Development of an automatic evaluation system for photooxidation and assessment of polyethylenes containing HALS and UVA

An automatic evaluation system for photooxidation has been developed by utilizing a chemiluminescence apparatus combined with a light irradiation system. The system is composed of a controller, a driving device, and irradiation equipment, which are integrated with the chemiluminescence measurement system. Various measurement conditions can be set independently, including irradiation time (fixed or variable), waiting time from irradiation to measurement, chemiluminescence measurement time, number of repetitions (up to 999 times), and measurement temperature. LLDPEs containing Hindered Amine Light Stabilizers (HALS) and Ultraviolet Absorbers (UVA) were evaluated using this system. The decay of chemiluminescence after UV irradiation was repeatedly measured at r.t. and 105℃, respectively, below the melting point of LLDPE, and the time-course of chemiluminescence was obtained by plotting time against I(t=0) for each instance. I(t=0) represent the rate of photooxidation under UV exposure, calculated using second-order analysis of the chemiluminescence decay. The chemiluminescence intensity increased significantly in the initial stage with irradiation time, maintained a stable intensity for a period, and then exhibited a substantial increase in the later stage. We termed the point at which this significant increase in chemiluminescence occurs as the induction time of photooxidation (photo-OIT). Using this system, the photo-OIT of LLDPE samples with HALS and UVA was measured, revealing the potential for assessing the synergistic effects of photooxidation stabilizers.