The addition of antioxidants plays a significant role in improving the degradation and stability of high-density polyethylene HDPE under various environmental conditions. HDPE, like other polymers, is susceptible to degradation due to factors such as heat, light, and oxygen. This degradation can lead to a reduction in the mechanical properties and performance of the material. Antioxidants are added to HDPE to counteract these negative effects and prolong the service life of the material.1. Thermal degradation: HDPE can undergo thermal degradation when exposed to high temperatures, leading to chain scission and a reduction in molecular weight. The addition of antioxidants, such as hindered phenols and phosphites, can help to stabilize the polymer by scavenging free radicals generated during the degradation process. This prevents the propagation of chain reactions and maintains the mechanical properties of the material.2. Photo-oxidation: Exposure to ultraviolet UV radiation can cause photo-oxidation of HDPE, resulting in the formation of carbonyl groups, crosslinking, and chain scission. Antioxidants, such as hindered amine light stabilizers HALS , can be added to the polymer to absorb UV radiation and convert it into less harmful forms of energy, such as heat. This helps to protect the HDPE from photo-oxidative degradation and maintain its mechanical properties.3. Oxidative degradation: The presence of oxygen can lead to the formation of peroxides and hydroperoxides in HDPE, which can initiate chain reactions and cause oxidative degradation. Antioxidants, such as phenolic antioxidants, can be added to the polymer to scavenge these reactive species and prevent the propagation of chain reactions. This helps to maintain the stability and performance of the material under oxidative conditions.4. Environmental stress cracking ESC : HDPE can be susceptible to ESC, which is the premature failure of the material under stress in the presence of certain chemicals. The addition of antioxidants can help to improve the resistance of HDPE to ESC by reducing the rate of chain scission and crosslinking, thereby maintaining the mechanical properties of the material.In summary, the addition of antioxidants to high-density polyethylene HDPE can significantly improve its degradation and stability under various environmental conditions, such as heat, light, and oxygen exposure. This helps to maintain the mechanical properties and performance of the material, prolonging its service life and making it more suitable for a wide range of applications.