3D-printing of hierarchical porous monoliths using emulsion gels stabilized by lignin-containing cellulose nanofibrils for thermal insulation

Abstract

3D printing of cellulose-based porous materials with tailored architecture is of significant interest for advanced thermal insulation applications. However, most existing approaches lack internal hierarchical porosity, thereby limiting their insulation efficiency. Here, we propose an emulsion gel ink strategy based on high internal phase Pickering emulsions (HIPPEs) stabilized by lignin-containing cellulose nanofibrils (LCNFs) and reinforced with sodium alginate (SA). This approach integrates emulsion templating with direct ink writing (DIW), enabling simultaneous control of macroscopic geometry and microscopic pore structure. LCNFs with tunable lignin content and surface charge effectively stabilize oil-water interfaces, while SA provides a viscoelastic matrix, ensuring high printability. After freeze-drying, the printed porous monoliths exhibit low density (~17.7 mg·cm^-3), high porosity (> 98 %), and hierarchical pores templated by emulsified droplets and LCNF-SA network. The resulting structures combine excellent mechanical resilience and low thermal conductivity (~0.031 W·m^-1·K^-1). This work provides a scalable route to bio-based 3D-printed porous materials with programmable porosity and multifunctional performance.

Keywords: 3D-printing; Emulsion gel ink; Lignin-containing cellulose nanofibrils; Porous monoliths.