An attempt has been made to study the internal structure of cellulose I fibril aggregates in cellulose rich pulps and hydrogels (polymeric glucose content &gt; 96 %). In the fibre wall of cellulose rich pulps, ‘accessibility’ can be limited by structural restrictions imposed by the supramolecular structure of cellulose I, e.g. interstitial liquid molecules may only interact directly with fibril surfaces. A supramolecular structure may also impose transport restrictions by narrow passages and tortuosity. As demonstrated by Saito and others (T.Saito et al. Biomacromolecules 7(6) 2006, A. Fall et al. Langmuir 27 2011) it is possible to manufacture TEMPO oxidized cellulose fibrils with yields above 95 %, despite an extensive degree of aggregation of fibrils in fibre wall cellulose. One rationale for explaining this phenomenon could be that cellulose fibril aggregates possess an internal structure, exposing some of the internal fibril surface area, rather than only the fibril aggregate envelope area, towards the reagents used during TEMPO oxidation. Typical wood cellulose fibrils have thicknesses of 3 - 5 nm and aggregate thicknesses are in the range 10-50 nm. Due to the comparative smallness of these systems, studies of the internal structure in aggregates are challenging and prone to indirect measurements. In the used approach a mixture of water and heavy water 2H2O has been used for probing the existence of an internal structure in cellulose fibril aggregates. Results from by CP/MAS 13C-NMR (cellulose structure) were combined with results obtained by 2H Nuclear Magnetic Relaxation Dispersion (NMRD) measurements (water dynamics) performed on water confined in fibre walls and in water rich β-(1,4)-D-glucan gels. By combining information on cellulose supramolecular structure with results describing the dynamic processes governing the magnetic field dependence in the 2H spin-lattice relaxation time (T1) some insights regarding the internal structure of cellulose fibril aggregates were obtained. Preliminary results indicate that 2H-exchange between water and cellulose hydroxyls hydrogens/deuterons can be the dominating 2H spin-lattice relaxation mechanism and that the compactness of cellulose fibril aggregates varies depending on isolation procedure and temperature.

Internal structure of cellulose I fibril aggregates studied by a combination of structure and dynamics measurements

251st National Meeting (2016)

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