Cellulose (2012) 19:1619-1629 New insights into nano-crystalline cellulose structure and morphology based on solid-state NMR Clark H. Lemke and Ronald Y. Dong and Carl A. Michal and Wadood Y. Hamad Received: 3 May 2012/Accepted: 26 July 2012/Published online: 4 August 2012 Abstract The phase structure of nanocrystalline cellulose (NCC) is studied with solid-state NMR experiments on NCC samples subjected to 2 H/ 1 H exchange in order to label regions accessible to water. These novel results show partial but similar exchange in portions of the 13 C spectrum previously assigned to both highly crystalline and disordered/surface cellulose. Exchange in liquid D 2 O occurs rapidly, faster than the time-scale required to dry the samples, while exposure to D 2 O vapor reveals a single time constant of ∼ 30 hours to build up to the liquid exposed ex- change level. In both cases ca. 37% of the expected exchange- able sites are found to contain 2 H. These results, along with those from relaxation experiments requiring multi-component or stretched-exponential fits, together with X-ray diffraction re- sults suggest the NCC particles contain distributions of environ- ments distinguished by their structures and crystalline perfec- tion. The incomplete exchange of the disordered/surface regions suggests that the NCC crystallites contain abundant disordered domains in their interiors that are protected from exchange. Pre- liminary 31 P/ 13 C REDOR experiments on phosphoric-acid hy- drolyzed NCC samples provide a 13 C spectrum of accessible sur- face sites, but are of relatively low signal-to-noise. These exper- iments suggest a phosphate coverage of 2.6 per 100 anhydroglu- cose monomers, similar to sulfate coverage measured previously for sulfuric acid hydrolyzed samples. The final publication is available at www.springerlink.com. doi 10.1007/s10570-012-9759-4 Clark H. Lemke · Ronald Y. Dong · Carl A. Michal Department of Physics and Astronomy, The University of British Columbia, 6224 Agricultural Road, Vancouver, V6T 1Z1, Canada E-mail: michal@physics.ubc.ca Wadood Y. Hamad FPInnovations, 3800 Wesbrook Mall, Vancouver, V6S 2L9, Canada E-mail: Wadood.hamad@fpinnovations.ca Keywords Chiral nematic, NCC, Phase structure, REDOR, Deuterium exchange Introduction Cellulose-based nanomaterials offer potentially significant ben- efits in a wide variety of applications, not only due to their abil- ity to contribute improved mechanical properties to composites owing to their high strength and large specific surface area, but also due to their unique chiral, optical and magnetic properties (Hamad 2006). Suspended in water and at a critical concentra- tion, nanocrystalline cellulose (NCC) spontaneously forms a bi- phasic suspension where the anisotropic crystallites are respon- sible for forming an iridescent chiral nematic phase whose or- der persists in dried films (Hamad 2006). The tunable nature of the chiral nematic phase has recently been used to produce re- markable inorganic materials with potential as tunable reflective filters and sensors (Shopsowitz et al 2010). Nanocrystalline cellulose (NCC) is extracted as a colloidal suspension by acid hydrolysis of, typically, bleached chemical wood pulps, but other cellulosic materials, such as bacteria, cell- ulose-containing sea animals (e.g. tunicate), or cotton can also be used (Hamad 2006; Hamad and Hu 2010). NCC is com- posed of cellulose chains, a linear polymer of β (1→4) linked D-glucose units, forming crystalline and acicular suprastructure held together by hydrogen bonding. NCC is further character- ized by a degree of polymerization (DP) in the range 90 ≤ DP ≤ 110, and a surface sulfate abundance (introduced by sulfuric acid hydrolysis) of 1.4-6.7 per 100 anhydroglucose units (Hamad and Hu 2010). The crystallites have aspect ratios between 10 and 20. Their physical dimensions depend on the raw material used in the extraction, which ranges between 5-15 nm in cross-section and 100-150 nm in length for bleached kraft pulp.(Revol et al 1994) When dried, NCC forms an agglomeration of parallelepiped spindle-like structures characterized by a high degree of bulk