The kinetics of the thermal decomposition of thermoplastic polyurethane elastomers under thermoplastic processing conditions

Abstract

A theoretical approach to the kinetics of the thermal decomposition of molten thermoplastic polyurethane elastomers, under conditions of thermoplastic processing is described. On the basis of these considerations, the thermal decomposition in different instruments (melt index analyser and measuring extruder) can be described quantitatively and the various results can be compared. As a result, identical conditions of decomposition of the melt can be defined accurately, thus opening up the possibility of combining experimental values from different instruments. The fundamental kinetic equation obtained for the kinetics of the thermal decomposition of thermoplastic polyurethanes describes the decomposition reaction and the reverse reaction (formation reaction) - which is dependent on the system of measurement and processing - as a function of the molar mass (end-group concentration) of the original product determined from the velocity constants for the decomposition reaction and back reaction. The consideration of the limiting value for t --> infinity is in agreement with the equilibrium constant. Consequently, the development of physical characteristic functions of thermoplastic polyurethane elastomers - independent of the system of measurement is possible.