Fiber Engineering for Extreme Environments
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CitationGonzalez, Grant. 2019. Fiber Engineering for Extreme Environments. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
AbstractTextile fibers in clothing have provided protection from heat, high-performance fibers in body armor have enabled protection from fragmentation injuries, and fiber-reinforced composites have increased the life span of products undergoing abrasive wear. All these environments provide extreme conditions for materials. A material used in each of these environments is poly(p-phenylene terephthalamide) (PPTA) fibers. With the common PPTA building block, its ultimate structure dictates its function: fiber weaves provide mechanical protection, fibers turned into a pulp act as insulation, and short fibers mixed into composites improve wear. The material's functionality is therefore limited by its structure. To protect from improvised explosive devices (IEDs) in the desert, a material needs to provide both mechanical and heat protection simultaneously. To enable this material, we hypothesized combining the PPTA structure of continuous fibers with the porosity of aerogels would achieve these properties simultaneously. To create the porous network, however, the fibers would need to be on the scale of 1 um in diameter, the length scale of nanofibers. As no method exists to create PPTA nanofibers, we first developed a method to produce PPTA nanofibers. After scaling that system to produce PPTA nanofiber sheets with porous networks, we performed fragmentation and heat insulation testing to reveal that the nanofiber sheets had a 15% lower fragmentation protection and 20x the insulation ability of commercial PPTA fiber weaves. With a slight loss in fragmentation protection, the material gained the ability to provide heat protection simultaneously. In addition to providing simultaneous structures and functions, the PPTA nanofibers also improved the wear of fiber reinforced composites by changing the mechanism of wear from a volumetric wear rate to a fracture wear mechanism based on the interaction of the fiber with the matrix. The PPTA nanofibers enabled novel structure to improve functionality of materials in extreme environments.
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