The photo-stabilising action of metal chelates in polypropylene: Part IX—Practical synergism with other commercial systems and the importance of calcium stearate

The photo-stabilising action of three metal chelates (Cyasorb UV 1084, Irganox 1425 and Irgastab 2002) in a number of synergistic formulations with three commercial stabilising systems (Weston 618, Cyasorb UV 531 and Tinuvin 770), in polypropylene films has been examined. The results show that, although antagonistic effects are observed at some mass ratios, synergistic effects prevail at others. The effects are a function of the particular formulation.The addition of calcium stearate to the stabilising mixture can have marked effects on the observed behaviour. Thus, an antagonistic effect can become synergistic if calcium stearate is used in the formulation. The results have scientific and technological implications as calcium stearate is often used as a processing aid in the stabilisation of polypropylene.