Effect of Diphenyl carbonate derivatives and Cobalt stearate on photo-degradation of low-density polyethylene

This study reports the results of the investigation on photo-oxidative degradation of low-density polyethylene (LDPE) in the presence of nonmetallic and metallic photo-initiators. In this regard, a mixture of cobalt stearate along with diphenyl carbonate (DPC) and its derivatives were added to LDPE and photo-degradation behaviors of LDPE films containing nonmetallic pro-oxidant (DPC and its derivatives) and cobalt stearate were investigated under ultraviolet (UV)-A radiation. The derivatives of DPC (4,4-dichloro DPC, 4,4-dinitro DPC, 4,4-dihydroxy DPC, and 4,4-dimethoxy DPC) were synthesized using the substitution reaction of phenol and DPC in aqueous phase. LDPE films of 70 +/- 7 mu m in thickness containing varying amounts of pro-oxidant (0.1, 0.3, 0.5 wt%) were prepared in an extruder by film blowing process. LDPE films with and without pro-oxidant were subjected to the UV-A exposure at 27 degrees C for extended time periods. The physical and chemical changes induced by UV exposure have been monitored by various techniques like Fourier Transform Infrared spectroscopy, density and viscosity measurements, tensile, and gravimetric analysis. The changes in carbonyl index (CI), molecular weight, and mechanical properties (tensile strength and elongation at break) showed that the incorporation of a combination of metallic/nonmetallic photo-initiators was highly effective in accelerating the photo-degradation of LDPE films and pro-oxidants had a higher degradation rate compare to blank samples. Moreover, it has been demonstrated that the best performance was observed for 4,4-dinitro DPC (0.5 wt%) with a CI and number of chain scission (CS) of 21.24 and 2.25, respectively, after UV exposure of 200 h; while the CI and CS values were lower for LDPE with no additive (2.83 and 0.092, respectively). Furthermore, in the case of films containing a combination of pro-oxidant cobalt stearate (0.1wt%) and 4,4-dinitrodiphnyle carbonate, synergistic effects on photo-degradation behavior of LDPE have been experimentally observed.