Oxidation aging tests

W. M. Sanford, and K. A. Saum. Accelerated oxidative aging testing of UHMWPE. Trans Orthop Res Soc 20,119 (1995). 

The most common test used to study the oxidation resistance of mbber compounds involves the accelerated aging of tensile dumbbell samples in an oxygen-containing atmosphere. Brown et al. [22] recently reviewed long-term and accelerated aging test procedures. The ASTM practices (D 454 (09.01) D 865 (09.01) D 2000 (09.01, 09.02) D3137 (09.01) D 572 (09.01) D 3676 (09.02) D 380 (09.02)) for these tests clearly state that they are accelerated tests and should be used for relative comparisons of various compounds and that the tests may not correlate to actual long-term... 

Many researchers have found that differences in film deposition techniques and deposition parameters profoundly influence the oxidation and stability of MO layers. For example, increases of Ar pressure and bias voltage, leading to more porous structures, result in easier oxidation and quicker changes in aging tests [168-172], Such films are particularly corrosion-prone. 

In an automobile s catalytic converter, CO and hydrocarbons present in the exhaust gases are oxidized. Unfortunately the effectiveness of these units decreases with use. The phenomenon was studied by Summers and Hegedus in /. Catalysis, 51, 185 (1978) by means of an accelerated aging test on a palladium impregnated porous pellet packed bed converter. From the reported data on hydrocarbon conversion shown below, develop an expression to represent the deactivation rate of this catalyst. 

The NSR technology is regarded as the most reliable and attractive de-NOx method. However, catalyst degradation by SOx poisoning is a big problem. Sulfate was detected on the NSR catalyst after the aging test. S02 is oxidized and reacts with the NOx storage materials to form sulfates, which means the... 

Fio. 35. (a) The concept of complex oxide of zirconia, titania and alumina (AZT) and (b) its effect on thermal durability after thermal aging test at 1,000°C. 

Most ageing tests are carried out on vulcanised or thermoplastic compounds, but there has been a need to assess the oxidative effects of storage on natural rubber. Various accelerated procedures using ovens or infra-red lamps have been used with visual assessment of deterioration. A more satisfactory procedure based on the measurement of plasticity after oven ageing has been standardised as ISO 293033 and the result is known as the plasticity retention index. 

Another approach to curing SSL by oxidative polymerization employs the use of enzymes (54 ) In that study, SSL was treated with the white-rot fungus Fomes annosus and a laccase-inducing phenoloxidase until the solution reached a honeylike consistency. This viscous liquid was then subsequently used to bond wood particles together at a pressure of 0.03 kg cm-2. It now needs to be established whether the mechanical properties of these boards survive accelerated aging tests. 

Values denoting oxidative deterioration increase gradually during the shelf-life of an oil. Determinations of induction times in rapid-aging tests also reflect the oxidative stability of commercial refined oils. Grompone et al. (84) studied the stability of commercial regular sunflower oils. The oil samples were stored at ambient conditions in their original PET bottles for a one-year period. The OSI induction time... 

Evidence exists that at least three reactions, hydrolysis, oxidation, and cross-linking, contribute to the deterioration of paper (4, 5, 6). The magnitude and rate of change of a specific physical property will depend on the extent one reaction proceeds relative to the others. It must also be recognized that each degradatlve reaction is affected differently by environmental variables and the results obtained from an accelerated aging test will depend on the selection of the environmental variables. It is therefore necessary to establish the relative importance of each environmental variable. 

The EMMAQUA test, which includes the effects of UV, heat and moisture, is more representative of solar panel aging than are the oven aging tests. It has a much lower acceleration factor, however, on the order of about 20X which includes approximately 6-8X in UV-visible solar flux and about 3-4X in temperature above which these particular solar panels would ordinarily run. It is therefore a much slower, more elaborate process that should follow oven aging as a screening tool with which to eliminate from further consideration those polymers that have insufficient resistance to long term oxidation. 

The types of stress relaxation test standardized (for rubbers) split into the two intended purposes. Seals are commonly stressed in compression or in a complex mode of stressing that compression can represent. Hence, sealing force tests arc usually made in compression. The bulk of such test pieces slows oxidative aging and also the uptake of any fluid. but swelling and aging effects do have to be considered in long-term applications. 

In comparison with the effects of liquids on plastics, very little testing is carried out on the effect of gases other than air aging tests, which were covered in the previous section of this chapter. Ozone, which is of particular concern to many elastomers (sec Chapter 15), has no special effect on most plastics, beyond the normal oxidative degradation processes, as these are fully saturated in the main. The main concern of the effect of gases is through their permeability, a subject dealt with in Chapter. 0. 

---