All ETDs from UAB

Advisory Committee Chair

Sergey Vyazovkin

Advisory Committee Members

Amber Genau

Tracy Hamilton

Eugenia Kharlampieva

Andrei Stanishevsky

Document Type

Dissertation

Date of Award

2019

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

The processes that naturally occur on heating such as thermal decompositions and polymerizations can be made to proceed on cooling. Studying the resulting cooling kinetics is the major objective of this work. The kinetics of the reactions are explored by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) in combination with isoconversional kinetic analysis. The kinetic parameters obtained on cooling are compared to the ones evaluated on heating and physical insights into the differences and similarities in the kinetics of the processes on heating and cooling are proposed. The study is driven by the hypothesis that the kinetics on heating and cooling should be similar for single-step processes but differ significantly for the multi-step ones. The first three chapters examine the kinetics of the thermal decompositions during continuous cooling. The processes under study are decompositions of isotactic polystyrene and ammonium nitrate as examples of single-step processes as well as decompositions of nickel(II) oxalate, lithium sulfate monohydrate, calcium sulfate dihydrate, and calcium oxalate monohydrate as examples of multi-step processes. It is determined that the decomposition kinetics on cooling can be measured by applying fast heating followed by significantly slower cooling. In agreement with our hypothesis the kinetic parameters on heating and cooling remain the same for single-step processes but differ significantly for the multi-step ones. For the reversible thermal decompositions, it is discovered that in the heating experiments the activation energy decreases with increasing temperature while in the cooling runs it increases. The fourth and fifth chapters expand the research of the kinetics on cooling to polymerizations. Nonstoichiometric and stoichiometric reactions of diglycidyl ether of bisphenol A (DGEBA) epoxy and m-phenylenediamine (m-PDA) are studied as examples of respectively single- and multi-step kinetics. Similar kinetic parameters and glass transition temperatures on heating and cooling are discovered for the single-step nonstoichiometric polymerization of DGEBA and m-PDA. The aforementioned parameters differ significantly for the stoichiometric curing. Differences in the heating and cooling kinetics manifest themselves in the Arrhenius plots of the opposite curvature. The obtained results emphasize the importance of further kinetic studies of the processes during continuous cooling.

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