Fiber-reinforced thermoplastics (i.e., thermoplastic composites) are emerging in industries as a replacement for metals due to their durability and light weight. However, it is difficult to achieve high levels of strength and toughness in thermoplastic composites, which hampers their ability to be manufactured at rapid rates.
Funded by the National Science Foundation (NSF) Faculty Early Career Development (CAREER) award, Dr. Amir Asadi, assistant professor in the Department of Engineering Technology and Industrial Distribution at Texas A&M University, has developed a method using hybrid nanomaterials capable of creating high-performance thermoplastic composites with favorable mechanical properties in a few minutes.
Fiber-reinforced thermoplastics are replacing metals at high rates due to their inherent properties – they are light, strong, recyclable and malleable. They can be used in various applications including manufacturing, automotive and aerospace industries as they are both cost effective and durable.
“Based on the principle that a 10% reduction in vehicle weight leads to a 6% to 8% increase in fuel efficiency and a 325 kilogram reduction in its annual carbon dioxide emissions, this project provides a scalable solution to compete with the fabrication of metal parts in the automotive industries,” Asadi said. “Furthermore, this project addresses the need to reduce weight and manufacturing costs in aerospace, making the economic case for manufacturing small air vehicles for imaging, radar, surveillance and deliveries, and expedites the certification of high-speed composites for commercial aircraft.
High performance thermoplastic composites are typically semi-crystalline, containing both crystalline and amorphous regions. In polymers, crystals are the regions where the polymer chains are in a specific order, and amorphous regions are those with random structures.
However, thermoplastic makeup presents a paradox: it will be brittle if the strength is improved by increasing the number of crystals, but if the brittleness is addressed by having more amorphous regions, the strength decreases significantly. A rapid manufacturing process would induce this paradox due to the rapid heating and cooling process that does not allow sufficient time for crystals to form, making it difficult to produce solid thermoplastics.
“Making structures with properties that work against each other is a challenge,” Asadi said. “However, these structures exist in nature. For example, an elephant’s trunk is strong enough to lift hundreds of pounds, stiff in fights, but also soft, flexible, and delicate enough to handle small vegetables. At the same time, it serves versatile functions such as communication, drinking and showering. The key to these incredible functions is the complex microstructure of the trunk, which we can consider as an example of how we can achieve paradoxical properties in a structure.
To address this challenge, the researchers proposed to engineer the crystalline-amorphous microstructure during fabrication using hybrid nanomaterials. These nanomaterials can adapt the crystals to the desired architecture by controlling the nucleation, growth, orientation and size distribution of the crystals. The development of the microstructure during production produces a thermoplastic composite that is both strong and resistant to breakage.
Their new method could potentially produce fiber-reinforced thermoplastics faster and more cheaply. Additionally, it could present a scalable solution that can compete with metals in manufacturing.
“This project accelerates manufacturing platforms that could benefit the economy and national security of the United States by equipping the automotive, aerospace, and marine industries with rapid manufacturing technology,” Asadi said.
Going forward, the researchers will seek to provide physical evidence that their manufacturing process mirrors their molecular simulations. To accomplish this task, they work with the Air Force Research Laboratory to determine if the results of their research will be compatible with manufacturing processes.
The NSF CAREER program supports early-career faculty who show potential in the academic community and strive to advance the goals of their department or organization.
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