Antioxidants are added in the polymer resins during processing to inhibit degradation caused by the thermo-mechanical stress. Their mechanism of action helps to extend the materials life by enhancing the appearance and maintaining its strength, stiffness and flexibility. Primary antioxidants are typically phecolic based substances and act during the process or as long term heat stabilisers. Secondary antioxidants like phosphites act initially at high temperature and shear rate protecting polymers and other additives.