Kinetics of thermal degradation

Random thermal degradation can usually be described as a first-order reaction (loss of weight as a parameter) if the decomposition products are volatile. For the mathematical treatment we refer to Van Krevelen et al. (1951), Reich (1963,1967) and Broido (1969). 

Chain depolymerisation has been extensively studied (Simha and Wall, 1952). The two factors that are important for the course of the depolymerisation are  

Also this type of degradation can be described by an overall quasi-first-order reaction, but the kinetic scheme may be complicated. Besides the rate constant two other parameters can be obtained by kinetic analysis  

For polyethylene Akin 0 (no monomer produced) for poly(methyl methacrylate) 

Arnold C, Stability of High -Temperature Polymers , J Polym Sci Macromol Rev, 14 (1979) 265-378. 

A valuable approach for measuring thermal degradation kinetic parameters is controlled-transformation-rate thermal analysis (CRTA) - a stepwise isothermal analysis and quasi-isothermal and quasi-isobaric method. In this method, some parameters follow a predetermined programme as functions of time, this being achieved by adjusting the sample temperature. This technique maintains a constant reaction rate, and controls the pressure of the evolved species in the reaction environment. CRTA is, therefore, characterised by the fact that it does not reqnire the predetermined temperature programmes that are indispensable for TG. This method eliminates the nnderestimation and/or overestimation of kinetic effects, which may resnlt from an incomplete understanding of the kinetics of the solid-state reactions normally associated with non-isothermal methods. 

In particnlar, CRTA gives improved sensitivity and resolution of the thermal analysis curve since imiform conditions are maintained throughout the sample by means of an 

Another study addressed the uncertainty of extracting the kinetic parameters solely from thermograms [a.9, a.47]. Thus, modification of the Ozawa method [a.49] was introduced to tackle complex TG curves, since the traditional approach of the integral method has major limitations in extracting reliable kinetic parameters. The method implemented in extracting the multiple decomposition kinetics was based on subtraction of the mass of a specific event from the total mass loss, and then addressed the following event on the TG curve. For PMMA, the results demonstrated that decomposition could be described in terms of both depolymerisation and vaporisation, while for polytetrahydrofuran (PTHF) it can be described in terms of vaporisation only. 

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X.-G. Li, M.-R. Huang, and H. Bai, Kinetics of thermal degradation of liquid-crystalUne aromatic poXymets, Die Angewandte Makromolekulare Chemie, 256, 9 (1998). 

Friedman, H.L. Kinetic of thermal degradation of char forming plastics liom thermogravimetry-application of phenoUc plastics. J. Polym. ScL C6, 183-195 (1965)... 

Friedman, H.L. (1964). Kinetics of thermal degradation of char-forming plastics from thermogravimetry. Application to phenolic plastic. Journal of Polymer Science Part C, Vol. 6, pp. 183-195 ISSN 0449-2994... 

The kinetics of thermal degradation have generally been studied using isothermal and nonisothermal methods. In earlier literature, isothermal methods were mostly employed for the study of the kinetics of solid-state reactions. During the past three decades, however, nonisothermal methods, for example, the Doyle method [17, 18], Freeman and Carroll method [19], Coats and Redfem method [24], Ozawa method [20], Flynn and Wall method [21, 22], Friedman method [25], and Kissinger method [26], have received more attention. 

Persenaire O., Alexandre M., Degee E, Dubois E Mechanisms and kinetics of thermal degradation of poly(e-caprolactone). Biomacromolecules 2 (2001) 288. 

Guinesi L.S., da R6z A.L., Corradini E., Mattoso L.H.C., de Teixeira E., da S. Curvelo A.A. Kinetics of thermal degradation applied to starches from different botanical origins by non-iso-thermal procedures, Thermochim. Acta 447 (2006) 190. 

Hamciuc Corneliu, Vlad-Bubulac Tachita, Petreus Oana, and Lisa Gabriela. Kinetics of thermal degradation in non-isothermal conditions of some phosphorus-containing polyesters and polyesterimides. Eur. Polym. J. 43 no. 3 (2007) 980—988. 

Burnham, A.K. and Weese, R.K. (2005) Kinetics of thermal degradation of explosive binders Viton A, Estane and Kel-F. Thermochim. Acta, 426, 85-92. 

H. L. Friedman, Kinetics of Thermal Degradation of Char-Forming Plastics from Thermogravimetry. Apphcation to a Phenolic Plastic, J. Polymer Sci. C6, 183-195 (1964). 

The thermal cure characteristics, kinetics of thermal degradation and pyrolysis of four different addition cured phenolic resins were investigated using various techniques, including DSC, DMA, FTIR spectroscopy, TGA and X-ray diffraction. Resins investigated were propargyl ether resins and phenyl azo-, phenyl ethynyl-andmaleimide-functional resins. A comparison of the data obtained for all the phenolic resins was made as a function of molecular structure. 12 refs. 

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