Thermo- and Photo-Degradation of LDPE and PP Films Using Metal Oxides as Catalysts

Abstract

Degradation of LDPE and PP films using the photo sensitive metal oxides or pro-oxidants (e.g. Fe2O3, CuxO, ZnO, and TiO2 at various particle sizes) as the catalysts in both thermo- and photo-oxidation of plastic films with oxygen followed by photolytic process to give free radicals has been studied. Our preliminary study in hexane solution found that the carbonyl index (CI) increased under the shortwave ultraviolet (254nm) significantly greater than under the longer wave (366nm) due to its greater energy and highly absorbed by the pro-oxidants generating more free radical concentration which could then be photolysed into carbonyl compounds. The pro-oxidant blended PE and PP films under ultraviolet (254nm) irradiation showed the carbonyl index elevation at the beginning and then reducing to a constant level similarly in most cases. This probably suggested that the carbonyl primarily formed and degraded into other free radicals. Under shortwave ultraviolet irradiation for 72 hours, the LDPE films containing nano-sized rutile-TiO2 and nano-sized anatase-TiO2 (1%w/w) were able to reduce the film tensile strength by 32% and 55%, respectively. The film containing micron-sized commercial TiO2 lower the film tensile strength only by 7-10%. However, the tensile strength of the TiO2 blended PP films tends to increase possibly because the rate of cross linkage exceeds the rate of scission.