Thesis defense: Jia Hui LIM | GlycoAlps - Université Grenoble Alpes

Soutenance

On November 12, 2024

Saint-Martin-d'Hères - Domaine universitaire

Jia Hui Lim will defend her thesis "Order and disorder in cellulose microfibrils"" on Tuesday, November 12, 2024, 9:30 am, DPM- conference room, Domaine Universitaire of Grenoble

ellulose exists as crystalline microfibrils in various organisms. While the crystal structures of native cellulose are well established, less is known about the structural features of cellulose at the microfibril level, which includes variations in size, shape, and inherent disorder and defects. These characteristics are essential for understanding the properties of cellulosic materials and tissue formation in organisms but remain underexplored due to the limitations of available methods. By addressing three different themes, this thesis explores these characteristics at the nanoscale, focusing on native cellulose microfibril (CMF) structure and the disordering of cellulose crystal structure by swelling.

1. Morphogenesis of cotton CMFs. Cotton CMFs are wider than those of other plants, measuring between 5–7 nm compared to 3 nm for wood. This difference suggests that factors other than biosynthesis influence CMF width. Never-dried cotton CMFs were around 3 nm wide, which increased to 4–5 nm after oven-drying, with increased crystallinity measured by solid-state NMR spectra. By comparison, in wood, it is the removal of hemicelluloses that caused the coalescence of CMFs, even without drying. These results show how drying and matrix components impact the morphology of CMFs, offering strategies to design tunable cellulosic materials.

2. Characterization of kink defects in nanocrystals. Kink defects in cellulose nanocrystals (CNCs) influence their mechanical properties but are poorly understood at the molecular level. This study combined scanning nanobeam electron diffraction (SNBED), atomic force microscopy-infrared spectroscopy (AFM-IR), and molecular dynamics (MD) simulations. Two kink types were identified in tunicate CNCs: simple kinks along the [1 1 0] zone axis with partial crystallinity loss, and zigzag kinks along the [1 0 0] axis, which retain crystalline order. Sulfate signals at kink points revealed by AFM-IR indicated that molecular disorganization was linked to sulfation during sulfuric acid hydrolysis. Kink defects at the crystalline level are thus governed by the anisotropic properties of crystals, chemical modification, and drying effects.

3. Cellulose-solvent interactions and crystalline complexes. Cellulose is insoluble in most common solvents due to the tightly packed crystalline structure, limiting its industrial applications. In this study, the swelling of cellulose was studied in acidic solvents, including phosphoric acid and ZnCl₂ hydrates. In phosphoric acid at −40°C, cellulose formed a crystalline complex with a 7-fold helical conformation, confirmed by solid-state NMR. In ZnCl₂ hydrates (64–76%), cellulose maintained a 2-fold helical conformation, dissolving above 80%. A phase diagram was established to show ZnCl₂ concentration and temperature effects. These findings suggest strategies to improve cellulose dissolution and regeneration.

Date

On November 12, 2024

9:30 am

Localisation

Saint-Martin-d'Hères - Domaine universitaire

DPM
Conference Room
Domaine Universitaire
Grenoble