Catalyzed degradation mechanism

Surface-catalyzed degradation of pesticides has been examined in the context of research on contaminant-clay interactions. Such interactions were observed initially when clay minerals were used as carriers and diluents in the crop protection industry (Fowker et al. 1960). Later specific studies on the persistence of potential organic contaminants in the subsurface defined the mechanism of clay-induced transformation of organophosphate insecticides (Saltzman et al. 1974 Mingelgrin and Saltzman 1977) and s-triazine herbicides (Brown and White 1969). In both cases, contaminant degradation was attributed to the surface acidity of clay minerals, controlled by the hydration status of the system. 

From the base-catalyzed degradation of D-fructose (pH 8.0), Shaw and coworkers147 identified 18 compounds, none of which was (a) isomeric with the starting material, or (b) a simple dehydration product. Among the products, the hydroxy-2-butanones and 1-hydroxy-2-propanone (acetol) were shown to participate in forming the carbo-cyclic products identified, but the mechanism of their formation was not elucidated. Several furan derivatives were isolated, but no lactic acid was isolated. In a similar study but with weak acid,41 most of the products were formed by a combination of enolization and dehydration steps, with little fragmentation. 

Levulinic Acid. Levulinic acid is formed by the acid catalyzed degradation of hexose sugars via the intermediacy of hydroxymethylfurfural (145). Although its formation was reported as early as 1836 (143), the mechanism of its formation has been studied at least as recently as 1985 (147). 

Thus, the observed biodegradation of PHB showed coexistence of two different degradation mechanisms in hydrolysis in the polymer enzymatically or nonenzymatically catalyzed degradation. Although nonenzymati-cal catalysis occurred randomly in homopolymer, indicated by loss rate in PHB, at some point in a time, a critical molecular weight is reached whereupon enzyme-catalyzed hydrolysis accelerated degradation at the surface because easier enzyme/polymer interaction becomes possible. 

The history of CNP began over 60 years ago, when Rmby (1952) reported for the first time that colloidal suspensions of cellulose can be obtained by controlled sulfuric-acid-catalyzed degradation of cellulose fibers. Currendy, CNP (nanowhiskers) are prepared by hydrolysis of cellulose samples with 55—65 wt% sulfuric or 25—30 wt% hydrochloric acids at moderate temperatures (40—60 °C) and subsequent mechanical or ultrasound disintegration of the hydrolyzed cellulose in aqueous medium (Habibi et al., 2010 Hubbe et al., 2008 loelovich, 2014a Li and... 

To characterize the polymerization behavior of FA and to investigate how the presence of MMT influences this polymerization, FTIR spectra were collected before and during the resiniflcation process. The dispersion of the MMT in the PFA matrix is shown both directly and indirectly. The direct evidence consists of the XRD patterns of the FA-MMT suspension, which was used to monitor the process of intercalation and exfoliation of the MMT at various stages of resinifica-tion. The dispersion is indirectly evidenced in increased thermal stability of the MMT-PFA nanocomposite, as measured by TGA. The thermal stability is discussed and compared to the pure polymer and to the CW-PFA nanocomposites. In addition, the important differences between oxidative and nonoxidative degradation of the NaMMT-PFA nanocomposite is discussed, and a mechanism is proposed to explain the difference in terms of acid-catalyzed degradation. 

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