All Title Author
Keywords Abstract

Enthalpy-Entropy Compensation in Polyester Degradation Reactions

DOI: 10.1155/2012/782346

Full-Text   Cite this paper   Add to My Lib


In an earlier work the author had studied the degradation kinetics of polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), and polybutylene terephthalate (PBT) under nonisothermal conditions in air and N2 at heating rates of 5, 10, 15, and 20°C/min. In this paper the kinetic degradation parameters of PET, PTT, and PBT were estimated using the Coats-Redfern method for two different weight loss regions ranging from 2–8% (Zone I) and 8–40% (Zone II). A comparative analysis of the enthalpy-entropy compensation effect for these polyesters in air and N2 is presented. A linear relationship was found to exist between entropy and enthalpy values. The following criteria were applied to establish an enthalpy-entropy compensation effect and to check the presence of an isokinetic temperature: (a) Exner’s plot of log versus log , and (b) Krug et al. linear regression of ΔH versus ΔG. By the use of the latter two methods, varying isokinetic temperatures were obtained. These temperatures were not in the range of the experimental work conducted, indicating that these systems do not display compensation phenomena. 1. Introduction Kinetic studies carried out on similar compounds with a correctly chosen mechanism function ( is the weight fraction of material decomposed at temperature and time ) exhibit a linear relationship between the logarithm of the preexponential factors and activation energies known as the compensation effect [1–5]. Several theories and explanations for such compensation behavior have been put forth [6–8]. In the case of thermal decomposition of solids, the existence of the compensation effect permits certain conclusions concerning the decomposition mechanism and thermal characteristics of the compounds under investigation. The changes of Gibbs energy ( ), enthalpy ( ), and entropy ( ) for the degradation reactions can be obtained by studying the kinetics of the thermal decomposition of solid compounds with nonisothermal heating using the thermogravimetric (TG) curves and a correct algebraic expression of the conversion function, . The reaction mechanism for polymer degradation is a very complex chain mechanism that includes initiation, propagation, and termination reactions. Normally, two types of reaction models, the first order and the second order , are used for the thermal degradation studies of polymers. The author has previously reported [5] the kinetic parameters characterizing the degradation of PET, PTT, and PBT in air and N2 using data from nonisothermal thermogravimetry and the calculation procedure of Coats and Redfern


