Nanostructural Effects on Polymer and Water Dynamics in Cellulose Biocomposites: ²H and ¹³C NMR Relaxometry

Abstract

Improved moisture stability is desired in cellulose biocomposites. In order to clarify nanostructural effects, a new approach is presented where water and polymer matrix mobilities are characterized separately. Nanocomposites from cellulose nanofibers (CNF) in the xyloglucan (XG) biopolymer matrix are investigated at different hydration states. Films of XG, CNF, and CNF/XG composites are subjected to detailed (2)H and (13)C NMR relaxation studies. Since the (2)H NMR signal arises from heavy water and the (13)C signal from the polysaccharides, molecular water and polymer dynamics is for the first time investigated separately. In the neat components, (2)H transverse relaxation (T2) data are consistent with water clustering at the CNF fibril surfaces, but bulk spread of moisture in XG. The new method results in a description of water interaction with the nanoscale phases. At low hydration, water molecules at the CNF/XG interface exhibit higher water mobility than in neat CNF or XG, due to locally high water concentration. At the same time, CNF-associated interphase segments of XG show slower NMR-dynamics than that in neat XG.

Characterization of water in hydrated Bombyx mori silk fibroin fiber and films by 2H NMR relaxation and 13C solid state NMR

“…In this study, we investigated the dynamics of 2 H nuclei. For 2 H nuclei, the relaxation mechanism is dominated by fluctuation of the quadrupolar interaction, which is greater than that of 1 H- 1 H, 2 H- 2 H, and 2 H- 1 H dipolar interactions, and a more sensitive probe of molecular motion [31, 32, 43]. These 2D 2 H relaxation data thus provide more detailed information than previous 1 H DQF NMR measurements regarding the distribution and dynamics of water reservoirs in the water-SF system [17].…”

The states of water in Norway spruce (Picea abies (L.) Karst.) studied by low-field nuclear magnetic resonance (LFNMR) relaxometry: assignment of free-water populations based on quantitative wood anatomy

“…In addition, the relative amplitudes (multiexponential fit) and the relative area under each peak (Contin) were evaluated. The latter was evaluated as dS/d(lnT 2 ) (Terenzi et al 2015).…”

Water in cellulose: evidence and identification of immobile and mobile adsorbed phases by 2H MAS NMR

“…As a consequence, 2 H nuclei are more sensitive probes of the intra-molecular dynamics of WAC than 1 H nuclei, and this has been recently proven to be of practical advantage when studying water mobility in cellulose nanocomposites. 25,26 In general, broad 2 H NMR spectra of ''Pake pattern'' (or, ''powder pattern'') character 20,23,24,27 are expected for immobile molecules, as opposed to the narrow Lorentzian peaks typical of mobile domains, with characteristic motionally averaged spectral shapes for molecules experiencing intermediate dynamical regimes. 26,28,29 The most direct precursors and motivators to our present work are both 2 H and 1 H spectroscopic studies of WAC.…”