Porous model nanocellulose films

Research on cellulose and nanocellulose foams is a fast-developing field helping the industry meet pressing needs in materials development. Applications of these foams include, for example, packaging, insulation, water purification, and porous scaffolds. Many foams are produced by first incorporating air bubbles into a slurry to make an aqueous foam, followed by drying. The high surface area, and porous structure stemming from the bubbles can affect the interactions between cellulose and other foam components. For example, different polymers are often used as additives in cellulose foams to improve their stability and mechanical strength, however, model systems to elucidate cellulose-additive interactions in foams do not exist. One method to study cellulose-additive interactions is the quartz crystal microbalance with dissipation (QCM-D). While thin model films can be made from nanocellulose or regenerated cellulose by spin-coating or dip-coating, these homogenous ultra-thin films do not mimic the porous nature of cellulosic foams.
In this study, porous films from TEMPO-oxidized cellulose nanofibrils were prepared to model cellulosic foams for QCM-D measurements. Pore size and total porosity were varied to obtain micro- and nanoscale pores and the surface area was tailored by the assembly conditions. Sacrificial templates were used to create the pores and the thin layers were deposited on top of a regenerated cellulose thin film. As proof of principle, the adsorption of cationic chitosan to these anionic model porous films was investigated by QCM-D. The effect of porosity and surface area on the adsorption of this polymer used as an additive in cellulose-based materials prepared by foam forming was studied suggesting that polymer charge, molecular weight, and solution conditions (salt, pH, presence of surfactants) play an important role. These model porous nanocellulose films will enable new investigations that are not possible with ultra-thin smooth model films to support the development of novel cellulosic materials.