Development of Low-Cost and Sustainable Composites 9 views

Composites harness the unique properties of reinforcement materials such as carbon fiber (CF), carbon nanotubes, and graphene. By taking advantage of the unique strength to weight ratios, stiffness to weight ratios, thermal, and electrical properties of their reinforcements, composites push the boundaries of material properties and enable technologies such as space launch vehicles, ballistic body armor, and supercapacitors. Composites are a key component in improving vehicle efficiency which is critical due to the large volume of global emissions currently produced from the transportation sector. However, the production of these highly engineered materials is expensive and has negative impacts on the environment. Therefore, low cost and sustainable avenues for creating composites and their constituent materials are essential for the incorporation of these materials in everyday life and for the long-term health of the environment. The aim of this dissertation is to establish methodologies for reducing the costs associated with composite production and to further our understanding of how these manufacturing processes affect the resultant mechanical properties. This work focuses on creating composites from recycled materials and reducing the costs of CF, an essential reinforcing material in high performance composites. The costs and environmental impact of CF production can be reduced by creating fiber from pitch, a byproduct of coal and petroleum manufacturing. The vast majority of global CF is produced from specially designed polymers that require harmful solvents to successfully form fibers that can be converted to CF. Pitch fibers can be produced by melt spinning, which is a less expensive and more environmentally friendly. However, current pitch-based CF production costs are too high for adoption into commercial markets, and their strengths lag significantly behind those of polymer-based CF. The processing conditions during fiber extrusion have a large impact on the underlying microstructure and texture of pitch, which determine the properties of the CF. Manipulating variables such as the extrusion temperature has been shown to alter the shape and texture of pitch-based CFs, however no mechanical data was reported. Studies which have reported CF mechanical properties employed a very narrow range of extrusion temperatures and were unsuccessful in significantly changing the fiber shape. To better understand the development of pitch-based fiber microstructure the effects of extrusion temperature on the crystallographic and molecular arrangement was examined by producing CFs over a broad range of temperatures. It was found that extruding beyond a temperature of 340°C caused the fiber to split, but improved the average crystallite size. The geometry of the extrusion orifice also plays a significant role in pitch-based fiber microstructure evolution, but iterative nozzle design is costly and time consuming. Thus, 3D printer nozzles were examined as possible hardware for melt spinning pitch fibers and studying the effects of extrusion orifice geometry. The nozzle geometry could control the fiber microstructure, producing CFs with improved strength. Beyond reducing the costs of CF, composite production costs can also be reduced by using recycled materials. Due to its abundance, recycled polypropylene was combined with recycled graphene nanoplatelets to create a composite with improved impact properties and to offset the degradation from plastic recycling. Creating composites in such a manner is a promising strategy for giving waste materials a second life. The work described in this dissertation advances low cost methodologies for composites and their reinforcing materials and deepens our understanding of how processing schemes impact the resulting microstructure and properties of CFs and composites. Improving our understanding of these processing-structure-property relationships in composites will enable their widespread deployment in more efficient vehicles. Finally, recommendations for future work are discussed in the last chapter of this dissertation.

PHD (Doctor of Philosophy)

Carbon fiber, mesophase pitch, melt spinning, recycling, polypropylene, graphene nanoplatelets, nanocomposites

Hydrogen and Fuel Cell Technologies Office (DE-EE0009239) and Vehicle Technologies Office (DE-EE0010602)

English

All rights reserved by the author (no additional license for public reuse)

2025-12-11