Figure 6 The relative content of the color-related-oxidation-products from the oxidized oil samples
After the typical color related oxidation products are selected (as shown in Table 1s), the integral area values of the chemicals are calculated and listed in the Table 1s-8s according to the Figure 3s-6s. For ease of reading, the data are converted to Figure 6 which presents the variation trend more intuitive. It should be noted that all of the base oils with antioxidants (T501, Tz516 and T531) would generate more CORP after Cu sheet applied in the reactions. The phenomenon could be easily seen from the Figure 6c and 6d, which is the CORP of the oxidized PAO and Tz516, the amount of CORP with Cu sheet is almost 500 times more than the CORP without Cu sheet. As shown in the Figure 6, several CORP (4, 7, 12 and 15 in Table 1) sharply increase with increasing oxidation time whether Cu sheet is applied or not. The chemical formula of the CORP 4 and 12 (actually same chemicals) in Table 1 are mainly the diradical termination reaction products of T501 (shown in Figure 7).However, the CORP 7 and 15 might hard to find suitable reaction mechanism to explain the actually relations occurs in the complex system of PAO with Tz516 and DIOS with T531. As shown in Figure 7, the CORP 4 (or 12) is suggested to be produced by the biradical termination reaction through Figure 7b route after the T501 is oxidized by free radicals by Figure 7a route. The hydrogen transfer is easy to occur in the alkane substituted benzoquinone structure because of the conjugated system. Compared with CORPA, the CORPB have relative small amount in oxidized oil samples. In the oxidation reactions catalyzed by Cu sheet, most CORPB distinctly increase while the oxidation time was increasing (Table 1s-8s, CORPB 4, 7, 12 and 15). The result is positive for both PAO and DIOS oil samples.