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.

Thermal conductivity of hygroscopic foams based on cellulose nanofibrils and a nonionic polyoxamer

“…Low density, isotropic CNF-and nonionic polyoxamer-based foams were prepared by a previously reported method that involved foaming an aqueous CNF-based dispersion containing a non-ionic polyoxamer copolymer, Pluronic P123, and crosslinking the CNF by calcium ions that were released by a triggered pH decrease using gluconic acid d-lactone (GDL) (Gordeyeva et al 2016). The wet foams were ovendried at 60°C to obtain dry foams with a final composition of 46.3 wt% CNF, 32.4 wt% P123, 4.6 wt% CaCO 3 and 16.7 wt% GDL (Fig.…”

“…The TEMPO-mediated oxidation was performed for 3 h, at pH 10. The CNF were then obtained by disintegrating the oxidized pulp by repeatedly passing the dispersion four times through the 400 and 200 lm chambers of a high pressure (1600 bars) Microfluidizer (M-110EH, Microfluidics) (Gordeyeva et al 2016).…”

“…The obtained mixture was foamed using a dispersing tool, Ultra-Turrax (T18 IKA Werke, Germany) for 3 min at 7000 rpm with the dropwise addition of GDL performed at the last minute of the foaming (Gordeyeva et al 2016).…”

“…Nanocellulose features an attractive combination of properties like a high elastic modulus, low thermal expansion coefficient, and tunable surface chemistry (Klemm et al 2011;Moon et al 2011;Duong and Nguyen 2016). From nanocellulose gel-like suspension, ultralight weight (density B 10 kg/m 3 ) and highly porous (porosity C 99%) foams can be produced via different techniques such as ice templating (Wicklein et al 2014;Munier et al 2016), supercritical drying (Medina-Gonzalez et al 2012;Lavoine and Bergström 2017) or blending (Gordeyeva et al 2016). The controlled surface chemistry, interparticle bonding and assembly of nanocellulose can result in nanocellulose foams with a high compressive strength and low thermal conductivity (Lavoine and Bergström 2017).…”

Steady-shear and viscoelastic properties of cellulose nanofibril–nanoclay dispersions

“…CNFs and other forms of nanocellulose are of interest for use in a wide range of applications, e.g., as additives in food, cosmetics, and paints, and as rheology modifiers (Klemm et al 2011). CNFs can also be used to produce strong and transparent nanopapers (Henriksson et al 2008), flexible filaments (Hakansson et al 2014;Iwamoto et al 2011), lightweight foams Wicklein et al 2016), and hydrogels (Klemm et al 2011;Munier et al 2016).…”