Ageing and spectroscopic properties of polyethylenes: comparison with metallocene polymer

The thermal and photooxidative stabilities of high, linear low and metallocene grade polyethylenes are compared using FTIR and hydroperoxide concentration analysis and thermal methods (DSC, TGA). The thermal ageing of solid films follow the order LLDPE > metallocene > HDPE while for light stability the order is LLDPE > HDPE > Metallocene. Derivative UV and FTIR spectroscopic analysis of the three polyethylene types show that the vinyl types and concentrations are different and that they reflect the thermal stability of the polymer materials. Hydroperoxide levels also appear to be important and correlate with the carbonyl index oxidation rates. Differences in catalyst residues play a less prominent role although the effect of the Ti levels may be important. The fluorescence and phosphorescence excitation and emission spectra of the three types of polyethylene are similar confirming earlier identities on the role and presence of unsaturated carbonyl species. There are however, significant differences in a long wavelength component in the fluorescence emission indicating the presence of other active chromophores. These were found to be significant in the case of the metallocene polymer. These chromophores may contribute to the differences in the light stability of the polymers with the metallocene exhibiting the greatest intensity and least stability followed by HDPE and LLDPE. (C) 1999 Elsevier Science Ltd. All rights reserved.