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Chemical modification of cellulose-rich fibres to clarify the influence of the chemical structure on the physical and mechanical properties of cellulose fibres and thereof made sheets
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.ORCID iD: 0000-0002-7410-0333
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
2018 (English)In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 182, p. 1-7Article in journal (Refereed) Published
Abstract [en]

Despite the different chemical approaches used earlier to increase the ductility of fibre-based materials, it has not been possible to link the chemical modification to their mechanical performance. In this study, cellulose fibres have been modified by periodate oxidation, alone or followed either by borohydride reduction, reductive amination or chlorite oxidation. In addition, TEMPO oxidation, and TEMPO oxidation in combination with periodate oxidation and further reduction with sodium borohydride have also been studied. The objective was to gain understanding of the influence of different functional groups on the mechanical and structural properties of handsheets made from the modified fibres. It was found that the modifications studied improved the tensile strength of the fibres to different extents, but that only periodate oxidation followed by borohydride reduction provided more ductile fibre materials. Changes in density, water-holding capacity and mechanical performance were also quantified and all are dependent on the functional group introduced.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 182, p. 1-7
Keywords [en]
Borohydride reduction, Cellulose fibres, Chemical modification, Chlorite oxidation, Periodate oxidation, Structure-property relationship, TEMPO oxidation
National Category
Polymer Technologies
Identifiers
URN: urn:nbn:se:kth:diva-218909DOI: 10.1016/j.carbpol.2017.11.006ISI: 000418661800001Scopus ID: 2-s2.0-85032914983OAI: oai:DiVA.org:kth-218909DiVA, id: diva2:1161795
Funder
VINNOVA
Note

QC 20171201

Available from: 2017-12-01 Created: 2017-12-01 Last updated: 2018-07-11Bibliographically approved
In thesis
1. Chemical Modification of Cellulose Fibres and Fibrils for Design of New Materials
Open this publication in new window or tab >>Chemical Modification of Cellulose Fibres and Fibrils for Design of New Materials
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Due to the growing interest in biobased materials in today’s society, where the need for a cyclic economy is obvious, there has been a huge increase in the  interest for using cellulose due to its excellent mechanical and chemical properties. However, the properties of cellulose have to be modified and improved in order to satisfy advanced material applications where the cellulose properties can be tuned to fit the properties of other components in composite mixtures. This thesis explores the heterogeneous chemical modification of cellulose for improved material properties of cellulose-based materials and the use of cellulose fibres and fibrils in novel applications.

In the first part of the work described in this thesis, a fundamental study was performed to clarify how the chemical composition and the fibre/fibril structure of the cellulose following chemical modification affect the material properties. The second part of the work was aimed at exploring the potential for using the chemically modified fibres/fibrils in novel material applications. 

Lignocellulosic fibres with different chemical compositions were modified by periodate oxidation and borohydride reduction, and it was found that the most important factor was the amount of holocellulose present in the fibres, since lignin-rich fibres were less reactive and less responsive to the treatments. Despite the lower reactivity of lignin-rich fibres, it was however possible to improve their mechanical properties and to achieve a significant increase in the compressive strength of papers prepared from modified unbleached kraft fibres.

The chemical modifications were then expanded to nine different molecular structures and two different degrees of modification. Fibres modified at low degrees of modification were used to prepare handsheets, followed by mechanical and physical characterization. Highly modified fibres were also used to prepare cellulose nanofibrils (CNFs). It was found that the properties of handsheets and films prepared from modified fibres/fibrils are highly dependent on the chemical structure of the modified cellulose and, as an example, the ductility was greatly improved by converting secondary alcohols to primary alcohols. A detailed analysis of the modified fibres and fibrils also showed that, due to the heterogeneous chemical reaction used, the modified fibrils had a core-shell structure with a shell of modified cellulose with a lower crystalline order surrounding a core of crystalline cellulose. The results also showed that the chemical structure of the modified shell dramatically affects the interaction with moisture. Materials from fibrils containing covalent crosslinks have shown to be less sensitive to moisture at the cost of being more brittle. 

In a different application, modified CNFs were used as paper strength additives. Three differently modified CNFs were used: carboxymethylated CNFs, periodate-oxidised carboxymethylated CNFs and dopamine-grafted carboxymethylated CNFs. The properties of these CNFs were compared with that of a microfibrillated cellulose from unbleached kraft fibres. In general, a great improvement in the dry mechanical properties of handsheets was observed with the addition of the periodate-oxidised oxidised and dopamine-grafted modified fibrils, whereas only the periodate-oxidised carboxymethylated CNFs improved the wet strength.

Finally, it was found that the chemically modified fibres could be used to prepare a novel low-density material with good mechanical strength, both wet and dry, and excellent shape recovery capacity in the wet state after mechanical compression. The fibre networks were produced by solvent exchange from water to acetone followed by air drying at room temperature. The properties of the fibre networks could also fairly easily be tuned in terms of porosity, density and strength.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 68
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2018:1
Keywords
borohydride reduction, cellulose-based materials, chemical modification, chlorite oxidation, fibres, fibrils, periodate oxidation, TEMPO oxidation
National Category
Paper, Pulp and Fiber Technology
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-232090 (URN)978-91-7729-670-6 (ISBN)
Public defence
2018-02-23, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180711

Available from: 2018-07-11 Created: 2018-07-11 Last updated: 2018-07-11Bibliographically approved

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Larsson, Per A.

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