Temperature effect degradation rate

Within the standard deviations of the rate constants, k, (approximately 10%), it can be seen that 1) the rate constants for the changes in tensile properties are different for each property at a constant temperature 2) degradation rates increase with temperature at different rates for each property and, 3) Parylene-C has no effect on silk tensile property degradation rates. 

Results for the sodium salt were interpreted as indicating a sequential two step degradation. The trihydrate showed first order kinetics at 37 and 50 C but at the higher temperatures its degradation rate was consistent with formation of a solid plus a gas. Rate constants were derived which were extrapolated to 20°C and used to calculate the time for 10% degradation as 1.25 and 3.2 years for the sodium salt and trihydrate respectively. However, these authors made no mention of the possible effect of water content which is well known to be important for the solid state stability of all penicillins. 

From Equation (6.11), it can be seen that reaction rates increase exponentially with the ERH. The values for B typically range from 0 to 0.09. This means that in going from dry conditions (10% RH) to moist conditions (75% RH) at a fixed temperature, the degradation rate will range from equal (B = 0) to 347 times faster (B = 0.09) at the damp conditions compared to the dry conditions. To put another perspective on this, in the latter case, a pharmaceutical product with a shelf-life of only 1 week at 75% RH would increase to 6.7 years with effective desiecant. 

The oxygen effect is severe, particularly at low temperatures. The degradation rate can be multiplied by a factor of as large as six for an oxygen concentration of 90 ppm at 240 °C it is multiplied by 1.2 at 280 °C and 2 at 240 °C for a concentration of 20 ppm. The water content of the carrier gas is not as critical at least for ethylene-propylene copolymers and does not appreciably affect the thermal degradation. 

Chul Kim, U. R. and van Rooyen, D., Strain rate and temperature effects on the stress corrosion cracking of Inconel 600 steam generator tubing in the (PWR) primary water conditions , Proc. 2nd Int. Conf. on Environmental Degradation of Materials in Nuclear Power Systems-VIalet Reactors, Monterey, USA, 9-12 Sept. 1985, American Nuclear Society, pp. 448-55 (1986)... 

Chemical Effects of Temperature. Changes in temperature also affect the chemical properties of materials. The rate at which most chemical reactions take place, for example, is roughly doubled when the temperature of the reactants increases by 10°C. Consequently, any increase in temperature intensifies the rate at which most materials react with substances in the environment such as oxygen, water, and atmospheric and soil pollutants, and hastens their chemical degradation. 

Table 11.5 shows the flow activation energies, a, for PET, PTT and PBT [68], PTT has a higher a compared to PET but similar to that of PBT. The change in its melt viscosity is therefore less sensitive to temperatures changes than PET. However, due to the higher degradation rate, increased melt processing temperatures can have deleterious effect on the melt viscosity and IV. 

A similar combination of ultrasound and photocatalysis has also been reported to destroy 2,4,6-trichlorophenol in aqueous solution [39]. An ultrasonic probe (22 kHz) with a uv light source (15 W) was used to examine the effect of changing such operating conditions as ultrasonic intensity, reaction temperature and uv transmission. The experiments involved using 2,4,6-trichlorophenol (100 ppm) and TiOj (0.1 g L ) and showed that the degradation rates increased with the temperature of the solution. The cumulative effect was more pronounced at lower ultrasonic intensities with little additional benefit derived at increased ultrasonic powers. 

The effect of temperature on the rate of degradation can be seen by inspecting the degradation plots in Figures 5 and 13 where Weedone and Treflan had been respiked. The respiking... 

The influence of temperature on the degradation rate appears to be most important, and this factor also interacts with the two others. Without discussing all the details, the results show that a temperature increase is generally favorable, which is certainly the consequence of a simultaneous increase of the rate of the secondary thermal reactions. This effect is logically more pronounced at high DOC0. 

Temperature will affect the degradation rate of different organic pollutants. Weir et al. (1987) reported that benzene and hydrogen peroxide are insensitive to temperature because photochemically induced reactions often have low activation energies. Koubek (1975) stated that temperature has little effect on the oxidation of refractory organics however, Sundstrom et al. (1986) observed that the decomposition rates of some halogenated aliphatics increased with temperature. 

Takahashi et al. (1994) showed the pH effect on the rate constant for 2-CP and 4-CP. Taking an approximate value for pH vs. k, Table 14.13 can be obtained. Figure 14.18 indicates that as pH increased, the degradation rate of 2- and 4-CP increased. In the temperature range from 287 to 318 K, the reaction temperature will barely have any effect on the observed degradation... 

Using the information provided in Tables 1 and 2, it is straightforward to calculate the effect of temperature on the degradation rate to enable... 

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