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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diamond prism. The reasons for this effect are described in detail in Thermo Scientific Application Note 50829. Despite the noises in the form of the peaks, the obtained spectra of the samples are quite informative. After UV irradiation (Fig. 2), additional peaks appeared in the composite spectra at 1713 and 875 cm -1 , and there is also an increase in the intensities of the absorption bands in the region of 1000-1100 cm -1 . Peaks at 875 cm -1 and 1713 cm -1 are observed in all compounds after irradiation despite the stabilizer. It is noteworthy that the peak intensity at 875 cm -1 substantially depends on the composite. The intensity of this band gradually decreases in the lines of СО 3> СО 4> Stafen. In the spectrum of the composite without stabilizers, this band is hardly noticeable. This peak, according to Hamzah et al. (2018), should be referred to fluctuations of the vinylidene group (–CH=CR 1 R 2 ). However, by Abdelhafidi et al. (2015), Ź enkiewicz et al. (2003), Gardette et al. (2013) was studied PE degradation, authors refer the peak at 888 cm -1 to vinylidene groups. The difference between the position of the peaks (875 cm -1 and 888 cm -1 ) can probably be explained by the formation of cyclic structures. It leads to a shift of the band referred to fluctuations of vinylidene groups in linear structures (890 cm -1 ) to the typical frequency referred to cyclic structures (875 cm -1 ), as described by Kalsi (1995). The peak at 1713 cm -1 refers to valent fluctuations of the carbonyl group (C=O). This peak is a composite peak. It has several “shoulders”, separating which one can determine the frequencies of its peaks with sufficient accuracy. Method of peak separation used by Aragão and Messaddeq (2008) applied in this case. Fig. 3 shows the result of peak at 1713 cm -1 separation.

Fig. 3. Separation of the peak at 1713 cm -1 of irradiated 273-83/PE1296.

Fig. 3 shows that the peak at 1713 cm -1 consists of four peaks at 1738, 1712, 1687, and 1664 cm -1 . The peak at 1738 cm -1 refers to valent fluctuations of the carbonyl group (C=O) in esters. Besides the absorption peak of the carbonyl group at 1738 cm -1 , the esters have absorption bands at 1036 and 1090 cm -1 , corresponding to valent fluctuations of C-O-C, which, as noted above, also are in the spectra of composites. The peak at 1712 cm -1 can be a cause of valent fluctuations of the carbonyl group (C=O) in carboxylic acids. Gardette et al. (2013), Carlsson and Wiles (1969), Nguyen et al. (2018) also observed this peak. The peak at 1687 cm -1 refers to valent fluctuations of the aldehyde group (C=O) in unsaturated hydrocarbons. The peak at 1664 cm -1 can be a cause of valent fluctuations of C=C bonds (vinyl group). All studied composites have the same peak shape at 1713 cm -1 , it indicates that all composites after irradiation have the mentioned functional groups. Thus, under UV radiation on composites, there are the following formations: 1) carboxylic acids; 2) ethers (complex and simple, possibly cyclic); 3) unsaturated aldehydes; 4) vinyl groups; 5) vinylidene groups. To evaluate the number of oxidized and unsaturated groups in the samples, we calculated the carbonyl and vinyl indices, as described by Hamzah et al. (2018), using the following equations: