Optimization of Microfibrillated and Nanofibrillated Cellulose Coating to Improve Performance of Paperboard Intended for Food Packaging Applications

Paper and paperboards represent about 31% of the global food packaging market. However, they show some limits and critical issues (migration of Mineral Oil Hydrocarbons-MOH, poor barrier towards gas, water and grease, no sealability). To overcome these limits, they are often coupled with synthetic polymers, but there is growing interest in the use of natural and biobased coatings. Given the interest in using sustainable processes and recyclable, biodegradable and/or compostable materials, this study aims to optimize the application method of a biobased coating made up of water suspension of micro/nano cellulose fibrils together with some natural functional ingredients. A cellulose-rich biomass was subjected to various high-pressure homogenization cycles and properly formulated. The coating suspension was characterized for pH, dynamic viscosity, dry matter content, ratio between micro and nano fibrils; moreover, dynamic light scattering (DLS) measurements, FTIR and TEM observation were also carried out. The optimization of the paperboard coating process was based on a factorial design with three levels and two factors for each of the two coating methods selected (bar coating and spray coating). The coated paperboards were evaluated for coating grammage, grease resistance (Kit test) and heptane vapour transmission rate (HVTR). On the best conditions selected from both experimental designs water absorption (Cobb Test), water and castor oil contact angle, water vapour transmission rate (WVTR) and surface morphology (SEM and AFM observations) were tested. The results showed that low grammage (< 10 g m(-2)) guarantees excellent resistance to grease, achieving the highest Kit test rating, and a significantly reduced HVTR compared to uncoated and commercial samples. Moreover, the comparison between the results obtained showed that spray coating resulted in less use of suspension and faster process, leading to the best results in terms of barrier against contaminants and grease resistance.