Browsing by Subject "MICROFIBRILS"

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  • King, Alistair William Thomas; Mäkelä, Arto Valtteri; Kedzior, Stephanie; Laaksonen, Tiina Marjukka; Partl, Gabriel Julian; Heikkinen, Sami Mikael; Koskela, Harri Tapani; Heikkinen, Harri August; Holding, Ashley; Cranston, Emily; Kilpeläinen, Ilkka Antero (2018)
    Recent developments in ionic liquid electrolytes for cellulose or biomass dissolution has also allowed for high-resolution 1H and 13C NMR on very high molecular weight cellulose. This permits the development of advanced liquid-state quantitative NMR methods for characterization of unsubstituted and low degree of substitution celluloses, for example, surface-modified nanocelluloses, which are insoluble in all molecular solvents. As such, we present the use of the tetrabutylphosphonium acetate ([P4444][OAc]):DMSO-d6 electrolyte in the 1D and 2D NMR characterization of poly(methyl methacrylate) (PMMA)-grafted cellulose nanocrystals (CNCs). PMMA-g-CNCs was chosen as a difficult model to study, to illustrate the potential of the technique. The chemical shift range of [P4444][OAc] is completely upfield of the cellulose backbone signals, avoiding signal overlap. In addition, application of diffusion-editing for 1H and HSQC was shown to be effective in the discrimination between PMMA polymer graft resonances and those from low molecular weight components arising from the solvent system. The bulk ratio of methyl methacrylate monomer to anhydroglucose unit was determined using a combination of HSQC and quantitative 13C NMR. After detachment and recovery of the PMMA grafts, through methanolysis, DOSY NMR was used to determine the average self-diffusion coefficient and, hence, molecular weight of the grafts compared to self-diffusion coefficients for PMMA GPC standards. This finally led to a calculation of both graft length and graft density using liquid-state NMR techniques. In addition, it was possible to discriminate between triads and tetrads, associated with PMMA tacticity, of the PMMA still attached to the CNCs (before methanolysis). CNC reducing end and sulfate half ester resonances, from sulfuric acid hydrolysis, were also assignable. Furthermore, other biopolymers, such as hemicelluloses and proteins (silk and wool), were found to be soluble in the electrolyte media, allowing for wider application of this method beyond just cellulose analytics.
  • Beaumont, Marco; Otoni, Caio G.; Mattos, Bruno D.; Koso, Tetyana V.; Abidnejad, Roozbeh; Zhao, Bin; Kondor, Anett; King, Alistair W. T.; Rojas, Orlando J. (2021)
    A new regioselective route is introduced for surface modification of biological colloids in the presence of water. Taking the case of cellulose nanofibers (CNFs), we demonstrate a site-specific (93% selective) reaction between the primary surface hydroxyl groups (C6-OH) of cellulose and acyl imidazoles. CNFs bearing C6-acetyl and C6-isobutyryl groups, with a degree of substitution of up to 1 mmol g(-1) are obtained upon surface esterification, affording CNFs of adjustable surface energy. The morphological and structural features of the nanofibers remain largely unaffected, but the regioselective surface reactions enable tailoring of their interfacial interactions, as demonstrated in oil/water Pickering emulsions. Our method precludes the need for drying or exchange with organic solvents for surface esterification, otherwise needed in the synthesis of esterified colloids and polysaccharides. Moreover, the method is well suited for application at high-solid content, opening the possibility for implementation in reactive extrusion and compounding. The proposed acylation is introduced as a sustainable approach that benefits from the presence of water and affords a high chemical substitution selectivity.
  • Lyczakowski, Jan J.; Bourdon, Matthieu; Terrett, Oliver M.; Helariutta, Ykä; Wightman, Raymond; Dupree, Paul (2019)
    The woody secondary cell walls of plants are the largest repository of renewable carbon biopolymers on the planet. These walls are made principally from cellulose and hemicelluloses and are impregnated with lignin. Despite their importance as the main load bearing structure for plant growth, as well as their industrial importance as both a material and energy source, the precise arrangement of these constituents within the cell wall is not yet fully understood. We have adapted low temperature scanning electron microscopy (cryo-SEM) for imaging the nanoscale architecture of angiosperm and gymnosperm cell walls in their native hydrated state. Our work confirms that cell wall macrofibrils, cylindrical structures with a diameter exceeding 10 nm, are a common feature of the native hardwood and softwood samples. We have observed these same structures in Arabidopsis thaliana secondary cell walls, enabling macrofibrils to be compared between mutant lines that are perturbed in cellulose, hemicellulose, and lignin formation. Our analysis indicates that the macrofibrils in Arabidopsis cell walls are dependent upon the proper biosynthesis, or composed, of cellulose, xylan, and lignin. This study establishes that cryo-SEM is a useful additional approach for investigating the native nanoscale architecture and composition of hardwood and softwood secondary cell walls and demonstrates the applicability of Arabidopsis genetic resources to relate fibril structure with wall composition and biosynthesis.