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A cellulose nanocomposite biopolymer foam competing with expanded polystyrene (EPS): hierarchical structure effects on energy absorption
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.ORCID iD: 0000-0001-5818-2378
(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
URN: urn:nbn:se:kth:diva-9655OAI: diva2:126837
QC 20100913Available from: 2008-11-26 Created: 2008-11-24 Last updated: 2010-09-13Bibliographically approved
In thesis
1. 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.
Trita-CHE-Report, ISSN 1654-1081 ; 2008:75
starch, cellulose nanofibers, foam, nanocomposites, cushioning materials, biodegradable, expanded polystyrene, mechanical properties, diffusion
National Category
Polymer Chemistry
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)
QC 20100913Available from: 2008-12-03 Created: 2008-11-26 Last updated: 2011-09-05Bibliographically approved

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Svagan, AnnaBerglund, Lars A.
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