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Bio-inspired cellulose nanocomposites and foams based on starch matrix
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.ORCID iD: 0000-0002-4583-723X
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 [en]
starch, cellulose nanofibers, foam, nanocomposites, cushioning materials, biodegradable, expanded polystyrene, mechanical properties, diffusion
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-9666ISBN: 978-91-7415-189-3 (print)OAI: oai:DiVA.org:kth-9666DiVA: diva2:126926
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
List of papers
1. Biomimetic polysaccharide nanocomposites of high cellulose content and high toughness
Open this publication in new window or tab >>Biomimetic polysaccharide nanocomposites of high cellulose content and high toughness
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%.

Keyword
Biomimetics, Cellulose, Field emission microscopes, Polysaccharides, Scanning electron microscopy, Stiffness, Tensile strength, Toughness, X ray diffraction analysis
National Category
Biomaterials Science
Identifiers
urn:nbn:se:kth:diva-6717 (URN)10.1021/bm0703160 (DOI)000248755000029 ()17655354 (PubMedID)2-s2.0-34548253109 (Scopus ID)
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: 2011-09-05Bibliographically approved
2. Reduced water vapour sorption in cellulose nanocomposites with starch matrix
Open this publication in new window or tab >>Reduced water vapour sorption in cellulose nanocomposites with starch matrix
2009 (English)In: Composites Science And Technology, ISSN 0266-3538, Vol. 69, no 3-4, 500-506 p.Article in journal (Refereed) Published
Abstract [en]

The effects of microfibrillated cellulose nanofibers from wood on the moisture sorption kinetics (30% RH) of glycerol plasticized and pure high-amylopectin starch films were studied. The presence of a nanofiber network (70 wt% cellulose nanofibers) reduced the moisture uptake to half the value of the pure plasticized starch film. The swelling yielded a moisture concentration-dependent diffusivity. Quite surprisingly, the moisture diffusivity decreased rapidly with increasing nanofiber content and the diffusivity of the neat cellulose network was, in relative terms, very low. It was possible to describe the strong decrease in zero-concentration diffusivity with increasing cellulose nanofiber/matrix ratio, simply by assuming only geometrical blocking using the model due to Aris. The adjusted model parameters suggested a "simplified" composite structure with dense nanofiber layers oriented in the plane of the film. Still, also constraining effects on swelling from the high modulus/hydrogen bonding cellulose network and reduced amylopectin molecular mobility due to strong starch-cellulose molecular interactions were suggested to contribute to the reductions in moisture diffusivity.

Keyword
Nanocomposites, Modelling, Moisture diffusion
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-9652 (URN)10.1016/j.compscitech.2008.11.016 (DOI)000263996000026 ()2-s2.0-59149098652 (Scopus ID)
Note
QC 20100913. Uppdaterad från accepted till published (20100913).Available from: 2008-11-26 Created: 2008-11-24 Last updated: 2010-09-13Bibliographically approved
3. Biomimetic Foams of High Mechanical Performance Based on Nanostructured Cell Walls Reinforced by Native Cellulose Nanofibrils
Open this publication in new window or tab >>Biomimetic Foams of High Mechanical Performance Based on Nanostructured Cell Walls Reinforced by Native Cellulose Nanofibrils
2008 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 20, no 7, 1263-1269 p.Article in journal (Refereed) Published
Abstract [en]

 A bioinspired foam in which cellulose nanofibrils are used to reinforce cell walls (ca. 3 mu m) is presented. The nanocomposite foams are prepared by a lyophilization technique and show composite structure at the cell-wall scale. The nanocellulosic network shows remarkable mechanical performance, expressed in much-improved modulus and yield strength compared with the neat starch foam.

Place, publisher, year, edition, pages
Weinheim: Wiley-VCH Verlag GmbH, 2008
Keyword
ABS resins, Biodegradable polymers, Biomimetics, Cellulose, Cellulose derivatives, Dewatering, Hydrolysis, Metallic matrix composites, Microbial fuel cells, Nanocomposites, Nanostructured materials, Polymer matrix composites, Polysaccharides, Reinforcement, Water content
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9653 (URN)10.1002/adma.200701215 (DOI)000255348900007 ()2-s2.0-54949096154 (Scopus ID)
Note
QC 20100901Available from: 2008-11-26 Created: 2008-11-24 Last updated: 2010-09-13Bibliographically approved
4. Towards tailored hierarchical structures in starch-based cellulose nanocomposite foams prepared by freeze-drying
Open this publication in new window or tab >>Towards tailored hierarchical structures in starch-based cellulose nanocomposite foams prepared by freeze-drying
Show others...
(English)Manuscript (Other academic)
Abstract [en]

The properties of nanocomposite foams depend both on cell wall composition and cell structure. In order to fully realize the potential of these materials, both cell wall composition and cell structure must be controlled and tailored. The effect of freezing and freeze-drying temperature on cell structure in nanocomposite foams based on starch and microfibrillated cellulose (MFC) is studied. Freezing experiments are combined with DSC and NMR-analysis of bound water content in order to determine a suitable freeze-drying temperature. The freeze-drying temperature is critical in order to avoid cell structure collapse, as found from cell structure studies by FE-SEM microscopy. Based on this, a foam with mixed open and closed cell structures and as much as 70% MFC in the cell wall was successfully prepared. The study clarifies the interdependence of how the starch-MFC-water suspension composition, in combination with freezing and freeze-drying temperature, will control cell structure of the foams.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-9654 (URN)
Note
QC 20100913Available from: 2008-11-26 Created: 2008-11-24 Last updated: 2010-09-13Bibliographically approved
5. A cellulose nanocomposite biopolymer foam competing with expanded polystyrene (EPS): hierarchical structure effects on energy absorption
Open this publication in new window or tab >>A cellulose nanocomposite biopolymer foam competing with expanded polystyrene (EPS): hierarchical structure effects on energy absorption
(English)Manuscript (Other academic)
Abstract [en]

Starch is an interesting biofoam candidate as replacement of expanded polystyrene (EPS) in packaging materials. The main technical problems with starch foam include its hygroscopic nature, sensitivity of its mechanical properties to moisture content and much lower energy  absorption than EPS. In the present study, a starch-based biofoam is able to reach comparable mechanical properties (Young’s modulus, compression yield strength) to expanded polystyrene at 50% relative humidity. The reason is the cellulose nanocomposite concept in the form of a cellulose nanofiber network reinforcing the hygroscopic amylopectin matrix in the cell wall. The biofoams are prepared by freeze-drying and subjected to compressive loading. Cell structure is characterized by FE-SEM of cross-sections. Mechanical properties are related to cell structure and cell wall nanocomposite composition. Hierarchically structured biofoams are demonstrated to be interesting materials with potential for strongly improved mechanical properties. The present study also highlights the challenges involved in preparation and analysis of nanocomposite foams structured at several different scales.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-9655 (URN)
Note
QC 20100913Available from: 2008-11-26 Created: 2008-11-24 Last updated: 2010-09-13Bibliographically approved

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