Investigation of Mechanisms of Polyethylene Degradation under the Action of Natural Climatic Factors

The operating conditions of products made of polymeric materials significantly affect their service life. Herein we have investigated the influence of duration of natural climatic factors of the Republic of Sakha (Yakutia) (very cold climate zone) impact on the structure and properties of polyethylene grade 273-83. IR spectroscopic studies have shown that radical oxidative reactions causing a decrease in the polymer molecular weight occur in the material during long-term natural exposure. Investigation of the melt flow index has shown that, besides the reactions accompanied by rupture of the macromolecular chains, crosslinking processes also occur in the polymer. These processes lead to a decrease in the polymer molecular weight and broadening of the molecular weight distribution. It has been shown that the change in the degree of crystallinity and the lamellas thickness is non-monotonic and is determined by the weather conditions during the exposure period. Changes in the intensity of solar radiation, as well as average daily and seasonal temperatures of the ambient air, together with chemical changes occurring in the polymer during natural exposure, lead to the appearance of areas of ordered structures in the amorphous phase, resulting in the decrease in thickness of the amorphous phase which determines the material plasticity. Therefore, the stresses in the macromolecular chains of the polymer in the amorphous phase are so much increased that the polymer exhibits the behavior of a brittle material.