Effect of selected residual Ziegler-Natta and metallocene catalysts on the UV-induced degradation of unstabilized ethylene homopolymer films

Catalyst creates new grades of polyethylenes while their degradation phenomena determine the resulting application profiles. The resins and the end-products eventually contain residual catalysts. Therefore, the effects of the following two residual catalysts-one Ziegler-Natta [PQ Silica/Bu2Mg/tBuCl/TiCl4], and the other metallocene [PQ Silica/MAO/(nBuCp)2ZrCl2]-on the UV-induced degradation of the resulting unstabilized ethylene homopolymer films were studied. The MetCat HomoPE film was found to be more susceptible to UV-induced degradation degradation than the Z-N HomoPE one despite the residual Zr level was 1/15th of the Ti content. Therefore, the zirconocene residual catalyst better (i) facilitated the UV-initiated reaction, and (ii) decreased the activation energy required for the decomposition of the resulting hydroperoxide. These findings were explained from the differences in (i) electronic configuration and atomic radius, and (ii) surface chemistry and solid-state electronic environment of these catalyst systems. In both films, Tpm and Tpc did not significantly vary with the exposure time. The change of % crystallinity showed to be irregular and disturbed. As a function of carbonyl index, Tpm and Tpc,varied in a similar fashion in the MetCat HomoPE film. However, they significantly differed for the Z-N HomoPE film. Here, Tpm did not appreciably change whereas Tpc initially increased very mildly; then it did not essentially differ.