Effect of Zinc Oxide and Titanium Dioxide on Heat and Light Stability of Ethylene Propylene Terpolymers

Oven aging properties at 350° F and 300° F of EPT polymers were substantially improved with additions of zinc oxide up to 10 and 20 phr. Zinc oxide enhanced the elongation retention after aging, and the improvement was significantly greater with French than with American Process zinc oxides. Finer particle size French Process zinc oxides imparted somewhat better aging properties than did the coarser zinc oxides of the same type. The aging advantage for high loadings of zinc oxide was notable both with whiting and clay-filled EPT compounds with low and normal amounts of sulfur. When the pigmentation of the EPT polymer was 50 phr of FEF black, the aging differences between the several American and French Process oxides at loadings of three to 20 phr were less prominent. Replacement of three per cent of EPT with an equal amount of several unsaturated elastomers increased the cure rate of the compound appreciably. Tear resistance was improved and compression set properties lowered. Improvement in heat resistance depends on the polymer added. Several anatase and rutile pigments were essentially equal in heat aging resistance at an equal volume loading in EPT. The reflectance of stocks with zinc oxide alone or in combination with titanium dioxide in an unfilled stock increased during the first three days of Atlas Weather-Ometer exposure. Beyond this point, there was a gradual degradation in reflectance with the loss in reflectance being somewhat greater with a zinc oxide-titanium dioxide blend than straight zinc oxide. These results reflect the observed differences in ultraviolet opacity between zinc oxide and titanium dioxide. In a comparison of anatase and rutile in a whiting loaded stock, anatase was poorer than rutile in reflectance through the initial exposure stages in the Atlas Weather-Ometer; however, after prolonged exposure, there was a reversal in reflectance, due to the chalk layer developed in the anatase sample. EPT stocks pigments with 79.5 phr of whiting with titanium dioxide between 18.5 and 25 phr, and activation amounts of zinc oxide showed no visible sunlight degradation after 70 weeks outdoors.