Spray freeze-dried nanofibrillated cellulose aerogels with thermal superinsulating properties

•Nanofibrillated cellulose aerogels were successfully prepared by conventional freeze-drying and spray freeze-drying process.•Drastic changes appear in the morphology and the microstructure depending on the process used.•Spray freeze-drying allows the preparation of nanostructured aerogel with a fibril skeleton morphology, having thermal superinsulating properties. Nanofibrillated cellulose (NFC) aerogels were prepared by spray freeze-drying (SFD). Their structural, mechanical and thermal insulation properties were compared to those of NFC aerogels prepared by conventional freeze-drying (CFD). The purpose of this investigation is to develop superinsulating bioaerogels by reducing their pore size. Severe reduction of the aerogel pore size and skeleton architecture were observed by SEM, aerogels prepared by SFD method show a fibril skeleton morphology, which defines a mesoporous structure. BET analyses confirm the appearance of a new organization structure with pores of nanometric sizes. As a consequence, the thermal insulation properties were significantly improved for SFD materials compared to CFD aerogel, reaching values of thermal conductivity as low as 0.018W/(mK). Moreover, NFC aerogels have a thermal conductivity below that of air in ambient conditions, making them one of the best cellulose based thermal superinsulating material.