Air-dried cellulosic fibril foams prepared from one-pot Pickering emulsion

• Bio-based foams were prepared from Pickering emulsions dried at room temperature. • Cellulose fibrils, lignin nanoparticles and polyvinyl alcohol constituted the foams. • Oils with low boiling point allowed for energy-efficient drying at room temperature. • Foams with low thermal conductivity and strong mechanical properties were achieved. • These bio-based foams with tunable properties are alternative to fossil-based foams. Cellulosic foams are considered ideal green alternatives for insulation or as absorbents but often lack mechanical strength. Their preparation involves freeze drying, chemical crosslinking, or other steps decreasing the sustainability and scalability of the process. This study proposes a novel one-pot preparation to fabricate binder-free, mechanically robust, and high-performance cellulosic-based foam at room temperature. Pickering emulsion templating was used for the wet foam preparation by simultaneous mixing of lignin nanoparticles, polyvinyl alcohol, high-consistency microfibrillated cellulose (MFC), and oil phase. Drying these foams at room temperature resulted in strong and insulating dry foams without added surfactants or chemical cross-linking. The foam structure and its properties were tuned by adjusting MFC content (0–30 % wt of total dry weight) and heptane:pentane ratio (1:1, 2:1, 3:1). Foams with low density (0.10–0.16 g cm −3 ), high porosity (>87 %), low thermal conductivity (36–62 mW m -1 K −1 ), robust mechanical properties (0.17–0.63 MPa compressive stress at 50 % strain), and promising sound absorption performance (average sound absorption coefficient of 0.3 at 1/3 octave frequency bands) were obtained. This research introduces an approach to create scalable and eco-friendly bio-based foams that could substitute currently used fossil foams, such as polyurethane foam, in thermal insulation application.