Non-linear behaviour of nanofibrillar cellulose foams

Nanofibrillar cellulose (NFC) is a cellulose-based material that can be used to create porous foams. The material has several advantages over various synthetic polymers that can be used to create foams as NFC is both abundant and biodegradable. Both the microstructure of the NFC foam and the material properties of the NFC affect the foam’s mechanical properties, with the material properties being difficult to extract experimentally due to difficulties associated with performing micro-scale experiments. This work has been aimed at investigating whether it is possible to indirectly determine the material properties by using X-ray microtomography to reconstruct the microstructure of an NFC foam for use in finite element (FE) simulations. Through the use of different thresholding levels, multiple foam structures with similar geometries but different porosities can be obtained. These were then be used to obtain the macroscopic material properties through FE simulations of the uniaxial compression response of these geometries. The data from these simulations used to fit a power law relation equivalent to the classical scaling laws for foams. The relation was then used to determine the yield stress and Young’s modulus of the NFC material in the cell walls by extrapolating it to the known porosity of a foam used in a previous laboratory experiment and the measured material properties of this foam