Glyoxylic-Modified Lignin for Synthesis of Smart Elastomer and Composite Materials

Abstract: Sustainable development has become a global goal and the utilization of bioresources is a key way to achieve this crucial goal. Glyoxylic acid-functionalized lignin (GA-lignin) is one of the novel lignin derivatives extracted from beech wood (hardwood) and has great potential to be an industrially important bioresource. In this thesis work, epoxies prepared by GA-lignin and polyethylene glycol diglycidyl ether (PEGDE) were studied, and the feasibility to prepare smart materials based on these epoxies was explored. Three smart properties, including self-healing properties, thermoelectric properties and piezoelectric properties, were successfully embedded in the GA-lignin-based materials. Many applications are envisioned based on the unique properties of GA-lignin and the value-added materials based on this lignin, including adhesives, hydrogels, flexible electronics, etc. In the first part of this thesis work, different pathways were performed to synthesize GA-lignin/PEGDE epoxies: solvent-free pathway, NaOH solution pathway, DMSO solvent pathway and 1,4-dioxane solvent pathway. The elastomeric epoxy with 50wt% lignin was synthesized following the solvent-free pathway showing mild self-healing properties. The introduction of NaOH solution was found to have the ability to enhance self-healing properties. The epoxy obtained following the dioxane solvent pathway had a similar structure to the original one without any medium, therefore dioxane was chosen to be the solvent for further fabrication of nanocomposites. In the second part, two kinds of GA-lignin-based nanocomposites were fabricated with dioxane as solvent. The first kind of nanocomposite was filled with reduced graphene oxide nanoparticles (rGO). 1wt%, 2wt% and 3wt% of rGO nanoparticles were dispersed into the 50wt% GA-lignin/PEGDE epoxy matrix. Power factor analysis was performed, and the potential of GA-lignin-based thermoelectric nanocomposite was verified. The second nanocomposite was filled with barium titanate nanoparticles (BaTiO3). 7.5wt% and 15wt% of BaTiO3 were dispersed into the epoxy matrix and the piezoelectric response test was performed to show the embedded piezoelectric properties.