Nanocellulose aerogel-based porous coaxial fibers for thermal insulation

Abstract

Strong, continuous, and highly porous coaxial fibers with cellulose nanofibril (CNF) aerogel core and celluloserich sheath were fabricated by wet-spinning hollow fibers and infusing them with aerogel precursor for highperformance thermal insulators. The sheath contained multiscale pores, including microvoids (14.5 μm) and sub-micron pores (133 nm) in bulk, as well as ca. 25-26 nm surface nanopores, to function as a template and protective sheath for the microporous CNF aerogel core. The porous coaxial fibers had many desirable qualities, including low density (0.2 g cm 3), high porosity (85%), high specific tensile strength (23.5 � 2.5 MPa g cm À 3), wide working temperatures (À 20 to 150 � C), continuous and large-scale producibility, as well as biodegradability. The unique combination of multiscale porous sheath and ultra-low density aerogel core synergistically minimizes heat conductivity by all three mechanisms, i.e., restrain air circulation to limit convective heat transfer, while the poor conducting cellulose permitting little conductive heat transfer and the highly crystalline aerogel cellular walls prohibit infrared radiation, effectively suppresses radiative heat transfer under extreme temperatures.

Continuous, Strong, Porous Silk Firoin-Based Aerogel Fibers toward Textile Thermal Insulation

“…As can be seen in Figure 2a, the average outer diameter of CA/PAA hollow fiber is 964.21 ± 13.61 μm with an average wall thickness of 137.02 ± 9.55 µm. The wall shows high porous structures, which are considered to be caused by the combination of phase separation and mass transfer among CA/PAA (polymer), DMAc (solvent) and water (coagulation bath) during phase inversion [30].…”

“…The formation of graded pores in the hollow fiber wall may be owing to DMAc–water liquid–liquid demixing and mass transfer during the whole phase separation process [30,31]. The nanopores on the inner and outer surfaces are believed to be formed by rapid solidification or instantaneous stratification of the water inside and outside the fibers [32].…”

“…The nanopores on the inner and outer surfaces are believed to be formed by rapid solidification or instantaneous stratification of the water inside and outside the fibers [32]. The dense skins limit the solvent outflow to promote droplet nucleation and sub-micron pore formation in the sheath in which the CA/PAA/DMAc mixture phase separates into a solvent-rich or polymer-poor phase [30]. The micropores in the sheath may be formed by two generally accepted mechanisms: (a) diffusion assisted by the Marangoni effect, i.e., mass transfer along the interface between the two fluids due to surface tension gradients; (b) local surface instability, skin rupture, and solvent intrusion [32,33].…”

Nanocellulose‐Enabled Membranes for Water Purification: Perspectives

“…Recently, a bilayered aerogel scaffold composed of CNFs and CNTs has been demonstrated for sustainable solar steam generation. In this aerogel, CNFs were used as a porous scaffolding material (99.4% porosity) and thermal insulator,188 and the CNT substrate was chosen for efficient solar utilization (97.5%). The demonstrated aerogel exhibited solar energy conversion of ≈76.3% and solar irradiation of 1.11 kg m −2 h −1 at 1 kW m −2 189.…”

Adhesion and Stability of Nanocellulose Coatings on Flat Polymer Films and Textiles

“…These nanoparticles, owing to their dimensions, shape, and high mechanical characteristics, attracted great interest in the engineering of nanostructured materials [ 14 , 17 , 18 , 19 , 20 , 21 ]. Nanocellulose-based materials, including coatings, were explored for many applications, such as packaging films [ 22 , 23 , 24 , 25 , 26 ], engineered composites [ 27 ], adsorbents [ 28 ], materials for health care [ 29 ], cosmetics [ 30 ], thermal insulation [ 31 ], paper [ 32 ], and filtration [ 33 , 34 ].…”