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Nanocomposites made from nanoporous cellulose fibre
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis explores how to use the dry nanoporous structure of cellulosic fibres in new types of composite materials. A large effort was also given on how to correctly characterize the structure of fibres where the wet structure has been preserved also in the dry state.

Delignified wood fibres have an open fibrillar structure in their water-swollen state. In the present work, this open fibrillar structure was preserved in the dry state by performing a liquid exchange procedure and the samples were thereafter carefully dried with Ar(g). The samples of never-dried TEMPO-oxidized dissolving pulp had a specific surface area of 130 m2/g in the dry state, as measured using the Brunauer, Emmet, and Teller (BET) Nitrogen gas adsorption method. This open structure was also revealed using field emission scanning electron microscopy (FE-SEM).

The water-swollen and dry open structures were thoroughly characterized for various pulps. A new method for determining the pore size of water-swollen delignified cellulosic fibres is presented. By combining the results from solid state nuclear magnetic resonance NMR, measuring the specific surface area [m2/g] in the water-swollen state, with fibre saturation point (FSP), measuring the pore volume of fibres in water-swollen state [mass water/mass fibre], the average pore size can be determined without the need of assuming a certain pore geometry.

The dry nanoporous structure was then used as a scaffold for in-situ polymerization, to demonstrate how the properties of the fibrils in the fibre wall can be exploited without the need to disintegrate the fibre wall. Both poly(methylmethacrylate) (PMMA) and poly(butylacrylate) (PBA) were successfully used as the polymeric matrix, and both nanocomposites (i.e., fibre/PMMA and fibre/PBA) had a fibre content of approximately 20 w%. The structure of the composites was characterized using SEM and Atomic Force Microscopy (AFM) operated in the phase imaging mode. The AFM results indicate that the cellulose aggregates and polymeric matrix were successfully mixed on a nanoscale, creating a nanocomposite of interpenetrating polymer molecules and cellulose fibrils, rather than a microcomposite, when using microscopic cellulose fibres. The water absorption capacity of the nanocomposites was reduced significantly, indicating that almost all nanopores in the fibre wall were successfully filled with matrix polymer. The mechanical properties were investigated, showing the importance of nanosized reinforcement compared to fibres of micrometer size.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , 28 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:43
National Category
Paper, Pulp and Fiber Technology Materials Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-103342ISBN: 978-91-7501-479-1 (print)OAI: oai:DiVA.org:kth-103342DiVA: diva2:559814
Presentation
2012-10-26, K1, Teknikringen 56, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20121011

Available from: 2012-10-11 Created: 2012-10-10 Last updated: 2012-10-11Bibliographically approved
List of papers
1. Preparation of dry ultra-porous cellulosic fibres: Characterization and possible initial uses
Open this publication in new window or tab >>Preparation of dry ultra-porous cellulosic fibres: Characterization and possible initial uses
2013 (English)In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 92, no 1, 775-783 p.Article in journal (Refereed) Published
Abstract [en]

Dry ultra-porous cellulose fibres were obtained using a liquid exchange procedure in which water was replaced in the following order: water, methanol, acetone, and finally pentane: thereafter, the fibres were dried with Ar(g). The dry samples (of TEMPO-oxidized dissolving pulp) had a specific surface area of 130 m(2) g(-1) as measured using BET nitrogen gas adsorption. The open structure in the dry state was also revealed using field emission scanning electron microscopy. This dry open structure was used as a scaffold for in situ polymerization. Both poly(methyl methacrylate) and poly(butylacrylate) were successfully used as matrix polymers for the composite material (fibre/polymer), comprising approximately 20 wt% fibres. Atomic force microscopy phase imaging indicated a nanoscale mixing of the matrix polymer and the cellulose fibril aggregates and this was also supported by mechanical testing of the prepared composite where the open fibre structure produced superior composites. The fibre/polymer composite had a significantly reduced water absorption capacity also indicating an efficient filling of the fibre structure with the matrix polymer.

Keyword
Cellulose fibre, Composite, In situ polymerization, Liquid exchange, Open structure, Surface area
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-103402 (URN)10.1016/j.carbpol.2012.09.090 (DOI)000313146900110 ()2-s2.0-84868215766 (Scopus ID)
Note

QC 20130218. Updated from submitted to published.

Available from: 2012-10-11 Created: 2012-10-11 Last updated: 2017-12-07Bibliographically approved
2. A new, robust method for measuring average fibre wall pore sizes in cellulose I rich plant fibre walls
Open this publication in new window or tab >>A new, robust method for measuring average fibre wall pore sizes in cellulose I rich plant fibre walls
2013 (English)In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 20, no 2, 623-631 p.Article in journal (Refereed) Published
Abstract [en]

A new, robust method for measuring the average pore size of water-swollen, cellulose I rich fibres is presented. This method is based on the results of solid-state NMR, which measures the specific surface area (area/solids mass) of water-swollen samples, and of the fibre saturation point (FSP) method, which measures the pore volume (water mass/solids mass) of water-swollen samples. These results are suitable to combine since they are both recorded on water-swollen fibres in excess water, and neither requires the assumption of any particular pore geometry. The new method was used for three model samples and reasonable average pore size measurements were obtained for all of them. The structural characterization of water-swollen samples was compared with the dry structure of fibres as revealed using BET nitrogen gas adsorption after a liquid exchange procedure and careful drying. It was concluded that the structure of the water-swollen fibres sets an upper limit on what is obtainable in the dry state.

Keyword
Cellulose I, CP/MAS 13C-NMR, Fibre saturation point (FSP), Water retention value (WRV), BET, Pore size
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-103403 (URN)10.1007/s10570-012-9850-x (DOI)000315480400005 ()2-s2.0-84874521408 (Scopus ID)
Note

QC 20130402

Available from: 2012-10-11 Created: 2012-10-11 Last updated: 2017-12-07Bibliographically approved

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