INTERACTIONS IN THE THERMAL AND LIGHT STABILIZING ACTION OF NOVEL AROMATIC PHOSPHITES WITH A 2-HYDROXYBENZOPHENONE AND HINDERED PIPERIDINE STABILIZER IN POLYOLEFIN FILMS

The interactions of two novel phosphite stabilisers with a commercial polymeric hindered piperidine stabiliser, Chimassorb 944, and a 2-hydroxy-4-n-octoxybenzophenone stabiliser, Cyasorb UV 531, have been examined in the thermal and photooxidation of polypropylene and high density polyethylene films using FTIR spectroscopy. The two structures are based on a bis-hindered phenolic moiety coupled to a 2-hydroxybenzophenone and a 4-aminotetramethylpiperidine (3) chromophore. Thermal oven ageing and photooxidation of the polyolefin films showed that the hindered piperidine phosphite (phosphoramide) is synergistic over a wide concentration ratio with both commercial stabilisers. The only exception is in polyethylene with the Chimassorb 944, wherein the latter shows poor solubility in polyethylene. Generally, the phosphoramide is found to be more effective as a thermal antioxidant than as a UV antioxidant. The 2-hydroxybenzophenone phosphite was generally ineffective as a light stabiliser and exhibited unusual S-shaped profiles in combination with both the commercial stabilisers, suggesting the involvement of two distinct processes. With Cyasorb UV 531 the antagonistic/synergistic patterns were reversed from polypropylene to polyethylene. With Chimassorb 944 strong synergism is observed at high phosphite ratios while antagonism is prevalent at low ratios. In general, one interesting feature of the results is that the thermal and UV effects often exhibit a similar behaviour.