UBC Theses and Dissertations
Preparation and characterization of lignin nanofibre-based materials obtained by electrostatic spinning Dallmeyer, James Ian
Electrostatic spinning was investigated as a means to generate nanofibre-based materials from lignin. Kraft, organosolv, lignosulfonate, and pyrolytic lignins were found to be prone to electrospray, resulting in the formation of droplets instead of fibres upon electrical charging of their solutions in most cases. It was observed that the addition of a small amount of poly(ethylene oxide) (PEO) to the spinning solution was an effective strategy to promote the formation of uniform fibres. Studies on the shear and elongational rheology of the spinning solutions were conducted to understand the mechanism underlying the improved process stability that resulted from the addition of PEO to lignin solutions. It was found that the shear rheology was changed to a small extent upon addition of PEO to the spinning solution, while studies using capillary breakup extensional rheometry revealed that PEO addition induced non-Newtonian, strain hardening behaviour to lignin solutions, which was undetectable in shear rheology studies. The concentration of lignin in solution, concentration of PEO, and molecular weight of PEO were shown to influence the elongational fluid properties, which displayed a strong correlation with the fibre diameter. Once the rheology of the spinning solution was characterized, attention was focused on oxidative thermostabilization and carbonization of electrospun nonwoven fabrics. It was found that incorporating different amounts of Kraft lignin fractions in electrospun fibres allowed the preparation of interesting material morphologies depending on the thermal softening characteristics of Kraft lignin fractions. Two interesting types of materials were prepared by controlling the composition of lignin fabrics and processing parameters. The first was a novel stimuli-responsive film material with a reversible ability to change shape in response to moisture. The second type was an interconnected carbon nanofibre network which displayed interesting mechanical, surface, and electrical properties. The structure and properties of Kraft lignin fractions were investigated by thermo-rheological analysis, nuclear magnetic resonance spectroscopy, gel permeation chromatography, and light scattering to understand the role of lignin structure in determining the properties of thermostabilized and carbonized lignin fabrics. The electrospun fabrics were also characterized by atomic force microscopy, microtensile testing, nitrogen adsorption, X-ray diffraction, and Raman spectroscopy.
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