“Robust–Soft” Anisotropic Nanofibrillated Cellulose Aerogels with Superior Mechanical, Flame-Retardant, and Thermal Insulating Properties

Abstract

Advanced thermal insulation materials with low thermal conductivity and robustness derived from regenerative resources are badly needed for building energy conservation. Among them, nanofibrillated cellulose aerogels have huge application potential in the field of thermal insulation materials, but it is still a challenge to prepare cellulose aerogels of excellent comprehensive properties in a simple way. Herein, we demonstrate a unidirectional freeze-drying strategy to develop a novel “robust–soft” anisotropic nanofibrillated cellulose aerogel (NFC-Si-T) by integrating nanofibrillated cellulose (NFC) and Si–O–Si bonding networks under the catalytic dehydration of p-toluenesulfonic acid (TsOH). The anisotropic structure endows the NFC-Si-T with high flexibility that can be easily bent or even tied with a knot, and in addition, it possesses high Young’s modulus (1–3.66 MPa) that can resist the compression weight of 10,000 times of its own weight without deformation. Furthermore, the NFC-Si-T aerogels exhibit anisotropic thermal insulation performances with a low average thermal conductivity (0.028–0.049 W m–1 K–1). More importantly, the limited oxygen index of the NFC-Si-T reaches up to 42.6–51%, showing excellent flame-retardant performance. Therefore, the “robust–soft” anisotropic NFC-Si-T aerogels can be used as an advanced thermal insulation material for building thermal insulation applications.

Ultralight, Superelastic, and Washable Nanofibrous Sponges with Rigid-Flexible Coupling Architecture Enable Reusable Warmth Retention

“…Meanwhile, the stable bonding points derived from the cross-linked polymer networks connected rigid microfibers and flexible nanofiber matrix into a continuous whole for the reasonable distribution and transmissions of stress, thereby endowing the MNFS-50 with high mechanical stability. Figure S8 indicated that the resultant MNFS-50 imposed a lower bound on density compared with the other 3D porous materials. − Meanwhile, it presented only 5.7% residual strain and nondestructive macro/microstructures after 1000 cyclic compressions (Figure S9), far superior to those of previously reported almost 3D nanofibrous materials. − More interestingly, the MNFS-50 was highly resilient even after being compressed with a large deformation in liquid nitrogen (−196 °C) (Figure S10), demonstrating its low-temperature-resistant superelasticity. Additionally, the bending and tensile mechanical properties of the MNFS-50 were also investigated (Figures S11 and S12, see details in Supplementary Discussions).…”

“…The typical qualitative properties of MNFS-50@15WF and the reported nanofibrous sponges were further compared. Figure h showed that the combination of lightness, high warmth retention, superelasticity, hydrophobicity, oleophobicity, antifouling, and washability had not been observed in other nanofibrous sponges. − Additionally, the simple process and convenient tunability of this proposed methodology ensured obtained MNFS with various shapes and adjustable sizes (Figure i). The above-mentioned merits of MNFSs enabled them as attractive warmth retention materials to serve workers in low-temperature environments, such as polar researchers, divers in the deep sea, and outdoor sporters in winter.…”

A Stiff, Tough, and Thermally Insulating Air- and Ice-Templated Plant-Based Foam

“…AIT CNF‑MC‑TA had a specific compression Young’s modulus of 80 ± 20 kNm kg –1 (Figure b) along the direction of ice growth. Thus, despite being composed of plant-based organics, AIT CNF‑MC‑TA was as stiff per unit density as the stiffest CNF-based foams reported, including cross-linked (80 kNm kg –1 ) or composite (77 kNm kg –1 ) ice-templated foams and an isotropic cross-linked composite foam (74 kNm kg –1 ), as well as a holocellulose honeycomb (67 kNm kg –1 ) . AIT CNF‑MC‑TA was stiffer than an isotropic CNF-only foam that was templated around emulsion droplets (up to ∼50 kNm kg –1 ; ∼30 kNm kg –1 for a foam with a similar density to AIT CNF‑MC‑TA ) as well as a physically and chemically cross-linked CNF foam (∼34 kNm kg –1 ) .…”

“…(b) Compressive Young’s modulus as a function of density for AIT CNF-MC-TA , IT CNF , and some reported foams. 4 , 18 , 44 − 47 The data point for IT CNF has been reported. 27 (c–e) Digital photographs of an AIT CNF-MC-TA foam weighing 72.3 mg, without and with weights.…”

“…(a) Representative stress–strain curves for the compression of AIT CNF‑MC‑TA along and perpendicular to the direction of ice templating. (b) Compressive Young’s modulus as a function of density for AIT CNF‑MC‑TA , IT CNF , and some reported foams. ,,− The data point for IT CNF has been reported . (c–e) Digital photographs of an AIT CNF‑MC‑TA foam weighing 72.3 mg, without and with weights.…”