INVESTIGATION OF THE PROPERTIES OF COLD STORAGE BROWN CARDBOARD COATED WITH NANOPOLYURETHANE AND NANOCLAY

This study aims to investigate the properties of cold storage Kraft liner brown cardboard coated with nanopolyurethane and nanoclay, comparing the effects of single-layer and double-layer coatings on its performance. The Kraft liner cardboard, produced by Pishgaman Company, was tested after being coated with a solution applied at a rate of 15 g/m². Coated samples were allowed to dry at room temperature for one day before being stored in a refrigerator at -15 °C temperature for periods of 2 and 4 months. A secondary coating was applied using a wire bar coater at a rate of 27 g/m² to enhance surface properties and further reduce water absorption. Results indicated that the coatings effectively penetrated the paper pores, significantly decreasing water absorption, particularly in double-layer coatings. Additionally, the thickness and smoothness of the surface increased, with notable improvements maintained even after freezing. While the tensile index, burst index, and crushing index of the liners showed a reduction, tear resistance increased, especially in the machine direction, with more significant changes observed in double-layer coatings. In conclusion, the use of nanopolyurethane and nanoclay coatings significantly enhanced the properties of Kraft liner cardboard, making it suitable for applications in food packaging, such as liquid packaging cardboard for juices and milk. Further studies are recommended to explore these coatings on various packaging materials over different time periods.