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Structural analysis of nanocrystalline cellulose using solid-state NMR Lemke, Clark H.


Abstract Nanocrystalline cellulose (NCC) shows very unique properties – in suspension, it spontaneously forms a chiral nematic phase and, in high purity, exhibits iridescence. While native cellulose has historically been extensively studied in solution and solid-state NMR with success, the physical structure between NCC nanocrystallites is not fully known. Due to the complex structure of the nanocrystallites, conventional diffraction techniques cannot fully determine the structure. In this work ¹H-²H exchange coupled with the following NMR techniques were used to investigate the crystallite structure of NCC: ¹³C CP/MAS, ¹³C T₁, T₂ and T₁p measurements and ¹³C-²H and ¹³C-³¹P REDOR. Abstract Results suggest a broad distribution of regions possessing varied dynamical and structural properties. Based upon previously assigned peaks arising from crystalline and amorphous regions, approximately 40% of the NCC particles are characteristic of amorphous and/or surface regions. Even though NCC preparation is designed to remove amorphous regions, this result is remarkably similar to native, untreated cellulose. Proton-deuterium exchange experiments suggest an unequal proton exchangeability between the different possible exchange sites, and suggest that the samples consist not of sharply defined exchangeable and unexchangeable regions, rather they are more uniformly partially exchanged. We also describe a method to determine the number of surface phosphate groups remaining after hydrolysis treatment. ¹³C-³¹P REDOR experiments conclude that 2.6 ± 0.2 phosphate groups are attached to C₂ or C₃ per 100 monomers.

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