Strong, Water-Durable, and Wet-Resilient Cellulose Nanofibril-Stabilized Foams from Oven Drying

Porous materials from cellulose nanofibrils (CNFs) have been prepared using Pickering foams from aqueous dispersions. Stable wet foams were first produced using surface-modified CNFs as stabilizing particles. To better maintain the homogeneous pore structure of the foam after drying, the foams were dried in an oven on a liquid-filled porous ceramic frit. The cell structure was studied by scanning electron microscopy and liquid porosimetry, the mechanical properties were studied by compression testing, and the liquid absorption capacity was determined both with liquid porosimetry and by soaking in water. By controlling the charge density of the CNFs, it was possible to prepare dry foams with different densities, the lowest density being 6 kg m–3, that is, a porosity of 99.6%. For a foam with a density of 200 kg m–3, the compressive Young's modulus was 50 MPa and the energy absorption to 70% strain was 2.3 MJ m–3. The use of chemically modified CNFs made it possible to prepare cross-linked foams with water-durable and wet-resilient properties. These foams absorbed liquid up to 34 times their own weight and were able to release this liquid under compression and to reabsorb the same amount when the pressure was released.