Structure and properties of lignin-based composite carbon nanofibres

ii Lay Summary . iv Preface . v Table of Contents . vi List of Tables . x List of Figures . xii List of Symbols . xvii Acknowledgements . xix Dedication . xx Chapter 1: Introduction and Motivation . 1 Chapter 2: Literature Review . 8 2.1 Lignin Structure and Chemistry . 8 2.2 Lignin-Based Carbon Fibres . 9 2.3 Electrospinning . 14 2.4 Electrospun Carbon Nanofibres . 15 2.5 Mechanical Properties of Single Nanofibres and Fibrous Mats . 18 2.6 Structure and Properties of Carbon Nanotubes . 23 2.7 Carbon Nanotube-Reinforced Nanofibres . 24 2.8 Theories and Models of Mechanical Properties Translation with Different Nanofibre Assemblies . 25 2.9 Supercapacitors . 26 Chapter 3: Objectives . 31 vii Chapter 4: Materials and Experimental Methods . 35 4.1 Materials . 35 4.2 Lignin Fractionation . 35 4.3 Electrospinning Process . 36 4.4 Emulsion Electrospinning Process . 37 4.5 Heat Treatment Process . 38 4.6 Characterization . 39 4.6.1 Morphological and Structural Characterization . 39 4.6.2 Mechanical Properties Characterization . 39 4.6.2.1 Nanofibre Mats . 39 4.6.2.2 Single Nanofibres . 40 4.6.2.3 Atomic Force Microscopy (AFM) . 41 4.6.3 Fourier Transform Infrared Spectroscopy (FT-IR) . 42 4.6. 4 X-Ray Diffraction (X-RD) . 42 4.6. 5 Raman Spectroscopy . 43 4.7 Preparation and Characterization of Electrospun Carbon Nanofibre Electrodes . 43 4.7.1 Supercapacitor (SC) Unit Cell Preparation . 43 4.7.2 Electrical Conductivity Measurement . 44 4.7.3 Electrochemical Performance Measurement . 45 Chapter 5: Electrospinning Process Optimization of Lignin Nanofibres . 46 5.1 Introduction . 46 5.2 Choice of Parameters and Experimental Design . 47 5.2.1 Choice of Parameters and Range . 47 viii 5.2.2 Experimental Design . 49 5.3 Results and Discussion . 50 5.3.1 Fibre Morphology and Average Diameter . 50 5.3.2 Response Function . 52 5.4 Concluding Remarks . 55 Chapter 6: Mechanical Properties of Electrospun Lignin Nanofibre Mats . 57 6.1 Introduction . 57 6.2 Results and Discussion . 57 6.2.1 Mechanical Properties of As-spun Nanofibre Mats . 57 6.2.2 Mechanical Properties of Thermo-stabilized Nanofibre Mats . 61 6.2.3 Mechanical Properties of Random Carbon Nanofibre Mats . 71 6.2.3.1 Tensile Test of Random Carbon Nanofibre Mats . 71 6.2.3.2 X-Ray Diffraction (X-RD) Analysis of Carbon Nanofibres . 73 6.2.3.3 Raman Spectroscopy Analysis of Carbon Nanofibres . 75 6.2.4 Mechanical Properties of Aligned Nanofibre Mats . 78 6.3 Concluding Remarks . 82 Chapter 7: Single-Walled Carbon Nanotube-Reinforced Lignin Composite Nanofibres . 84 7.1 Introduction . 84 7.2 Results and Discussion . 85 7.2.1 Morphology and Mechanical Properties of SWNT/F4SKL Composite Nanofibres . 85 7.2.2 Raman Spectroscopy of SWNT/F4SKL Carbon Nanofibres . 95 7.3 Concluding Remarks . 98 ix Chapter 8: Mechanical Properties from Single Nanofibres to Fibre Assemblies . 99 8.1 Introduction . 99 8.2 Theoretical Analysis . 100 8.2.1 Weibull Distribution for Single Nanofibres . 100 8.2.2 Tensile Strength of Aligned Nanofibre Mats and Twisted Nanofibre Yarns . 101 8.3 Mechanical Properties of Single F4SKL Nanofibres . 104 8.4 Elastic Modulus Estimation of F4SKL Nanofibres via Statistical Modeling . 111 8.4.1 F4SKL As-spun Single Nanofibres to Nanofibre Assemblies . 111 8.4.2 Strength and Weibull Distribution of F4SKL Carbon Nanofibres . 116 8.5 Concluding Remarks . 118 Chapter 9: Lignin-Based Carbon Nanofibre Electrodes for Supercapacitors . 120 9.1 Introduction . 120 9.2 Results and Discussion . 120 9.2.1 Electrical Conductivity . 120 9.2.2 Cyclic Voltammetry Test . 121 9.2.3 Galvanostatic Charge/Discharge Test . 125 9.2.4 Electrochemical Impedance Spectroscopy .