Aging studies

Accelerated heat aging tests of vulcanized and thermoplastic rubber are conducted according to ISO standard.In respect to plasticized samples it is important to test materials in separate ovens to prevent cross-contamination of samples, which may contain, in addition to a plasticizer, other additives, which may be transferred from sample to sample, such as accelerators and antioxidants. 

Phthalate plasticizers are tested for color change after exposure to 180 C for 2 h. Diallyl phthalate is excluded from this test because of the risk of explosive polymerization. After aging, the color of the plasticizer is measured and reported in Hazen units. 

Samples of cellttlose acetate plasticized with dimethyl phthalate are subjected to laboratory molding at 200°C for 10 min. dscosity change is measured to estimate the effect of molding on material. Optical density can also be used to determine the effect of molding.  

Approximately 50 g of the plasticizer is slowly birmed and then heated at 600°C in the furnace until constant weight is obtained. Diallyl phthalate should be used in small portions and with a great caution due to the risks of its ejqrlosive polymerization. 

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Abraham, M., Williamson, V., Westbrook, S. (1994). A cross-age study of the understanding of five chemistry eoncepts. Journal of Research in Science Teaching, 31, 147-165. 

Novick, S., Nussbaum, J. (1981). Pupils understanding of the nature of matter A cross age study. 

Coll, R. K., Treagust, D. F. (2003). Learners mental models of metallic bonding A cross-age study. Science Education, 81, 685-707. 

Being cut from tires, the rubber samples in this work cannot always be studied using standard test procedures. The specific techniques used to measure rubber aging have been described in detail elsewhere and are summarized below [2]. The same techniques have been used to evaluate rubber aging in both field and the laboratory oven-aging studies. For reference. Figure 34.2 shows a diagram of the internal components of a radial-ply tire. 

The results from more recent studies have not clarified the issue. In a study of the general population in Belgium in which 2 sets of data were collected at a 6-year interval, Staessen et al. (1996) found that blood pressure was not correlated with PbB or ZPP concentrations in men or women. The study further found that the risk of becoming hypertensive was not associated with PbB or ZPP concentrations measured at the first data collection. Results from the evaluation of participants in the Normative Aging Study showed that an increase in tibia bone lead of about 29 pg/g was associated with an increased odds ratio of hypertension of 1.5 (Hu et al. 1996a). However, the authors acknowledged that the procedures used to... 

Hu H, Payton M, Korrick S, et al. 1996c. Determinants of bone and blood lead levels among community-exposed middle-aged to elderly men. The normative aging study. Am J Epidemiol 144(8) 749-759. 

Kim R, Rotnitzky A, Sparrow D, et al. 1996a. A longitudinal study of low-level lead exposure and impairment of renal function. The normative aging study. JAMA 275 1177-1181. 

Payton M, Riggs KM, Spiro A III, et al. 1998. Relations of bone and blood lead to cognitive function The VA normative aging study. Neurotoxicology and Teratology 20(1) 19-27. 

Bone, RA, Landrum, JT, Fernandez, L, and Tarsis, SL, 1988. Analysis of the macular pigment by HPLC Retinal distribution and age study. Invest Ophthalmol Vis Sci 29, 843-849. 

Solid-state NMR spectroscopy was also used to examine the post reaction behavior of pTrMPTrA samples prepared in bulk as thin films, as described in the experimental. All of the spectra in this aging study required a minimum of 720 scans on approximately 50 mg of sample with a 100 s pulse delay to achieve adequate signal/noise. Under these conditions, reliable peak areas could be obtained from the curve fits of the carbonyl region. Figure 3 depicts the evolution of the solid state spectrum of the sample stored under N2 over time and upon heating. The area of the peak at 174 ppm for the carbonyl adjacent to the reacted double bond increases as the peak at 166 ppm for pendant unsaturation decreases. The results of the aging study are given in Table I. 

Properties such as friction, gas permeability and thermal conductivity are only likely to have significant importance in specialised applications and it is not surprising that they are very rarely measured in ageing studies. 

The phenyl modified polymers possess the optimum combination of high temperature and elastomeric properties and were used in the study of formulation parameters These variables can have an important effect on the thermal stability and property profile of vulcanized systems For example, the use of reinforcing silicas, peroxide content, and oxidative stabilizers have been shown to be important ( 3, 10, in However, polymer-silica interactions had the most pronounced effect on retaining properties during high temperature aging studies ... 

Characterization. Differential scanning calorimetry and thermal mechanical analysis data were obtained on a DuPont 990 thermal analyzer coupled with a DuPont DSC or TMA cell. Isothermal aging studies were carried out with an automatic multisample apparatus. 

Hu, H. et al. (1996). The relationship of bone and blood lead to hypertension. The normative aging study, JAMA, 275, 1171-1176. 

Since the phosphate ester s only purpose was fire retardation, a new nonphosphate system was recommended for future applications. The following discussion addresses the results of an accelerated aging study on this formulation. 

In subsequent aging studies the polyol component showed virtually no change In acid number at any of the aging temperatures (ambient, 60 , 71 C) over 13 months. The Isocyanate was shown to age similarly to the Isocyanate In Formulation 2. As a result, the above formulation Is being employed In the field ... 

Finally, a third formulation was devised which excluded the use of Freon 11 In the polyol component. Freon 11 was placed In the Isocyanate component and both Isocyanate and polyol components were changed to meet viscosity considerations. Subsequent aging studies showed the Isocyanate to age similarly to the previously aged (Formulation 2) Isocyanate. The polyol showed virtually no Increase In acid number at any aging temperature over 13 months. Thus, at ambient temperature we would expect a 6-8 year system lifetime on the Isocyanate before a 10% change In analytical properties would dictate a material change-out. The polyol appears to have a greater lifetime, but would probably be replaced at the same time. 

Figure 4. Isothermal aging studies of the thermosetting resins derived from the mixtures of BCB and K-353, in comparison with those derived from pure BCB and K-353.

For comparative isothermal aging studies, all the samples of pure BCB and dlcyanate monomers, as well as their 1 1 molar mixtures, were cured in a single batch at 200-220°C for 40 hours under nitrogen atmosphere. The cured samples of BADCy, METHYLCy, and THIOCy were all transparent and yellow/amber, and their blends with BCB were also transparent but dark red in color. The cured sample of BCB was translucent and yellow. The Tg s (cure) of the thermosets derived from the dlcyanate monomers are relatively high, 224°-261°C as determined by thermomechanical analysis (TMA). There Is an increase of 10-31°C in Tg (cure) values in their blends with BCB. The ITGA results of the cured samples of BCB,... 

Dousma, J. de Bruyn, P.L. (1978) Hydrolysis-precipitation studies of iron solutions. II. Aging studies and the model for precipitation from Fe(III) nitrate solutions. J. Colloid Interface Sci. 64 154-170... 

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