Abstract
The intrinsically low carbon yield upon cellulose pyrolysis is one major challenge in producing carbon fibers from cellulosic precursors. In this dissertation, chitosan and keratin, natural amino group−containing biopolymers, are utilized as natural charring agents to increase the yield of cellulose−based carbon fibers. Cellulose pulp was co−dissolved with chitosan or keratin in the ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate, and then dry−jet wet spun via the so-called Ioncell® process. Thermogravimetric analysis showed that chitosan and keratin incorporation increased the char yield by >100 wt% and ~53 wt%, at ~21 wt% and ~30 wt% incorporation level, respectively. The role of chitosan and keratin as dehydration catalysts during cellulose pyrolysis up to 900 °C was confirmed through analysis of the volatile products. There was an enhanced production of water, CO2, and a reduced formation of levoglucosan. The change in the cellulose pyrolysis products was further seen in the increased production of several furanic compounds and acetic acid due to chitosan or keratin incorporation in the composite fibers. Mere physical contact between cellulose pulp and biopolymer powder did not alter the cellulose pyrolysis products, suggesting that close packing of the biopolymers in the composite fibers is needed for a synergistic interaction between cellulose and the additives during pyrolysis. Structural analyses revealed that chitosan was distributed homogeneously in the composite matrix. By contrast, keratin aggregates and open voids were found in the keratin composite fibers, leading to a suboptimum interaction between keratin and cellulose and, hence, a lower dehydration activity of keratin than chitosan. The same defects also led to a decrease in the mechanical properties of keratin-cellulose fibers. Chitosan and keratin introduced nitrogen to the composite- and resulting carbon fibers, respectively. The nitrogen might induce in-plane disorders in the aromatic carbon cluster, particularly at pyrolysis temperatures from 500 to 700 °C, but also promote the formation of crosslink structures due to the enhancement of the dehydration reaction. The cross-links increased the mechanical properties of carbon fibers derived from chitosan composite fibers, which can still be improved by further heat treatment such as higher carbonization temperatures. Open pores in the keratin composite fibers were also present in the resulting carbon fibers, resulting in fiber brittleness. However, nitrogen and open pores in carbon materials can be beneficial for electrochemical applications, with the possibility to tune them through tailored heat treatment protocols.
Translated title of the contribution | Strategies to enhance the carbon yield from cellulose-based precursor fiber through blending with other bio-based polymers as charring agents |
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Original language | English |
Qualification | Doctor's degree |
Awarding Institution |
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Supervisors/Advisors |
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Publisher | |
Print ISBNs | 978-952-64-2094-3 |
Electronic ISBNs | 978-952-64-2095-0 |
Publication status | Published - 2024 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- carbon
- cellulose-based
- biobased polymers
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Bioeconomy Research Infrastructure
Seppälä, J. (Manager)
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OtaNano – Low Temperature Laboratory
Savin, A. (Manager) & Rissanen, A. (Other)
OtaNanoFacility/equipment: Facility