Determinación de los parámetros termodinámicos del ácido poliláctico (PLA) sometido a condiciones de pirólisis mediante termogravimetría

Abstract

The present study aims to determine the thermodynamic parameters of polylactic acid (PLA) subjected to pyrolysis conditions. The bioplastic was sampled as a form random, characterized and analyzed by dynamic thermogravometry at three ramps of heating, with inert nitrogen atmosphere and a temperature program of 25 to 900 °C. The data were treated using the Friedman (FR), Kissinger – Akahira – Sunose (KAS) and Flynn – Wall – Ozawa (FWO) is conversional kinetic models. Using a range of degrees of advance X in which the linear fit is adequate to determine the activation energy (E) and pre-exponential factor (A) from the slope and ordered product of the linear regression characteristic of each model. The Arrhenius equation was used to fit the DTG curves once the Contraction Sphere reaction model was established: two-dimensional phase boundary reaction (R2) from a relationship and certain considerations of the model geometry. The mean statistical indicator of absolute error was used to minimize the Error Objective Function and optimize the models adjusting the experimental DTG deviation with the calculated one. The appropriate model for each warming rate was determined by the coefficient of determination R2 closest to one and from which the kinetic parameters for each rate were used and thus obtain the thermodynamic parameters such as enthalpy, Gibbs free energy and entropy, whose values turned out to be 140.540 J.mol-1, 170.579 kJ.mol-1 and -49.474 J.mol-1 respectively for the rate of 5°C.min-1, 125.744 kJ.mol-1, 171.646 kJ.mol-1 and -73.463 J.mol-1 for the rate of 10 °C.min-1 and 113.344 kJ.mol-1, 172.709 kJ.mol-1 and -94.081 J.mol-1 for the rate of 15°C.min-1.