Delamination and deinking of colored multilayer flexible plastic packaging via selective aminolysis of polyurethane and acrylate based adhesives

Abstract

The demand for efficient recycling processes towards closed-loop recycling of multilayer plastic packaging is increasing. Delamination enables recovery of intact polymer layers without degrading main materials, offering economic and environmental benefits. Yet, scientific studies on the mechanisms of delaminating and deinking multilayer packaging remain limited despite strong industrial interest. This work presents key findings on the delamination and deinking mechanisms of multilayer flexible packaging films using selective aminolysis of the polyurethane and acrylate based adhesives. While aminolysis is widely used in plastic recycling, this study provides first insights into its targeted use for depolymerizing adhesives without affecting the main polymer layers. To investigate the relationship between specific amine properties and their effectiveness in deinking various types of plastic films including chemically stable UV-based inks, a quadratic model was developed. Among different properties, heat capacity, boiling point as proxy for polarity and molecular weight, dipole moment, and polar surface area emerged as key properties influencing deinking efficiency across different plastic films. The mechanism of selective aminolysis of the adhesive was investigated through FTIR and NMR analyses. Kinetic tests, based on a central composite inscribed (CCI) design, were conducted using a selected amine to assess the effect of process conditions for the colored PET/PE multilayer sample. The optimal conditions were identified as 65°C, a particle size of 0.5 cm, and an S/L ratio of 0.01 g/mL. The impact of addition of chemical reagents on deinking and delamination efficiency was also explored, showing positive results depending on film composition.