title: Directional Freezing of Nanocellulose Dispersions Aligns the Rod-Like Particles and Produces Low-Density and Robust Particle Networks.
abstract: We show that unidirectional freezing of nanocellulose dispersions produces cellular foams with high alignment of the rod-like nanoparticles in the freezing direction. Quantification of the alignment in the long direction of the tubular pores with X-ray diffraction shows high orientation of cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) at particle concentrations above 0.2 wt % (CNC) and 0.08 wt % (CNF). Aggregation of CNF by pH decrease or addition of salt significantly reduces the particle orientation; in contrast, exceeding the concentration where particles gel by mobility constraints had a relatively small effect on the orientation. The dense nanocellulose network formed by directional freezing was sufficiently strong to resist melting. The formed hydrogels were birefringent and displayed anisotropic laser diffraction patterns, suggesting preserved nanocellulose alignment and cellular structure. Nondirectional freezing of the hydrogels followed by sublimation generates foams with a pore structure and nanocellulose alignment resembling the structure of the initial directional freezing.
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University , 106 91 Stockholm, Sweden.|Chimie ParisTech 11, rue Pierre et Marie Curie Paris, FR 75005, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Munier
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University , 106 91 Stockholm, Sweden.
authors.forename: Korneliya
authors.initials: K
authors.lastname: Gordeyeva
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University , 106 91 Stockholm, Sweden.
authors.forename: Lennart
authors.initials: L
authors.lastname: Bergström
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University , 106 91 Stockholm, Sweden.
authors.forename: Andreas B
authors.initials: AB
authors.lastname: Fall
mesh_terms: D016880:Anisotropy; D002482:Cellulose / Q000737:chemistry*; D005615:Freezing; D020100:Hydrogels / Q000737:chemistry*; D057139:Nanofibers / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D020100:Hydrogels; D002482:Cellulose