[1]  R. López-Fonseca, I. Landa, M. A. Gutiérrez-Ortiz, and J. R. González-Velasco, “Non-isothermal analysis of the kinetics of the combustion of carbonaceous materials,” Journal of Thermal Analysis and Calorimetry, vol. 80, no. 1, pp. 65–69, 2005.
[2]  J. Norwisz and T. Musielak, “Compensation law again,” Journal of Thermal Analysis and Calorimetry, vol. 88, no. 3, pp. 751–755, 2007.
[3]  D. Dos Santos Dias, M. S. Crespi, and C. A. Ribeiro, “Non-isothermal decomposition kinetics of the interaction of poly(ethylene terephthalate) with alkyd varnish,” Journal of Thermal Analysis and Calorimetry, vol. 94, no. 2, pp. 539–543, 2008.
[4]  B. Jankovi?, L. Kolar-Ani?, I. Smi?iklas, S. Dimovi?, and D. Arandelovi?, “The non-isothermal thermogravimetric tests of animal bones combustion. Part. I. Kinetic analysis,” Thermochimica Acta, vol. 495, no. 1-2, pp. 129–138, 2009.
[5]  A. Al-Mulla, “Kinetic investigation of compensation effect in degradation of polyesters-1. Under revision in Euro,” Polymer Journal. In press.
[6]  M. E. Brown, D. Dollimore, and A. K. Galwey, “Reactions in the solid state,” in Comprehensive Chemical Kinetics, vol. 22, p. 1, 1980.
[7]  P. D. Garn, “The kinetic compensation effect,” in Proceedings of the 4th International Conference on Thermal Analysis (ICTA'74), I. Buzas, Ed., vol. 1 of Thermal Analysis, pp. 25–31, 1974.
[8]  A. V. Nikolaev, V. A. Logvinenko, V. M. Gorbatchov, and L. I. Myachina, “Thermal Analysis,” in in Proceedings of the 4th International Conference on Thermal Analysis (ICTA'74), vol. 1, p. 205, 1974.
[9]  A. W. Coats and J. P. Redfern, “Kinetic parameters from thermogravimetric data II,” Journal of Polymer Science Part B, pp. 3917–3920, 1965.
[10]  V. Indira and G. Parameswaran, “Thermal decomposition kinetics of Schiff base complexes of copper(II) and palladium(II),” Journal of Thermal Analysis, vol. 32, no. 4, pp. 1151–1162, 1987.
[11]  P. V. Khadikar, “Structure and thermal characterization of tris-thallium(III) glycollate,” Journal of Thermal Analysis, vol. 32, no. 3, pp. 737–748, 1987.
[12]  N. S. Petro and B. S. Girgis, “Dehydration kinetics of hydrated iron oxide from dynamic thermogravimetry,” Journal of Thermal Analysis, vol. 34, no. 1, pp. 37–45, 1988.
[13]  K. N. Ninan, “Kinetics of solid state thermal decomposition reactions,” Journal of Thermal Analysis, vol. 35, no. 4, pp. 1267–1278, 1989.
[14]  J. J. M. Orfao and F. G. Martins, “Kinetic analysis of solid state thermal decomposition reactions,” Thermochimica Acta, vol. 390, pp. 195–201, 2002.
[15]  I. Prigogine and R. Defay, Chemical Thermodynamics, Longmans Green and Co., London, UK, 1954.
[16]  O. F. Shlensky and E. F. Vaynshteyn, “Thermal analysis study of the dynamic decomposition of polymers during rapid heating, limiting temperatures of thermolysis,” Journal of Thermal Analysis and Calorimetry, vol. 35, no. 5, pp. 1477–1482, 1989.
[17]  E. F. Vainstein and G. E. Zaikov, “Role of chain length in degradation process (chain breakdown),” Journal of Applied Polymer Science, vol. 84, no. 10, pp. 1810–1817, 2002.
[18]  N. M. Emanuel and D. G. Knorre, Chemical Kinetics, Vysshaya Shkola, Moscow, russia, 1984.
[19]  M. A. Semiokhin, S. A. Strakhov, and A. N. Osipov, Kinetics of Chemical Reactions, Moscow State University, 1995.
[20]  J. Sestak, Thermochemical Properties of Solids, Academica, Prague, Czech Republic, 1984.
[21]  V. Indira and G. Parameswaran, “Thermal decomposition kinetics of salicylideneaminofluorene complexes of Cobalt(II) and Nickel(II),” Thermochimica Acta, vol. 101, pp. 145–154, 1986.
[22]  L. T. Vlaev, I. G. Markovska, and L. A. Lyubchev, “Non-isothermal kinetics of pyrolysis of rice husk,” Thermochimica Acta, vol. 406, no. 1-2, pp. 1–7, 2003.
[23]  L. H. McAmish and F. J. Johnston, “Sulfur exchange and decomposition kinetics in solid Na2S2O3,” Journal of Inorganic and Nuclear Chemistry, vol. 38, no. 3, pp. 537–540, 1976.
[24]  G. W. Collet and B. Rand, “Thermogravimetric investigation of the pyrolysis of pitch materials. A compensation effect and variation in kinetic parameters with heating rate,” Thermochimica Acta, vol. 41, pp. 153–165, 1980.
[25]  R. K. Agrawal, “On the compensation effect,” Journal of Thermal Analysis, vol. 31, no. 1, pp. 73–86, 1986.
[26]  J. M. Criado, L. A. Perez-Maqueda, and P. E. sanchez-Jimenez, “Dependence of pre-exponential factor on temperature,” Journal of Thermal Analysis and Calorimetry, vol. 82, pp. 671–678, 2005.
[27]  L. Liu and Q. X. Guo, “Isokinetic relationship, isoequilibrium relationship, and enthalpy-entropy compensation,” Chemical Reviews, vol. 101, no. 3, pp. 673–695, 2001.
[28]  O. Exner, “On the enthalpy-entropy-relationship,” Collection of Czechoslovak Chemical Communications, vol. 29, pp. 1094–1113, 1964.
[29]  L. D. Peterson and S. D. Kevan, “Desorption and molecular interactions on surfaces: CO/Cu(001) and Cu(011),” The Journal of Chemical Physics, vol. 94, no. 3, pp. 2281–2293, 1991.
[30]  R. R. Krug, W. G. Hunter, and R. A. Grieger, “Enthalpy-entropy compensation. 2. Separation of the chemical from the statistical effect,” Journal of Physical Chemistry, vol. 80, no. 21, pp. 2341–2351, 1976.


comments powered by Disqus