Chemiluminescence study on the oxidation of several polyolefins: II. Chemiluminescence from γ-irradiated polymers

Abstract

Chemiluminescence (CL) from isotactic polypropylene (i-PP) and several types of polyethylene, namely low density (LDPE), linear low density (LLDPE) and high density (HDPE), subjected to γ-irradiation in the presence of air, was recorded in both inert (nitrogen) and oxidative (oxygen or air) atmospheres. CL data can be related to the radiation-induced changes observed in the IR spectra of the polymers. The signal recorded in nitrogen may be accompanied by a thermo-luminescence emission, mainly occurring at the melting point of the polymers. The decay of CL emission at 170 °C seems to follow second-order kinetics. It could be related to the presence of two types of luminescent species, perhaps associated with free hydroperoxides. The stability of the polymers subjected to thermal oxidation after irradiation is found to depend on both the polymer type and post-irradiation treatments, such as the thermal decomposition in the inert atmosphere of radiation-induced peroxide products. The shape of the CL curves recorded in air from irradiated LDPE could be related to a competition between oxidation and scission.