Temperature plays a significant role in the degradation of polyethylene PE and polypropylene PP , which are both common thermoplastic polymers. As the temperature increases, the rate of degradation also increases, leading to changes in the physical and chemical properties of these polymers. The primary mechanisms of degradation for PE and PP are thermal degradation, oxidation, and photo-degradation.1. Thermal degradation: When PE and PP are exposed to high temperatures, the polymer chains break down due to the scission of the carbon-carbon backbone. This process leads to a decrease in molecular weight, resulting in a loss of mechanical properties, such as tensile strength and elongation at break. Thermal degradation can be mitigated by using stabilizers, such as antioxidants, which can prevent chain scission and maintain the polymer's properties.2. Oxidation: The presence of oxygen can lead to the formation of free radicals in PE and PP, which can cause chain scission and cross-linking, resulting in a change in the polymer's properties. Oxidative degradation can be accelerated by high temperatures, as well as exposure to UV light. To mitigate oxidation, antioxidants can be added to the polymer, which can neutralize the free radicals and prevent further degradation.3. Photo-degradation: Exposure to UV light can cause the formation of free radicals in PE and PP, leading to chain scission, cross-linking, and oxidation. This process can result in discoloration, embrittlement, and a loss of mechanical properties. To minimize photo-degradation, UV stabilizers, such as hindered amine light stabilizers HALS and UV absorbers, can be added to the polymer to absorb or neutralize the harmful effects of UV radiation.To extend the stability of PE and PP, a combination of stabilizers can be used, such as antioxidants, UV stabilizers, and processing stabilizers. These additives can help maintain the physical and chemical properties of the polymers, prolonging their useful life and reducing the impact of temperature on their degradation. Additionally, proper storage and handling of these polymers, such as avoiding prolonged exposure to high temperatures and UV light, can also help extend their stability.