Synthesis and Advanced Manufacturing of Polymer Structures and Their Composites
The following research work performed embodies three unique studies of polymer structures and their composites. In general, polymers are viscoelastic, insulative materials that are used for a wide variety of applications within industrial, aerospace, and biomedical fields. Polymers have been studied and optimized for any particular use by chemically synthesizing unique micro-structures, altering the physical properties through fabrication and post-processing, and utilizing 3D printing to achieve complex geometries. In the past decade, additive manufacturing (AM) has drawn extensive attention across academia, industry, and government agencies. It offers unprecedented advantages such as design freedom, rapid prototyping, and customization. In this work, three different optimizations of polymer structures coupled with AM were studied to investigate their thermal, mechanical, and electrical properties to produce complex and functional polymetric materials. First, the development of polysiloxane pore formers were desired to be incorporated into a PDMS matrix for increasing mechanical performance. The formation of monodisperse hollow microspheres is a competitive practice for mass-production manufacturing. Developing uniform pore formers within the range of 5-100 µm was executed by dispersion polymerization where they were loaded into polymer PDMS matrix for 3D printing using a direct write process. By synthesizing the polymer microspheres, it is feasible to control the molecular weight, shell thickness, sphere uniformity, and physical properties as well as lending itself for up-scale production systems. Thus, optimizing the structural integrity and mechanical properties of the 3D printed polymer structures with pore formers can be achieved. Second, performing thermal post-processing of 3D printed polyetheretherkeytone (PEEK) to enhance the mechanical properties were studied. Different annealing temperatures and cooling rates employed onto the 3D printed PEEK dogbone specimens provided unique mechanical properties. Achieving theoretical mechanical performance of conventionally molded PEEK through additive manufacturing would further the use of this high temperature polymer. Combining the freedom of design 3D printing technique with influencing thermal post- processing and printing parameters are shown to critical in the resulting mechanical properties. Also, functionalizing the polymer backbone to increase the electrical performance of the PEEK was done by a process of sulfonation. This functionalization was of interest to identify a fabrication process that utilizes piezoelectric fillers to increase conductivity of the polymer matrix with the intent of fabricating a high-temperature piezoelectric filament. Third, incorporating a piezoelectric ceramic into a polyvinylidene fluoride (PVDF) matrix that is introduced to an additive manufacturing process was executed. Piezoelectric materials are known to be useful active materials in which they serve as sensors and actuators. Their multifunctional properties derive from their unique capability of coupling mechanical and electrical energy. Thus, the 3D printed multifunctional nanocomposite sensors demonstrated the successful freedom of design methodology paired with improvements in mechanical and electrical properties. Overall, the subsequent three chapters embody different projects, however, they all introduce either synthesized, functionalized, or composite materials into an additive manufacturing process.
Wilburn, Bethany Rose, "Synthesis and Advanced Manufacturing of Polymer Structures and Their Composites" (2020). ETD Collection for University of Texas, El Paso. AAI28002712.