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.

Cellulose from wood fibers can be modified for use in flame-retardant composites as an alternative to halogen-based compounds. For this purpose, sulfite dissolving pulp fibers have been chemically modified by phosphorylation, and the resulting material has been used to prepare cellulose nanofibrils (CNF) that have a width of approximately 3 nm. The phosphorylation was achieved using (NH4)2HPO4 in the presence of urea, and the degree of substitution by phosphorus was determined by X-ray photoelectron spectroscopy, conductometric titration, and nuclear magnetic resonance spectroscopy. The presence of phosphate groups in the structure of CNF has been found to noticeably improve the flame retardancy of this material. The nanopaper sheets prepared from phosphorylated CNF showed self-extinguishing properties after consecutive applications of a methane flame for 3 s and did not ignite under a heat flux of 35 kW/m2, as shown by flammability and cone calorimetry measurements, respectively.

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For the first time, deoxyribonucleic acid (DNA) from herring sperm has been employed as a novel flame retardant system for enhancing the thermal stability and flame retardant properties of cotton fabrics.Indeed, DNA could be considered an intrinsically intumescent flame retardant as it contains the three main components that are usually present in an intumescent formulation, namely: the phosphate groups, able to produce phosphoric acid, the deoxyribose units acting as a carbon source and blowing agents (upon heating a (poly)saccharide dehydrates forming char and releasing water) and the nitrogen-containing bases (guanine, adenine, thymine, and cytosine) that may release ammonia. The flammability tests in horizontal configuration have clearly shown that after two applications of a methane flame for 3 s, the DNA-treated cotton fabrics do not burn at all. Furthermore, when exposed to an irradiative heat flux of 35 kW m À2 , no ignition has been observed. Finally, an LOI value of 28% has been achieved for the treated fabrics as opposed to 18% of the untreated fabric.