Doctor of Philosophy in Forestry (PhD)
Bioplastic from agroforestry waste: end-of-life management
The urgent necessity for replacing fossil resources has driven researchers to develop moresustainable materials from technical lignin. However, the heterogeneous nature of this complexmaterial must be improved, as industrial feedstocks require a large degree of uniformity.Therefore, the hydroxyethyl modification of lignin was first developed as a platform derivatizationmethod to convert the phenolics and carboxylic acids of industrial lignins into aliphatic hydroxyls.Ethylene carbonate was used as both the reagent and solvent resulting in a variety of hydroxyethyllignins (HELignins) derived from technical lignin resources. The HELignin derivative was furtherutilized as a polyol and reacted with diisocyanates to make polyurethane foams. While effectiveat various substitution levels of polyol, HELignins only had partial solubility in the polyol. As aresult, the reaction conditions that led to increased lignin molecular weight and low solubilityrequired optimization to avoid crosslinking. Addressing this issue, an in situ real-time monitoringtechnique was created to control the quality of the resulting HELignin. An empirical model wasbuilt to ensure the reaction could reach near completion without significant by-product formation.The optimized reaction conditions created a HELignin that could be further modified; a catalystfree esterification was developed using organic acid as solvent and reagent. Due to the highselectivity toward aliphatic hydroxyl groups, HElignin which had over 85% aliphatic hydroxyls,showed an advance as a starting material useful for lignin esters with tailored thermal propertiesbased on the organic acid of choice. In one application for an aqueous hydrophobic coating,inspired by the natural suberin compounds, oleic acid was used as a solvent and reagent to esterifythe HELignin and subsequently transformed into an aqueous dispersion. These coating materialssignificantly improved the hydrophobic properties of wood-based products. Critically, the abovehydroxyethylation and esterification of lignin satisfied many green chemistry requirementsincluding the adoption of solvent-free reactions, low environment factor (E-factor) reactions, highatom economy, high pot economy, the adoption of low-toxic reagents, and real-time monitoring.Overall, the reaction of lignin with ethylene carbonate led to a greener modification route toconvert technical lignin into more sustainable feedstock for society.
In this study, composite nanofibres were fabricated from solvent fractionated softwood kraft lignin (SKL), NCC and polyethylene oxide (PEO) by electrospinning. The molecular organization of lignin was investigated in the form of spun fibres and films with and without NCC. Subsequently, the as-spun composite nanofibre mats were thermally stabilized in the air under controlled conditions. The chemical and mechanical properties were studied as a function of the processing conditions. The oxidized nanofibres were then carbonized at 1000 ºC in inert nitrogen atmospheres. The responses investigated include changes in yield, diameter/distribution of nanofibres, thermal stability, elemental composition, the molecular structure and mechanical properties. Lastly, effects of NCCs on lignin structure in the fibres at different stages of heat treatments were determined. Lignin molecules demonstrated organization within aligned electrospun fibres and within solvent cast lignin films. The nanofibres and films of lignin with and without NCC had birefringence as revealed with polarized optical microscope. Also, through heat treatment, the lignin-based nanofibres mats with or without NCC, showed improved mechanical and thermal-chemical properties after thermal stabilization and carbonization processes. Specifically the properties of thermally stabilized samples were more variable than carbonized samples. Furthermore, NCC loadings gave a significant reduction in mobility of lignin molecules during heat treatment allowing for direct carbonization for lignin carbon fibres production with NCC loadings for 5 wt.%. NCC overall did not enhance the mechanical properties of the electrospun fibre. However significant interactions between the NCC and lignin were revealed with FTIR spectroscopy and thermal rheological analysis. In summary, the work investigated how thermal treatments can enhance the performance of lignin-based materials and further enhanced by the presence of nanofillers. This study investigated extensively the effect of NCC in lignin-based composite nanofibres through fundamental understanding of the interaction between lignin and NCC during the different heat treatment stages for carbon fibre production.
There is a growing demand to replace non-renewable fossil-based materials like many one use plastics with renewably sourced alternatives that fit within the circular bioeconomy model and demonstrate a favourable end of life. One such option is lignin, found in all woody plants with its desirable aromatic polymeric structure and potential utilization as a byproduct in the pulping and paper industry. However, complications arise because of lignins’ complex non-uniform heterogenous structure which is often remedied through harsh carcinogenic chemical pathways. In this study softwood kraft lignin was fractionated in a one step process using acetone, modified first with ethylene carbonate, then with propionic acid, and finally melt-blended with completely biodegradeable Ecoflex™ in order to develop an alternative to thermoplastics like non-degradable polyethylene and polypropylene. The acetone fractionation separated the lignin by molecular weight. The reaction with ethylene carbonate etherified the lignin creating a more uniform structure. Finally, the reaction with propionic acid esterified the lignin thus masking reactive hydroxyl groups. Nine lignin powders ready for blend with Ecoflex™ were developed using green chemistry practices: unfractionated (UF), acetone soluble (ASKL) and acetone insoluble (AIKL) fractions each unmodified (UN) and modified via hydroxyethyl ether (HE) and esterification (E). The lignin samples were melt-blended, extruded, mould injected and underwent extensive tensile testing to determine how each fraction with or without modification behaved in comparison to the as received softwood kraft lignin. In addition, detailed thermal and structural testing was carried out using DSC, TGA, and FT-IR analysis. The acetone soluble fraction without modification (ASKL_UN) increased the tensile properties (tensile strength and toughness) at lower lignin loadings (5-10 wt%) in comparison to neat Ecoflex™ and the acetone insoluble fraction. The acetone soluble esterified lignin (ASKL_E) maintained tensile properties up to a 40 wt% lignin loading in comparison to neat Ecoflex™ and the acetone insoluble fraction. In summary, this work used green chemistry practices to develop lignins that were processible with the biodegradeable polyester Ecoflex™ and found an improvement in tensile properties. This has great implication in valorizing lignin-based polymeric materials as this work showed a simple acetone fractionation is capable of improving mechanical properties.