Rapid preparation of electrospun nanofibre sponges through supercritical CO2 drying

Abstract

Nanofibre sponges (NFS) – also known as nanofibre aerogels – are an intriguing class of ultralight, highly porous and flexible materials currently produced by self-assembly of prefabricated nanofibre building blocks. The synthesis of NFS involves a time-consuming freeze-drying step. Here, we report a fast method for the preparation of NFS using rapid critical point drying (CPD). Highly porous NFS were prepared from electrospun polyamid-6 (PA6) nanofibres by conventional freeze-drying and CPD with supercritical CO₂ (scCO₂). Their microscopic architecture and macroscopic properties such as mechanical strength, permeability, and liquid filtration properties towards microplastics were compared and a filtration mechanism was elaborated. Processing time was significantly reduced from a 48-hour drying step to <1 h by using CPD. The final nanofibre sponges were similar in porosity and mechanical strength, but their microscopic architecture and filtration behaviour (99.4% to 99.998%) were distinctive. The CPD process, already industrially used for the preparation of silica aerogels, has the potential for large-scale fabrication of nanofibre-based porous materials. Moreover, CPD is considered as an additional tool for tuning the microscopic architecture of such materials to the desired application.