| Abstract: | In this report, we study the reaction kinetics of bisphenol A diglycidyl ether (DGEBA) and a curing agent (Jeffamine T403) and demonstrate new techniques to print multi-layered structures using localized RF heating and curing. We first characterized isothermal curing of DGEBA resin using rheometry and Differential Scanning Calorimetry to understand the curing kinetics. The in situ curing behavior of RF-heated DGEBA-CNT resin was monitored using a rheometer to show that RF heating allows for rapid volumetric heating and curing of thermosetting resins. We developed a technique to build up a multi-layered printed structure using RF heating and localized curing. Multi-layered structures were printed by moving the RF applicator relative to the resin reservoir, selectively curing the resin exposed to the field; this process was repeated for each layer. Thermal and mechanical characterization was performed for RF printed samples, and conventionally cured (oven-cured) samples. The two samples show similar glass transition temperatures and storage moduli, but the RF-heated samples show a more uniform morphology and better mechanical properties. The selective curing process was also modeled using multi-physics simulation of curing kinetics and heat transfer; the simulation calculates the conversion and temperature at each point in space and time. Simulation results show that our proposed technique can be used to create complex structures like the Texas A&M logo, thus demonstrating the scope of this method in printing complex structures. In the last study, currently in progress, we demonstrate that the use of a co-planar RF applicator, which generates an electric field, to rapidly heat and cure DIW-printed, nano-filled epoxy composites. This proposed method involves a layer-by-layer, print and cure cycle which allows for printing high resolution, multi-layered structures. Here, each printed layer is partially cured using RF heating before a new layer is deposited. This print-and-cure cycle allows the printed structure to maintain its integrity and hold its own weight without collapsing as subsequent layers are printed. Commercial epoxy resin with varied nano-filler loadings were examined as DIW candidates. Rheological characterization was used to assess curing kinetics and printing behavior, and RF sweeps were used to determine RF heating capabilities of the candidate resins. After printing, the thermo-mechanical properties, surface finish, and shape retention of RF-cured samples were evaluated and found to be comparable against samples conventionally cured in an oven. This method of manufacturing establishes RF heating as a suitable alternative to conventional methods, thereby facilitating rapid, free-form processing of thermosetting resins. The electronic version of this dissertation is accessible from https://hdl.handle.net/1969.1/197732 |
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