BMe Research Grant
The aim of our work is to replace the above mentioned synthetic, phenolic stabilizers with natural antioxidants during the processing of polyolefins. Stabilizing efficiency of these antioxidants were compared to the frequently applied synthetic stabilizer Irganox 1010 [L5], but it turned out soon, that the examined antioxidants outperformed the reference stabilizer [6,B1]. Based on these early results, the direction of the work shifted toward the investigation of relationship between the molecular structure, the applied concentration and the efficiency of these natural substances. Changes in the properties of the polymer during its repeated processing were analyzed according to the industrial practice, and interactions between the applied primary and secondary stabilizers were characterized too.
Figure 2.: Melt flow rate of the polymer plotted against the residual PEPQ concentration in the samples
Figure 3.: Base molecular structure of flavonoids
OIT values of samples containing different types of flavonoid antioxidants were plotted against the applied concentration of the stabilizers on Figure 4 after the first extrusion step. It can be seen that the amount of phenolic hydroxyl groups of the different types of flavonoids is the determining factor of stabilizing efficiency, at least in the case of complete oxidation of the sample. Residual concentration of PEPQ is represented in Figure 5 in the case of samples containing the same amounts of natural antioxidants after the first extrusion step. The values are plotted against the lowest O-H bond dissociation energy (BDE) [L12] of the different flavonoids. The value of this property depends mostly on the chemical environment of the hydroxyl group. The lower the BDE values is, the more efficiently hinders the stabilizer the decomposition of PEPQ, which is highly important in order to maintain the mechanical properties of polyethylene.
Figure 4.: OIT values of samples containing different flavonoids, after the first extrusion step [B6]
Figure 5.: Dependence of residual PEPQ concentration on BDE values of different flavonoids, after the first extrusion step [B6]