Effect of Lignin Particle Size on the Properties of Cellulose Nanofiber/Lignin Composite Sheets

Cellulose and lignin have been widely studied to develop a bio‐based alternative to replace fossil‐based packaging materials and coatings. Lignin can be used to improve the water vapor barrier properties of cellulose‐based sheets due to its hydrophobicity. In this study, composite sheets based on cellulose nanofiber (CNF) and lignin are formed via spray deposition the effects of lignin particle size and concentration on the properties of the composite sheets are investigated. Scanning electron microscopy and atomic force microscopy with infrared spectroscopy analysis show that lignin nanoparticles (LNPs, particle diameter <100 nm) migrate to the top surface during drying to form a dense layer. The water vapor permeability of the sheet including LNPs is reduced to 4.5 × 10−11 g·s−1·m−1·Pa−1, which is ≈20% lower than the value for CNF alone. This improvement is related to the dense LNP layer on the top surface. Water contact angle measurements indicate that the layer of LNPs also increases the surface hydrophobicity. Overall, this study provides a simple process to produce a fully bio‐based option for packaging material with enhanced water vapor barrier properties and surface hydrophobicity.