Construction of functional cellulose aerogels via atmospheric drying chemically cross-linked and solvent exchanged cellulose nanofibrils

Nanocellulose aerogels have been used as "green" components in thermal insulation, catalyst supports and environmental remediation due to their outstanding mechanical properties and tunable surface chemistry. However, the drying process, a critical aspect of the aerogel preparation, represents a bottle-neck in terms of processing time and energy consumption. Atmospheric drying would solve both of these issues, however, to achieve this it would be necessary to first examine the forces within the pore walls during the drying process. It was found that strengthening the pore network structure and decreasing the surface tension of the solvent were viable strategies for achieving atmospheric drying of nanocellulose aerogels. In this study, glycidoxypropyltrimethoxysilane (GPTMS) and branched polyethyleneimine (b-PEI) were used to improve the mechanical properties of the pore walls. After freezing and thawing, Soxhlet extraction was used to replace the water in the gel with acetone. This effectively decreased the capillary pressure within the pores due to its lower surface tension, thus cellulose aerogels were obtained after drying. As a result of this new process, atmospheric dried aerogels possess a much higher (4.3 times) specific surface area than freeze-dried cellulose aerogels while maintaining flexibility. More importantly, this atmospheric drying method could be used to construct functional cellulose aerogels, such as flame retardant cellulose aerogels. Furthermore, the present method has enormous potential to facilitate the mass production of functional cellulose aerogels.