Temperature dependence of the inhibited oxidation parameters of polyethylene

Accelerated Aging, Photochemical and Thermal Aspects

“…Even subtle forms of motion within the polymer structure can effect deterioration. The data of Wandelt (1986) illustrates this possibility ( (Shlyapnikov et al 1987). Reproduced with permission of the publisher.…”

“…This observation can be used to monitor the progressive extent of aging of many materials. Shlyapnikov et al (1987) refers to this procedure as a "combined test": determining the time-to-failure of unexposed material upon accelerated thermal aging and monitoring the properties of the naturally aged material under the same accelerated thermal aging. Kramer and Koppelmann (1987) call the procedure a "residual lifetime" test; Cope and Revirand (1982-83) call it "residual thermal stability.…”

“…If one attempts to extend a plot of log k vs. 1/T to ever higher temperatures, the polymer system may change its physical state at some point, either by melting, as in the case of crystalline or partially crystalline substances ( Fig. 10.2; Shlyapnikov et al 1987), or by passing from a glassy state to that of a highly viscous liquid at the secondorder transition temperature or glass temperature (Tg). This is a major limitation that can be cited regarding the use of the Arrhenius relationship, limiting how far one may extrapolate the experimental data to very much higher or lower temperatures.…”

“…Theberge and Cloud (1978), Chodak and Zimanyova (1984), and River (1984) cite examples where predictions of stability would have been in error if the fact that tests have been carried out at temperatures above Tg were not considered. The effect of a wide range in test temperature can become particularly troublesome in the case of systems that contain inhibitors (Shelton et al 1953;Hawkins et al 1959a;Shlyapnikov et al 1987).…”

“…The energy of activation in air and at high partial pressures of oxygen proved to be the same, thus suggesting that the same reactions took place under either condition. Shlyapnikov et al (1987) use heating times to failure at high oxygen pressure…”