How does the color of polyethylene change over time outdoors?

Polyethylene, a widely used plastic, undergoes noticeable color changes when exposed to outdoor conditions over time. The primary factors contributing to this transformation include ultraviolet (UV) radiation, oxidation, and environmental stressors.

UV radiation from sunlight is the most significant cause of polyethylene discoloration. Prolonged exposure breaks down the polymer chains, leading to the formation of chromophores—chemical structures that absorb light and cause yellowing or browning. This process, known as UV degradation, is accelerated in regions with intense sunlight.

Oxidation also plays a critical role. When polyethylene is exposed to oxygen, especially at elevated temperatures, it undergoes oxidative degradation. This results in the formation of carbonyl groups, which contribute to the material's yellowing and brittleness.

Environmental factors such as humidity, pollution, and temperature fluctuations further exacerbate these changes. For instance, high humidity can accelerate hydrolysis, while pollutants can introduce additional chemical reactions that alter the polymer's structure.

To mitigate color changes, manufacturers often add UV stabilizers and antioxidants to polyethylene. These additives slow down degradation but cannot entirely prevent it. Over time, even treated polyethylene will exhibit some degree of discoloration when exposed to outdoor conditions.

Understanding these processes is crucial for industries relying on polyethylene for outdoor applications, such as construction, packaging, and agriculture. By anticipating color changes, manufacturers and users can better manage material performance and longevity.