Oxidation dose rate

Fluoropolymers utilizing high molecular weights and copolymerized and alloyed with polyethylene, should be used in most radiation applications. High-dose-rate E-beam processing may reduce oxidative degradation. When irradiated, PTFE and PFA are... 

It should be noted that temperature can have a significant effect on the degradation as it controls both the rate of oxygen diffusion into the material and the rates of reaction of the products of the irradiation. The diffusion of oxygen is a limiting factor (as it is with heat ageing) and oxidation is directly connected to the dose rate effect. 

LDPE/EVA blend was irradiated using gamma-irradiation and then expanded by heat as a foamed material. The EVA content in the blend was optimised to form a gel. The effects of atmospheres and of irradiation dose rate were studied. The ETIR spectra of the foam revealed the oxidation level. The relations between gel fraction of LDPE/EVA blend, expansion ratio, apparent density, average cell diameter and tensile properties of the foam are discussed. 8 refs. 

The lack of an oxygen effect is surprising, particularly at the lower dose rates. It could be caused by its consumption by easily oxidized groups in the wool produced by the radiolysis. However, it seems more... 

In special cases, where no liquid ozone can be measured and where the ozone mass transfer rate is equal to the reaction rate (E = 1), the ozone dose rate can be used to describe the amount of ozone available for reaction. Gottschalk (1997) was able to correlate the oxidation rate of an organic substrate (atrazine) with the ozone dose and absoiption rates. 

A drawback to chlorine dioxide is that it is subject to photochemical decomposition, so may require higher dose rates or longer application periods than with chlorine. A further problem is that, because of its high oxidative strength, it can degrade some organic inhibitors, and therefore an awareness of program compatibility is vital. 

While BSO interferes with the biosynthesis of GSH (Biaglow et al. 1983 Romero and Sies 1984), DIAMIDE oxidizes GSH to the disulfide [reaction (87) Harris 1982]. It has also been considered to act as a sensitizer by preventing low 02 concentrations from being depleted at high dose rates (Clark et al. 1983). 

The fallout pattern of the oxide particles in the vicinity of the piles was assessed in 1955-6 by Geiger counter surveys of the beta-dose rate near the ground, and subsequently, in 1958/61 by measurements of 90Sr and 137Cs in soil (Ellis et al., 1960 Booker, 1962 Chamberlain, 1987). The 90Sr/137Cs ratio in the oxide particles was near unity, there being little fractionation by volatilisation at the low temperatures of oxidation. 

Irradiation Procedure. 30% w/w solutions of poloxamer were prepared in distilled water by the cold process and saturated with nitrous oxide. This agent is a known scavenger of hydrated electrons and is known to enhance crosslinking of poly(oxyethylene) chains (9). Vials containing these solutions were irradiated at ambient temperature in a 2000 Ci ° Co source at a dose rate of 0.5 Mrad h- Physicochemical measurements were performed on solutions prepared by dilution of these irradiated samples. 

Weller E, Long N, Smith A, Williams P, Ravi S, Gill J, Henessey R, Skornik W, Brain J, Kimmel C, Kimmel G, Holmes L, Ryan L (1999) Dose-rate effects of ethylene oxide exposure on developmental toxicity. Toxicol Sci, 50(2) 259-270. 

Pure radio-oxidation predominates at high dose rates (typically higher than about 0.5 Gy.s ) and is characterized by a TOL quasi-proportional to the reciprocal dose rate. 

A non-empirical kinetic model was developed for the lifetime prediction of polymer parts in their normal use conditions. This model gives access to the spatial distribution (in the sample thickness) of the structural changes at the different scales and the resulting changes of normal use properties. Its efficiency was demonstrated for many substrates in large temperature and dose rate ranges. Here, we have paid special attention to PE radio-thermal oxidation. 

---