Available at: https://digitalcommons.calpoly.edu/theses/1406
Date of Award
MS in Polymers and Coatings
Carbon nanomaterials provide applications in a wide variety of roles, including as reinforcing materials, thermal and electrical conductors, and optical absorbers. While their benefits can be applied as bulk materials, their implementation into polymer materials as fillers allows for efficient enhanced properties with a small amount of material. These blended materials, referred to as nanocomposites, integrate the beneficial properties of both the polymer and carbon nanomaterials to create cheap solutions to construction and product development that bulk materials could not accomplish. However, major challenges must be overcome to allow for their adoption in industry. Among these problems is the interfacial interactions between the nanomaterials with the polymer matrix. Weak interactions between fillers and polymer can cause the fillers to aggregate out of the polymer phase and greatly reduce the transfer of load, heat, or electricity from the polymer to the filler. As a result, studies must be done to understand and improve these interactions. In order to study these interactions, transcrystals can serve as a model for observing the interface between polymer and filler. Transcrystals are oriented lamella, which are linearly-organized folded polymer chains, forming from a heterogeneous nucleation site at a substrate or a fiber. Transcrystals formed from fibers can greatly improve the mechanical strength and thermal stability of the polymer due to increased ordering of polymer chains as well as the load and heat transfer from the polymer to the fiber. Transcrystallization has been well studied with carbon nanotube fibers and other fibers, like nylon and polytetrafluoroethylene.
Graphene is one such filler that can provide substantial benefits due to its high strength, thermal conductivity, and electrical conductivity, but the interactions between these materials have not been studied extensively. Because of this, graphene remains an untapped solution in polymer composite products. In order to study these interactions, this study reports the transcrystallization of isotactic polypropylene in the presence of reduced graphene oxide fibers. Carbon nanotube-induced transcrystals were studied alongside the reduced graphene oxide fibers to compare differences in structure between the two fibers and provide better understanding for the applications of both interfaces in composite development. The kinetics of this transcrystallization was also studied for both fibers to better understand this process as well as to compare the nucleating abilities of both fibers. The fold surface free energies and interfacial free energy differences were calculated to provide a quantitative means of comparison between the two interfaces. This study provides a foundation for creating graphene-polymer composites as well as the transcrystals produced can serve as reinforced materials to be implemented in high-performance products.