Research Summary: Flow function data for systematic variations in well-characterized polymer structures for a variety of shearing modes are critically needed for the development and evaluation of constitutive equations relating viscoelastic flow functions to polymer structure. The effect on the flow functions of molecular weight, weight distribution, stiffness, and complexity will be determined for linear polymers. Additionally, for branched polymers, the effects of branch number, length, and uniformity for star polymers, and branch distribution for comb and randomly branched polymers will be determined. The flow functions will include the viscosity, and especially the first and second normal stress differences, N1 and N2, and derived functions in steady shearing, oscillatory, stress growth and relaxation, and step strain deformations. Low compliance Weissenberg and Rheometries rheometers will be used in cone-plate and parallel plate shearing. Modification of constitutive equations, especially relaxation functions, will be studied. Technical Impact/Practical Applications: The complete flow function data will provide a basis for the formulation of realistic constitutive equations for use with the transport equations in the design of polymer production and processing equipment. Some applications follow: Extrudate Swell. The control of extrudate swell is critically important in such operations as the extrusion of plastic pipe, rods, and plastic vessel parisons. The rarely available ratio of N2 to N1 has been shown to be a major factor in extrudate swell. The proposed research will generate the required high shear-rate data and instrumentation to acquire such data. Wire Coating. Second normal stress difference and fluid dynamic forces act to center the wire in a coating of plastic. Dies designed to utilize these forces could reduce the average coating thickness, meet thickness specifications, and reduce material costs. The instrumentation developed by this proposal will make possible for the first time the acquirement of the required high shear-rate N2 data. Shaft Climbing on the shafts of mixers and reactors in the food and polymers or plastics industries must be managed. In one case, polymers climbed up the shaft and into the drive of a large mixer and forced a costly shutdown. With a knowledge of the ratio of N2 to N1 (currently rarely available), rod climbing can be predicted and mixers can be designed to avert the problems. Reverse Flow. In stirred tank polymer and biological reactors and mixers, significant normal stresses cause radially inward flow towards the mixer shafts (vs. radially outward). Mass and heat transfer and efficiency are importantly reduced by major changes in flow patterns. With a knowlege of the ratio of N2 to N1, reverse flow can be predicted and design measures taken to improve performance.
