Cellulose nanofibers/protein nanofibrils nanocomposite aerogels: Preparation and characterization

Bio-nanocomposites are a group of polymer nanocomposites constructed from the combination of biodegradable polymers and inorganic solids, in which at least one of their dimensions is in the nanometer range. Aerogels are materials with 3D porous interconnected structures, consisting of various polymer components. Regarding their spectacular features such as high specific surface, high porosity, and very low density, aerogels have interesting and broad potential applications in various sciences. In this research, biocompatible nanocomposite aerogels are produced from non-toxic, sustainable, and renewable materials, which are mostly by-products of the dairy industry and agricultural wastes. These nanocomposite aerogels contain large amounts of polysaccharides and proteins. These aerogels have properties of non-toxic nature, renewability, and biodegradability and can be broadly applied in various fields.

This study prepared several nanocomposite aerogels composed of various cellulose nanofibrils, chitosan, and protein nanofibrils using the freeze-drying method. The obtained aerogels were evaluated via multiple techniques to verify their components and evaluate their compatibilities. Consequently, an anionic dye was chosen as a model dye to investigate the efficiency of these aerogels in removing azo dye from water.

Ultralight (15 mg cm-3) and highly porous (98.91%) aerogels were produced. Cellulose nanofibers reinforced the structure and chitosan and protein nanofibrils added extra functional groups to the aerogel. The results obtained from the evaluation of Thioflavin-T confirmed the presence of protein nanofibrils (PNF) in composition. Overall, by reducing the cellulose fraction and increasing the protein proportion, the stability of hybrid aerogels of cellulose nanofibers/chitosan decreases up to 90% in a wet state. In contrast, the wet strength of composite aerogel containing cellulose nanofiber/chitosan/protein increased, even though the protein fraction was at its highest value, and these aerogels revealed the highest efficiency in removing anionic dye from water as well.

The results of this research study show that adding natural fillers such as cellulose nanofibers has a striking effect on promoting the mechanical stability of composite aerogels. The highly porous structure of three-component aerogel consists of optimum fractions of cellulose nanofibrils, chitosan, and protein nanofibrils perfectly prepared via establishing ionic and hydrogen bonds after the drying process in freeze-drying. Comparing the results of dimensional stability and water absorption of composite aerogels, it can be claimed that, nanocomposite aerogel containing 50% cellulose with equal proportions of chitosan/protein nanofibrils can be regarded as the optimum sample for further studies. Notably, all three-component aerogels containing PNF exhibited a maximum absorption capacity of 70 mg g-1 and the highest 100% removal efficiency for Congo red anionic dye.