11.12.2024
Doctoral thesis in Chemical Technology (Natural Materials Technology)
M.Sc. (Eng.) Rui Liu’s doctoral thesis in Chemical Technology (Natural Materials Technology) will be put forth for public defence at the Faculty of Science and Engineering at Åbo Akademi University.
The thesis is entitled Heterogeneity of Softwood Kraft Lignin: Effects on Fractionation and Nanoparticles Formation.
The public defence of the doctoral thesis takes place on 16 December 2024 at 1PM in auditorium Helikon, Arken, Tehtaankatu 2, Turku. You can also follow the defence online. Professor Martin Lawoko, KTH Royal Institute of Technology, Sweden, will serve as opponent and Professor Chunlin Xu, Åbo Akademi University, as custos.
Summary
Industrial kraft pulping processes provide abundant lignin feedstocks, which are renewable and valuable resources for developing diverse chemicals and functional materials. However, this industrial-grade lignin usually exhibits a strong odor, dark color, heterogeneous chemical structure, and even complex chemical constituents depending on the wood species utilized, the delignification process employed, and the subsequent steps involved in lignin recovery. The high heterogeneity in structure and chemical constituents can result in variations in the quality of downstream products, posing a significant challenge in developing industrial lignin for high-value-added products.
The presented thesis focused on clarifying the heterogeneity in chemical constituents and sublinkage compositions of industrial softwood kraft lignin (ISKL). Additionally, it aimed to elucidate the effects of these heterogeneities on lignin fractionation, the physicochemical properties of lignin fractions, and the formation of lignin nanoparticles.
Results on the chemical constituents showed that ISKL consisted of heterogeneous lignin polymers, lignin-carbohydrate complexes, extractives, aromatic monomers, and other products generated during the kraft delignification process. The sublinkage compositions of lignin fractions obtained through a novel solvent fractionation approach indicated that the lignin can be classified as follows: 1) One fraction exhibited a higher proportion of sublinkages with reduced side chain (stilbenes and enol ether) while containing a lower amount of native sublinkages. It also presented a lower molar mass, a higher phenolic hydroxyl groups (PhOH) content than aliphatic hydroxyl groups (AlkOH), a higher carbon content, and stronger solubility in a low polarity solvent. 2) One fraction showed a relatively stable proportion of native sublinkages and stilbenes, while the proportion of resinol and benzyl ethers increased with their increased molar mass. This fraction also maintained a relatively constant content of PhOH and AlkOH, and elemental composition. 3) One fraction primarily consisted of native sublinkages, a certain amount of carbohydrates, and a smaller percentage of sublinkages with reduced side chains. It also presented a higher molar mass and an elevated content of AlkOH compared to PhOH. These structural characteristics collectively contributed to its reduced carbon content and improved solubility in solvents with a moderate dispersion and a stronger hydrogen bonding capacity. 4) A low-yield fraction exhibited a moderate molar mass, a high content of native sublinkages, carbohydrates, and fewer sublinkages with reduced side chains. The variation in the sublinkages composition of different fractions results in them presenting different thermal degradation behaviors and variable abilities to form lignin nanoparticles. Finally, the heterogeneous chemical constituents, especially, fatty acids play a major role in the formation of hollow lignin nanoparticles rather than lignin itself.
Rui Liu can be reached by phone +358 41 053 703 or email rui.liu@abo.fi.
The doctoral thesis can be read online through the Doria publication archive.
No photo of the doctoral student available.
Instructions for following the doctoral defence remotely:
To follow the defence, you need the Zoom software or the Google Chrome browser. You do not need to create a Zoom account to follow the defence. If you install the application, you participate by clicking on the meeting link, after which you should allow the link to open in the Zoom app.