PSI - Issue 30

E.S. Petukhova et al. / Procedia Structural Integrity 30 (2020) 105–112 Petukhova E.S. and Fedorov A.L. / Structural Integrity Procedia 00 (2020) 000–000

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1. Introduction During climatic aging, there are various oxidative radical chain chemical reactions in polymers under the influence of heat, light, and oxygen in the air. These reactions described in many of investigations conducted by Tochá č ek and Vrátní č ková (2014), Yousif and Haddad (2013), Abdelhafidi et al. (2015), Andrady et al. (1998). There are special additives called stabilizers, which prevent these reactions in industrial polymeric materials. The mechanisms of action of some stabilizers are given by Kucuk et al. (2018), Gray (1998), Huang et al. (2016), Liu et al. (2018). As is known by Gijsman (2012), Reingruber and Buchberger (2010), De la Rie (1988) the effectiveness of stabilizing additives is determined by their chemical structure, which controls the rate and duration of effect of the additive as an inhibitor of radical chain reactions. In previous work, Petukhova and Fedorov (2019) presented the study of the climatic resistance of polyethylene (PE) of grade 273-83 containing various stabilizing additives. The study showed that stabilizing additives can increase the lifetime of PE products by 25% or more. The effectiveness of various brands of stabilizing additives was determined by studying the mechanical properties of PE composites, changes in color, and supramolecular structure after different exposure periods at the open-air testing area in the climatic conditions of the Republic of Sakha (Yakutia). At the same time, the question remains open about the mechanisms of reactions in the polymer, which cause product failure. Infrared spectroscopy is an effective method for evaluating changes in the material. This method makes it possible to detect new oxidized functional groups and unsaturated bonds. This article presents the results of the IR spectroscopy study of stabilized PE composites after intense UV radiation. 2. Materials and methods The objects of accelerated climate tests were the PE mixture of grade 273-83 (PJSC Kazanorgsintez) with a PE electrically conductive compound of grade PRE-ELEC PE1296 (Premix, Finland) in a ratio of 50/50 wt.%. This polyethylene composite material is used to produce containers for transporting fuels to remote areas of the Republic of Sakha (Yakutia) that are not covered by a network of gas stations. OJSC Sakhaneftegazsbyt produces containers using these composites, transport, and distribute fuels in them. Stabilizers СО 3, СО 4, and Stafen brands (N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry SB RAS (NIOCH SB RAS)) were used as inhibitors of radical chain reactions. The paper by Petukhova and Fedorov (2019) contains the chemical and structural formulas of these stabilizers. Krysin et al. (2015) showed that sulfur-containing stabilizers СО 3 and СО 4, which are spatially hindered phenols, can have not only strong antioxidant properties but can also chemically modify polyolefins. Model experiments described in this article showed that under heating, these stabilizers could interact with the polymer, significantly increasing its mechanical characteristics. De la Rie (1988) describes the mechanism of binding of spatially hindered phenol molecules with the polymer macromolecules. Besides the antioxidant properties, Stafen stabilizer is used as an accelerator for hardening epoxy resins, as described in the copyright certificate by Antipov et al. (2015). The method described in the patent by Gerasimov (2013) No. 136172 "Device for aging" was used for accelerated climate tests. According to the instructions described in this patent, we constructed a device allowing to intensively irradiate the test material with the UV radiation in a short period. The position of the sample and the UV lamp in the foci of a straight elliptical cylinder with a reflective inner surface is a feature of the device. This configuration provides that all the radiation from the lamp directly hits the sample. Fig. 1 shows a scheme of the device. The exposure time under UV radiation was 36 hours. For the study we used samples of type 2 (GOST 11262-80). The technical process includes the following: weighed samples of PE granules of grades 273-83 and PE1296, in a 1:1 ratio, were put into a plastic mixer Brabender PL2200 (Germany) preheated to 180°C. Mixing time was 10 min, the rotation speed of the mixer rolls was 30 rpm. The stabilizers were added after the complete melting of the granules. The average time was approximately 40-60 seconds after putting them into the mixer. After mixing, the obtained melts were taken out and crushed until suitable fragments for the extruder.