The Perfect Package - Nanoparticles to improve bioplastics

Plastic is the most used material for food packaging because of its robust character, its low cost, light weight, higher versatility, flexibility, transparency, heat saleability, and good mechanical and barrier properties. The downside of using plastic is the tremendous generated waste and especially traditional petrol-based plastics are problematic as most of them are non-renewable and non-biodegradable. For that reason, the packaging and agrifood sector are looking for alternatives.

Bio-based and biodegradable materials exist, and among them poly lactic acid (PLA) is the most promising due to its excellent environmental footprint, perfect optical properties, and high tensile strength. Unfortunately, it is also rigid and brittle which limits its applications. To improve the film properties, PLA has been mixed with nanoparticles such as nanoclays or layered silicates. These composites alter the mechanical properties and show a decreased gas water permeability. Chitin is a perfect candidate for plastic reinforcement as it is biodegradable, non-toxic, and an abundant polymer. Since chitin has antimicrobial and antifungal functionality, it could be of special interest for the food industry. Despite chitin’s attractive properties, relatively little is known about the reinforcing effect of chitin nano crystals in PLA films.

A pilot study at Wageningen University, showed that the incorporation of chitin nanoparticles (Fig 1) successfully improved film properties of PLA plastics. The water vapour permeability was lowered by 50 %, thereby enhancing barrier properties. Also increased UV-blockage was found which could potentially protect products vulnerable for photo-oxidation. In addition the film elongation as well as stiffness could be turned by the amount of nanoparticles and the plasticizer concentration (GTA). Although this newly developed film showed promising properties, there are still some challenges. Full dispersion and distribution of the chitin nano crystals into the matrix is rather difficult because of poor compatibility between hydrophobic PLA and hydrophilic chitin. In addition, chitin nano crystals tend to aggregate during drying because of its high surface area and the formation of hydrogen bonds. If these challenges are overcome, the film properties could be improved even further.

In the current study it is aimed to improve the properties of the bioplastic PLA by the incorporation of chitin nano crystals. Particle modification and different production processes could improve the compatibility and/or mixing between the chitin nanoparticles and PLA. An increased compatibility between the nanoparticles and the matrix could have a positive effect on the mechanical, thermal and optical properties of reinforced PLA films.