Moisture and oil retention in coated papers for flexible food packaging: A study on barrier properties and surface characteristics

Abstract

Coated paper exhibits promising potential for application in flexible food packaging due to its positive sustainability perception among consumers, recyclability potential, good formability, and printability. One crucial aspect of food packaging is its ability to retain moisture in food items such as fruits/vegetables and prepared meals, as well as to prevent the loss of oil in products with high oil content. Additionally, maintaining a low humidity environment is important for preserving the crispness of dry foods, such as cookies and spices. In its natural state, paper possesses weak barriers against moisture and oil. Therefore, the coating applied to the paper must offer adequate barrier properties against water vapor, water, and oil to meet these requirements and ensure sufficient shelf life for the food items. Within the framework of the CORNET-TETRA project HBC.2021.0288 REPAC², a total of 15 commercially available coated papers were selected based on their production process, composition, and performance characteristics such as heat sealability, as well as permeability to oxygen gas and water vapor. To assess moisture and oil retention, water vapor permeability was measured at 23°C and 85% relative humidity, and Cobb water and oil absorption were evaluated after 1800 seconds. Additionally, water and oil contact angles were measured to assess the polarity of the coated surface. Notably, the water vapor permeability 2 values, which are crucial for preserving dry foods, exhibited high variation among the different coated papers, ranging from 0.2 g/m².d to immeasurably high values. The Cobb water and oil absorption values, important for respectively preserving moist and oily foods, showed a slightly lesser extent of variation, ranging from 0.5 to 95 g/m² for water and 0.8 to 46 g/m² for oil. In conclusion, this study provides valuable insights into the relationship between the barrier properties and physical surface properties of coated papers utilized in flexible food packaging.