3.3. Gel permeation chromatography (GPC)
The GPC analysis results showed that untreated soybean oil has a single peak at a retention time of 25.3 min, corresponding to the soybean oil triglycerides, as shown in Fig. 5. A second peak (retention time at 24.4min) was observed for 2h, 4h, and 6h treated liquid samples, with an increased area of 25.2±2.3%, 29.9±1.6%, and 32.2±1.6%, respectively. Corresponding to an average number molecular weight (\(\overset{\overline{}}{\text{Mn}}\)) of 1569±17.3, 1626±12.2, and 1705±12.2g/mol, respectively. This result indicates the formation of a dimer, as explained in the proposed Diels-Alder (Smith, 2017) reaction between the triglyceride molecules forming a dimer (Fig. 4). It is clearly can be proposed that HVACP treatment may induce polymerization of soybean oil, forming dimers and oligomers (Ionescu & Petrovic, 2009; Zhao, Yang, Tao, & Xu, 2014). The \(\overset{\overline{}}{\text{Mn}}\)obtained in GPC is an almost double mass of n untreated triglyceride, which means the dimerization.
Figure 5 – about here GPC