Public defence in Chemical Engineering, M.Sc.(Tech.) Lukas Fliri

The title of the thesis: Carbonyls in Cellulose: An Investigation into Formation Mechanisms, Analytical Methods, and their Consequential Properties for Fiber Engineering Applications

Thesis defender: Lukas Fliri
Opponent: Professor Stephen Eichhorn, University of Bristol, United Kingdom
Custos: Professor Michael Hummel, Aalto University School of Chemical Engineering

Investigating oxidative and thermal treatments of cellulose  

This thesis aimed to advance the utilization of man-made cellulosic fibers (MMCFs) for non-standard applications. More specifically, it was attempted to generate renewable alternatives for two synthetic materials that currently dominate certain areas in the fiber market: 1) for polyurethane-based Elastane fibers which are used to enhance the stretchability of textiles. 2) for polyacrylonitrile (PAN) fibers, which represent the main precursor to produce carbon fibers (CFs) with acceptable mechanical properties. 

For both endeavors the introduction of carbonyl functionalities into the cellulose structure was of major interest. To increase the flexibility of MMCFs the introduction of ring-opened dialdehyde cellulose (DAC) moieties into the rigid cellulose structure was examined. To enhance the yield of cellulose-based CFs the mechanism of the thermal dehydration reactions below 300 °C was investigated in detail. 

The introduction of carbonyl functionalities seemingly only represents a minor change to the chemical structure of cellulose. However, it causes major changes to the solubility and stability of the materials, which also results in significant analytical challenges and has consequences for the materials properties. To obtain a better understanding of the operative processes they were investigated with state-of-the-art analytical techniques. Consequently, some pitfalls and side reactions in DAC chemistry could be highlighted and an updated mechanistic view on the initial thermal dehydration reactions of cellulose could be achieved. 

Keywords: Cellulose modification; periodate oxidation; dialdehyde cellulose; carbonization; thermostabilization; carbon fibers; NMR spectroscopy; size exclusion chromatography

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/

Contact details: lukas.fliri@aalto.fi

Doctoral theses in the School of Chemical Engineering: https://aaltodoc.aalto.fi/handle/123456789/51