Control of structure and properties of cellulose nanofibrils (CNF)-based foam materials by using ethanol additives prior to freeze-drying

Cellulose nanofibrils (CNF)-based foam materials are promising candidates for replacing traditional plastic, petroleum-based foams because they are biodegradable and sustainable. Exploring ways to control the foam microstructure is of great importance for obtaining CNF foam materials with different structures and functional properties. This study used CNF/water suspensions as the substrate and ethanol as an additive to prepare CNF foams. The results showed that the addition of varied ethanol amounts can significantly adjust the microstructure and properties of the corresponding foamed materials. Compared with the control sample (foam without ethanol addition), the foams prepared with ethanol, particularly at its optimum 5% concentration, featured a more uniform pore area and pore distribution, and much smaller pore anisotropy ratio. However, with a further increase in the ethanol content, the contribution of densely layered structure increased; the pore density and pore distribution uniformity decreased; the Young’s modulus and yield strength decreased; and the thermal conductivity increased.