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Cellulose-water interaction: a spectroscopic study
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The human society of today has a significantly negative impact on the environment and needs to change its way of living towards a more sustainable path if to continue to live on a healthy planet. One path is believed to be an increased usage of naturally degradable and renewable raw materials and, therefore, attention has been focused on the highly abundant biopolymer cellulose. However, a large drawback with cellulose-based materials is the significant change of their mechanical properties when in contact with water. Despite more than a century of research, the extensively investigated interaction between water and cellulose still possesses many unsettled questions, and if the answer to those were known, cellulose-based materials could be more efficiently utilized.

It is well understood that one interaction between cellulose and water is through hydrogen bonds, established between water and the hydroxyl groups of the cellulose. Due to the very similar properties of the hydroxyl groups in water and the hydroxyl groups of the cellulose, the specific interaction-induced effect on the hydroxyl groups at a cellulose surface is difficult to investigate.  Therefore, a method based on 2H MAS NMR spectroscopy has been developed and validated in this work. Due to the verified ability of the methodology to provide site-selective information regarding the molecular dynamics of the cellulose deuteroxyl groups (i.e. deuterium-exchanged hydroxyl groups), it was shown by investigating 1H-2H exchanged cellulose samples that only two of the three accessible hydroxyl groups (on the surface of cellulose fibrils) exchange with water. This finding was also verified by FT-IR spectroscopy, and together with MD simulations we could establish that it is O(2)H and O(6)H hydroxyl groups (of the constituting glucose units) that exchange with water. From the MD simulations additional conclusion could be drawn regarding the molecular interactions required for hydrogen exchange; an exchanging hydroxyl group needs to donate its hydrogen in a hydrogen bond to water.

Exchange kinetics of thin cellulose films were investigated by monitoring two different exchange processes with FT-IR spectroscopy. Specific information about the two exchanging hydroxyl/deuteroxyl groups was then extracted by deconvoluting the changing intensities of the recorded IR spectra. It was recognized that the exchange of the hydroxyl groups were well described by a two-region model, which was assessed to correspond to two fibrillary surfaces differentiated by their respective positions in the fibril aggregate. From the detailed deconvolution it was also possible to estimate the fraction of these two surfaces, which indicated that the average aggregate of cotton cellulose is built up by three to four fibrils.                      

2H MAS NMR spectroscopy was used to examine different states of water in cellulose samples, hydrated at different relative humidities of heavy water. The results showed that there exist two states of water adsorbed onto the cellulose, differentiated by distinct different mobilities. These two states of water are well separated and had negligible exchange on the time scale of the experiments. It was suggested that they are located at the internal and external surfaces of the fibril aggregates.

By letting cellulose nanofibrils undergo an epoxidation reaction with a mono epoxide some indicative results regarding how to protect the cellulose material from the negative impact of water were presented. The protecting effect of the epoxidation were examined by mechanically testing and NMR spectroscopy. It was proposed that by changing the dominant interaction between the fibril aggregates from hydrophilic hydrogen bonds to hydrophobic π-interactions the sensitivity to moisture was much reduced. The results also indicated that the relative reduction in moisture sensitivity was largest for the samples with highest moisture content.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , p. 48
Keyword [en]
cellulose, water, hydrogen exchange, deuterium, NMR spectroscopy, FT-IR spectroscopy
National Category
Physical Chemistry
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-199200ISBN: 978-91-7729-146-6 (print)OAI: oai:DiVA.org:kth-199200DiVA, id: diva2:1060635
Public defence
2017-01-27, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20161229

Available from: 2016-12-29 Created: 2016-12-29 Last updated: 2016-12-29Bibliographically approved
List of papers
1. Site-resolved H-2 relaxation experiments in solid materials by global line-shape analysis of MAS NMR spectra
Open this publication in new window or tab >>Site-resolved H-2 relaxation experiments in solid materials by global line-shape analysis of MAS NMR spectra
2016 (English)In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 268, p. 18-24Article in journal (Refereed) Published
Abstract [en]

We investigate a way one can achieve good spectral resolution in H-2 MAS NMR experiments. The goal is to be able to distinguish between and study sites in various deuterated materials with small chemical shift dispersion. We show that the H-2 MAS NMR spectra recorded during a spin-relaxation experiment are amenable to spectral decomposition because of the different evolution of spectral components during the relaxation delay. We verify that the results are robust by global least-square fitting of the spectral series both under the assumption of specific line shapes and without such assumptions (COmponent-REsolved spectroscopy, CORE). In addition, we investigate the reliability of the developed protocol by analyzing spectra simulated with different combinations of spectral parameters. The performance is demonstrated in a model material of deuterated poly(methacrylic acid) that contains two H-2 spin populations with similar chemical shifts but different quadrupole splittings. In H-2-exchanged cellulose containing two H-2 spin populations with very similar chemical shifts and quadrupole splittings, the method provides new site-selective information about the molecular dynamics.

