Accelerated: ageing

Many cellular plastic products are available with different types of protective faces, including composite metal and plastic foils, fiber-reinforced plastic skins, and other coatings. These reduce but do not eliminate the rate of aging. For optimum performance, such membranes must be totally adhered to the foam, and other imperfections such as wrinkles, cuts, holes, and unprotected edges should be avoided because they all contribute to accelerated aging. 

Liquid Fabric Softeners. The principal functions of fabric softeners are to minimize the problem of static electricity and to keep fabrics soft (see Antistatic agents). In these laundry additives, the fragrance must reinforce the sense of softness that is the desired result of their use. Most fabric softeners have a pH of about 3.5, which limits the materials that can be used in the fragrances. For example, acetals cannot be used because they break down and cause malodor problems in addition, there is the likelihood of discoloration from Schiff bases, oakmoss extracts, and some specialty chemicals. Testing of fragrance materials in product bases should take place under accelerated aging conditions (eg, 40°C in plastic bottles) to check for odor stabiUty and discoloration. 

Types of Latex Compounds. For comparison with dry-mbber compounds, some examples of various latex compounds and the physical properties of their vulcanizates are given in Table 23. Recipes of natural mbber latex compounds, including one without antioxidant, and data on tensile strength and elongation of sheets made from those, both before and after accelerated aging, are also Hsted. The effects of curing ingredients, accelerator, and antioxidant are also Hsted. Table 24 also includes similar data for an SBR latex compound. A phenoHc antioxidant was used in all cases. 

Ackroyd, M. L., A Survey of Accelerated Ageing Techniques for Solderable Substrates, Int. Tin Research Inst., London, Publication No. 531 (1976)... 

The above tests for characterising coating properties necessarily continue to involve a certain amount of empiricism. The intelligent use of these tests, however, has shown that wide variations of physical and electrochemical characteristics of coatings as a function of composition may be obtained, and further, that significant changes in these characteristics, that can be measured before the usual evidence of failure appears, occur upon natural and accelerated ageing. 

The accelerated aging test should take into account the associated materials as well as the atmosphere that will be encountered in actual use, since they are also controlling factors. It is helpful to include materials of known performance against which to rate the new material, since this allows a check of controlling factors and further validates the extrapolation. Thus, existing data from long term tests may be of considerable value. 

The influence of ambient aging at 70°F and accelerated aging at 160°F on the stress-strain behavior of carboxy-terminated polybutadiene, polybutadiene-acrylic acid, polybutadiene-acrylic acid-acrylonitrile, and hydroxy-terminated polybutadiene composite propints is shown in Figures 10 and 11. The elastomers and curative agents for these formulations are listed below... 

Report 84 Rheology and its Role in Plastics Processing, P. Prentice, The Nottingham Trent University. Report 110 Long-Term and Accelerated Ageing Tests on Rubbers, R.P. Brown, M.J. Forrest and G. Soulagnet, Rapra Technology Ltd. 

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... 

Baldwin, J.M. Accelerated Aging of Tires, Part I. Presented at a meeting of the Rubber Division, American Chemical Society. 2003. Cleveland, OH. 

Thomas, R. E. Gaines, B. G. "Methodology for Designing Accelerated Aging Tests for Predicting Life of Photovoltaic Arrays" Department of Energy/National Bureau of Standards Workshop on Stability of Thin Film Solar Cells and Materials, Washington, D.C., May 1-3, 1978. 

The influence of pH, Emulsifier, and Accelerated Ageing upon Preservative Requirements of O/W Emulsions, by Gene Jacobs, M.S. at all Soc. Cosmet. Chem., 26,105-117 (February, 1975)... 

Accelerated aging and crystal transformation rates have also been traced to high residual moisture content. Ando et al. studied the effect of moisture content on the crystallization of anhydrous theophylline in tablets [9]. Their results also indicate that anhydrous materials convert to hydrates at high levels of relative humidity. In addition, if hygroscopic materials (e.g., polyethylene glycol 6000) are also contained in the formulation, needle-like crystals form at the tablet surface and significantly reduce the release rate of the theophylline. 

These findings clearly illustrate how the results of so-called "accelerated-aging" tests can be affected by the high temperatures in ordinary xenon- and carbon-arc equipment and can, therefore, lead to erroneous conclusions regarding the photochemical behavior of materials at near-normal temperatures (23). 

For the copolymers, the stabiliser is less affected during accelerated ageing due to the presence of the comonomer units. 

M. Regert, S. Colinart, L. Degrand, O. Decavallas, Chemical alteration and use of beeswax through time accelerated ageing tests and analysis of archaeological samples from various environmental contexts, Archaeometry, 43, 549 569 (2001). 

R.L. Feller, Accelerated Aging, Photochemical and Thermal Aspects, The Getty Conservation Institute, Los Angeles, 1994. 

Figure 7.2 Summary of the main chemical transformations undergone by beeswax during accelerated ageing tests. Reprinted from Archaeometry, 2001, 43, 549 569, Regert, Col inart, Degrand and Decavallas, with permission from Wiley Blackwell...

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