Antioxidants are used to protect polymers from degradation, both during processing (=short term stabilization) and during use (=long term stabilization). Polymer degradation generally results in gel formation and changing melt flow index, loss of mechanical and esthetical properties (crazing, gloss reduction, chalking), and discoloration.
A complete range of anti-oxidants exist, starting from cheaper, general purpose anti-oxidants, up to anti-oxidants specially designed for high end applications like hot water pipes. High end anti-oxidants typically have better properties towards discoloration (yellowing/pinking), migration/chalking or hydrolysation.
Selection of specific applications is made considering various critical factors like, high speed and high temperature extrusion.