Melt viscosity behavior of some engineering thermoplastics

Abstract

AbstractFrequently, the enhanced elevated‐temperature rigidity of engineering thermoplastics (ETPs) is a consequence of high glass‐transition temperature, and many ETPs contain aromatic ring structures in the backbone chain. These factors can lead to difficulty in melt processing, or fabrication, of parts. Thus, the definition of the melt rheology of such systems is of considerable technological, as well as scientific importance. The investigation reported here first defines the viscosity‐temperature dependence of five ETPs over a relatively narrow range of temperatures appropriate to melt processing in terms of superposition methodology. The five ETPs studied were bisphenol A polycarbonate, polysulfone, the condensation polymer of bisphenol A and mixed iso‐ and terephthalic acids, and two experimental condensation polymers: bisphenol A/isophthalic acid and 1,2 bis(4,4′‐hydroxy phenyl) ethane/isophthalic acid. Viscous flow energies of activation are examined in terms of polymer chain structure. In the second portion of the investigation it is shown that, for the latter two condensation polymers, the molecular weight, temperature, and shear rate dependence of the viscosity may be expressed in terms of a modified Carreau model. The Newtonian limiting low‐shear viscosity dependence on molecular weight and that of the shear rate shift factor (relaxation time) are found to be somewhat greater than that normally observed.