Lennart Bergström, Department of Materials and Environmental Chemistry, Stockholm University 

Nanocellulose-based Hybrids and Foams

Nanocellulose is a renewable nanomaterial with outstanding properties that is attracting a rapidly growing scientific and technological interest with applications such as composites, barrier films, scaffold materials, and multifunctional foams and aerogels. Nanocellulose combines a versatile chemical-modification capacity, low thermal expansion, and excellent mechanical properties with a high surface area.

In this presentation, we will show how nanocellulose can be processed, often in combination with inorganic materials, to produce composite films and foams with useful properties. We discuss the liquid crystal ordering phenomena with CNC suspensions and compare with the corresponding self-assembly processes of other liquid crystal-forming rod-like nanoparticles. The competition between liquid crystal and glass formation is highlighted and we also present a method for guiding the helix during film formation that dramatically improves the homogeneity together with recent in-situ small angle X-ray scattering data of the assembly process during drying.

We will demonstrate how the microstructure and magnetic, mechanical, and optical properties of various inorganic-nanocellulose hybrids can be tailored by controlling the foaming and assembly of nanocellulose and how the properties can be tailored by nucleation and growth of inorganic nanoparticles onto the nanocellulose surfaces. Examples include hybrids based on nanocellulose crystals and amorphous calcium carbonate results in transparent and hard hybrid coatings and hybrids of cellulose nanofibrils and titania nanoparticles that result in transparent and flexible free-standing films with a hardness comparable to concrete.

Finally, we will show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods can produce super-insulating, fire-retardant and strong anisotropic foams. The ultralight foams exhibit a thermal conductivity of 15 mW m^-1 K^-1, which is about half the value for expanded polystyrene. The sepiolite and graphene oxide contribute together with the cross-linker boric acid to the excellent strength combustion resistance, being significantly better than traditional polymer-based insulating materials.

Selected publications

1. D. Gebauer, V. Olinyk, M. Salajkova, J. Sort, Q. Zhou, L. Bergström, and G. Salazar-Alvarez, Nanoscale, 3, 3563-3566, 2011
2. C. Schütz et al., PLoS ONE2012, 01/2012 7(10):e45828
3. N. T. Cervin, L. Andersson, J. Ng Boon Sing, P. Olin, L. Bergström and L. Wågberg, Biomacromolecules, 14, 503-511 2013.
4. J. P. F. Lagerwall, C. Schütz, M. Salajkova, J. Noh, J. Hyun Park, G. Scalia, and L. Bergström, NPG Asia materials2014. 

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Host: Associate professor Henrik Birkedal, Dept. of Chemistry & iNANO, Aarhus University