What is the primary cause of deterioration in polymers, particularly thermoplastics?

The primary cause of deterioration in polymers, particularly thermoplastics, is due to exposure to oxygen and ultraviolet (UV) light. When thermoplastics are exposed to UV light, it leads to photodegradation, where the chemical structure of the polymer is altered. This process can break down the polymer chains, resulting in a loss of mechanical strength, flexibility, and overall integrity of the material.

Oxygen plays a crucial role in this deterioration as well, as it can react with the polymer chains, further accelerating the degradation process. Together, UV light and oxygen contribute significantly to the aging and deterioration of thermoplastics, especially when these materials are exposed to outdoor environments.

While heat exposure can also cause polymers to degrade by accelerating their thermal degradation and leading to softening or deforming, and moisture can initiate hydrolysis in some polymer types, the combined effect of oxygen and UV light is typically more pronounced in leading to significant degradation over time. High pressure may affect the physical structure during processing but is not a primary factor in the ongoing deterioration of standard thermoplastic materials in normal use.