An undergraduate kinetic experiment of the thermal decomposition of solids by microscopic observation and thermal analysis was developed by investigating a suitable reaction, applicable techniques of thermal analysis and microscopic observation, and a reliable kinetic calculation method. The thermal decomposition of sodium hydrogen carbonate is selected as the suitable reaction for the student experiments, because its physico-geometrical reaction mechanism is approximately described by the twodimensional phase boundary controlled model, and its reaction kinetics are less sensitive to the measurement conditions of thermal analyses. On the basis of simple microscopic observations of this reaction, development of the physico-geometrical reaction model and derivation of the kinetic model function are imposed on students. The kinetic analysis is also performed using the kinetic rate data recorded by a single thermogravimetric run under modulated temperature conditions. This reduces the time spent in the laboratory and enables the application of a two-step kinetic calculation that provides reliable kinetic results. From the results, students can interpret the kinetics, which are closely related to the physico-geometrical characteristics of the reaction. A one-day undergraduate course in a thermal analysis laboratory is proposed from research and trials conducted in our university.
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.
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