abstract
This work explores the dynamics of hydrogen bond networks in cellulose through inelastic neutron scattering (INS) and periodic CASTEP calculations. Estimated spectra were based on the crystal structure of cellulose I alpha and I beta and replicate the INS spectrum of cellulose samples with remarkable similarity, allowing a reliable assignment of INS bands to vibrational modes of cellulose. Comparison of cellulose samples from varied sources, from bacterial to kraft pulp, allows the identification of characteristic INS bands, arising from C2-OH torsional motions, which easily identify which allomorph-I alpha or I beta-is prevalent. A high crystallinity index is revealed by the presence of well-defined INS bands associated with highly cooperative CH bending modes along the chain. Hydrating kraft cellulose samples clearly affects those INS bands related with the hydroxymethyl group, identified as the preferred binding site for water molecules. At high humidity content level, a significant proportion of the water molecules is aggregated in clusters within the amorphous cellulose domains. The formation of ice microcrystals leads to a partial disruption of the hydrogen-bond network, as can be concluded from the observed red-shift of the torsional OH vibrational modes. The full assignment and interpretation of cellulose's INS spectra herein provided is a sound basis for future use of INS spectroscopy in the characterization of functionalized cellulose fibers and composite materials.
keywords
DENSITY-FUNCTIONAL THEORY; FT-RAMAN-SPECTROSCOPY; SYNCHROTRON X-RAY; VIBRATIONAL-SPECTRA; INFRARED-SPECTROSCOPY; NATIVE CELLULOSE; TERAHERTZ SPECTROSCOPY; CRYSTAL-STRUCTURE; I CRYSTALLINITY; BOUND WATER
subject category
Biochemistry & Molecular Biology; Chemistry; Polymer Science
authors
Araujo, C; Freire, CSR; Nolasco, MM; Ribeiro-Claro, PJA; Rudic, S; Silvestre, AJD; Vaz, PD
our authors
Armando Jorge Domingues Silvestre
Full professor
Carmen Sofia da Rocha Freire Barros
Coordinating Researcher
Catarina Araújo
PhD Student
Mariela Martins Nolasco
Assistant Researcher
Paulo Ribeiro-Claro
Associate Professor with Aggregation
Pedro Miguel Duarte Vaz
CollaboratorGroups
G4 - Renewable Materials and Circular Economy
G6 - Virtual Materials and Artificial Intelligence
Projects
CICECO - Aveiro Institute of Materials (UID/CTM/50011/2013)
Projeto de Investigação Exploratória: Mariela Nolasco (IF/01468/2015)
Other
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Mediaacknowledgements
This work was developed within the scope of the Project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013), financed by Portuguese funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement. M.M.N. and C.S.R.F. also acknowledge FCT for researcher contracts under the Program IF 2015, IF/01468/2015, and under the Program IF 2012, IF/01407/2012, respectively. The STFC Rutherford Appleton Laboratory is acknowledged for access to neutron beam facilities. CASTEP calculations were made possible due to the computing resources provided by STFC Scientific Computing Department's SCARF cluster.