Thermal superinsulating properties of biobased materials are investigated via the structuration of aerogels through a biphasic system. Highly stable Pickering emulsions are produced using TEMPO-oxidized cellulose nanofibrils (NFC) adsorbed at an oil/water interface. NFCs form an entangled system of clusters of droplets that lead to excellent mechanical properties. The emulsions produced are strong gels that are further used as template to form aerogels. The freeze-dried emulsions result in porous bioaerogels with extremely low densities (0.012-0.030 g/cm3). We describe a hierarchical morphology with three levels of porosity: an alveolar organization of larger macropores due to ice crystals, spherical smaller macropores induced by the emulsion template, and mesoporous domains localized at the pore walls level. The low-density bioaerogels have compression moduli as high as 1.5 MPa and can be deformed up to 60% strain before the structure collapse. NFC aerogels have thermal superinsulating properties; the lowest thermal conductivity obtained is 0.018 W/(m·K). In the context of the development of sustainable materials, we demonstrate that NFC-stabilized Pickering emulsions are excellent templates to produce fully biobased, mechanically strong thermal superinsulating materials.
Keywords: Pickering emulsion; aerogel; biopolymer; freeze-drying; nanofibrillated cellulose (NFC); nanoparticle; thermal superinsulation.