Date of Award

Spring 1-1-2021

Degree Type

Thesis

Degree Name

Master of Science In Chemical Engineering Degree

Department

Chemical And Biomedical Engineering

First Advisor

Ao, Geyou

Second Advisor

Dr. Orhan Talu

Third Advisor

Dr. Shawn Ryan

Abstract

Boron nitride nanotubes (BNNTs) have promising optical, mechanical, and thermal properties which make them one of the most promising material candidates for fabricating protective and multifunctional fibers with remarkable thermal and chemical stabilities, electrically insulating, and ultraviolet radiation shielding capabilities. Here, we have demonstrated an effective method to produce stable dispersions of BNNTs coated by surfactants and fabricate continuous BNNTs and polyvinyl alcohol (PVA) composite fibers via a wet-spinning approach. BNNTs/polymer composite fibers were spun by combining SDC-coated BNNT dispersions with aqueous solutions of PVA and coagulating the resulting mixtures in the flow of a solvent, such as methanol (MeOH), ethanol (EtOH), and MeOH/acetone cosolvent. We examined the effects of various parameters, such as pristine versus purified BNNT material, the concentrations of BNNTs and PVA, and the specific coagulation solvent, on the overall mechanical properties of the composite fibers. Specifically, we compared the tensile strength, Young’s modulus, and toughness of neat PVA and BNNT/PVA composite fibers containing either pristine or purified BNNTs. Our results indicate that increasing the BNNT content, in composite fibers with 5 mass% PVA and spun in EtOH, to 0.1 mass % increases the tensile strength and Young’s modulus by 140% and 520%, respectively, for pristine BNNTs and by 200% and 543% for purified BNNTs compared to neat PVA fiber. Reducing the PVA concentration, for the same composite fibers, to 2.5 mass % improves the tensile strength and Young’s modulus by v 308% and 1179%, respectively, compared to neat PVA fiber. Fibers formed in MeOH/acetone exhibited higher toughness, but lower strength, compared to fibers formed in MeOH and EtOH which showed relatively similar average mechanical properties. Combined, our results provided insights into the structure-processing-property relationships of BNNT/polymer fibers and the vast potential for producing BNNT-based assemblies with controlled alignment and properties.

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