THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING
GEORGIA INSTITUTE OF TECHNOLOGY
Under the provisions of the regulations for the degree
DOCTOR OF PHILOSOPHY
on Monday, July 2nd, 2018
in MRDC 3515
will be held the
"Processing, Structure, and Properties of Polyacrylonitrile-Nanocellulose Composite Films and Fibers"
Dr. Satish Kumar, Advisor, MSE
Dr. Robert J. Moon, Advisor MSE
Dr. Yulin Deng, ChBE
Dr. Kyriaki Kalaitzidou, ME
Dr. Meisha Shofner, MSE
The objective of this work is to evaluate the effect of the incorporation of nanocellulose into polyacrylonitrile (PAN). The effect the nanocellulose will have on the rheological properties on the solution/suspension were studied. Additionally, the effect nanocellulose has on the structure development, along with the changes in the mechanical, thermal, and optical properties on the films and/or fibers were determined. Since these composites can potentially be converted to carbon materials the changes in the stabilization were also investigated. Functionalization of cellulose nanofibrils (CNF) were also studied to improve the dispersibility.
Through this work we made highly loaded CNC-polymer composite films that showed linear increased in tensile properties with increasing CNC loading up to 40 wt% CNC loading. We demonstrated that CNC could lower the energy needed for the PAN stabilization. CNF was functionalized with surface chemistries that has not been demonstrated on CNF before. We also studied the effect surface functionalization has on the resulting mechanical properties on the PAN-CNF fiber.
It was found that PAN-cellulose nanocrystal (CNC) suspension’s viscosity at low shear rates would increase over time. In this work PAN-CNC films were made with up to 40 wt% cellulose with no decrease in optical clarity, while the glass transition temperature increased from 92 to 118 °C. These films also demonstrated a 68% increase in elastic modulus and a 76% increase in tensile strength. The experimental tensile data was fit into micro-mechanical models. These models determined that the interfacial shear strength of 27 MPa between the PAN and CNC was 27 MPa.
The stabilization of the PAN/CNC films were studied by differential scanning calorimetry, Fourier transform infrared spectroscopy, and wide angle x-ray diffraction. It was found that the thermal stability of the CNC was higher in the composite than in a neat CNC film. The activation energy for cyclization of PAN was also found to decrease by 16% in all PAN-CNC composites compared to neat PAN irrespective of CNC loading.
A quick 1 step sulfonation method of CNF was used, and it was found that with as low as 5 minutes of reaction time, significant improvement in dispersibility in dimethylformamide (DMF) and water could be achieved. This method was much quicker than the commonly used 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) oxidation method for CNF. It was also found that TEMPO oxidized CNF (TCNF) and sulfonated CNF (SCNF) could undergo surface chemistry changes when dispersed in DMF. The TCNF would form dimethylammonium carboxyl groups, while the SCNF would form formate groups.
Amination of CNF was also done and the reinforcement properties of the amine functionalized CNF (ACNF) compared to TCNF in PAN fibers. The effect of different processing parameters were studied to see how they affect the resulting fiber properties. It was also found that the TCNF increased the viscosity of the suspensions significantly more than that of the ACNF. At 1 wt% CNF loading, the PAN-ACNF fibers had 30% higher tensile strength than the PAN-TCNF fibers, and at 5 wt% CNF loading the PAN-ACNF fiber had a 78% higher tensile strength than the PAN-TCNF. The PAN-ACNF fiber at 1 wt% ACNF loading only had a tensile strength that was 9% higher than that of the neat PAN fiber. This 9% increase is a statistically significant increase.