Study on Multi-factor Coupling Aging Kinetics of Polyolefins: Yearly and Monthly Aging Speed Maps

Natural aging of polyolefins is the comprehensive result of multiple environmental factors, such as UV irradiation, temperature, humidity and oxygen. But till now natural aging result is difficult to be simulated by accelerated aging. In this study, a lab-developed system was used to realize an in situ multi-factor aging evaluation under adjustable UV irradiance, temperature, humidity and oxygen concentration. Gaseous degradation products (CO2 is typical) were detected and the formation rate of CO2 was exploited to evaluate the stability. High formation rate (high aging speed) corresponds to low stability. By this system, single-factor aging speed equation of aging speeds of polypropylene (PP) and polyethylene (PE) versus UV irradiance, or temperature, or humidity, or oxygen concentration were established. Furthermore, multi-factor aging speed kinetics models of PP and PE were established and the parameters were fitted. Based on the multi-factor aging kinetics equations, the yearly aging speed "maps" in China and monthly aging speed "spectra" in some cities of PP and PE were drawn. This information is instructive to practical outdoor applications of PP and PE. The sensitivity of PP and PE to environmental factors was analyzed. It was found that PP is much more sensitive to irradiance and humidity than PE, a little more sensitive to oxygen concentration than PE, but is less sensitive to temperature than PE. This strategy can also be used for other polymer materials to establish their own multifactor aging kinetics equations.