Teaching

Current Research Topics

Miscellaneous Information 

Research Theme: Professor Baird’s research group is concerned with the application of rheology and non-Newtonian fluid mechanics to the processing of polymers and polymer composites. A combination of both experimental and
mathematical(numerical methods) techniques are used to design materials with improved processing performance.

1. Processing of PAN/MA Plasticized with CO2(PhD)
PAN/MA copolymers are solution spun to form textile fibers and precursors for carbon fiber. Solution spinning, using highly toxic solvents, is required
because polymers with AN content greater than 85 to 90% are unstable at temperatures where they can be melt processed. They undergo crosslinking and
cyclization reactions. It has been found that low levels(5 to 10 wt%) of CO2 dissolved in PAN/MA lowers its glass transition temperature by about 40 oC and, hence, reduces the temperature for melt spinning to a level where the polymer remains stable. Not only is CO2 environmentally benign, but its use will significantly reduce the cost of producing PAN/MA fibers. This project is concerned with developing a processing methodology for spinning fibers in the
presence of CO2. Rheological properties are needed under conditions where the CO2 remains dissolved in the polymer. Fibers must be spun into a pressurized environment to keep the CO2 dissolved in the PAN/MA.

2. Rotomolding of High Performance Thermoplastic Materials(PhD)
Rotomolding is a process used to generate large hollow objects such as underground water storage tanks and recreational equipment. Polymer powder is fused by sintering in a large mold rotating on two axes. HDPE is the most frequently used polymer. Our goal is to extend this procedure to high performance materials which would allow the production of objects with higher strength and stiffness. In particular, we would like to use thermotropic liquid crystalline polymers, TLCP’s, which consist of rod-like molecules and which exhibit high strength and stiffness and thermoplastics reinforced with microfibrils of TLCP’s. This project requires the development of a basic model for the sintering process and an evaluation of the model using a laboratory scale rotomolding device developed in our laboratory.

3. Identification of the Topology of Metallocene Catalyzed Polyethylenes Containing Sparse Long Chain Branching Using Molecular Rheology(PhD)
Some remarkable changes in the rheology of metallocene catalyzed polyethylenes (mc-PE) occur in the presence of less than one long branch per polymer chain. For example, it has been observed that the viscosity increases by a factor of 3 and the onset of shear thinning occurs at a shear rate reduced by a factor of nearly 100 in the presence of one LCB in three molecules relative to a linear system of similar molecular weight. At the same time these melts exhibit strain hardening somewhat reminiscent of highly branched LDPE. The drastic changes in rheology for these randomly branched PE’s appear to be related to the MW between branch points, Mb, as long as the MW of the branch, Ma, is greater than the critical entanglement MW, Mc, rather than the branching architecture(e.g., stars, combs, H-polymers, etc.). Recent theories based on the tube model of Doi and Edwards have been extended to capture the rheology of some branched architectures. The purpose of this proposal is threefold. First, the phenomenological theory of Janzen and Colby which accounts for the increase and then decrease of viscosity with increasing number of branches will be investigated using a series of mcPE’s. Furthermore, the extensional properties will be determined as a function of branching density to determine if the strain hardening is directly related to the number of branches or some other architectural feature. Finally, using a combination of molecular theory based on modifications of the tube model to handle various types of branching topologies(e.g. stars, combs, H, and Pom-Poms) and linear viscoelasticity, non-linear shear, and extensional flow measurements, it is our intention to determine the branching architectures of sparsely branched metallocene-catalyzed polyethylenes. It appears that a key to determining the branching topology of systems of this nature, where we can only speculate at the topology, is extensional flow measurements. The significance of this work rests in establishing a methodology for assessing the subtle differences which can arise in the topology of sparsely branched systems as a result of variations in the nature of the metallocene catalyst or reactor conditions.

4. Injection Molding of Wholly Thermoplastic Composites
A novel technique is used to generate thermoplastics reinforced with thermotropic liquid crystalline polymer(TLCP) microfibrils. The microfibrils are about 1 to 2 microns in diameter and theoretically can be made smaller. Injection molded materials have mechanical properties similar to glass reinforced materials but exhibit much smoother surfaces suitable for painting and the potential to be recycled. One of the major problems with injection molding fiber reinforced thermoplastics to make thin flat panels is warpage. This work is concerned with designing the material to exhibit a minimum degree of warpage while maintaining the mechanical properties. Various avenues are being explored including the matrix rheology, reducing the absolute length of the fiber reinforcement while maintaining the aspect ratio, and interaction between the reinforcing fibers and the matrix.

5. High Performance Rapidly Processable Materials for BiPolar Plates in Fuel Cells
There is considerable interest in the development of improved cheaper fuel cells. One of the most expensive parts of the fuel cell is the outer plate or the
bipolar plate when used in stacks of many cells. The bipolar plate must be highly conductive(~100 Seamans/cm), stiff and durable, and a barrier to hydrogen, oxygen, and water. At present they are made by machining channels in a graphite plate generated by a sintering procedure. Our efforts are centered on developing materials which meet all the property requirements but can be produced by rapid processing techniques such as compression molding or injection molding. Materials are being developed which can be processed by these techniques.


Suuporting Agencies: Department of Energy, Environmental Protection Agency, NASA, DaimlerChrysler, National Science Foundation