Study on the antioxidant activities of benzofuranones in melt processing of polypropylene

The antioxidant activities of four benzofuranones in melt processing of polypropylene (PP) have been investigated using multiple extrusions. The antioxidant activities of those four benzofuranones with different substituent groups have been evaluated using melt flow index (MFI) and yellowness index (Y.I.) of multiple-extruded PP stabilized with those antioxidants. The change of MFI values indicates as follows: firstly, the position of substituent group has a very important effect on the antioxidant activity of benzofuranone in the melt processing of PP i.e. methyl group of 2′-position may prevent the hydrogen donation of benzofuranone toward PP radicals and make the antioxidant activity of benzofuranone in PP decrease; secondly, electronic property of substituent group of para position to 3-reactive hydrogen has little influence on the antioxidant activity. Furthermore, the theory that the formation of antioxidative products due to the dimerization and disproportionation of benzofuranyl radicals is the main reason that induces the discoloration of stabilized PP has been predicted for the first time.