Primary degradation

In general, stabilizers function by reaction with proplnt decompn products. A number of methods have been described and a preliminary evaluation of these methods was conducted by several labs under a cooperative program. Based on results from these screening tests, the PicArsn spec tropho tome trie methods for available stabilizer and primary degradation products were selected for further study. The initial phase of this program was an attempt to standardize the necessary spectrophotometric factors. Significant differences with regard to the factors obtained... 

Conley showed that die primary degradation route for resole networks is oxidation regardless of the atmosphere.6 By contrast, Morterra and Low found tiiat... 

Marches JR, SA Owen, GF White, WA House, NJ Russell (1994) SDS-degrading bacteria attach to riverine sediment in response to the surfactant or its primary degradation product dodecan-l-ol. Microbiology (UK) 140 2999-3006. 

Detection, identification and quantification of these compounds in aqueous solutions, even in the form of matrix-free standards, present the analyst with considerable challenges. Even today, the standardised analysis of surfactants is not performed by substance-specific methods, but by sum parameter analysis on spectrophotometric and titrimetric bases. These substance-class-specific determination methods are not only very insensitive, but also very unspecific and therefore can be influenced by interference from other compounds of similar structure. Additionally, these determination methods also often fail to provide information regarding primary degradation products, including those with only marginal modifications in the molecule, and strongly modified metabolites. 

The determination of bismuth activity as an indicator of non-ionic surfactants also suffers from interference in environmental samples. Substance group specific methods also failed to detect different types of fluorine-containing anionic, cationic and non-ionic surfactants. Already marginal modifications in the precursor surfactant due to primary degradation or advanced metabolisation implicated their lack of detection [45]. 

To reduce the potential risk of environmentally harmful surfactants, requirements of a minimum primary degradation amounting to 80% for anionic and non-ionic surfactants was stipulated as far back as 1977 [4]. However, within this early regulation no restraints were included regarding cationic or amphoteric surfactants as these did not hold a significant market share when the laws came into force. 

The conversion rates of individual components in a commercial LAS mixture are dependent on the molecular structure. For example, the length of the alkyl chain is positively correlated with the primary degradation rate, and as such, isomers with the phenyl substituted at central positions are degraded more slowly than other isomers [79,80]. Both effects are a direct consequence of the enzymatic attack on the hydrophobic moiety. The relation between surfactant structure and the biodegradation has been termed as Swisher s distance principle which, in summary, describes that an increased distance between... 

Moisture levels are also expected to influence the degradation process of the silicone surfactants. The degradation of surfactants on soils and peat is known to increase with soil moisture content [61], and this will also be expected for the primary degradation (hydrolysis) of silicone surfactants. Further studies of these compounds under different... 

The available data summarised in this review support previous conclusions that trisiloxane silicone surfactants should be relatively benign in the natural environment. Primary degradation is rapid and ultimate degradation to naturally occurring compounds, i.e. C02, H20 and Si(OH)4, is indicated, though not yet demonstrated unequivocally. 

Static die-away tests were performed by Potter et al. with an A9PEO7 24 mixture in water from a vertically well-mixed estuary in Florida [36]. Lag times of 0—12 days were observed, and after 4—24 days, primary degradation was complete. These rates are similar to those reported by Kvestak and Ahel [6]. It is likely that the microorganisms in these experiments were pre-acclimated to biodegrade nonionic surfactants, as a municipal sewage treatment plant discharge is present a few kilometres upstream. 

This is the primary degradation process accompanying processing of the polymer. The early stage of the dehydrochlorination process is uncomplicated by interfering processes. The only product observed by evolved gas analysis is hydrogen chloride (scheme 1). The sample... 

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