The process of photooxidative destruction of high density polyethylene films containing different organic complexes of polyvalent metals as pro-oxidant additives after UV-irradiation was studied. During exposure to UV-irradiation, the more significant changes in the mechanical and thermal properties were detected for the foils containing pro-oxidant additives compared to initial high density polyethylene. This indicated for the higher degree of oxidation in these samples and confirmed the effectiveness of thеsе additives in promoting the oxidation of high density polyethylene during UV-irradiation. It was found that the decrease of the strength of the initial high density polyethylene foils was more pronounced for the samples with pro-oxidants cobalt (III) acetylacetonate and manganese (II) acetylacetonate. The use of 2 mmol/kg iron (III) acetylacetonate and 4 mmol/kg cobalt (III) acetylacetonate as pro-oxidants gave the highest decrease of elongation at break of the polyethylene foils.

The thermal, tensile and other properties of high density polyethylene films containing iron (III) acetylacetonate as pro-oxidant additive have been studied after exposure to UV irradiation for up to 300 h. The effect of photooxidation on polyethylene films with and without pro-oxidant was estimated by Fourier transform infrared spectroscopy, X-ray diffraction analysis, Differential scanning calorimeter measurements and the tensile properties. It was observed that UV irradiation had almost no effect on the melting temperature of the different samples. After exposure, the degree of crystallinity increased from 69 %t o7 2% for the initial polyethylene samples without pro-oxidant additive and by 3% for the samples containing iron (III) acetylacetonate. It was found that the increase in the carbonyl index of initial HDPE was not significant even after 60 he xposure to UV irradiation while samples with pro-oxidant suffered substantial degradation still for 35 h. It was observed that the decrease of the tensile strength is more pronounced for the samples with pro-oxidant under irradiation for 60 to 70 h. The films containing pro-oxidant lose * 90 % of its initial elongation at break after 35 he xposure. 2E xperimental MaterialsPowdery high density polyethylene (HDPE), product of Lukoil-Neftochim Co., Burgas, Bulgaria, with melting temperature 130 8 C, melt index 0.16 g/10 min (190 8 C, 2.160 kg) and density 0.948 g/cm 3 was used for the preparation of the films. The pro-oxidant -i ron acetylacetonateF e(acac) 3 with chemical formula Fe(C 5 H 7 O 2 ) 3 ,m elting temperature 180 -183 8 C, molar weight 353.17 g/mol and density 5.24 g/cm 3 ,product of Merck, Germany. Sample PreparationThe compositions containing 2mmol/kg Fe(acac) 3 were mixed with HDPE and homogenized in al aboratory mixer Carl Hanser Verlag, Munich Intern. Polymer Processing XXIX (2014) 5