Study of the features of climatic aging of stabilized low-presure polyethylene in severe natural and climatic conditions

Northern regions of Siberia and the Far East are characterized by extreme natural and climatic conditions, including significant seasonal (from –60 to 40°C) and daily (up to 30°C) temperature fluctuations with repeated transitions through 0°C, high humidity and intense solar radiation. The paper presents the results of a study of the climatic resistance of high-density polyethylene (HDPE) in difficult natural and climatic conditions. HDPE grade 273-83 containing the stabilizer grade SO-4 was studied. Full-scale exposure at the test site was carried out for 15 months. When studying the relative elongation at break, it was found that materials containing 1.0 wt.% SO-4 have the highest climatic resistance. In addition, the stabilizer makes it possible to significantly increase the resistance of HDPE to oxidative processes, without participating in the Norrish II reaction, accompanied by the formation of terminal vinyl groups. The analysis of the melt flow index showed that during aging at the initial stages (up to 3 months), predominantly crosslinking reactions of macromolecular chains occur in the materials. With increasing exposure time, reactions accompanied by macromolecular chain scission reactions begin to prevail over crosslinking processes, leading to a decrease in melt viscosity. The use of a stabilizing additive makes it possible to reduce the rate of both competing reactions. It was found that the efficiency of the stabilizer is determined by its optimal concentration, which depends on the solubility of the additive in the polymer matrix. An insufficient amount of the stabilizer leads to its premature consumption during inhibition of radical chain reactions occurring under the influence of UV radiation and oxygen of air. With an excess, part of the additive appears on the surface of the material, causing the formation of internal defects leading to embrittlement of HDPE. The obtained results can be used to assess the reliability and durability of parts and structures made of HDPE and stabilized materials based on it under direct exposure to specified natural and climatic conditions, to assess their service life and prevent equipment failures during operation.

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