Multistep Kinetic Behavior in the Thermal Degradation of Poly(l-Lactic Acid): A Physico-Geometrical Kinetic Interpretation

Abstract

A physico-geometrical kinetic interpretation of the thermal degradation of poly(l-lactic acid) (PLLA) is described based on the results of a kinetic study using thermogravimetry (TG) and the microscopic observation of the reaction process. From the physico-geometrical viewpoint, the reaction process is separated into two different stages characterized by a surface reaction of the molten PLLA in the initial reaction stage followed by continuous bubble formation and disappearance in the established reaction stage. The generally reported trend of variation in the apparent activation energy as the reaction advances is explained by the partial overlapping of these two reaction stages. The kinetic rate data obtained using TG were kinetically separated into those for the respective reaction stages by optimizing the kinetic parameters. The significance of the kinetic results is discussed in terms of the physico-geometrical characteristics of the reaction. Such systematic kinetic analyses demonstrate the importance of considering the physico-geometrical perspective when interpreting the kinetic results for the thermal degradation of polymers.

Kinetic analysis of overlapping multistep thermal decomposition comprising exothermic and endothermic processes: thermolysis of ammonium dinitramide

“…In addition to the chemical scheme of the reaction, the formation of gaseous products in a viscous liquid and removal of those gases from the reaction system accompanied by the decrease in the reactant liquid volume significantly influence the experimentally resolved shape and position of the thermoanalytical curves, as is sometimes observed for the thermal degradation of polymeric materials. 65,66 Even allowing for the empirical kinetic modeling for the overall rate behavior, the first reaction step involves at least three distinguishable a 1 regions with different E a,1 values, and these involve changing behaviors as evaluated from the isoconversional method (Fig. 6).…”

ICTAC Kinetics Committee recommendations for analysis of multi-step kinetics

“…Reactions studied by thermal analysis are in many cases heterogeneous processes defined by the reaction geometry and kinetics of nucleation and interfacial reaction [125,126,127,128]. Similar issues may apply to the reactions in viscous liquid [129,130]. It is generally difficult to formulate rigorous kinetic equations for multi-step reactions whose steps defined by interplay of physical and geometrical factors because of the heterogeneous distributions of the reactive sites and the reaction interfaces in each reaction step [128].…”

Poly(lactic acid)/modified gum arabic based bionanocomposite films: Thermal degradation kinetics

“…Where , , , and are the fractional conversion, the Arrhenius pre‐exponential factor, the apparent activation energy, and the kinetic model function that describes the physicochemical or physico‐geometrical mechanism of the reaction, respectively .…”

“…The thermal degradation study of PLA with novel biofillers will provide insight into the determination of decomposition temperature, decomposition reaction pathway and byproducts . For the determination of decomposition temperature and decomposition steps, thermogravimetric analysis/differential thermal analysis (TGA/DTG) technique is very useful, and hence is widely used .…”

“…Thermal degradation kinetics of the polymeric blends has been effectively studied by TGA . Thermal degradation of polymers has been studied by thermoanalytical kinetics to reveal the information about chemical reaction mechanism and to establish relationships between temperature, extent of conversion and process rate than that of thermally stimulated processes . The kinetic modeling of decomposition is done by crucial, reliable, and accurate prediction of material behavior under high‐temperature applications or working conditions such as processing, storage of materials and service lifetime over a particular period of time and temperature.…”