Browsing by Author "Hummel, Michael, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland"
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- Carbonyls in Cellulose: An Investigation into Formation Mechanisms, Analytical Methods, and their Consequential Properties for Fiber Engineering Applications
School of Chemical Technology | Doctoral dissertation (article-based)(2025) Fliri, LukasThis thesis focused on the introduction of carbonyls into the cellulose structure with the wider aim to expand the scope of applications of cellulosic fibers. Thereby, two separate reaction classes were critically re-investigated. First, the periodate oxidation of cellulose combined with modification of the resulting aldehyde functionalities. Second, the carbonization mechanism of cellulose with a focus on the thermal dehydration reactions below 300 °C. Periodate oxidation was investigated for its potential to introduce more flexible segments in the rigid cellulose structure. The low temperature dehydration represents a key yield determining step during the preparation of cellulose-based carbon fibers. To obtain further insights into these well researched topics novel analytical techniques were applied. A recently developed solution state NMR method relying on an ionic liquid electrolyte for the dissolution of crystalline cellulosic materials proved to be useful and was further expanded to a full analytical protocol. The studies on periodate oxidation were significantly hampered by different side reactions. Thus, the research focus shifted on their quantification and mitigation. An updated workup scheme for dialdehyde celluloses was elaborated and an indirect size exclusion chromatography protocol allowed to follow the partial depolymerization reactions in the early stages of periodate oxidation. For further modification the applicability of reductive amination and borohydride reduction was screened. Also there, issues with unwanted degradation or incomplete conversion were encountered and could be highlighted. Overall, the studies on periodate oxidation resulted in an improved understanding of the underlying side reactions. However, they ultimately prevented a meaningful application of this modification strategy for fiber engineering purposes. In the fundamental studies on the thermal dehydration reactions of cellulose different reaction intermediates could be isolated and identified. Application of solution state NMR showed that the first thermal transformations result in depolymerization to levoglucosan end capped structures. In contrast to prevailing mechanistic proposals in the cellulose-based carbon fiber community, the initial dehydration reactions do not include elimination reactions in the pyranose structures. Instead, a polyfuran was isolated as first carbonization intermediate and could be thoroughly characterized. This suggested a localized dehydration mechanism occurring on the reducing end groups, as recently postulated in the literature focusing on other fields of cellulose pyrolysis. This observation also suggests that the chemistry of cellulose carbonization is similar to the carbonization reactions of other sugars. Moreover, the occurrence of a polyfuran intermediate has considerable implications for the potential reactions occurring at higher temperatures, which so far evaded proper analytical characterization. - Towards a Closed Loop Economy in Textile Industry: Separation, Dyeing and Re-Spinning of Cellulose Rich Textile Waste
School of Chemical Technology | Doctoral dissertation (article-based)(2020) Haslinger, SimoneThis thesis targeted to improve the waste management in textile industry in terms of material identification, waste valorization and implementation of sustainable alternatives to commercial dyes and finishing agents. A solid-state NMR method was developed to quantify the amount of cellulose in cotton polyester blends, employing a relationship between distinct peak ratios and the cellulose concentration. Furthermore, the Ioncell technology allowed to utilize both, cotton polyester blends and dyed cellulose waste, to spin new, textile grade cellulose fibers via an ionic liquid solvent system. The produced filaments displayed tensile properties superior to commercial Viscose and Tencel with titers down to the microfiber range (<1 dtex). It was also shown that the ionic liquid, 1,5-diazabicyclo[4.3.0]non-5-ene acetate, enabled to dissolve cellulose, while leaving behind a polyester residue, which could be recovered for conventional recycling procedures. Similarly, dyed pre- and post-consumer cotton waste was converted to pristine, colored staple fibers, which were used to manufacture a scarf and a baby jacket. In many cases, the original color of the waste fabrics translated to the new textile products, although a certain amount of leaching could be observed during the spinning process. This behavior was dependent on the nature of the dyes and was hence more pronounced for reactive dyes such as Remazoles than for vat dyes. Eventually, gold and silver nanoparticles were assessed to replace potentially polluting dyes and finishing agents. Via a hydrothermal in-situ synthesis approach, spherical nanoparticles were prepared on bleached prehydrolyzed kraft pulp, which was subsequently dry-jet wet spun to colored, UV protective man-made cellulose fibers. As a result of the incorporation technique, the fibers exhibited a better wash fastness than substrates coated via immersion or in-situ reduction only. This demonstrated that the Ioncell process offers versatile opportunities for waste reduction as it tolerates different raw materials and impurities such as synthetic fibers and colorants.