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Theses

Preparation of cellulose oligomers by acid hydrolysis

Abstract : The study was motivated by the necessity to produce cellulose oligomers with controlled molecular weight and molecular weight distribution by a simple, scalable and aqueous-solution based method, with the purpose of understanding the mechanisms in the swelling, dissolution, hydrolysis and regeneration processes and establishing characterization methods of molecular weight distribution of cellulose oligomers. The swelling behavior of cellulose in sulfuric acid was followed at -20 ˚C using X-ray diffraction. At low temperature, a cellulose-sulfuric acid crystalline complex was found as the first example of cellulose-acid crystallosolvate. This crystalline complex had an orthorhombic unit cell (a = 18.24 Å, b = 25.98 Å, c = 25.05 Å) that contained 4 cellulose chains, 48 sulfuric acid molecules and 144 water molecules. This complexation was acid-concentration dependent and occurred only above 62 wt%, indicating that the lack of water molecules drove the complexation to form a stable hydration state of sulfuric acid. To characterize the molecular weight of cellulose oligomers, derivatization methods of cellulose and the different characterization methods were compared. Compared to nitration, carbanilation was more suitable for size exclusion chromatography (SEC) since light scattering is more sensitive to cellulose carbanilates than to cellulose nitrates. For determining the degree of substitution (DS) of cellulose carbanilate, a liquid-state 1H nuclear magnetic resonance (NMR) based method using N-H proton intensity has smaller error from side products compared to other methods such as elemental analysis. Four different methods were compared to characterize the degree of polymerization (DP) and DP distribution of cellulose oligomers, namely, liquid-state 1H NMR and solid-state 13C cross polarization magic angle spinning (CP/MAS) NMR spectroscopies, mass spectroscopy (MS) and SEC. SEC was found to be suitable for relatively higher molecular weight oligomer fractions, while the other three spectroscopic methods were suitable for lower molecular weight fractions. The effects of various hydrolysis and regeneration conditions, and acid species on the DP and DP distribution of cellulose were investigated. Different conditions provided oligomers with different average DP values (5
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https://tel.archives-ouvertes.fr/tel-03407425
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Submitted on : Thursday, October 28, 2021 - 2:06:14 PM
Last modification on : Friday, March 25, 2022 - 9:40:52 AM
Long-term archiving on: : Saturday, January 29, 2022 - 7:26:21 PM

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  • HAL Id : tel-03407425, version 1

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Wei Li. Preparation of cellulose oligomers by acid hydrolysis. Other. Université Grenoble Alpes [2020-..], 2021. English. ⟨NNT : 2021GRALV036⟩. ⟨tel-03407425⟩

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