et al. (1965) studied this question.
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