Degradation curves

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Fig. 50. Yield for chain scission as a function of strain rate for different fractions of polycarbonate (PC) in benzyl alcohol/dioxan (90 10 v.v) at 20 °C. A normal PC with Mp = 417000 B normal PC with Mp = 321000 C normal PC with Mp = 256000 D PC with weak bonds, Mp = 217000 Mp molecular weight at peak maximum sc critical strain rate for chain scission (extrapolated from the linear portion of the degradation curve)...

As shown in Fig. 3, TGA experiments were carried out to evaluate the stability of ferrierite. Ferrierite was used 5 times without regeneration. Until the 3rd run, ferrierite showed almost similar degradation curves. The 4th and the 5th runs resulted in a little shift to hi er temperatures. This implies that ferrierite may have high catalytic stability for the PP... 

In modern systems, the applied electric power is increased over time to compensate for the decreasing intensity. However, this adjustment uses the average degradation curve of a lamp as a reference, not the actual values of the lamps mounted in a particular sunbed. A radiation sensor could be used to control an active circuit that regulates the intensity of radiation. 

Fig. 5.1.18. Degradation curve of C10-AG and formation of metabolite C4-glucamide acid.

If the data shows departure from the accepted model it is a sure sign that even modest predictions are likely to be invalid. Any sign or expectation of a transition or discontinuity in the form of the degradation curve (e.g., a knee ) is a barrier to extrapolation, unless there is knowledge that justifies it. Generally, extrapolation should not be made across a material transition unless it can be demonstrated, not assumed, that the process and property being studied is not affected by the transition. 

The shapes of the degradation curves (Fig. 5.31b), and the increase in Mn can be rationalised in terms of a higher probability and more rapid degradation of the larger R.M.M. sample (peak B, Fig. 5.31a) giving rise to molecules with ahigher R.M.M. than... 

Figure 4.10 CTT diagram showing gelation, vitrification, and degradation curves. 

Usually, experimental DSC curves obtained at a constant heating rate are processed to obtain the polymerization kinetics (the inverse problem). In this case it is advisable to plot the experimental trajectories in the CTT diagram and to use only the portions of the trajectories that do not intercept the vitrification or degradation curves. 

Sequential Processes. In many cases (anhydride cured-epoxies, amine-cured epoxies, etc.), thermal degradation curves, for instance gravimetric ones, exhibit two distinct stages (Lehuy et al., 1991). The first one corresponds to a relatively fast, pseudo-first-order process, whereas the sec-... 

Figure 6. Degradation curves of 2,6-difiuorobenzamide and 2,6-difluorobenzoic acid after incubation of clay hydrosoil with 3H-2,6-difluorobenzamide. Recovery in percentage of applied dose.

The degradation curves of several kinds of electrodes in lOOmL (lOOmgL-1) phenol solution are shown in Fig. 14.4. Compared with other electrodes, higher catalytic activity was observed for the electrodes obtained by electrodeposition with a pyrolysis temperature of 550°C. 

Figure 2C compares three kraft pulps. Two bleached pine kraft pulps, SKA and BPC, show a relative crossover in their degradation curves and a bleached birch kraft pulp, BBC, shows an initial loss of weight at a lower temperature but has about the same residue as the other two pulps. 

Figure 2D compares a number of sulfite pulps. Two of them, an unbleached spruce sulfite, USS, and an unbleached mixed hardwood sulfite, HS, have remarkably similar degradation curves but show different final residues. A bleached neutral sulfite semichemical pulp, FB, and an unbleached semichemical birch sulfite, SBS, have similar and much steeper initial degradation curves than the other two pulps. The semichemical birch sulfite pulp, SBS, has a degradation curve which crosses over those of the other three pulps shown in Figure 2D. 

Usually the determination of the amount of drug substance at four or more different time points of the degradation experiment is necessary for the determination of the reaction order and construction of the degradation curve, which can then be used to determine the rate constant at a particular temperature. 

A program for simulating runs makes it possible to study the expected behavior of single samples and their mixtures for arbitrarily assigned values of the parameters of the kinetic model. The parameters which are primarily responsible for the shapes of the rate vs time degradation curves are k-, the fraction of chains started per sec, and tne fraction of a started chain unzipping per sec. 

Crystallinity of never-melted PTFE is in the range of 92-98%, consistent with an unbranched chain structure while FEP, a copolymer of tetrafluoroethylene and hexafluoropropylene, has an as-polymerized crystallinity of 40-50%. In FEP, the pendent CF3 group is bonded to a tertiary carbon that is less thermally stable than primary and secondary carbon atoms. Degradation curves (Fig. 3) indicate degradation onset temperatures of 300°C for FEP (0.02% weight loss) and 425°C for PTFE (0.03%i weight loss). 

The sample storage time should be determined so that every degradation can be adequately characterized (i.e., at a sufficient frequency to determine with reasonable confidence the nature of the degradation curve). A stability test may be performed at 3-month intervals during the first year, 6-month intervals during the second year, and yearly thereafter. 

The normal and acceptable statistical approach for analyzing quantitative properties that change over time is to calculate the time it takes for the 95% one-sided confidence limit for the mean degradation curve to intersect the acceptable specification limit. If the data show that batch-to-batch variability is small, it may be worthwhile to combine the data into one overall estimate. This can be done by first applying the appropriate statistical tests to the slopes of the regression lines and zero time intercepts for the individual batches. If the data from the individual batches cannot be combined, the shortest time interval any batch remains within acceptable limits may determine the overall re-test period. 

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