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3D (X-Ray nanotomography) (left) and 2D (SEM) micrographs (right) showing the structures of CNF foams along the freezing direction ez within Zone 2 at various studied relative densities q=q s : 0.003 (a, b), 0:0063 (c, d), 0:01 (e, f), 0:05 (g, h) and0:079 (i, j).
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Ice-templated cellular materials made of entangled networks of slender cellulose nanocrystals (CNCs) or cellulose nanofibrils (CNFs) exhibit excellent specific physical properties but their mechanical properties are still insufficient: these biosourced systems cannot be used as structural materials, e.g., as cores of composite sandwich structures....
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Context 1
... increasing the relative density q=q s . For example, at standard relative densities (q=q s < 0:0063Þ, the foams exhibit columnar structures with slender pores which are orientated along the freezing direction e z with more or less isotropic shapes in the perpendicular ðe x ; e y Þ plane. This is revealed by scrutinizing the micrographs shown in Fig. 6a-d and Fig. 7a, respectively. These observations are also in line with those already reported for these relative densities, type of TEMPOoxidised CNFs, and ice-templating processing conditions ...
Context 2
... strength and viscosity) of the CNF hydrogels were presumably sufficiently low enough to allow the growth of ice-crystals towards the temperature gradient direction e z [15]. However, a radical alteration of the CNF foam microstructures occurred when processing them with highly concentrated native hydrogels, i.e., for foams with q=q s > 0:01 ( Fig. 6e-f). Indeed, as emphasised in Fig. 6g-j, the pore structures switch from columnar ones to much less anisotropic ones, with more spheroidal pores. This is illustrated in Fig. 10a where a substantial decrease of DA is observed in this regime, towards values close to 0.2. In parallel, the anisotropy decrease is accompanied with a noticeable ...
Context 3
... hydrogels were presumably sufficiently low enough to allow the growth of ice-crystals towards the temperature gradient direction e z [15]. However, a radical alteration of the CNF foam microstructures occurred when processing them with highly concentrated native hydrogels, i.e., for foams with q=q s > 0:01 ( Fig. 6e-f). Indeed, as emphasised in Fig. 6g-j, the pore structures switch from columnar ones to much less anisotropic ones, with more spheroidal pores. This is illustrated in Fig. 10a where a substantial decrease of DA is observed in this regime, towards values close to 0.2. In parallel, the anisotropy decrease is accompanied with a noticeable decrease of the mean pore size d À ...
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