Flexible Cellulose Nanofiber (CNF)-Nano- Montmorillonite (MMT) Composite Sheet Structure and Water Vapor Barrier Performance

Abstract

One of the newly developed nanomaterials for functioning as high-performance packaging materials to replace synthetic plastics such as low-density and high-density polyethylene (LDPE, HDPE) is cellulose nanofiber (CNF). These substances are biodegradable, recyclable, and renewable. While cellulose nanofiber-based films have substantially better water vapor permeability than traditional packaging polymers, they have extremely low oxygen permeability. Water vapor permeability (WVP) of the spray-coated composites was decreased via spraying nano-montmorillonite (MMT) content into CNF suspension and also high-pressure homogenization of CNF-MMT suspension. The process for spraying cellulose nanofiber (CNF)-nano-montmorillonite (MMT) suspension on the stainless-steel surface was developed to produce a high-barrier performance composite. The two types of composites were prepared via spraying of raw CNF with MMT and fibrillated CNF with MMT via high-pressure homogenization. The structure and barrier performance of these composites were investigated with SAXS and ASTM E96/E96M-05. Before homogenization, the MMT is agglomerated, while after homogenization it is more exfoliated, which is split up into individual sheets. The water vapor permeability could be reduced by adding up to 20 wt. % montmorillonite and dispersing montmorillonite with two passes in a high-pressure homogenizer. With montmorillonite addition above 20 wt. %, the water vapor permeability started to increase due to aggregation of the montmorillonite in the homogenized composite. At the optimal addition level, the best performance achieved with spraying was a water vapor permeability of 8.3 x 10^-12 g/m.s.pa. The air permeability of the composite was evaluated to be less than 0.003 µm/Pa.s. This value confirms an impermeable composite for packaging applications. Considering the orientation of MMT in the composite, the composite’s structure can decide the barrier performance and can be altered by further fibrillation process of cellulose nanofibers via high-pressure homogenization.