1D and 2D NMR of nanocellulose in aqueous colloidal suspensions

Abstract

a b s t r a c tThis is the first report on surface structural elucidation of individual nanocellulose as colloidal suspensions by 1D 1 H, 2D heteronuclear single quantum coherence (HSQC) as well as 13 C nuclear magnetic resonance (NMR).1 H NMR of rice straw CNCs (4.7 nm thick, 143 nm long, 0.04 sulfate per AG or 19.0% surface hydroxyl to sulfate conversion) resembled that of homogeneous cellulose solution. Conventional 2D HSQC NMR of CNC, CNF 1.5 (2-14 nm thick, several micrometers long, 0.10 COOH per AG) and CNF10 (2.0 nm thick, up to 1 m long, 0.28 COOH per AG) gave H1:H2 ratios of 1.08:1, 0.97:1 and 0.94:1, respectively, all close to the theoretical 1:1 value for cellulose. The H1:H6 ratios determined from 2D HSQC NMR for CNCs, CNF1.5 and CNF10 were 1:1.47, 1:0.88 and 1:0.14, respectively, and corresponded to 26%, 56% and 93% C6 primary hydroxyl conversion to sulfate and carboxyl groups, consistent with, but more sensitive than those by conductometric titration and X-ray diffraction. Both 1 H and 2D HSQC NMR data confirm that solution-state NMR detects nanocellulose surface carbons and protons primarily, validating this technique for direct surface characterization of nanocellulose in aqueous colloidal suspensions, presenting a sensitive and meaningful NMR tool for direct characterizing individual nanocellulose surfaces in never-dried state.

Cellulose nanocrystal isolation from tomato peels and assembled nanofibers

“…Nanocellulose, the fibrillar crystalline domains in plant cells and most prominently wood, has drawn significant interest due to its extraordinary elastic modulus of 150 GPa (Iwamoto, Kai, Isogai, & Iwata, 2009) and low axial thermal expansion coefficient of 10 −7 K −1 (Nishino, Matsuda, & Hirao, 2004). In addition to these unique physical properties and nanoscale dimensions, abundant surface hydroxyls (Jiang, Dallas, Ahn, & Hsieh, 2014), high specific surface areas and chemical reactivities (Jiang & Hsieh, 2014a,b) make nanocellulose highly desirable natural nanobuilding block for materials. Nanocellulose can also be derived from other sources including agricultural residues, such as rice straw (Abe, & Yano, 2009;Jiang, Han, & Hsieh, 2013;Lu & Hsieh, 2012b), rice husk (Rosa, Rehman, de Miranda, Nachtigall, & Bica, 2012), grape pomace (Lu & Hsieh, 2012a), wheat straw (Helbert, Cavaille, & Dufresne, 1996), potato peels (Chen, Lawton, Thompson, & Liu, 2012), banana plants (Mueller, Weder, & Foster, 2014), coconut husk (Rosa et al, 2010), pineapple leaf (Cherian, http://dx.doi.org/10.1016/j.carbpol.2014.12.064 0144-8617/© 2015 Elsevier Ltd. All rights reserved.…”

Cellulose nanofibrils improve dispersibility and stability of silver nanoparticles and induce production of bacterial extracellular polysaccharides

“…30 The TEMPO mediated oxidation regioselectively converts over 93% surface C6 primary hydroxyls of CNFs to carboxyls and produces negatively charged CNFs.…”

Synthesis of Cellulose Nanofibril Bound Silver Nanoprism for Surface Enhanced Raman Scattering

“…54 The surface carboxylate contents were determined to be 1.68 mmol/g of cellulose or over 93% conversion of surface primary hydroxyls. 55 Assuming a cylindrical cross-section with a 2 nm diameter and 1.6 g/cm 3 bulk density, the surface carboxylate density on CNFs is calculated to be −0.81 e/nm 2 . All CNF carboxylates are preserved in sodium salt form under basic pH 10 after TEMPO oxidation to facilitate binding with Ag + while avoiding an increased acidity of carboxylic for AgNPs synthesis.…”