Degradation: chemical factor

Another problem occurs when some fire retardant formulations ate exposed to elevated temperatures (eg, when used as roof tmsses or as roof sheathing) thermal-induced strength reductions can occur in-service. The thermo-chemical factors were discussed by LeVan and Winandy (26), and a kinetic degrade model was developed (27). The treater should be consulted to obtain appropriate in-service modifications for specific fire retardant treatments. 

B. Chemical Factors Contributing to Aging Many propint systems have built-in defects which contribute to degradation of the polymer system and reduce service life. The poly are ... 

Wolfe NL, Kitchens BE, Macalady DL, et al. 1986. Physical and chemical factors that influence the anaerobic degradation of methyl parathion in sediment systems. Environ Toxicol Chem 5 1019-26. 

The major part of the biosphere is aerobic and consequently priority has been given to the study and assessment of biodegradability under aerobic conditions. Nevertheless, there are environmental compartments that can be permanently (e.g. anaerobic digesters) or temporarily anaerobic (e.g. river sediments and soils) and surfactants do reach these. The majority of surfactants entering the environment is exposed to and degraded under aerobic conditions. This is the predominant mechanism of removal even in cases of absence of wastewater treatment practices (direct discharge) and it is estimated that less than 20% of the total surfactant mass will potentially reach anaerobic environmental compartments [1]. Only in a few cases, however, will the presence of surfactants in these compartments be permanent. The presence of surfactants in anaerobic zones is not exclusively due to the lack of anaerobic degradation. Physico-chemical factors such as adsorption or precipitation play an important role as well as the poor bioavailability of surfactant derivatives (chemical speciation) in these situations. 

The relative rate of recovery also can be estimated. For example, fish populations in a stream are likely to recover much faster from exposure to a degradable chemical than from habitat alterations resulting from stream channelization. It is critical to use knowledge of factors such as the temporal scales of organisms life histories, the availability of adequate stock for recruitment, and the interspecific and trophic dynamics of the populations in evaluating the relative rates of recovery. A fisheries stock or forest might recover in several decades, a benthic infaunal community in years, and a planktonic community in weeks to months. 

Wolfe, N. L., B. E. Kitchens, D. L. Macalady, and T. J. Grundl (1986), Physical and Chemical Factors that Influence the Anaerobic Degradation of Methyl Parathion in Sediment Systems, Environ. Toxicol. Chem. 5, 1019-1026. 

In addition to physical and chemical factors, all degradation reactions require energy in the form of heat, light or radiation. 

In addition to the chemical factors, implants can also be subjected to abrasion or stress under actual use conditions. Some examples would be replacement joints, tendons, and dental appliances. Essentially all polymeric materials show some chemical and/or mechanical degradation under actual physiological conditions, but often polymeric materials survive better than some ceramic or metallic materials. 

The occurrence and abundance of microorganisms in a particular environment is controlled by the complex interaction of nutrients with physical and chemical factors (temperature, redox, pH, etc.) present in the environment, which may evolve over time. The presence and success of a specific organism or consortia of microorganisms responsible for degrading hydrocarbons in a contaminated subsurface ecosystem depends on both nutrient requirements and tolerance for the range of physical and chemical conditions. 

The majority of investigations on the degradation of cellulose acetate have been conducted on photographic film (cellulose triacetate) rather than moulded material. like cellulose nitrate, cellulose acetate (CA) is deteriorated by both physical and chemical factors and the physical cause of degradation is plasticizer loss. Three-dimensional objects moulded from cellulose acetate comprise 20-40 per cent by weight plasticizer. Typical plasticizers include triphenyl... 

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