Enhancing the compatibility of low-value multilayer plastic waste in bitumen mixtures using atmospheric cold plasma and thermal oxidation

Abstract

Multilayer plastic (MP) commonly used in food and beverage packaging is difficult to recycle due to its layered structure, resulting in its accumulation over time; the consequent environmental harm is further exacerbated by its short lifespan. This study investigates recycled low-value MP as a modifier for polymer-modified bitumen (PMB). However, the difference in polarity between MP and PMB mixtures is a challenge, resulting in their poor compatibility and reduced mechanical properties. To overcome this, low-value MP was treated with atmospheric cold plasma and thermal oxidation to enhance its compatibility with PMB. The results indicate that plasma and thermal treatments increase the hydrophilicity of low-value MP through the formation of low-molecular-weight oxidized molecules containing hydrophilic hydroxyl (–OH) and carbonyl (C = O) groups that act as an intermediary boundary layer between the low-value MP and asphaltene-rich bitumen. Further, the optimal oxidation conditions for MP are revealed as 60 s of plasma treatment followed by heating at 150 °C for 60 min. Mixtures of PMB and optimally oxidized MP have optimal compositions of 1 wt.%, with ductility and penetration values of 87.7 cm and 57.4 mm, respectively.