Enhanced analysis of cellulose nanofibril film structure

Structural analysis of cellulose nanofibril (CNF) films remains challenging due to the stochastic assembly of fibres and presence of nanopores. This limits our ability to link the film structures to their properties, restricting their commercial use. While X-ray micro-computed tomography (μCT) is a powerful technique to map the structure of traditional and commercial paper, there has been limited success in its application for CNF films due to the poor contrast between pores and material, making the reconstructed images difficult to segment and analyse. Mercury intrusion porosimetry (MIP) can be used to measure film pore size distributions down to the nanoscale, but provides limited information on the pore morphology. Here, we demonstrate the power of combining both methods. Samples are first subjected to MIP. Then, μCT measurements at 0.7 μm voxel size are performed on the mercury intruded samples. The contrast between mercury-filled pores and fibres is drastically enhanced, allowing for direct binarisation of the 3D volume with conventional segmentation, which is not possible without mercury. Detailed information on the pore morphology and connectivity could be determined with μCT, while MIP provided complementary information about the nanoscale pores.