Degradation autocatalytic

Under normal processing conditions at 300—350°C, Tefzel resins are not subject to autocatalytic degradation. However, extended overheating can result in "blow-backs" through extmder feed hopper or barrel front. 

Carbodiimides have been found to stabilize the polyester polyurethanes by blocking the carboxyl group formed when the chain has been broken. This helps prevent further autocatalytic degradation. The action is most pronounced when amines are used as the curative in caprolactone polyurethanes. 

To prove the presence of formaldehyde and NMMO-derived carbenium-iminium ions under Lyocell mixtures was a key issue here, as the occurrence of the latter is critical with regard to autocatalytic degradation and instabilities of Lyocell solutions. Again, trapping methodology was used for this purpose, it served also to investigate the general chemistry of the NMMO-derived carbenium-iminium ions. 

The occurrence of these intramolecular reaction sequences leads to an increased rate of formation of hydroperoxide, which results in a reinforced autocatalytic degradation of the hydrocarbons. 

Rubnov S, Shats I, Levy D et al. (1999b). Autocatalytic degradation and stability of obidoxime. J Pharm Pharmacol, 51, 9-14. 

Delaage and Lazdunski (29) have shown that the binding of a single calcium atom per mole of trypsin accounts for its well known stabilization by this metal. Because trypsin undergoes rapid autocatalytic degradation at alkaline pH, the diisopropylfluorophosphate-treated enzyme, also... 

Autocatalytic degradation n. A type of breakdown in which the initially generated products accelerate the rate at which later degradation proceeds. 

See also artificial weathering, autocatalytic degradation, biodegradation, corro-sion resistance, decomposition, deterioration, dew-cycle weathering test discoloration, pink staining, and xenon-arc aging. 

The autocatalytic degradation kinetics have been evidenced by experimental data (Li, 1999, 2006 Li and Vert, 1999). Fig. 2.1 shows the plot of Ln(Mw) versus degradation time of initially amorphous PLAioo during degradation in a pH 7.4 phosphate buffer at 37°C. An almost linear relationship was obtained. The reaction constant, k, was found to be 0.0584 week It should be noted that the kinetics shown in Eq. (2.2) are valid only prior to the onset of weight loss. 

The internal autocatalytic degradation mechanism well explains the bimodal SEC chromatograms reported in literature and systematically assigned to semicrystallinity even though the studied polymers are intrinsically amorphous (Vert et al., 1984 Makino et al., 1985). It has been confirmed by many authors in their studies on... 

Scheme 13.1 Chemical reaction process indicating hydrolytic degradation of polyesters. Hydrolysis results in the evolution of acidic hy-products, which causes a local reduction in pH and further stimulate hydrolysis, in a process called autocatalytic degradation.

Keywords Degradation mechanism Hydrolytic degradation Autocatalytic degradation Bulk erosion Surface erosion Strength and mass loss profile Critical device dimension Hydrolysis... 

The fuel, coolant, and internal structural materials are chemically compatible such that clad/coolant chemical interaction is avoided with control of coolant chemistry and such that run beyond clad breach due to manufacturing flaws would not lead to autocatalytic degradation - even for the very long duration of refuelling operations. In situ monitoring of coolant and cover gas conditions would be used to confirm normality of conditions. 

It is believed that the decomposition of hydroperoxides exposed to NO and light leads to autocatalytic degradation of PS. 

The mechanism and kinetics of a novel autocatalytic degradation of A-methylmor-pholine A-oxide (70) into morpholine and formaldehyde, induced by carbenium-iminium ions (Mannich intermediates) has been explored. " The study was prompted by the observation that NMMO as an oxidant is often consumed far beyond the stoichiometric ratio, with generation of morpholine and some formaldehyde, and at a rate faster than its reaction with reductant. Decomposition of NMMO was apparently promoted by the combination of products mentioned and could also be induced by dimethyl(methylene)iminium iodide. The proposed mechanism is in Scheme 8. Addition of small amounts of base favour the abstraction of the proton from the A-methyl group but do not prevent carbenium-iminium ion formation however, larger concentrations of base terminate the reaction. The presence of only trace amounts of water is prerequisite for the protonation-deprotonation steps to proceed. 

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