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Biomimetic polysaccharide nanocomposites of high cellulose content and high toughness
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-4583-723X
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0001-5818-2378
2007 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 8, no 8, 2556-2563 p.Article in journal (Refereed) Published
Abstract [en]

Plant cell walls combine mechanical stiffness, strength and toughness despite a highly hydrated state. Inspired by this, a nanostructured cellulose network is combined with an almost viscous polysaccharide matrix in the form of a 50/50 amylopectin-glycerol blend. Homogeneous films with a microfibrillated cellulose (MFC) nanofiber content in the range of 10-70 wt % are successfully cast. Characterization is carried out by dynamic mechanical analysis, field-emission scanning electron microscopy, X-ray diffraction, and mercury density measurements. The MFC is well dispersed and predominantly oriented random-in-the-plane. High tensile strength is combined with high modulus and very high work of fracture in the nanocomposite with 70 wt % WC. The reasons for this interesting combination of properties include nanofiber and matrix properties, favorable nanofiber-matrix interaction, good dispersion, and the ability of the MFC network to maintain its integrity to a strain of at least 8%.

Place, publisher, year, edition, pages
2007. Vol. 8, no 8, 2556-2563 p.
Keyword [en]
Biomimetics, Cellulose, Field emission microscopes, Polysaccharides, Scanning electron microscopy, Stiffness, Tensile strength, Toughness, X ray diffraction analysis
National Category
Biomaterials Science
Identifiers
URN: urn:nbn:se:kth:diva-6717DOI: 10.1021/bm0703160ISI: 000248755000029PubMedID: 17655354Scopus ID: 2-s2.0-34548253109OAI: oai:DiVA.org:kth-6717DiVA: diva2:11505
Note
Uppdaterad från manuskript till artikel(20101118) Tidigare titel: Biomimetic polysaccharide nanocomposites of high cellulose content. QC 20101118Available from: 2007-01-10 Created: 2007-01-10 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Bio-inspired polysaccharide nanocomposites and foams
Open this publication in new window or tab >>Bio-inspired polysaccharide nanocomposites and foams
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Today, the majority of materials used for single-use packaging are petroleum-based synthetic polymers. With increased concern about the environmental protection, efforts have been made to develop alternative biodegradable materials from renewable resources. Starch offers an attractive alternative since it is of low cost and abundant. However, the starch material is brittle without plasticizer and the mechanical properties of starch materials are highly sensitive to moisture.

In nature, the plant cell walls combine mechanical stiffness, strength and toughness despite a highly hydrated state. This interesting combination of properties is attributed to a network based on cellulose microfibrils. Inspired by this, microfibrillated cellulose (MFC) reinforced starch-based nanocomposites films and foams were prepared. Films with a viscous matrix and MFC contents from 10 to 70wt% were successfully obtained by solvent casting. The films were characterized by DSC, DMA, FE-SEM, XRD, mercury density measurements, and dynamic water vapor sorption (DVS). At 70wt% MFC content a high tensile strength together with high modulus and high work of fracture was observed. This was due to the nanofiber and matrix properties, favourable nanofiber-matrix interaction, a good dispersion of nanofibers and the MFC network.

Novel nanocomposite foams were obtained by freeze-drying aquagels prepared from 8wt% solutions of amylopectin starch and MFC. The MFC content was varied from 10 to 70wt%. For composite foam with MFC contents up to 40wt%, improved mechanical properties were observed in compression. The mechanical properties depended both on the cell wall properties and the cell-structure of the foam. The effect of moisture (20-80% RH) on the dynamical properties of composite foam with 40wt% MFC was also investigated and compared to those of neat starch foam. Improved storage modulus was noted with MFC content, which was a result of the nanofiber network in the cell-wall. In addition, the moisture content decreased with MFC content, due to the less hydrophilic nature of MFC.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 27 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:44
Keyword
cellulose, starch, microfibrillated cellulose, biomimetic, nanocomposite, nanocomposite foam, mechanical properties
National Category
Biomaterials Science
Identifiers
urn:nbn:se:kth:diva-4260 (URN)
Presentation
2007-01-31, K1, teknikringen 56, KTH, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101118Available from: 2007-01-10 Created: 2007-01-10 Last updated: 2010-11-18Bibliographically approved
2. Bio-inspired cellulose nanocomposites and foams based on starch matrix
Open this publication in new window or tab >>Bio-inspired cellulose nanocomposites and foams based on starch matrix
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In 2007 the production of expanded polystyrene (EPS) in the world was over 4 million tonnes and is expected to grow at 6 percent per year. With the increased concern about environmental protection, alternative biodegradable materials from renewable resources are of interest. The present doctoral thesis work successfully demonstrates that starch-based foams with mechanical properties similar to EPS can be obtained by reinforcing the cell-walls in the foams with cellulose nanofibers (MFC).

High cellulose nanofiber content nanocomposites with a highly plasticized (50/50) glycerol-amylopectin starch matrix are successfully prepared by solvent-casting due to the high compatibility between starch and MFC. At 70 wt% MFC, the nanocomposites show a remarkable combination of high tensile strength, modulus and strain to failure, and consequently very high work to fracture. The interesting combination of properties are due to good dispersion of nanofibers, the MFC network, nanofiber and matrix properties and favorable nanofiber-matrix interaction.

The moisture sorption kinetics (30% RH) in glycerol plasticized and pure amylopectin film reinforced with cellulose nanofibers must be modeled using a moisture concentration-dependent diffusivity in most cases. The presence of cellulose nanofibers has a strong reducing effect on the moisture diffusivity. The decrease in zero-concentration diffusivity with increasing nanofiber content could be due to geometrical impedance, strong starch-MFC molecular interaction and constrained swelling due to the cellulose nanofiber network present.

Novel biomimetic starch-based nanocomposite foams with MFC contents up to 40 wt% are successfully prepared by freeze-drying. The hierarchically structured nanocomposite foams show significant increase in mechanical properties in compression compared to neat starch foam. Still, better control of the cell structure could further improve the mechanical properties. The effect of cell wall composition, freeze-drying temperature and freezing temperature on the resulting cell structure are therefore investigated. The freeze-drying temperature is critical in order to avoid cell structure collapse. By changing the starch content, the cell size, anisotropy ratio and ratio between open and closed cells can be altered. A decrease in freezing temperature decreases the cell size and increases the anisotropy ratio.

Finally, mechanical properties obtained in compression for a 30 wt% MFC foam prepared by freeze-drying demonstrates comparable properties (Young's modulus and yield strength) to expanded polystyrene at 50% RH and similar relative density. This is due to the reinforcing cellulose nanofiber network within the cell walls.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. viii, 50 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:75
Keyword
starch, cellulose nanofibers, foam, nanocomposites, cushioning materials, biodegradable, expanded polystyrene, mechanical properties, diffusion
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-9666 (URN)978-91-7415-189-3 (ISBN)
Public defence
2008-12-16, F3, Lindstedrsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100913Available from: 2008-12-03 Created: 2008-11-26 Last updated: 2011-09-05Bibliographically approved

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