Nanocomposites from Clay, Cellulose Nanofibrils, and Epoxy with Improved Moisture Stability for Coatings and Semistructural Applications

A new type of high reinforcement content clay-cellulose-thermoset nanocomposite is proposed, where epoxy precursors diffuse into a wet porous clay-nanocellulose mat, followed by curing. The processing concept was scaled to >200 mu m thickness composites, the mechanical properties were high for nanocomposites, and the materials showed better tensile properties at 90% RH compared with typical nanocellulose materials. The nanostructure and phase distributions were studied using transmission electron microscopy; Young's modulus, yield strength, ultimate strength, and ductility were determined as well as moisture sorption, fire retardancy, and oxygen barrier properties. Clay and cellulose contents were varied as well as the epoxy content. Epoxy had favorable effects on moisture stability and also improved reinforcement effects at low reinforcement content. A more homogeneous nano- and mesoscale epoxy distribution is still required for further property improvements. The materials constitute a new type of three-phase nanocomposite, of interest as coatings, films, and laminated composites for semistructural applications.