Ozawa method determination

Figure 4.5 Determination of from Ozawa method (experimental data and fitted straight lines for different conversion degrees of decomposition) [12]. (With permission from Elsevier.)...

DMA, the kinetic parameters of the glass transition can be determined by multicurves methods such as the Ozawa method (see Chapter 4). While only one heating rate is available here, the modified Coats-Redfern method is used [13, 14] as demonstrated in the following. Integration of Eq. (2.12) leads to ... 

Determination of Apparent Activation Energy by Ozawa Method (Ozawa-Flynn-Wall Method) [9]... 

This method has an extra advantage over the modifed Ozawa method employed in the literature for the determination of activation energy of crystallization that the intercept of In (jS/ Tp) against 1000/ Tp gives the value of pre-exponential... 

The Flynn-Wall-Ozawa method [142, 143] has been used to determine the activation energy from dynamic tests by plotting the logarithm of heating rate as a function of the inverse of the temperature, at different conversions. Being integrated with the initial condition of a = 0 at r= To, the equation (24) can be arranged as follows ... 

Workers in India [18] have also blended both waste plastic and waste rubber. In this instance they took scrap computer plastics (e.g., acrylonitrile-butadiene-styrene and styrene-acrylonitrile) and blended them with waste NBR powder. The blends were analysed by TGA in a nitrogen atmosphere and their activation energies of decomposition determined using Friedman and Flynn-Wall-Ozawa methods. 

For single reactions with uncomplicated kinetics and with availability of a truly representative sample, the DSC can be used with different scan speeds (temperature/time) to determine kinetic constants in the Arrhenius equation. This method, proposed by Ozawa [83] has been accepted by the ASTM Method E698. After determining kinetic constants by this method, it is desirable to check the constants by running an isothermal DSC aging test for a period of time followed by a DSC scan to see if the predicted fraction decomposition... 

Iwaski, I., S. Utsumi, K. Hagino, and T. Ozawa, A New Spectropho-tometric Method for the Determination of Small Amounts of Chloride Using the Mercuiy Thiocyanate Method, Bull. Chem. Soc. Jpn., 29, 860-864 (1956). 

T Gomyo, M Ozawa, S Kobayashi. Analytical method for determining the total content of methyl benzimidazole carbamate fungicides in water by column switching liquid chromatography mass spectrometry. Anal Sci 8 687-690, 1992. 

The random degradation and reaction kinetics of high-molecular weight polymers can be determined by an approximate integral method (Ozawa 1965, Hirose and Hatakeyama 1986). Generally, the fractional weight, W, of a reacting material can be expressed as a function of the fraction of a structural quantity which is represented by x, i.e.,... 

Ozawa H, Tsukioka T. Gas chromatographic separation and determination of chloroacetic acids in water by difluoroanilide derivatization method. Analyst 1990 115 1343-1347. 

DSC ts widely used to predict the potential explosive hazard of materials in an ASTM method. The basis of the method, developed by Committee E 27, is the determination of the reaction kinetics using Ozawa s procedure (206). Ozawa employs a ploi of the logarithm of the DSC heating rate versus the peak maxima temperatures E. Z, k. and t can be calculated from this plot. The ASTM method has been used to evaluate the thermal stability of irinitrotoluene (207). nitrocellulose (208). and many other substances. 

For lifetime determination, the jump method is described by Flynn JH, Dickens B (1976) Thermochim Acta 15 1-16. The isoconversion method, by Ozawa T (1965) Bull Chem Soc, Japan 38 1881-1886. 

Based on Kissinger s method, the computation of the apparent activation energy is found to be 224 kJ/mol and 202 kJ/mol in nitrogen and air environments, respectively, for polyimide. The activation energies determined from the Ozawa and Kissinger methods are comparable. 

Usually the TG curve should be determined at a slow heating rate, and E was estimated for low conversion (say mass loss 5%) by using the Ozawa-Flynn-Wall method. If we assume t( = 20 000h, Tf equals the thermal index of the material. With the use of higher temperatures, the shorter is the lifetime, as shown in Figure 5.1. 

In the non-isothermal method, the values of the Avrami parameter, n, are determined from the Ozawa equation (Qelikbilek et al., 2011 Ozawa, 1971 Prasad Varma, 2005) ... 

In general, such differential methods of the kinetic data determination are very sensitive to the quality of experimental data, especially to the determination of instantaneous rates, a and the related differences, A. For this reason, and in view of the inaccuracy of this determination in the initial and final reaction stages, they are not so extensively used. However, on rearrangement and upon assuming constant values of a and/or a the following ratio is found useful for another direct estimation of E from several parallel measurements by the so-called iso-conversional and iso-rate cross sections, as introduced (and often labeled) by Flynn and Ozawa [503,504] (a = const Alna/A(l/T) = E/R = Ain Z f(oc)/A In (1/T) (<= a = const). 

Similarly, as in the case of the Avrami analysis of isothermal crystallization, the discrepancies between experimentally determined curves and predictions of the Ozawa equation originate mainly from oversimplified assumptions concerning the polymer crystallization. Those discrepancies inspired some authors to search for other equations enabling a better description and analysis of nonisothermal crystallization. For instance, the classic isothermal Avrami analysis based on Equation (7.5) with E expressed by Equation (7.10) was applied to nonisothermal crystallization [65, 66]. Such an approach has no theoretical justification. Even if a straight line Avrami plot is obtained, the parameters k and n are, at best, two adjustable parameters without a clear physical meaning. The Jeziomy method [67] deserves similar criticism. Jeziomy proposed using Equation (7.5) and Equation (7.10) and characterizing the process with the parameter kc defined as ... 

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