The main purpose with antioxidants is to protect polymers during processing and end use.
Typical process-stabilisers are vitamin E, phosphites (phosphonites), hydroxyl amines, amine oxides and lactones and the typical performance test is multiple extrusions in a PP homopolymer. Unstabilised PP is preblended with additives, compounded under inert conditions followed by multiple extrusions under air atmosphere. MFI and yellowness index are measured after 0, 1st, 3rd and 5th extrusion.
Typical AO for end use is sterically hindered phenols, aromatic amines and sulfur based synergists (e.g. DSTDP). After compounding of agreed recipes, the PP based samples are injection moulded (1 mm test specimens) followed by oven ageing at 135 and 150 °C and time to degradation is measured.