Barrier Performance of Spray Coated Cellulose Nanofiber–Montmorillonite (MMT) Composites

Abstract

Cellulose nanofibers are one of the most promising nanomaterials for developing high-performance paper-based packaging. This nanomaterial has renewable, recyclable, biodegradable and eco-friendly substrates in nature. While cellulose nanofiber layers have very lowest oxygen permeability when comparing with synthetic plastics, their water vapour permeability is significantly higher than that of conventional packaging plastics, such as Low-Density Poly-ethylene (LDPE). Water vapour permeability has been decreased by forming composites of cellulose nanofibers and inorganic nanoparticles, such as Montmorillonite (MMT) clay. However, the addition of the nanoparticles further reduces the already poor drainage when layers are formed through vacuum filtration. The method for spray-coating a cellulose nanofiber-montmorillonite layer is developed to produce composite. It improves both the ease of preparation and reduces the water vapour permeability. The effect of high-pressure homogenization treatment to the suspension before composite preparation on the barrier performance is also investigated. The permeability could be reduced below that achieved with vacuum filtration by adding up to 20 wt. % Montmorillonite and dispersing Montmorillonite with two passes in a high-pressure homogeniser. With Montmorillonite addition above 20 wt. %, the water vapour permeability started to increase due to aggregation of the Montmorillonite. At the optimal addition level, the best performance achieved with spraying was a water vapour permeability of 8.3 x 10-12 g/m.s.pa. The air permeability of composite is evaluated to be less than 0.003 μm/Pa.s. This value confirms an impermeable composite for packaging applications. Considering the barrier performance, spray coated nanocomposites can perform as an effective barrier material and a potential alternative to synthetic plastics.