Enthalpy-Entropy Compensation in Polyester Degradation Reactions

Abstract

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 N 2 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 CoatsRedfern 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 N 2 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 k 3T1 versus log k 3T2 , 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.

Rate Theory and Relaxation Map Analysis of Iodine-Doped Poly(Ethyl Methacrylate) composite films using Thermally Stimulated Depolarization Current-Thermal Sampling (TSDC-TS) Technique

“…This linear relation between S and H is result of changes in the structure of the material towards the equilibrium state with increasing the temperature. This behaviour is fully consistent with what has already been published for many polymeric materials [45][46]. The compensation temperature (Tc) has been calculated again by knowing the slope of S-H relationship according to the following empirical formula [43],…”

Characterization the Thermal Degradation E Kinetic of Unsaturated Polyester and Polyester/Silica Nanoparticles Composites by TGA and DSC Analysis

“…Figure 9 shows there is a linear relationship between activation energy, Ea and Entropy, ΔS with accuracy R 2 =99.3% [24][25]. Table 5 shows that the activation energy increases with increasing entropy and the positive values of internal energy means the degradation process is not spontaneous" [26].…”

Isoconversional Methods in Thermodynamic Principles

“…by demonstrating the relationship between the thermodynamic functions of activation (according to Eyring’s theory) − and observing enthalpy–entropy compensation (EEC). − …”

“…However, the thermodynamic aspects of the isoconversional methods of thermal decomposition processes, which are used to discuss other processes but primarily phase transformations, were omitted . Regarding chemical reactions of the type v A A(s) ↔ v B B(s) + ∑ ν c C­(g) or v A A(s) ↔ ∑ ν c C­(g), and the elements of phenomenological and applied thermodynamics in a wider assessment, the use of the elements of chemical thermodynamics is observed in three dimensions: as relationships between the conversion degrees: the equilibrium conversion degree for isothermal conditions with dynamic conditions brought to it in the form of an equation, later called the Holba–Šesták equation, as a result of using semiempirical methods of quantum chemistry to determine selected values of thermodynamic functions, presented in many papers by Błażejowski and co-workers, − by demonstrating the relationship between the thermodynamic functions of activation (according to Eyring’s theory) − and observing enthalpy–entropy compensation (EEC). − …”