Thermally insulating and fire-retardant lightweight anisotropic foams based on nanocellulose and graphene oxide

Abstract

High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal conductivity of 15 mW m(-1) K(-1), which is about half that of expanded polystyrene. At 30 °C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials.

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

“…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).…”

“…Recent works have shown that nanocellulose foams can display thermal conductivity below 25 mW/mK (Wicklein et al 2014;Sakai et al 2016), which classifies them as superinsulating materials. Depending on the cellulose source and how the foams/ aerogels have been produced, the thermal conductivity of nanocellulose foams and aerogels varied between 20 and 40 mW/mK (Jelle 2011;Kobayashi et al 2014;Sakai et al 2016;Jimenez-Saelices et al 2017).…”

“…Depending on the cellulose source and how the foams/ aerogels have been produced, the thermal conductivity of nanocellulose foams and aerogels varied between 20 and 40 mW/mK (Jelle 2011;Kobayashi et al 2014;Sakai et al 2016;Jimenez-Saelices et al 2017). To date, however, studies on the thermal conductivity of nanocellulose-based foams and aerogels are sparse and have primarily assessed the thermal conductivity of the porous materials at constant temperature and/or constant relative humidity (Silva et al 2010;Isogai et al 2011;Nguyen et al 2014;Wicklein et al 2014;Jimenez-Saelices et al 2017).…”

Composite Hydrogels with Tunable Anisotropic Morphologies and Mechanical Properties

“…19,20,24,25,[32][33][34][35][36] In this method, precursor solutions or suspensions of monomers or polymers are frozen under a unidirectional temperature gradient, thereby excluding the solute from the ice lattice into the space between the growing ice crystals. [37][38][39] To form a hydrogel, the resulting free-standing microporous scaffold is swollen with water.…”

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

“…Nanoclays (Bailey et al 2015) are commonly used as an additive in CNF-based composite materials to improve, e.g., their mechanical properties (Gabr et al 2013;Wang et al 2014) or fire retardancy (Liu et al 2011;Wicklein et al 2015), and to tailor the selectivity and flux of membranes (Zheng et al 2014). Notably, it has been shown that CNF-bentonite dispersions display properties suitable for use as drilling fluids (Li et al 2015).…”