Weathering polymeric materials effects

IR spectroscopy can be used to characterise not only different rubbers, but also to understand the structural changes due to the chemical modification of the rubbers. The chemical methods normally used to modify rubbers include hydrogenation, halogenation, hydrosilylation, phosphonylation and sulfonation. The effects of oxidation, weathering and radiation on the polymer structure can be studied with the help of infrared spectroscopy. Formation of ionic polymers and ionomeric polyblends behaving as thermoplastic elastomers can be followed by this method. Infrared spectroscopy in conjunction with other techniques is an important tool to characterise polymeric materials. 

The effects of temperature on the aging behavior of polymeric materials became especially clear when materials for the interior equipment of motor vehicles were tested. Since these are often exposed to solar radiation at high temperatures, the test conditions for artificial weathering must be selected accordingly. A specific black panel temperature is set in the weathering devices. 

M. B. Neiman, Aging and Stabilization of Polymers, Consultants Bureau, New York, 1965. S. H. Pinner, Weathering and Degradation of Plastics, Columbine Press, Manchester, 1966. J. Voigt, Die Stabilisierung der Kunststoffe gegen Ucht und Wdrme, Springer, Berlin, 1967. D. V. Rosato and R. T. Schwartz, Environmental Effects on Polymeric Materials, Interscience, New York, 1968. 

Exposure to the outdoor environment affects not only the polymeric material itself but also other components within the matrix, such as dyes, pigments, processing additives, and stabilizers. Complex interactions of the combination of weather factors with the polymer and its components result in irreversible changes in the chemical structures and physical properties in a direction that generally changes both the appearance and mechanical properties and reduces the useful life of the material. Most organic polymeric materials require the use of one or more types of stabilizers for protection against the effects of the environment in order... 

WEATHER FACTORS AND THEIR EFFECTS ON POLYMERIC MATERIALS... 

Weather Factors and Their Effect on Polymeric Materials... 

Laboratory accelerated weathering devices have been used for more than 80 years with increasing importance concomitant with the development of more weather-able materials and the need to determine in a short time the effects of natural exposures over prolonged periods. The importance of these devices lies in their ability to accelerate the weathering processes imder controlled and reproducible conditions. They are particularly useful in research and development of new polymeric formulations. They are also used for quality control and specification testing. However, their application to prediction of service life under use conditions is still under development (see section on Laboratory Accelerated Versus Natural Weathering). 

Effect of SPD of the Radiation Source on Weathering. The wavelengths responsible for degradation of a specific polymeric material vary with the SPD of the radiation source. Differences between the laboratory accelerated test source and the natural source in the wavelengths that degrade a material, which are identified by the activation spectra (see section on Spectral Effects of Solar Radiation Activation Spectra), can have the following consequences (53) ... 

Laboratory accelerated weathering tests have played an important role in development of polymeric materials with highly improved weatherability. However, since all stresses present in an outdoor exposure cannot be simulated in a laboratory accelerated test, the latter cannot replace natural exposure. It is a complimentary technique, the usefulness of which largely depends on how closely it reproduces the chemistry and weathering effects caused by the slower outdoor exposures. Thus, correlation is a fundamental issue which must be considered when selecting a laboratory accelerated weathering method. It depends on reasonably representing... 

Acceleration factors are material dependent and can be significantly different for each material and for different formulations of the same material. Therefore, it is erroneous to attempt to establish a single acceleration factor for a laboratory accelerated test to be used to predict lifetimes under natural weather conditions for a variety of materials and formulations. Because of the complex nature of the interaction of the combined weather stresses with a material, there is presently no simple way to estimate the acceleration factor for a material. Increase in irradiance cannot be equated with acceleration of degradation. For most polymeric materials, the rate of degradation is not simply a linear function of the level of irradiance. Also, it does not take into account the effect of temperature, moisture, and other weather factors. Thus, there is no substitute for determining the acceleration factor for a given material experimentally. 

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