AbstractAn elastomer developed for superior processing characteristics, Neoprene WB, has been studied in a capillary rheometer from 80–125°C. and shear rates of 0.4–11,000 sec.−1Both the viscous and elastic properties of the bulk polymer are evaluated from pressure drop measurements. Per cent increase in diameter of the elastomer when extruded (“die swell”) and its surface characteristics provide direct evidence of extrusion processibility. A principle of corresponding shear rates at different temperatures simplifies the understanding and application of rheometer data. Data on all responses obtained at a low temperature can be laterally superposed to higher shear rate to agree with data obtained at higher temperature. Equilibrium shear stress vs. shear rate curves show Neoprene WB undergoes shear thinning with, for example, viscosity at 100°C. dropping from over 106poise at low shear rate to 5 × 102poise at high. The entrance or elastic effect drops very slowly to a minimum with increasing shear and then rises rapidly. This shear rate‐temperature condition at which the entrance effect is a minimum is a critical condition for the polymer; it is the transition from smooth to rough extrudate. Die swell of smooth extrudates increases as the shear rate is increased but decreases with greater orifice length to diameter ratio. Above the transition the die swell of rough extrudates drops to a minimum and then rises again at still high
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