PSI - Issue 20

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Petukhova E. S. et al. / Procedia Structural Integrity 20 (2019) 75–80 Petukhova E. S. and Fedorov A. L./ Structural Integrity Procedia 00 (2019) 000 – 000

Fig. 1. Structural formulas of: (a) CO3 - b is3,3′ -[(3,5-di-tert.butyl-4-hydroxyphenyl) propyl]sulfide; (b) CO4 - b is3,3’ -[(3,5-di-tert.butyl-4 hydroxyphenyl)-propyl]disulfide; (c) Stafen - bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propyl]phthalate.

These compounds are designed for light and thermal stabilization of polypropylene, high and low pressure polyethylene, polystyrenes, ABS plastics, radiation or peroxide crosslinked polyethylene, epoxy resins, rubber, etc. The mechanical characteristics of the composites were determined by the universal tensile testing machine UTS 20K according to GOST 11262-80 and 9550-81 (State Standards). To estimate the efficiency of stabilizers, a program of full-scale tests of the climate resistance was created according to the instructions of GOST 7.908-83 (State Standard). As the control indicators of the properties, we use the study results of elongation at rupture (GOST 11262-80 (State Standard)) after months 0, 1, 3, 6, 9, 12 and 18 of testing, as well as electron microscopic studies of the structure. The surface of the samples and their color after their exposure were also analyzed. Two sets of samples were produced for testing: 1. control samples were stored in a darkened room at room temperature; 2. testing samples were stored at the open-air testing area of Institute of Oil and Gas Problems, SB RAS. 3. Results and discussion Since the chosen compounds affect the mechanical characteristics of polymers, first we analyzed composites containing 0.1, 0.3, and 0.5 wt% of stabilizers CO3, CO4, and Stafen. These concentrations are selected taking into account the studies described by Glukhov et al. (2012) and Beknazarov et al. (2018). Table 2 presents the research results. Analysis of the data presented in the Table 2 allowed us to identify the following stabilized composites, which are distinguished by a stable and high set of mechanical properties: PE 273-83 + 0.5 wt% CO3, 273-83 + 0.3 wt% CO4, 273-83 + 0.5 wt% Stafen. These compositions were chosen for climate resistance testing. Figure 2 shows photographs of the samples storing at the open-air testing area for 1 and 3 months. It has been found that composites containing stabilizers CO3 and CO4 are colored yellow. The color change is caused by the decomposition of stabilizing additives accompanied by the formation of colored quinone derivatives as shown by De la Rie (1988). It should be noted that with further exposure of these samples at the open-air testing area, the intensity of the color does not change. The original polyethylene and composites containing the Stafen stabilizer did not change their color during the entire test period. One of the most sensitive characteristics of polymeric material aging is elongation at rupture (Lipp-Symonowicz et al. (2006) and Gijsman et al. (1996)). Figure 3 presents the research results of the elongation at rupture for the control and testing samples.