Effect of Supercritical Carbon Dioxide Treatment on Physical Properties of Polypropylene Films

Abstract

Supercritical carbon dioxide (ScCO₂) is becoming an important “green” solvent, primarily due to its low toxicity, recyclability, and environmental sustainability compared with conventional organic solvents. Recent advancements in large-scale manufacturing technology have made ScCO₂ increasingly feasible and attractive for a wide range of industrial applications, such as foaming and coffee extraction. In this paper, we investigate the physical properties of commercial polypropylene (PP) mono-oriented films after treatment with ScCO₂. We have observed a remarkable increase of over 40% in elongation at break and a 30% increase in tensile strength along the machine direction (MD) concurrently, a rather unusual phenomenon. Additionally, the smoothness of the film surface is significantly enhanced. Various studies have been conducted to uncover the underlying mechanism. The newly formed γ-crystal structure may contribute to the improved mechanical properties along the MD. Other important contributing factors may include increased free volume and chain relaxation resulting from the ScCO₂ treatment. These findings hold considerable promise for various industrial applications, thanks to the low cost, simplicity, scalability, and environmental benefits associated with the ScCO₂ treatment process.