Transparent montmorillonite/cellulose nanofibril nanocomposite films: the influence of exfoliation degree and interfacial interaction

To obtain high performance of nanocomposite films made of cellulose nanofibrils (CNFs) and montmorillonites (MMTs), highly ordered nanostructures and abundant interfacial interactions are of extreme importance, especially for CNF film with high MMT content. Here, we tend to unveil the influence of exfoliation degree of MMTs and their interfacial interactions with CNFs on the properties of ensuing nanocomposite films. Monolayer MMTs (ML-MMTs) prefer to form highly ordered nanostructure during water evaporation induced self-assembly. The obtained nanocomposite film with 30 wt% ML-MMTs exhibits a tensile strength of 132 MPa, a total light transmittance of 90.2% (550 nm), and water vapor transmission rate (WVTR) of 41.5 g mm/m2 day, better than the film made of original MMTs (O-MMTs) and CNFs (30 MPa strength, 60% transparency, and 78.7 g mm/m2 day WVTR). Moreover, the physical properties (153 MPa strength and 20.9 g mm/m2 day WVTR) of nanocomposite film can be further enhanced by constructing ionic interactions between the ML-MMT and CNF using 0.5 wt% cationic polyethylenimine (PEI). However, as the amount of PEI continues to increase, its performance will be deteriorated dramatically because of the disordered orientation of ML-MMTs. This work could provide an insight into the fabrication of high performance MMT/CNF nanocomposite film for advanced applications.