Biodegradable and recyclable bio-based laminated films of poly (lactic acid) and cellulose nanocrystals for food barrier packaging

Exploring food packaging films from environmentally friendly materials and their practical manufacturing routes are important research topics for academia and industry. Poly (lactic acid) (PLA) is a bio-based plastic being used commercially but with low barrier performance for food packaging applications. Cellulose nanocrystals (CNCs), as renewable materials, show potential use in packaging applications, attributed to their excellent oxygen barrier performance. However, pure CNC films cannot be readily produced and used because of their brittleness and water sensitivity. Creating a multilayer structure may be a promising way to address the issues associated with PLA or CNCs if applied as a single-component packaging material. In this work, CNC suspensions mixed with 15 wt% polyvinyl alcohol (PVA) or kappa-carrageenan (CG) were directly coated on a PLA substrate, followed by lamination without any petroleum-based tie layer or adhesive addition. These three-layer laminate films exhibited enhanced barrier properties. The oxygen permeability of the multilayer film was more than 70 times lower than pure PLA film, and the water vapor permeability decreased 7-fold compared with the pure CNC film. Moreover, the PLA film protects the inner CNC film from water and mechanical damage. In addition, the PLA film could be easily separated and recycled from the multilayer film by soaking it in water after the end of use. The fabricated multilayer PLA-CNC films are ideal for eco-friendly, recyclable, high-performance food packaging applications.