Keyword
Solid state NMR, Magic angle spinning, Spectral resolution, Chemical shift, Longitudinal relaxation
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-189795 (URN)10.1016/j.jmr.2016.04.014 (DOI)000378185900003 ()27152833 (PubMedID)2-s2.0-84967017601 (Scopus ID)
Note

QC 20160721

Available from: 2016-07-21 Created: 2016-07-15 Last updated: 2017-11-28Bibliographically approved
2. Non-exchanging hydroxyl groups on the surface of cellulose fibrils: The role of interaction with water
Open this publication in new window or tab >>Non-exchanging hydroxyl groups on the surface of cellulose fibrils: The role of interaction with water
Show others...
2016 (English)In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 434, p. 136-142Article in journal (Refereed) Published
Abstract [en]

The interaction of water with cellulose stages many unresolved questions. Here 2H MAS NMR and IR spectra recorded under carefully selected conditions in 1H-2H exchanged, and re-exchanged, cellulose samples are presented. It is shown here, by a quantitative and robust approach, that only two of the three available hydroxyl groups on the surface of cellulose fibrils are exchanging their hydrogen with the surrounding water molecules. This finding is additionally verified and explained by MD simulations which demonstrate that the 1HO(2) and 1HO(6) hydroxyl groups of the constituting glucose units act as hydrogen-bond donors to water, while the 1HO(3) groups behave exclusively as hydrogen-bond acceptors from water and donate hydrogen to their intra-chain neighbors O(5). We conclude that such a behavior makes the latter hydroxyl group unreactive to hydrogen exchange with water.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
2H MAS NMR, Cellulose, Deuterium exchange, FT-IR, Hydroxyl groups, Molecular-dynamics simulation
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-195208 (URN)10.1016/j.carres.2016.09.006 (DOI)000386861400018 ()2-s2.0-84988316977 (Scopus ID)
Funder
Swedish Foundation for Strategic Research , ICA10-0086Swedish Research Council, VR 2012-03244
Note

QC 20161206

Available from: 2016-12-06 Created: 2016-11-02 Last updated: 2017-11-29Bibliographically approved
3. Surface accessibility of cellulose fibrils studied by hydrogen-deuterium exchange with water
Open this publication in new window or tab >>Surface accessibility of cellulose fibrils studied by hydrogen-deuterium exchange with water
2016 (English)In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 24, no 1, p. 21-33Article in journal (Refereed) Published
Abstract [en]

A problem with cellulose-based materials is that they are highly influenced by moisture, leading to reduced strength properties with increasing moisture content. By achieving a more detailed understanding of the water–cellulose interactions, the usage of cellulose-based materials could be better optimized. Two different exchange processes of cellulose hydroxyl/deuteroxyl groups have been monitored by transmission FT-IR spectroscopy. By using line-shape-assisted deconvolution of the changing intensities, we have been able to follow the exchange kinetics in a very detailed and controlled manner. The findings reveal a hydrogen exchange that mainly is located at two different kinds of fibril surfaces, where the differences arise from the water accessibility of that specific surface. The slowly accessible regions are proposed to be located between the fibrils inside of the aggregates, and the readily accessible regions are suggested to be at the surfaces of the fibril aggregates. It was also possible to identify the ratio of slowly and readily accessible surfaces, which indicated that the average aggregate of cotton cellulose is built up by approximately three fibrils with an assumed average size of 12 × 12 cellulose chains. Additionally, the experimental setup enabled visualizing and discussing the implications of some of the deviating spectral features that are pronounced when recording FT-IR spectra of deuterium-exchanging cellulose: the insufficient red shift of the stretching vibrations and the vastly decreasing line widths.

Place, publisher, year, edition, pages
Springer, 2016
Keyword
Cellulose, Deuterium, FT-IR, Hydrogen bond, Exchange, Morphology
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-199199 (URN)10.1007/s10570-016-1122-8 (DOI)000392070700003 ()2-s2.0-84995741409 (Scopus ID)
Note

QC 20161230

Available from: 2016-12-29 Created: 2016-12-29 Last updated: 2017-11-29Bibliographically approved
4. Water in cellulose: evidence and identification of immobile and mobile adsorbed phases by 2H MAS NMR
Open this publication in new window or tab >>Water in cellulose: evidence and identification of immobile and mobile adsorbed phases by 2H MAS NMR
(English)Manuscript (preprint) (Other academic)
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-199195 (URN)
Note

QC 20161230

Available from: 2016-12-29 Created: 2016-12-29 Last updated: 2016-12-30Bibliographically approved
5. Interface tailoring through covalent hydroxyl-epoxy bonds improves hygromechanical stability in nanocellulose materials
Open this publication in new window or tab >>Interface tailoring through covalent hydroxyl-epoxy bonds improves hygromechanical stability in nanocellulose materials
Show others...
2016 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 134, p. 175-183Article in journal (Refereed) Published
Abstract [en]

Wide-spread use of cellulose nanofibril (CNF) biocomposites and nanomaterials is limited by CNF moisture sensitivity due to surface hydration. We report on a versatile and scalable interface tailoring route for CNF to address this, based on technically important epoxide chemistry. Bulk impregnation of epoxide-amine containing liquids is used to show that CNF hydroxyls can react with epoxides at high rates and high degree of conversion to form covalent bonds. Reactions take place inside nanostructured CNF networks under benign conditions, and are verified by solid state NMR. Epoxide modified CNF nanopaper shows significantly improved mechanical properties under moist and wet conditions. High resolution microscopy is used in fractography studies to relate the property differences to structural change. The cellulose-epoxide interface tailoring concept is versatile in that the functionality of molecules with epoxide end-groups can be varied over a wide range. Furthermore, epoxide reactions with nanocellulose can be readily implemented for processing of moisture-stable, tailored interface biocomposites in the form of coatings, adhesives and molded composites.

Keyword
Nano composites, Wood, Nanopaper, Biocomposites, Interphase
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-192103 (URN)10.1016/j.compscitech.2016.08.002 (DOI)000384868500020 ()2-s2.0-84983683523 (Scopus ID)
Note

QC 20160906

Available from: 2016-09-05 Created: 2016-09-05 Last updated: 2017-11-21Bibliographically approved

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