What are the differences in gas permeability between polyethylene and polypropylene?

Polyethylene (PE) and polypropylene (PP) are two widely used plastics with distinct gas permeability properties. Polyethylene, particularly low-density polyethylene (LDPE), has higher gas permeability due to its less crystalline and more branched structure, allowing gases like oxygen and carbon dioxide to diffuse more easily. In contrast, polypropylene's higher crystallinity and tighter molecular arrangement result in lower gas permeability, making it a better barrier material.

The differences arise from their polymer structures: PE's flexible chains create more free volume for gas molecules to pass through, while PP's stiffer chains and higher melting point reduce diffusion rates. These properties influence their applications—LDPE is often used for breathable packaging, while PP is preferred for containers requiring strong gas barriers. Understanding these differences helps in selecting the right material for specific industrial or packaging needs.