ABSTRACT

Combinations of hindered phenols with aromatic phosphites or phosphonites have been used for effective melt stabilization of polyolefins. It was evidenced by multiple extrusion tests (46) that phosphite 44, used in excess, reduces consumption of phenol 18 at processing temperatures. Lower amounts of 18 may be added, and more effective long-term stabilization has been reached by the residual 18 during the subsequent polyolefin aging. It was postulated that phosphite 44 protects phenols from destruction by hydroperoxides and converts discoloring quinone methides 86 (arising from phenols) by 1,6-addition in aromatic colorless compounds (e.g., 247) (29,54). The resistance of polyolefins against discoloration is improved by doping with a phenol-phosphite combination (9).