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Interface tailoring through covalent hydroxyl-epoxy bonds improves hygromechanical stability in nanocellulose materials
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.ORCID iD: 0000-0001-7870-6327
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Innventia AB, Sweden.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0002-0231-3970
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.ORCID iD: 0000-0003-3201-5138
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2016 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 134, 175-183 p.Article 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.

Place, publisher, year, edition, pages
2016. Vol. 134, 175-183 p.
Keyword [en]
Nano composites, Wood, Nanopaper, Biocomposites, Interphase
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-192103DOI: 10.1016/j.compscitech.2016.08.002ISI: 000384868500020Scopus ID: 2-s2.0-84983683523OAI: oai:DiVA.org:kth-192103DiVA: diva2:958027
Note

QC 20160906

Available from: 2016-09-05 Created: 2016-09-05 Last updated: 2016-12-29Bibliographically approved
In thesis
1. Cellulose-water interaction: a spectroscopic study
Open this publication in new window or tab >>Cellulose-water interaction: a spectroscopic study
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. 48 p.
Keyword
cellulose, water, hydrogen exchange, deuterium, NMR spectroscopy, FT-IR spectroscopy
National Category
Physical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-199200 (URN)978-91-7729-146-6 (ISBN)
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

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Ansari, FarhanLindh, Erik L.Furo, IstvanJohansson, Mats K.G.Berglund, Lars A.
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