## 3 Ice-Templating of Nanocellulose Suspensions
### Effect on the End-Use Properties  
As shown in the previous sections, ice-templated nanocellulose-based materials can exhibit a wide variety of microstructures, depending on the choice of the nanocellulose suspension, their formulation, and the processing conditions. Ice-templated materials can have medium to high porosity \(\varepsilon\) (80% \(\leq\varepsilon\)\(\leq\) 99%), cellular, tubular, or lamellar structures with nano- and/or micro-sized pores (average pore size ranging from 0.1 \(\upmu\)m to 800 \(\upmu\)m). Obtaining materials with tailored microstructures is of great interest for materials engineering owing to the broad diversity of performances that these materials can exhibit. Indeed, the physical and mechanical properties of porous materials can vary widely, depending on the choice of the solid from which they are made, the volume fraction of the solid \(\phi\), and the geometry of the pores/cells [43]. For instance, [PERSON] et al. [40] investigated the effect of the density \(\rho\) (or porosity) on the compression properties of CNF foams. The authors observed that the compression modulus \(E\) and the yield stress \(\sigma_{y}\) of the foams increased from 56 to 5310 kPa and 8 to 516 kPa with increasing the density \(\rho\) from 7 to 103 kg m\({}^{-3}\). [PERSON] et al. [56] also investigated the effect of the density \(\rho\) on the compression behaviour of CNF foams. Both the compression modulus \(E\) and the yield stress \(\sigma_{y}\) were found to be power-law functions of the volume fraction of solid \(\phi\), i.e. ; \(E\propto\phi^{n}\) and \(\sigma_{y}\propto\phi^{m}\). However, the authors observed that the values of \(n\) and \(m\) were affected by the foam architecture, namely the regularity and geometry of the cells. The scaling exponents (\(n=2.29\) and \(m=2.22\)) of TEMPO-oxidised CNF foams were close to those expected for classical cellular materials with well-defined microstructures and deformation mechanisms such as open (\(n=2\) and \(m=1.5\)) or closed foams without thickening of edges (\(n=3\) and \(m=2\)) [43; 56]. In contrast, the scaling exponents (\(n=3.11\) and \(m=3.04\)) of enzymatic CNF foams were close to those usually obtained for aerogels [44; 153], i.e., \(3<n<4\) and \(2.5<m<3.5\). This behavior could be related to the disordered  
Figure 16: AFM images of CNFs (**a**) and CNCs (**b**). The nanocellulose particles are electrostatically adsorbed onto cationised mica substrates. The magnification is the same in both images and the scale bar is 500 nm. SEM micrographs of CNF (**c,d**) CNC foams obtained by ice-templating from a 0.5 wt% CNF suspension and a 1.5 wt% CNC suspension, respectively. (Adapted with permission from [PERSON] et al. [120]. Copyright 2016 American Chemical Society). cellular structure of these foams and more precisely to the existence of numerous dangling masses or branches that hung off the cell walls [153; 154]. Ice-templated materials are also widely studied owing to their high thermal insulation properties. As for the mechanics, thermal properties vary with the density and the microstructural features of porous materials [43]. [PERSON] et al. [119] observed that the apparent thermal conductivity \(\lambda\) of CNF foams with quasi-isotropic cellular microstructures increased from 38 to 43 mW m\({}^{-1}\)K\({}^{-1}\) with increasing the density \(\rho\) from 12 to 43 kg m\({}^{-3}\). [PERSON] et al. [41] produced CNF foams of density \(\rho\) = 5.6 kg m\({}^{-3}\) with anisotropic tubular porous microstructures. The authors reported that the thermal conductivity \(\lambda\) measured in the axial direction (along the pore) was close to 170 mW m\({}^{-1}\)K\({}^{-1}\), whereas those measured in the radial direction was significantly lower, i.e., close to 15 mW m\({}^{-1}\) K\({}^{-1}\). These examples emphasise the undeniable role of the porous architecture on the resulting performances of nanocellulose-based materials.